30589302714

Committed 30 Jul 2026 11:03PM UTC coverage: 82.354% (+1.1%) from 81.264%

Build # 30589302714

Build Type

Pull #72

github

Committed by

web-flow

Commit Message

Merge 04a205866 into e9404b875

Pull Request Pull Request #72: Fix continuation and recurring scheduling correctness issues

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284 of 306 new or added lines in 6 files covered. (92.81%)

2 existing lines in 2 files now uncovered.

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82.88

/src/Immediate.Jobs.EntityFrameworkCore/EntityFrameworkCoreJobStorage.cs

using System.Data.Common;
using Microsoft.EntityFrameworkCore;

// TODO: remove and fix diagnostics
#pragma warning disable MA0015 // Specify the parameter name in ArgumentException

namespace Immediate.Jobs.EntityFrameworkCore;

/// <summary>An optimistic-concurrency EF Core implementation of <see cref="IJobStorage"/>.</summary>
/// <typeparam name="TContext">The application context containing the Immediate.Jobs model.</typeparam>
/// <param name="contextFactory">The factory used to create application database contexts.</param>
/// <param name="timeProvider">The clock used for storage timestamps, or <see langword="null"/> to use the system clock.</param>
public sealed class EntityFrameworkCoreJobStorage<TContext>(
        IDbContextFactory<TContext> contextFactory,
        TimeProvider? timeProvider = null
) : IRecurringJobStorage, IJobGraphStorage, IJobStorageReplica
        where TContext : DbContext
{
        private const int MaxConcurrencyAttempts = 5;
        private const int MaxConsecutiveFailedFairClaims = 5;
        private readonly TimeProvider _timeProvider = timeProvider ?? TimeProvider.System;

        /// <inheritdoc />
        public ValueTask DisposeAsync() => ValueTask.CompletedTask;

        /// <inheritdoc />
        public async ValueTask InitializeAsync(CancellationToken cancellationToken = default)
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                _ = context.Model.FindEntityType(typeof(ImmediateJobEntity))
                        ?? throw new ImmediateJobException("Immediate.Jobs entities are not configured. Call modelBuilder.AddImmediateJobs() from OnModelCreating.");
        }

        /// <inheritdoc />
        public async ValueTask EnqueueAsync(JobRecord job, CancellationToken cancellationToken = default)
        {
                ArgumentNullException.ThrowIfNull(job);
                await ExecuteWithStrategyAsync(
                        operationCancellationToken => EnqueueCoreAsync(job, operationCancellationToken),
                        cancellationToken
                ).ConfigureAwait(false);
        }

        private async Task EnqueueCoreAsync(JobRecord job, CancellationToken cancellationToken)
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                if (job.GroupId is { } groupId && !await HasLiveGroupJobsAsync(
                        context,
                        job.QueueName,
                        groupId,
                        cancellationToken
                ).ConfigureAwait(false))
                {
                        var cursor = await context.Set<ImmediateFairQueueGroupEntity>()
                                .SingleOrDefaultAsync(
                                        group => group.QueueName == job.QueueName && group.GroupId == groupId,
                                        cancellationToken
                                )
                                .ConfigureAwait(false);
                        if (cursor is not null)
                                _ = context.Remove(cursor);
                }

                _ = context.Set<ImmediateJobEntity>().Add(ToEntity(job));
                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public async ValueTask EnqueueContinuationAsync(
                JobRecord job,
                IReadOnlyList<JobContinuationEdge> edges,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(job);
                ArgumentNullException.ThrowIfNull(edges);
                await ExecuteGraphInsertAsync(batch: null, [job], edges, cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public async ValueTask EnqueueBatchAsync(
                JobBatchRecord batch,
                IReadOnlyList<JobRecord> jobs,
                IReadOnlyList<JobContinuationEdge> edges,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(batch);
                ArgumentNullException.ThrowIfNull(jobs);
                ArgumentNullException.ThrowIfNull(edges);
                if (jobs.Count == 0)
                        throw new ImmediateJobException("An atomic batch cannot be committed without jobs.");
                await ExecuteGraphInsertAsync(batch, jobs, edges, cancellationToken).ConfigureAwait(false);
        }

        private ValueTask ExecuteGraphInsertAsync(
                JobBatchRecord? batch,
                IReadOnlyList<JobRecord> jobs,
                IReadOnlyList<JobContinuationEdge> edges,
                CancellationToken cancellationToken
        ) => RetryConcurrencyAsync(
                operationCancellationToken => InsertGraphCoreAsync(batch, jobs, edges, operationCancellationToken),
                cancellationToken
        );

        private async Task InsertGraphCoreAsync(
                JobBatchRecord? batch,
                IReadOnlyList<JobRecord> jobs,
                IReadOnlyList<JobContinuationEdge> edges,
                CancellationToken cancellationToken
        )
        {
                var jobIds = jobs.Select(static job => job.Id).ToHashSet(StringComparer.Ordinal);
                if (jobIds.Count != jobs.Count)
                        throw new ImmediateJobException("A batch or continuation insert contains duplicate job identifiers.");
                if (batch is not null && jobs.Any(job => !string.Equals(job.BatchId, batch.Id, StringComparison.Ordinal)))
                        throw new ImmediateJobException("Every atomic batch member must carry the committed batch identifier.");

                var edgeEntities = edges.Select(ToEntity).ToArray();
                if (edgeEntities.Any(edge => !jobIds.Contains(edge.ChildJobId)))
                        throw new ImmediateJobException("Every continuation edge must target a job inserted by the same operation.");
                if (edgeEntities.DistinctBy(static edge => (edge.ChildJobId, edge.ParentKind, edge.ParentId)).Count() != edgeEntities.Length)
                        throw new ImmediateJobException("Duplicate continuation edges are not allowed.");
                ThrowIfCyclic(jobIds, edgeEntities);

                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var jobEntities = jobs.Select(ToEntity).ToDictionary(static job => job.Id, StringComparer.Ordinal);
                await EvaluateInitialDependenciesAsync(
                        context,
                        jobEntities,
                        edgeEntities,
                        _timeProvider.GetUtcNow(),
                        cancellationToken
                ).ConfigureAwait(false);

                if (batch is not null)
                {
                        var terminal = jobEntities.Values.Where(static job => IsTerminal(job.State)).ToArray();
                        var pending = jobEntities.Count - terminal.Length;
                        var succeeded = terminal.Count(static job => job.State == JobState.Succeeded);
                        var failed = terminal.Count(static job => job.State == JobState.Failed);
                        var cancelled = terminal.Count(static job => job.State == JobState.Cancelled);
                        _ = context.Add(new ImmediateJobBatchEntity
                        {
                                Id = batch.Id,
                                CreatedAt = batch.CreatedAt,
                                TotalJobs = jobEntities.Count,
                                PendingCount = pending,
                                SucceededCount = succeeded,
                                FailedCount = failed,
                                CancelledCount = cancelled,
                                StartedAt = batch.StartedAt,
                                CompletedAt = pending == 0 ? batch.CompletedAt ?? _timeProvider.GetUtcNow() : null,
                                State = pending == 0 ? GetTerminalBatchState(failed, cancelled) : BatchState.Executing,
                                ConcurrencyStamp = Guid.NewGuid(),
                        });
                }

                context.AddRange(jobEntities.Values);
                context.AddRange(edgeEntities);
                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public async ValueTask<IReadOnlyList<JobRecord>> AcquireDueJobsAsync(
                JobAcquisitionRequest request,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(request);
                ArgumentException.ThrowIfNullOrWhiteSpace(request.WorkerId);
                ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(request.Lease, TimeSpan.Zero);
                ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(request.BatchSize, 0);
                if (request.FairQueues is not null)
                        return await AcquireDueJobsFairAsync(request, cancellationToken).ConfigureAwait(false);

                var now = _timeProvider.GetUtcNow();
                var acquired = new List<JobRecord>(request.BatchSize);
                foreach (var queue in request.Queues)
                {
                        var queueCapacity = Math.Min(queue.Capacity, request.BatchSize - acquired.Count);
                        if (queueCapacity <= 0)
                                continue;

                        var jobCapacities = queue.JobCapacities.ToDictionary(static pair => pair.Key, static pair => pair.Value, StringComparer.Ordinal);
                        while (queueCapacity > 0)
                        {
                                var eligibleNames = jobCapacities.Where(static pair => pair.Value > 0).Select(static pair => pair.Key).ToArray();
                                if (eligibleNames.Length == 0)
                                        break;

                                await using var readContext = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                                var candidates = await readContext.Set<ImmediateJobEntity>()
                                        .AsNoTracking()
                                        .Where(job => job.QueueName == queue.QueueName && eligibleNames.Contains(job.JobName) &&
                                                (((job.State == JobState.Scheduled || job.State == JobState.Pending) && job.DueAt <= now)
                                                        || (job.State == JobState.Active && job.LeaseExpiresAt <= now)))
                                        .OrderBy(job => job.DueAt)
                                        .ThenBy(job => job.CreatedAt)
                                        .ThenBy(job => job.Id)
                                        .Take(queueCapacity)
                                        .ToListAsync(cancellationToken)
                                        .ConfigureAwait(false);
                                if (candidates.Count == 0)
                                        break;

                                var selected = new List<ImmediateJobEntity>(candidates.Count);
                                var selectionCapacities = new Dictionary<string, int>(jobCapacities, StringComparer.Ordinal);
                                foreach (var candidate in candidates)
                                {
                                        if (selectionCapacities[candidate.JobName] <= 0)
                                                continue;
                                        selectionCapacities[candidate.JobName]--;
                                        selected.Add(candidate);
                                }

                                var claimed = await AcquireCandidatesAsync(
                                        selected,
                                        request.WorkerId,
                                        request.Lease,
                                        now,
                                        cancellationToken
                                ).ConfigureAwait(false);
                                foreach (var job in claimed)
                                {
                                        jobCapacities[job.JobName]--;
                                        queueCapacity--;
                                        acquired.Add(job);
                                }

                                if (claimed.Count == 0)
                                        break;
                        }
                }

                return acquired;
        }

        private async ValueTask<IReadOnlyList<JobRecord>> AcquireDueJobsFairAsync(
                JobAcquisitionRequest request,
                CancellationToken cancellationToken
        )
        {
                var now = _timeProvider.GetUtcNow();
                var acquired = new List<JobRecord>(request.BatchSize);
                foreach (var queue in request.Queues)
                {
                        var consecutiveFailedClaims = 0;
                        var queueCapacity = Math.Min(queue.Capacity, request.BatchSize - acquired.Count);
                        if (queueCapacity <= 0)
                                continue;

                        var jobCapacities = queue.JobCapacities.ToDictionary(
                                static pair => pair.Key,
                                static pair => pair.Value,
                                StringComparer.Ordinal
                        );
                        while (queueCapacity > 0)
                        {
                                var eligibleNames = jobCapacities
                                        .Where(static pair => pair.Value > 0)
                                        .Select(static pair => pair.Key)
                                        .ToArray();
                                if (eligibleNames.Length == 0)
                                        break;

                                await using var readContext = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                                var eligibleQuery = readContext.Set<ImmediateJobEntity>()
                                        .AsNoTracking()
                                        .Where(job => job.QueueName == queue.QueueName && eligibleNames.Contains(job.JobName) &&
                                                (((job.State == JobState.Scheduled || job.State == JobState.Pending) && job.DueAt <= now)
                                                        || (job.State == JobState.Active && job.LeaseExpiresAt <= now)));
                                if (!await eligibleQuery
                                        .AnyAsync(static job => job.GroupId != null, cancellationToken)
                                        .ConfigureAwait(false))
                                {
                                        var claimed = await AcquireFairFastPathAsync(
                                                queue.QueueName,
                                                jobCapacities,
                                                queueCapacity,
                                                request.WorkerId,
                                                request.Lease,
                                                now,
                                                cancellationToken
                                        ).ConfigureAwait(false);
                                        queueCapacity -= claimed.Count;
                                        acquired.AddRange(claimed);
                                        break;
                                }

                                var groupedHeads = await eligibleQuery
                                        .Where(static job => job.GroupId != null)
                                        .GroupBy(static job => job.GroupId)
                                        .Select(static group => group
                                                .OrderBy(job => job.DueAt)
                                                .ThenBy(job => job.CreatedAt)
                                                .ThenBy(job => job.Id)
                                                .First())
                                        .ToListAsync(cancellationToken)
                                        .ConfigureAwait(false);
                                var ungroupedHead = await eligibleQuery
                                        .Where(static job => job.GroupId == null)
                                        .OrderBy(job => job.DueAt)
                                        .ThenBy(job => job.CreatedAt)
                                        .ThenBy(job => job.Id)
                                        .FirstOrDefaultAsync(cancellationToken)
                                        .ConfigureAwait(false);
                                if (groupedHeads.Count == 0)
                                {
                                        var claimed = await AcquireFairFastPathAsync(
                                                queue.QueueName,
                                                jobCapacities,
                                                queueCapacity,
                                                request.WorkerId,
                                                request.Lease,
                                                now,
                                                cancellationToken
                                        ).ConfigureAwait(false);
                                        queueCapacity -= claimed.Count;
                                        acquired.AddRange(claimed);
                                        break;
                                }

                                var activeQuery = readContext.Set<ImmediateJobEntity>()
                                        .AsNoTracking()
                                        .Where(job => job.QueueName == queue.QueueName
                                                && job.State == JobState.Active
                                                && job.LeaseExpiresAt > now);
                                var totalInflight = await activeQuery
                                        .CountAsync(cancellationToken)
                                        .ConfigureAwait(false);
                                var groupedHeadIds = groupedHeads.Select(static job => job.Id).ToArray();
                                var cursorQuery = readContext.Set<ImmediateFairQueueGroupEntity>()
                                        .AsNoTracking()
                                        .Where(group => group.QueueName == queue.QueueName);
                                var groupStateQuery = eligibleQuery
                                        .Where(job => groupedHeadIds.Contains(job.Id));
                                var groupStates = request.FairQueues!.GroupRoundRobin
                                        ? await groupStateQuery
                                                .Select(job => new FairQueueCandidateState(
                                                        job.Id,
                                                        activeQuery.Count(active => active.GroupId == job.GroupId),
                                                        cursorQuery
                                                                .Where(cursor => cursor.GroupId == job.GroupId)
                                                                .Select(static cursor => cursor.LastServedSequence)
                                                                .FirstOrDefault()
                                                ))
                                                .ToDictionaryAsync(static state => state.JobId, StringComparer.Ordinal, cancellationToken)
                                                .ConfigureAwait(false)
                                        : await groupStateQuery
                                                .Select(job => new FairQueueCandidateState(
                                                        job.Id,
                                                        activeQuery.Count(active => active.GroupId == job.GroupId),
                                                        0
                                                ))
                                                .ToDictionaryAsync(static state => state.JobId, StringComparer.Ordinal, cancellationToken)
                                                .ConfigureAwait(false);
                                var nextSequence = 0L;
                                if (request.FairQueues.GroupRoundRobin)
                                {
                                        var maxSequence = await cursorQuery
                                                .MaxAsync(static group => (long?)group.LastServedSequence, cancellationToken)
                                                .ConfigureAwait(false);
                                        nextSequence = (maxSequence ?? 0) + 1;
                                }

                                var candidates = ungroupedHead is null ? groupedHeads : [.. groupedHeads, ungroupedHead];
                                var ranked = candidates.Select(job =>
                                {
                                        FairQueueCandidateState? state = null;
                                        if (job.GroupId is not null)
                                                _ = groupStates.TryGetValue(job.Id, out state);
                                        var noisy = IsNoisy(job.GroupId, state?.Inflight ?? 0, totalInflight, request.FairQueues);
                                        return new
                                        {
                                                Job = job,
                                                Noisy = noisy,
                                                NoisyInflight = noisy ? state!.Inflight : 0,
                                                LastServedSequence = state?.LastServedSequence ?? 0,
                                        };
                                });
                                var selected = ranked
                                        .OrderBy(static candidate => candidate.Noisy)
                                        .ThenBy(static candidate => candidate.NoisyInflight)
                                        .ThenBy(candidate => request.FairQueues.GroupRoundRobin
                                                ? candidate.LastServedSequence
                                                : 0)
                                        .ThenBy(static candidate => candidate.Job.DueAt)
                                        .ThenBy(static candidate => candidate.Job.CreatedAt)
                                        .ThenBy(static candidate => candidate.Job.Id, StringComparer.Ordinal)
                                        .First()
                                        .Job;
                                var claimedJob = request.FairQueues.GroupRoundRobin
                                        ? await AcquireFairCandidateAsync(
                                                selected,
                                                request.WorkerId,
                                                request.Lease,
                                                now,
                                                nextSequence,
                                                cancellationToken
                                        ).ConfigureAwait(false)
                                        : GetFirstOrDefault(await AcquireCandidatesAsync(
                                                        [selected],
                                                        request.WorkerId,
                                                        request.Lease,
                                                        now,
                                                        cancellationToken
                                                ).ConfigureAwait(false));
                                if (claimedJob is null)
                                {
                                        if (++consecutiveFailedClaims >= MaxConsecutiveFailedFairClaims)
                                                break;
                                        continue;
                                }

                                consecutiveFailedClaims = 0;
                                jobCapacities[claimedJob.JobName]--;
                                queueCapacity--;
                                acquired.Add(claimedJob);
                        }
                }

                return acquired;
        }

        private async ValueTask<IReadOnlyList<JobRecord>> AcquireFairFastPathAsync(
                string queueName,
                Dictionary<string, int> jobCapacities,
                int queueCapacity,
                string workerId,
                TimeSpan lease,
                DateTimeOffset now,
                CancellationToken cancellationToken
        )
        {
                var acquired = new List<JobRecord>(queueCapacity);
                while (queueCapacity > 0)
                {
                        var eligibleNames = jobCapacities
                                .Where(static pair => pair.Value > 0)
                                .Select(static pair => pair.Key)
                                .ToArray();
                        if (eligibleNames.Length == 0)
                                break;

                        await using var readContext = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                        var candidates = await readContext.Set<ImmediateJobEntity>()
                                .AsNoTracking()
                                .Where(job => job.QueueName == queueName && eligibleNames.Contains(job.JobName) &&
                                        (((job.State == JobState.Scheduled || job.State == JobState.Pending) && job.DueAt <= now)
                                                || (job.State == JobState.Active && job.LeaseExpiresAt <= now)))
                                .OrderBy(job => job.DueAt)
                                .ThenBy(job => job.CreatedAt)
                                .ThenBy(job => job.Id)
                                .Take(queueCapacity)
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
                        if (candidates.Count == 0)
                                break;

                        var selected = new List<ImmediateJobEntity>(candidates.Count);
                        var selectionCapacities = new Dictionary<string, int>(jobCapacities, StringComparer.Ordinal);
                        foreach (var candidate in candidates)
                        {
                                if (selectionCapacities[candidate.JobName] <= 0)
                                        continue;
                                selectionCapacities[candidate.JobName]--;
                                selected.Add(candidate);
                        }

                        var claimed = await AcquireCandidatesAsync(
                                selected,
                                workerId,
                                lease,
                                now,
                                cancellationToken
                        ).ConfigureAwait(false);
                        foreach (var job in claimed)
                        {
                                jobCapacities[job.JobName]--;
                                queueCapacity--;
                                acquired.Add(job);
                        }

                        if (claimed.Count == 0)
                                break;
                }

                return acquired;
        }

        private async ValueTask<JobRecord?> AcquireFairCandidateAsync(
                ImmediateJobEntity candidate,
                string workerId,
                TimeSpan lease,
                DateTimeOffset now,
                long nextSequence,
                CancellationToken cancellationToken
        )
        {
                await using var strategyContext = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var strategy = strategyContext.Database.CreateExecutionStrategy();
                return await strategy.ExecuteAsync(
                        operationCancellationToken => AcquireFairCandidateCoreAsync(
                                candidate,
                                workerId,
                                lease,
                                now,
                                nextSequence,
                                operationCancellationToken
                        ),
                        cancellationToken
                ).ConfigureAwait(false);
        }

        private async Task<JobRecord?> AcquireFairCandidateCoreAsync(
                ImmediateJobEntity candidate,
                string workerId,
                TimeSpan lease,
                DateTimeOffset now,
                long nextSequence,
                CancellationToken cancellationToken
        )
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var entity = Copy(candidate);
                _ = context.Attach(entity);
                entity.State = JobState.Active;
                entity.WorkerId = workerId;
                entity.LeaseExpiresAt = now + lease;
                entity.Attempt++;
                entity.CompletedAt = null;
                entity.ExecutionTraceId = null;
                entity.ExecutionSpanId = null;
                entity.ExecutionStartedAt = null;
                entity.ConcurrencyStamp = Guid.NewGuid();

                if (candidate.GroupId is { } groupId)
                {
                        var group = await context.Set<ImmediateFairQueueGroupEntity>()
                                .SingleOrDefaultAsync(
                                        item => item.QueueName == candidate.QueueName && item.GroupId == groupId,
                                        cancellationToken
                                )
                                .ConfigureAwait(false);
                        if (group is null)
                        {
                                _ = context.Add(new ImmediateFairQueueGroupEntity
                                {
                                        QueueName = candidate.QueueName,
                                        GroupId = groupId,
                                        LastServedSequence = nextSequence,
                                        ConcurrencyStamp = Guid.NewGuid(),
                                });
                        }
                        else if (group.LastServedSequence >= nextSequence)
                        {
                                // Selection observed an older cursor snapshot. Re-rank instead of moving this group backward.
                                return null;
                        }
                        else
                        {
                                group.LastServedSequence = nextSequence;
                                group.ConcurrencyStamp = Guid.NewGuid();
                        }
                }

                if (entity.BatchId is { } batchId)
                {
                        var batch = await context.Set<ImmediateJobBatchEntity>()
                                .SingleOrDefaultAsync(item => item.Id == batchId, cancellationToken)
                                .ConfigureAwait(false);
                        if (batch is not null && batch.StartedAt is null)
                        {
                                batch.StartedAt = now;
                                batch.ConcurrencyStamp = Guid.NewGuid();
                        }
                }

                try
                {
                        _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                        await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
                        return ToRecord(entity);
                }
                catch (DbUpdateException)
                {
                        // The job or its group cursor changed after candidate selection.
                        return null;
                }
        }

        private static JobRecord? GetFirstOrDefault(IReadOnlyList<JobRecord> jobs) =>
                jobs.Count == 0 ? null : jobs[0];

        private static bool IsNoisy(
                string? groupId,
                int inflight,
                int totalInflight,
                FairQueuePolicy policy
        )
        {
                return groupId is not null
                        && totalInflight > 0
                        && inflight >= policy.MinInflightForNoisy
                        && (double)inflight / totalInflight > policy.ConcurrencyShareThreshold;
        }

        private sealed record FairQueueCandidateState(
                string JobId,
                int Inflight,
                long LastServedSequence
        );

        /// <inheritdoc />
        public async ValueTask<IReadOnlyList<JobRecord>> AcquireJobsAsync(
                IReadOnlyCollection<string> jobIds,
                string workerId,
                TimeSpan lease,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(jobIds);
                ArgumentException.ThrowIfNullOrWhiteSpace(workerId);
                ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(lease, TimeSpan.Zero);
                if (jobIds.Count == 0)
                        return [];

                var now = _timeProvider.GetUtcNow();
                var ids = jobIds.ToArray();
                await using var readContext = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var candidates = await readContext.Set<ImmediateJobEntity>()
                        .AsNoTracking()
                        .Where(job => ids.Contains(job.Id) &&
                                (((job.State == JobState.Scheduled || job.State == JobState.Pending) && job.DueAt <= now)
                                || (job.State == JobState.Active && job.LeaseExpiresAt <= now)))
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);

                return await AcquireCandidatesAsync(candidates, workerId, lease, now, cancellationToken).ConfigureAwait(false);
        }

        private async ValueTask<IReadOnlyList<JobRecord>> AcquireCandidatesAsync(
                List<ImmediateJobEntity> candidates,
                string workerId,
                TimeSpan lease,
                DateTimeOffset now,
                CancellationToken cancellationToken
        )
        {
                var acquired = new List<JobRecord>(candidates.Count);
                foreach (var candidate in candidates)
                {
                        await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                        var entity = Copy(candidate);
                        _ = context.Attach(entity);
                        entity.State = JobState.Active;
                        entity.WorkerId = workerId;
                        entity.LeaseExpiresAt = now + lease;
                        entity.Attempt++;
                        entity.CompletedAt = null;
                        entity.ExecutionTraceId = null;
                        entity.ExecutionSpanId = null;
                        entity.ExecutionStartedAt = null;
                        entity.ConcurrencyStamp = Guid.NewGuid();
                        if (entity.BatchId is { } batchId)
                        {
                                var batch = await context.Set<ImmediateJobBatchEntity>()
                                        .SingleOrDefaultAsync(item => item.Id == batchId, cancellationToken)
                                        .ConfigureAwait(false);
                                if (batch is not null && batch.StartedAt is null)
                                {
                                        batch.StartedAt = now;
                                        batch.ConcurrencyStamp = Guid.NewGuid();
                                }
                        }

                        try
                        {
                                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                                acquired.Add(ToRecord(entity));
                        }
                        catch (DbUpdateConcurrencyException)
                        {
                                // Another scheduler claimed or changed this candidate first.
                        }
                }

                return acquired;
        }

        /// <inheritdoc />
        public ValueTask SetExecutionTelemetryAsync(
                string jobId,
                string workerId,
                string? traceId,
                string? spanId,
                DateTimeOffset startedAt,
                CancellationToken cancellationToken = default
        ) => MutateOwnedAsync(jobId, workerId, job =>
        {
                job.ExecutionTraceId = traceId;
                job.ExecutionSpanId = spanId;
                job.ExecutionStartedAt = startedAt;
        }, cancellationToken);

        /// <inheritdoc />
        public ValueTask RenewLeaseAsync(string jobId, string workerId, TimeSpan lease, CancellationToken cancellationToken = default)
        {
                ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(lease, TimeSpan.Zero);
                return MutateOwnedAsync(jobId, workerId, job => job.LeaseExpiresAt = _timeProvider.GetUtcNow() + lease, cancellationToken);
        }

        /// <inheritdoc />
        public ValueTask CompleteAsync(string jobId, string workerId, CancellationToken cancellationToken = default) =>
                CompleteWithContinuationsAsync(jobId, workerId, [], cancellationToken);

        /// <inheritdoc />
        public ValueTask CompleteWithContinuationsAsync(
                string jobId,
                string workerId,
                IReadOnlyList<JobContinuationAddition> additions,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(additions);
                return MutateOwnedWithDependenciesAsync(
                        jobId,
                        workerId,
                        error: null,
                        nextRetryAt: null,
                        succeeded: true,
                        additions,
                        cancellationToken
                );
        }

        /// <inheritdoc />
        public ValueTask AddBatchJobAsync(
                string currentJobId,
                JobRecord job,
                ContinuationOptions options,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(job);
                if (options == ContinuationOptions.Detached)
                        throw new ImmediateJobException("AddToBatchAsync cannot create a detached job.");
                return RetryConcurrencyAsync(
                        operationCancellationToken => AddBatchJobCoreAsync(
                                currentJobId,
                                job,
                                options,
                                operationCancellationToken
                        ),
                        cancellationToken
                );
        }

        /// <inheritdoc />
        public ValueTask FailAsync(
                string jobId,
                string workerId,
                string error,
                DateTimeOffset? nextRetryAt,
                CancellationToken cancellationToken = default
        ) => MutateOwnedWithDependenciesAsync(jobId, workerId, error, nextRetryAt, succeeded: false, [], cancellationToken);

        /// <inheritdoc />
        public async ValueTask UpsertRecurringAsync(RecurringJobSchedule schedule, CancellationToken cancellationToken = default)
        {
                ArgumentNullException.ThrowIfNull(schedule);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                if (await UpdateRecurringAsync(context, schedule, cancellationToken).ConfigureAwait(false) != 0)
                        return;
                await ThrowIfReplacingCodeDefinedScheduleAsync(context, schedule, cancellationToken).ConfigureAwait(false);

                _ = context.Add(ToEntity(schedule));
                try
                {
                        _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                }
                catch (DbUpdateException)
                {
                        // A competing node inserted the same schedule after our update attempt.
                        await using var retryContext = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                        if (await UpdateRecurringAsync(retryContext, schedule, cancellationToken).ConfigureAwait(false) != 0)
                                return;
                        await ThrowIfReplacingCodeDefinedScheduleAsync(retryContext, schedule, cancellationToken).ConfigureAwait(false);
                        throw;
                }
        }

        /// <inheritdoc />
        public async ValueTask RemoveObsoleteCodeDefinedRecurringAsync(
                IReadOnlyCollection<string> activeScheduleNames,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(activeScheduleNames);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var schedules = context.Set<ImmediateRecurringJobEntity>()
                        .Where(schedule => schedule.IsCodeDefined);
                if (activeScheduleNames.Count != 0)
                        schedules = schedules.Where(schedule => !activeScheduleNames.Contains(schedule.Name));
                _ = await schedules.ExecuteDeleteAsync(cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public async ValueTask RemoveRecurringAsync(string name, CancellationToken cancellationToken = default)
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(name);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var removed = await context.Set<ImmediateRecurringJobEntity>()
                        .Where(schedule => schedule.Name == name && !schedule.IsCodeDefined)
                        .ExecuteDeleteAsync(cancellationToken)
                        .ConfigureAwait(false);
                if (removed != 0)
                        return;
                if (await context.Set<ImmediateRecurringJobEntity>()
                        .AnyAsync(schedule => schedule.Name == name, cancellationToken)
                        .ConfigureAwait(false))
                {
                        throw new ImmediateJobException("Code-defined recurring schedules cannot be deleted.");
                }

                throw new KeyNotFoundException($"Recurring schedule '{name}' was not found.");
        }

        /// <inheritdoc />
        public ValueTask PauseRecurringAsync(string name, CancellationToken cancellationToken = default)
                => MutateRecurringAsync(name, schedule => schedule.IsPaused = true, cancellationToken);

        /// <inheritdoc />
        public ValueTask ResumeRecurringAsync(string name, CancellationToken cancellationToken = default)
                => MutateRecurringAsync(name, schedule => schedule.IsPaused = false, cancellationToken);

        /// <inheritdoc />
        public async ValueTask<IReadOnlyList<RecurringJobSchedule>> GetDueRecurringAsync(DateTimeOffset now, int batchSize, CancellationToken cancellationToken = default)
        {
                ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(batchSize, 0);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                return await context.Set<ImmediateRecurringJobEntity>()
                        .AsNoTracking()
                        .Where(schedule => !schedule.IsPaused && schedule.NextRunAt <= now)
                        .OrderBy(schedule => schedule.NextRunAt)
                        .Take(batchSize)
                        .Select(schedule => new RecurringJobSchedule
                        {
                                Name = schedule.Name,
                                JobName = schedule.JobName,
                                Cron = schedule.Cron,
                                TimeZone = schedule.TimeZone,
                                IsCodeDefined = schedule.IsCodeDefined,
                                IsPaused = schedule.IsPaused,
                                NextRunAt = schedule.NextRunAt,
                                LastRunAt = schedule.LastRunAt,
                        })
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
        }

        /// <inheritdoc />
        public async ValueTask<bool> MaterializeRecurringAsync(
                RecurringJobSchedule schedule,
                JobRecord job,
                DateTimeOffset nextRunAt,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(schedule);
                ArgumentNullException.ThrowIfNull(job);
                await using var strategyContext = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var strategy = strategyContext.Database.CreateExecutionStrategy();
                return await strategy.ExecuteAsync(
                        operationCancellationToken => MaterializeRecurringCoreAsync(
                                schedule,
                                job,
                                nextRunAt,
                                operationCancellationToken
                        ),
                        cancellationToken
                ).ConfigureAwait(false);
        }

        private async Task<bool> MaterializeRecurringCoreAsync(
                RecurringJobSchedule schedule,
                JobRecord job,
                DateTimeOffset nextRunAt,
                CancellationToken cancellationToken
        )
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var entity = await context.Set<ImmediateRecurringJobEntity>()
                        .SingleOrDefaultAsync(item => item.Name == schedule.Name, cancellationToken)
                        .ConfigureAwait(false);
                if (entity is null || entity.IsPaused || entity.NextRunAt != schedule.NextRunAt)
                        return false;

                entity.LastRunAt = schedule.NextRunAt;
                entity.NextRunAt = nextRunAt;
                entity.ConcurrencyStamp = Guid.NewGuid();
                _ = context.Add(ToEntity(job));
                try
                {
                        _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                        await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
                        return true;
                }
                catch (DbUpdateException)
                {
                        await transaction.RollbackAsync(cancellationToken).ConfigureAwait(false);
                        return false;
                }
        }

        /// <inheritdoc />
        public async ValueTask<JobMonitoringSnapshot> GetMonitoringSnapshotAsync(CancellationToken cancellationToken = default)
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var rawCounts = await context.Set<ImmediateJobEntity>()
                        .AsNoTracking()
                        .GroupBy(job => job.State)
                        .Select(group => new { State = group.Key, Count = group.LongCount() })
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                var counts = Enum.GetValues<JobState>().ToDictionary(static state => state, static _ => 0L);
                foreach (var item in rawCounts)
                        counts[item.State] = item.Count;

                var recurring = await context.Set<ImmediateRecurringJobEntity>()
                        .AsNoTracking()
                        .OrderBy(schedule => schedule.Name)
                        .Select(schedule => new RecurringJobSchedule
                        {
                                Name = schedule.Name,
                                JobName = schedule.JobName,
                                Cron = schedule.Cron,
                                TimeZone = schedule.TimeZone,
                                IsCodeDefined = schedule.IsCodeDefined,
                                IsPaused = schedule.IsPaused,
                                NextRunAt = schedule.NextRunAt,
                                LastRunAt = schedule.LastRunAt,
                        })
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                var cutoff = _timeProvider.GetUtcNow() - TimeSpan.FromMinutes(2);
                var servers = await context.Set<ImmediateJobServerEntity>()
                        .AsNoTracking()
                        .Where(server => server.LastHeartbeat >= cutoff)
                        .OrderBy(server => server.WorkerId)
                        .Select(server => new JobServerSnapshot(server.WorkerId, server.LastHeartbeat, server.ActiveWorkers, server.MaxWorkers))
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                return new(_timeProvider.GetUtcNow(), counts, recurring, servers)
                {
                        Capabilities = this.GetCapabilities(),
                };
        }

        /// <inheritdoc />
        public async ValueTask<IReadOnlyList<JobRecord>> QueryJobsAsync(JobQuery query, CancellationToken cancellationToken = default)
        {
                ArgumentNullException.ThrowIfNull(query);
                ArgumentOutOfRangeException.ThrowIfNegative(query.Skip);
                ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(query.Take, 0);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var jobs = context.Set<ImmediateJobEntity>().AsNoTracking();
                if (query.Id is { } id)
                        jobs = jobs.Where(job => job.Id == id);
                if (query.State is { } state)
                        jobs = jobs.Where(job => job.State == state);
                if (!string.IsNullOrWhiteSpace(query.QueueName))
                        jobs = jobs.Where(job => job.QueueName == query.QueueName);
                if (!string.IsNullOrWhiteSpace(query.JobName))
                        jobs = jobs.Where(job => job.JobName == query.JobName);
                if (!string.IsNullOrWhiteSpace(query.Search))
                {
                        var search = query.Search.ToUpperInvariant();
                        // The parameterless form is intentionally used because relational providers translate it to SQL.
#pragma warning disable CA1304, CA1311, CA1862, MA0011
                        jobs = jobs.Where(job => job.JobName.ToUpper().Contains(search));
#pragma warning restore CA1304, CA1311, CA1862, MA0011
                }

                var entities = await jobs.OrderByDescending(job => job.CreatedAt)
                        .ThenBy(job => job.Id)
                        .Skip(query.Skip)
                        .Take(query.Take)
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                return [.. entities.Select(ToRecord)];
        }

        /// <inheritdoc />
        public async ValueTask<BatchStatus?> GetBatchStatusAsync(
                string batchId,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(batchId);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var batch = await context.Set<ImmediateJobBatchEntity>()
                        .AsNoTracking()
                        .SingleOrDefaultAsync(item => item.Id == batchId, cancellationToken)
                        .ConfigureAwait(false);
                return batch is null ? null : ToStatus(batch);
        }

        /// <inheritdoc />
        public async ValueTask<IReadOnlyList<JobContinuationEdge>> GetIncomingEdgesAsync(
                IReadOnlyCollection<string> childJobIds,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(childJobIds);
                foreach (var childJobId in childJobIds)
                        ArgumentException.ThrowIfNullOrWhiteSpace(childJobId);
                if (childJobIds.Count == 0)
                        return [];

                var ids = childJobIds.Distinct(StringComparer.Ordinal).ToArray();
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var edges = await context.Set<ImmediateJobContinuationEntity>()
                        .AsNoTracking()
                        .Where(edge => ids.Contains(edge.ChildJobId))
                        .OrderBy(edge => edge.ChildJobId)
                        .ThenBy(edge => edge.ParentKind)
                        .ThenBy(edge => edge.ParentId)
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                return [.. edges.Select(ToContinuationEdge)];
        }

        /// <inheritdoc />
        public async ValueTask<IReadOnlyList<BatchStatus>> QueryBatchesAsync(
                JobBatchQuery query,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentNullException.ThrowIfNull(query);
                ArgumentOutOfRangeException.ThrowIfNegative(query.Skip);
                ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(query.Take, 0);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var batches = context.Set<ImmediateJobBatchEntity>().AsNoTracking();
                if (query.State is { } state)
                        batches = batches.Where(batch => batch.State == state);
                var entities = await batches.OrderByDescending(batch => batch.CreatedAt)
                        .ThenBy(batch => batch.Id)
                        .Skip(query.Skip)
                        .Take(query.Take)
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                return [.. entities.Select(ToStatus)];
        }

        /// <inheritdoc />
        public async ValueTask<IReadOnlyList<BatchMemberStatus>> QueryBatchMembersAsync(
                string batchId,
                BatchMemberQuery query,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(batchId);
                ArgumentNullException.ThrowIfNull(query);
                ArgumentOutOfRangeException.ThrowIfNegative(query.Skip);
                ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(query.Take, 0);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var jobs = context.Set<ImmediateJobEntity>()
                        .AsNoTracking()
                        .Where(job => job.BatchId == batchId);
                if (query.State is { } state)
                        jobs = jobs.Where(job => job.State == state);
                return await jobs.OrderBy(job => job.CreatedAt)
                        .ThenBy(job => job.Id)
                        .Skip(query.Skip)
                        .Take(query.Take)
                        .Select(job => new BatchMemberStatus(
                                job.Id,
                                job.JobName,
                                job.QueueName,
                                job.State,
                                job.Attempt,
                                job.CreatedAt,
                                job.CompletedAt,
                                job.LastError
                        ))
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
        }

        /// <inheritdoc />
        public async ValueTask<BatchGraph?> GetBatchGraphAsync(
                string batchId,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(batchId);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                if (!await context.Set<ImmediateJobBatchEntity>()
                        .AnyAsync(batch => batch.Id == batchId, cancellationToken)
                        .ConfigureAwait(false))
                {
                        return null;
                }

                var jobs = await context.Set<ImmediateJobEntity>()
                        .AsNoTracking()
                        .Where(job => job.BatchId == batchId)
                        .OrderBy(job => job.CreatedAt)
                        .ThenBy(job => job.Id)
                        .Select(job => new BatchGraphNode(job.Id, job.JobName, job.State))
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                var ids = jobs.Select(static job => job.JobId).ToArray();
                var edges = ids.Length == 0
                        ? []
                        : await context.Set<ImmediateJobContinuationEntity>()
                                .AsNoTracking()
                                .Where(edge => ids.Contains(edge.ChildJobId))
                                .OrderBy(edge => edge.ChildJobId)
                                .ThenBy(edge => edge.ParentKind)
                                .ThenBy(edge => edge.ParentId)
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
                return new(batchId, jobs, [.. edges.Select(ToGraphEdge)]);
        }

        /// <inheritdoc />
        public async ValueTask<JobStatus?> GetJobStatusAsync(
                string jobId,
                CancellationToken cancellationToken = default
        )
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(jobId);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var job = await context.Set<ImmediateJobEntity>()
                        .AsNoTracking()
                        .SingleOrDefaultAsync(item => item.Id == jobId, cancellationToken)
                        .ConfigureAwait(false);
                if (job is null)
                        return null;
                var edges = await context.Set<ImmediateJobContinuationEntity>()
                        .AsNoTracking()
                        .Where(edge => edge.ChildJobId == jobId)
                        .OrderBy(edge => edge.ParentKind)
                        .ThenBy(edge => edge.ParentId)
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                return new(
                        job.Id,
                        job.JobName,
                        job.QueueName,
                        job.State,
                        job.Attempt,
                        MaxAttempts: null,
                        job.CreatedAt,
                        job.DueAt,
                        job.CompletedAt,
                        job.LastError,
                        job.BatchId,
                        [.. edges.Select(ToGraphEdge)]
                );
        }

        /// <inheritdoc />
        public ValueTask CancelBatchAsync(string batchId, CancellationToken cancellationToken = default)
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(batchId);
                return ExecuteWithStrategyAsync(
                        operationCancellationToken => CancelBatchCoreAsync(batchId, operationCancellationToken),
                        cancellationToken
                );
        }

        private async Task CancelBatchCoreAsync(string batchId, CancellationToken cancellationToken)
        {
                var now = _timeProvider.GetUtcNow();
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var batch = await context.Set<ImmediateJobBatchEntity>()
                        .SingleOrDefaultAsync(item => item.Id == batchId, cancellationToken)
                        .ConfigureAwait(false)
                        ?? throw new KeyNotFoundException($"Batch '{batchId}' was not found.");
                if (batch.State != BatchState.Executing)
                        throw new ImmediateJobException("Only an executing batch can be cancelled.");

                var jobs = await context.Set<ImmediateJobEntity>()
                        .Where(job => job.BatchId == batchId)
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                foreach (var job in jobs)
                {
                        if (IsTerminal(job.State))
                                continue;
                        job.State = JobState.Cancelled;
                        job.CompletedAt = now;
                        job.WorkerId = null;
                        job.LeaseExpiresAt = null;
                        job.ConcurrencyStamp = Guid.NewGuid();
                        await PropagateTerminalAsync(context, job, now, cancellationToken).ConfigureAwait(false);
                }

                var terminalGroups = GetTerminalFairQueueGroups(context);
                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
                foreach (var (queueName, groupId) in terminalGroups)
                {
                        await TryRemoveFairQueueCursorAsync(queueName, groupId, CancellationToken.None).ConfigureAwait(false);
                }
        }

        /// <inheritdoc />
        public ValueTask DeleteBatchAsync(string batchId, CancellationToken cancellationToken = default)
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(batchId);
                return ExecuteWithStrategyAsync(
                        operationCancellationToken => DeleteBatchCoreAsync(batchId, operationCancellationToken),
                        cancellationToken
                );
        }

        private async Task DeleteBatchCoreAsync(string batchId, CancellationToken cancellationToken)
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var batch = await context.Set<ImmediateJobBatchEntity>()
                        .SingleOrDefaultAsync(item => item.Id == batchId, cancellationToken)
                        .ConfigureAwait(false)
                        ?? throw new KeyNotFoundException($"Batch '{batchId}' was not found.");
                if (batch.State == BatchState.Executing)
                        throw new ImmediateJobException("Only a terminal batch can be deleted.");

                var jobs = await context.Set<ImmediateJobEntity>()
                        .Where(job => job.BatchId == batchId)
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                var jobIds = jobs.Select(static job => job.Id).ToArray();
                var edges = await context.Set<ImmediateJobContinuationEntity>()
                        .Where(edge =>
                                jobIds.Contains(edge.ChildJobId)
                                || (edge.ParentKind == ContinuationParentKind.Job && jobIds.Contains(edge.ParentId))
                                || (edge.ParentKind == ContinuationParentKind.Batch && edge.ParentId == batchId))
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                context.RemoveRange(edges);
                context.RemoveRange(jobs);
                _ = context.Remove(batch);
                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public ValueTask RetryAsync(string jobId, CancellationToken cancellationToken = default)
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(jobId);
                return ExecuteWithStrategyAsync(
                        operationCancellationToken => RetryCoreAsync(jobId, operationCancellationToken),
                        cancellationToken
                );
        }

        private async Task RetryCoreAsync(string jobId, CancellationToken cancellationToken)
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var job = await context.Set<ImmediateJobEntity>()
                        .SingleOrDefaultAsync(item => item.Id == jobId && item.State == JobState.Failed, cancellationToken)
                        .ConfigureAwait(false);
                if (job is null)
                {
                        if (await context.Set<ImmediateJobEntity>()
                                .AnyAsync(item => item.Id == jobId, cancellationToken)
                                .ConfigureAwait(false))
                        {
                                throw new ImmediateJobException("Only failed jobs can be retried.");
                        }

                        throw new KeyNotFoundException($"Job '{jobId}' was not found.");
                }

                if (job.BatchId is { } batchId)
                {
                        var batch = await context.Set<ImmediateJobBatchEntity>()
                                .SingleAsync(item => item.Id == batchId, cancellationToken)
                                .ConfigureAwait(false);
                        batch.PendingCount++;
                        batch.FailedCount = Math.Max(0, batch.FailedCount - 1);
                        batch.State = BatchState.Executing;
                        batch.CompletedAt = null;
                        batch.ConcurrencyStamp = Guid.NewGuid();
                }

                job.State = JobState.Pending;
                job.DueAt = _timeProvider.GetUtcNow();
                job.WorkerId = null;
                job.LeaseExpiresAt = null;
                job.CompletedAt = null;
                job.LastError = null;
                job.ConcurrencyStamp = Guid.NewGuid();
                try
                {
                        _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                }
                catch (DbUpdateConcurrencyException)
                {
                        if (!await context.Set<ImmediateJobEntity>()
                                .AsNoTracking()
                                .AnyAsync(item => item.Id == jobId, cancellationToken)
                                .ConfigureAwait(false))
                        {
                                throw new KeyNotFoundException($"Job '{jobId}' was not found.");
                        }

                        throw new ImmediateJobException("Only failed jobs can be retried.");
                }

                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public ValueTask DeleteAsync(string jobId, CancellationToken cancellationToken = default)
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(jobId);
                return ExecuteWithStrategyAsync(
                        operationCancellationToken => DeleteCoreAsync(jobId, operationCancellationToken),
                        cancellationToken
                );
        }

        private async Task DeleteCoreAsync(string jobId, CancellationToken cancellationToken)
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var job = await context.Set<ImmediateJobEntity>()
                        .AsNoTracking()
                        .SingleOrDefaultAsync(item => item.Id == jobId
                                && (item.State == JobState.Succeeded || item.State == JobState.Failed || item.State == JobState.Cancelled), cancellationToken)
                        .ConfigureAwait(false);
                if (job is null)
                {
                        if (await context.Set<ImmediateJobEntity>()
                                .AnyAsync(item => item.Id == jobId, cancellationToken)
                                .ConfigureAwait(false))
                        {
                                throw new ImmediateJobException("Only terminal jobs can be deleted.");
                        }

                        throw new KeyNotFoundException($"Job '{jobId}' was not found.");
                }

                if (job.BatchId is not null)
                        throw new ImmediateJobException("Batch members are deleted with their batch so the workflow remains coherent.");
                _ = await context.Set<ImmediateJobContinuationEntity>()
                        .Where(edge => edge.ChildJobId == jobId ||
                                (edge.ParentKind == ContinuationParentKind.Job && edge.ParentId == jobId))
                        .ExecuteDeleteAsync(cancellationToken)
                        .ConfigureAwait(false);
                var removed = await context.Set<ImmediateJobEntity>()
                        .Where(item => item.Id == jobId &&
                                (item.State == JobState.Succeeded || item.State == JobState.Failed || item.State == JobState.Cancelled))
                        .ExecuteDeleteAsync(cancellationToken)
                        .ConfigureAwait(false);
                if (removed == 0)
                {
                        if (await context.Set<ImmediateJobEntity>()
                                .AnyAsync(item => item.Id == jobId, cancellationToken)
                                .ConfigureAwait(false))
                        {
                                throw new ImmediateJobException("Only terminal jobs can be deleted.");
                        }

                        throw new KeyNotFoundException($"Job '{jobId}' was not found.");
                }

                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public ValueTask PurgeJobsAsync(
                TimeSpan succeededRetention,
                TimeSpan failedRetention,
                CancellationToken cancellationToken = default
        )
        {
                var now = _timeProvider.GetUtcNow();
                return ExecuteWithStrategyAsync(
                        operationCancellationToken => PurgeJobsCoreAsync(
                                now - succeededRetention,
                                now - failedRetention,
                                operationCancellationToken
                        ),
                        cancellationToken
                );
        }

        /// <inheritdoc />
        public ValueTask PurgeBatchesAsync(
                TimeSpan batchSucceededRetention,
                TimeSpan batchFailedRetention,
                CancellationToken cancellationToken = default
        )
        {
                var now = _timeProvider.GetUtcNow();
                return ExecuteWithStrategyAsync(
                        operationCancellationToken => PurgeBatchesCoreAsync(
                                now - batchSucceededRetention,
                                now - batchFailedRetention,
                                operationCancellationToken
                        ),
                        cancellationToken
                );
        }

        private async Task PurgeJobsCoreAsync(
                DateTimeOffset succeededBefore,
                DateTimeOffset failedBefore,
                CancellationToken cancellationToken
        )
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var jobs = await context.Set<ImmediateJobEntity>()
                        .Where(job => job.BatchId == null
                                && ((job.State == JobState.Succeeded && job.CompletedAt < succeededBefore)
                                || ((job.State == JobState.Failed || job.State == JobState.Cancelled) && job.CompletedAt < failedBefore))
                        )
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                if (jobs.Count != 0)
                {
                        var jobIds = jobs.Select(static job => job.Id).ToArray();
                        var edges = await context.Set<ImmediateJobContinuationEntity>()
                                .Where(edge =>
                                        jobIds.Contains(edge.ChildJobId)
                                        || (jobIds.Contains(edge.ParentId) && edge.ParentKind == ContinuationParentKind.Job)
                                )
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
                        context.RemoveRange(edges);
                }

                context.RemoveRange(jobs);
                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
        }

        private async Task PurgeBatchesCoreAsync(
                DateTimeOffset batchSucceededBefore,
                DateTimeOffset batchFailedBefore,
                CancellationToken cancellationToken
        )
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var batches = await context.Set<ImmediateJobBatchEntity>()
                        .Where(batch => (batch.State == BatchState.Succeeded && batch.CompletedAt < batchSucceededBefore)
                                || ((batch.State == BatchState.Failed || batch.State == BatchState.Cancelled)
                                        && batch.CompletedAt < batchFailedBefore))
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                if (batches.Count != 0)
                {
                        var batchIds = batches.Select(static batch => batch.Id).ToArray();
                        var memberIds = await context.Set<ImmediateJobEntity>()
                                .Where(job => job.BatchId != null && batchIds.Contains(job.BatchId))
                                .Select(job => job.Id)
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
                        var edges = await context.Set<ImmediateJobContinuationEntity>()
                                .Where(edge =>
                                        (batchIds.Contains(edge.ParentId) && edge.ParentKind == ContinuationParentKind.Batch)
                                        || memberIds.Contains(edge.ChildJobId)
                                        || (memberIds.Contains(edge.ParentId) && edge.ParentKind == ContinuationParentKind.Job)
                                )
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
                        context.RemoveRange(edges);
                        context.RemoveRange(batches);
                }

                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public async ValueTask HeartbeatAsync(JobServerSnapshot server, CancellationToken cancellationToken = default)
        {
                ArgumentNullException.ThrowIfNull(server);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var cutoff = _timeProvider.GetUtcNow() - TimeSpan.FromMinutes(2);
                _ = await context.Set<ImmediateJobServerEntity>()
                        .Where(item => item.LastHeartbeat < cutoff)
                        .ExecuteDeleteAsync(cancellationToken)
                        .ConfigureAwait(false);
                var entity = await context.Set<ImmediateJobServerEntity>().FindAsync([server.WorkerId], cancellationToken).ConfigureAwait(false);
                if (entity is null)
                {
                        _ = context.Add(new ImmediateJobServerEntity
                        {
                                WorkerId = server.WorkerId,
                                LastHeartbeat = server.LastHeartbeat,
                                ActiveWorkers = server.ActiveWorkers,
                                MaxWorkers = server.MaxWorkers,
                        });
                }
                else
                {
                        entity.LastHeartbeat = server.LastHeartbeat;
                        entity.ActiveWorkers = server.ActiveWorkers;
                        entity.MaxWorkers = server.MaxWorkers;
                }

                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc />
        public async ValueTask<bool> IsHealthyAsync(CancellationToken cancellationToken = default)
        {
                try
                {
                        await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                        return await context.Database.CanConnectAsync(cancellationToken).ConfigureAwait(false);
                }
                catch (Exception exception) when (exception is DbException or InvalidOperationException)
                {
                        return false;
                }
        }

        private ValueTask MutateOwnedWithDependenciesAsync(
                string jobId,
                string workerId,
                string? error,
                DateTimeOffset? nextRetryAt,
                bool succeeded,
                IReadOnlyList<JobContinuationAddition> additions,
                CancellationToken cancellationToken
        ) => RetryConcurrencyAsync(
                operationCancellationToken => MutateOwnedCoreAsync(
                        jobId,
                        workerId,
                        error,
                        nextRetryAt,
                        succeeded,
                        additions,
                        operationCancellationToken
                ),
                cancellationToken
        );

        private async ValueTask RetryConcurrencyAsync(
                Func<CancellationToken, Task> operation,
                CancellationToken cancellationToken
        )
        {
                for (var attempt = 0; attempt < MaxConcurrencyAttempts; attempt++)
                {
                        try
                        {
                                await ExecuteWithStrategyAsync(operation, cancellationToken).ConfigureAwait(false);
                                return;
                        }
                        catch (DbUpdateConcurrencyException) when (attempt + 1 < MaxConcurrencyAttempts)
                        {
                                // The transaction rolled back, so the next attempt re-evaluates the graph from durable state.
                        }
                }
        }

        private async ValueTask ExecuteWithStrategyAsync(
                Func<CancellationToken, Task> operation,
                CancellationToken cancellationToken
        )
        {
                await using var strategyContext = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var strategy = strategyContext.Database.CreateExecutionStrategy();
                await strategy.ExecuteAsync(operation, cancellationToken).ConfigureAwait(false);
        }

        private async ValueTask MutateOwnedAsync(
                string jobId,
                string workerId,
                Action<ImmediateJobEntity> mutate,
                CancellationToken cancellationToken
        )
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var job = await context.Set<ImmediateJobEntity>()
                        .SingleOrDefaultAsync(item => item.Id == jobId && item.State == JobState.Active && item.WorkerId == workerId, cancellationToken)
                        .ConfigureAwait(false);
                if (job is null)
                        return;
                mutate(job);
                job.ConcurrencyStamp = Guid.NewGuid();
                try
                {
                        _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                }
                catch (DbUpdateConcurrencyException)
                {
                        // A stale worker must not update a lease that has been reclaimed.
                }
        }

        private async Task MutateOwnedCoreAsync(
                string jobId,
                string workerId,
                string? error,
                DateTimeOffset? nextRetryAt,
                bool succeeded,
                IReadOnlyList<JobContinuationAddition> additions,
                CancellationToken cancellationToken
        )
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var job = await context.Set<ImmediateJobEntity>()
                        .SingleOrDefaultAsync(item => item.Id == jobId && item.State == JobState.Active && item.WorkerId == workerId, cancellationToken)
                        .ConfigureAwait(false);
                if (job is null)
                        throw new ImmediateJobException($"Worker '{workerId}' does not own active job '{jobId}'.");

                var now = _timeProvider.GetUtcNow();
                job.WorkerId = null;
                job.LeaseExpiresAt = null;
                job.LastError = error;
                job.ConcurrencyStamp = Guid.NewGuid();
                if (!succeeded && nextRetryAt is { } retryAt)
                {
                        job.State = retryAt <= now ? JobState.Pending : JobState.Scheduled;
                        job.DueAt = retryAt;
                        job.CompletedAt = null;
                        _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                        await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
                        return;
                }

                if (succeeded && additions.Count != 0)
                {
                        await FlushContinuationAdditionsAsync(context, job, additions, cancellationToken).ConfigureAwait(false);
                        _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                }

                job.State = succeeded ? JobState.Succeeded : JobState.Failed;
                job.CompletedAt = now;
                await PropagateTerminalAsync(context, job, now, cancellationToken).ConfigureAwait(false);
                var terminalGroups = GetTerminalFairQueueGroups(context);
                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
                foreach (var (queueName, groupId) in terminalGroups)
                        await TryRemoveFairQueueCursorAsync(queueName, groupId, CancellationToken.None).ConfigureAwait(false);
        }

        private static (string QueueName, string GroupId)[] GetTerminalFairQueueGroups(TContext context) =>
                [
                        .. context.ChangeTracker
                                .Entries<ImmediateJobEntity>()
                                .Select(static entry => entry.Entity)
                                .Where(static job => job.GroupId is not null && IsTerminal(job.State))
                                .Select(static job => (job.QueueName, GroupId: job.GroupId!))
                                .Distinct(),
                ];

        private async ValueTask TryRemoveFairQueueCursorAsync(
                string queueName,
                string groupId,
                CancellationToken cancellationToken
        )
        {
                try
                {
                        await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                        if (await HasLiveGroupJobsAsync(context, queueName, groupId, cancellationToken).ConfigureAwait(false))
                        {
                                return;
                        }

                        var cursor = await context.Set<ImmediateFairQueueGroupEntity>()
                                .SingleOrDefaultAsync(
                                        group => group.QueueName == queueName && group.GroupId == groupId,
                                        cancellationToken
                                )
                                .ConfigureAwait(false);
                        if (cursor is null)
                                return;

                        _ = context.Remove(cursor);
                        _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                }
                catch (Exception exception) when (
                        !cancellationToken.IsCancellationRequested
                        && exception is DbException or DbUpdateException
                )
                {
                        // Cleanup is best-effort metadata maintenance and must not invalidate a committed transition.
                }
        }

        private static Task<bool> HasLiveGroupJobsAsync(
                TContext context,
                string queueName,
                string groupId,
                CancellationToken cancellationToken
        ) => context.Set<ImmediateJobEntity>().AnyAsync(
                job => job.QueueName == queueName
                        && job.GroupId == groupId
                        && (job.State == JobState.Pending
                                || job.State == JobState.Scheduled
                                || job.State == JobState.Active),
                cancellationToken
        );

        private async Task AddBatchJobCoreAsync(
                string currentJobId,
                JobRecord record,
                ContinuationOptions options,
                CancellationToken cancellationToken
        )
        {
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                await using var transaction = await context.Database.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);
                var current = await context.Set<ImmediateJobEntity>()
                        .SingleOrDefaultAsync(job => job.Id == currentJobId && job.State == JobState.Active, cancellationToken)
                        .ConfigureAwait(false)
                        ?? throw new ImmediateJobException($"The current active job '{currentJobId}' was not found.");
                if (current.BatchId is not { } batchId)
                        throw new ImmediateJobException("The current job does not belong to a batch.");
                if (options is not (ContinuationOptions.BesideContinuations or ContinuationOptions.BeforeContinuations))
                        throw new ArgumentOutOfRangeException(nameof(options));
                if (!string.Equals(record.BatchId, batchId, StringComparison.Ordinal))
                        throw new ImmediateJobException("The new job must belong to the current job's batch.");
                if (record.State is JobState.Active or JobState.AwaitingContinuation || IsTerminal(record.State))
                        throw new ImmediateJobException($"Concurrent batch member '{record.Id}' has invalid state '{record.State}'.");

                var batch = await context.Set<ImmediateJobBatchEntity>()
                        .SingleAsync(item => item.Id == batchId && item.State == BatchState.Executing, cancellationToken)
                        .ConfigureAwait(false);
                var job = ToEntity(record);
                _ = context.Add(job);
                batch.TotalJobs++;
                batch.PendingCount++;
                batch.ConcurrencyStamp = Guid.NewGuid();

                if (options == ContinuationOptions.BeforeContinuations)
                {
                        var waiters = await GetActiveWaitersAsync(context, currentJobId, cancellationToken).ConfigureAwait(false);
                        foreach (var waiter in waiters)
                        {
                                _ = context.Add(new ImmediateJobContinuationEntity
                                {
                                        ChildJobId = waiter.Id,
                                        ParentKind = ContinuationParentKind.Job,
                                        ParentId = job.Id,
                                        Trigger = ContinuationTrigger.Success,
                                });
                                waiter.RemainingDependencies++;
                                waiter.ConcurrencyStamp = Guid.NewGuid();
                        }
                }

                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);
        }

        private static async Task FlushContinuationAdditionsAsync(
                TContext context,
                ImmediateJobEntity current,
                IReadOnlyList<JobContinuationAddition> additions,
                CancellationToken cancellationToken
        )
        {
                var ids = new HashSet<string>(StringComparer.Ordinal);
                var trackedAdditions = 0;
                foreach (var addition in additions)
                {
                        ArgumentNullException.ThrowIfNull(addition);
                        ArgumentNullException.ThrowIfNull(addition.Job);
                        if (!ids.Add(addition.Job.Id))
                                throw new ImmediateJobException("Buffered continuations contain duplicate job identifiers.");
                        if (!Enum.IsDefined(addition.Trigger))
                                throw new ArgumentOutOfRangeException(nameof(additions), "Unknown continuation trigger.");
                        if (addition.Job.State is not (JobState.Pending or JobState.Scheduled))
                                throw new ImmediateJobException($"Dynamic continuation '{addition.Job.Id}' has invalid state '{addition.Job.State}'.");

                        if (addition.Options == ContinuationOptions.Detached)
                        {
                                if (addition.Job.BatchId is not null)
                                        throw new ImmediateJobException("A detached continuation cannot belong to a batch.");
                        }
                        else if (addition.Options is ContinuationOptions.BesideContinuations or ContinuationOptions.BeforeContinuations)
                        {
                                if (current.BatchId is null || !string.Equals(addition.Job.BatchId, current.BatchId, StringComparison.Ordinal))
                                        throw new ImmediateJobException("A batch-tracked continuation must belong to the current job's batch.");
                                trackedAdditions++;
                        }
                        else
                        {
                                throw new ArgumentOutOfRangeException(nameof(additions), "Unknown continuation option.");
                        }
                }

                var waiters = additions.Any(static addition => addition.Options == ContinuationOptions.BeforeContinuations)
                        ? await GetActiveWaitersAsync(context, current.Id, cancellationToken).ConfigureAwait(false)
                        : [];
                ImmediateJobBatchEntity? batch = null;
                if (trackedAdditions != 0)
                {
                        if (current.BatchId is not { } batchId)
                                throw new ImmediateJobException("The current job does not belong to a batch.");
                        batch = await context.Set<ImmediateJobBatchEntity>()
                                .SingleAsync(item => item.Id == batchId && item.State == BatchState.Executing, cancellationToken)
                                .ConfigureAwait(false);
                        batch.TotalJobs += trackedAdditions;
                        batch.PendingCount += trackedAdditions;
                        batch.ConcurrencyStamp = Guid.NewGuid();
                }

                foreach (var addition in additions)
                {
                        var job = ToEntity(addition.Job with
                        {
                                State = JobState.AwaitingContinuation,
                                RemainingDependencies = 1,
                        });
                        _ = context.Add(job);
                        _ = context.Add(new ImmediateJobContinuationEntity
                        {
                                ChildJobId = job.Id,
                                ParentKind = ContinuationParentKind.Job,
                                ParentId = current.Id,
                                Trigger = addition.Trigger,
                        });

                        if (addition.Options != ContinuationOptions.BeforeContinuations)
                                continue;
                        foreach (var waiter in waiters)
                        {
                                _ = context.Add(new ImmediateJobContinuationEntity
                                {
                                        ChildJobId = waiter.Id,
                                        ParentKind = ContinuationParentKind.Job,
                                        ParentId = job.Id,
                                        Trigger = ContinuationTrigger.Success,
                                });
                                waiter.RemainingDependencies++;
                                waiter.ConcurrencyStamp = Guid.NewGuid();
                        }
                }
        }

        private static async Task<List<ImmediateJobEntity>> GetActiveWaitersAsync(
                TContext context,
                string currentJobId,
                CancellationToken cancellationToken
        )
        {
                var waiterIds = await context.Set<ImmediateJobContinuationEntity>()
                        .Where(edge => edge.ParentKind == ContinuationParentKind.Job && edge.ParentId == currentJobId)
                        .Select(edge => edge.ChildJobId)
                        .Distinct()
                        .ToArrayAsync(cancellationToken)
                        .ConfigureAwait(false);
                return waiterIds.Length == 0
                        ? []
                        : await context.Set<ImmediateJobEntity>()
                                .Where(job => waiterIds.Contains(job.Id) && job.State == JobState.AwaitingContinuation)
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
        }

        private static async Task PropagateTerminalAsync(
                TContext context,
                ImmediateJobEntity terminalJob,
                DateTimeOffset now,
                CancellationToken cancellationToken
        )
        {
                var parents = new Queue<(ContinuationParentKind Kind, string Id, ContinuationParentOutcome Outcome)>();
                var processed = new HashSet<(ContinuationParentKind Kind, string Id)>();
                parents.Enqueue((
                        ContinuationParentKind.Job,
                        terminalJob.Id,
                        GetParentOutcome(terminalJob.State)
                ));
                await UpdateBatchForTerminalJobAsync(context, terminalJob, now, parents, cancellationToken).ConfigureAwait(false);

                while (parents.TryDequeue(out var parent))
                {
                        if (!processed.Add((parent.Kind, parent.Id)))
                                continue;
                        var edges = await context.Set<ImmediateJobContinuationEntity>()
                                .Where(edge => edge.ParentKind == parent.Kind
                                        && edge.ParentId == parent.Id
                                        && edge.ParentOutcome == ContinuationParentOutcome.Unsettled)
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
                        foreach (var edge in edges)
                        {
                                edge.ParentOutcome = parent.Outcome;
                                var child = await context.Set<ImmediateJobEntity>()
                                        .SingleOrDefaultAsync(job => job.Id == edge.ChildJobId, cancellationToken)
                                        .ConfigureAwait(false);
                                if (child is null || IsTerminal(child.State))
                                        continue;

                                if (child.State != JobState.AwaitingContinuation || child.RemainingDependencies <= 0)
                                        continue;
                                child.RemainingDependencies--;
                                if (parent.Outcome == ContinuationParentOutcome.Failed)
                                        child.FailedDependencies++;
                                if (child.RemainingDependencies == 0)
                                {
                                        var cancel = await ShouldCancelSettledContinuationAsync(
                                                context,
                                                child.Id,
                                                cancellationToken
                                        ).ConfigureAwait(false);
                                        if (cancel)
                                        {
                                                child.State = JobState.Cancelled;
                                                child.CompletedAt = now;
                                                parents.Enqueue((ContinuationParentKind.Job, child.Id, ContinuationParentOutcome.Other));
                                                await UpdateBatchForTerminalJobAsync(context, child, now, parents, cancellationToken).ConfigureAwait(false);
                                        }
                                        else
                                        {
                                                child.State = child.DueAt <= now ? JobState.Pending : JobState.Scheduled;
                                        }
                                }

                                child.ConcurrencyStamp = Guid.NewGuid();
                        }
                }
        }

        private static async Task<bool> ShouldCancelSettledContinuationAsync(
                TContext context,
                string childJobId,
                CancellationToken cancellationToken
        )
        {
                var edges = await context.Set<ImmediateJobContinuationEntity>()
                        .Where(edge => edge.ChildJobId == childJobId)
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                var requiresFailure = false;
                var anyFailed = false;
                foreach (var edge in edges)
                {
                        if (edge.Trigger == ContinuationTrigger.Success
                                && edge.ParentOutcome != ContinuationParentOutcome.Succeeded)
                                return true;
                        requiresFailure |= edge.Trigger == ContinuationTrigger.Failure;
                        anyFailed |= edge.ParentOutcome == ContinuationParentOutcome.Failed;
                }

                return requiresFailure && !anyFailed;
        }

        private static async Task UpdateBatchForTerminalJobAsync(
                TContext context,
                ImmediateJobEntity job,
                DateTimeOffset now,
                Queue<(ContinuationParentKind Kind, string Id, ContinuationParentOutcome Outcome)> parents,
                CancellationToken cancellationToken
        )
        {
                if (job.BatchId is not { } batchId)
                        return;
                var batch = await context.Set<ImmediateJobBatchEntity>()
                        .SingleAsync(item => item.Id == batchId, cancellationToken)
                        .ConfigureAwait(false);
                batch.PendingCount = Math.Max(0, batch.PendingCount - 1);
                switch (job.State)
                {
                        case JobState.Succeeded:
                                batch.SucceededCount++;
                                break;
                        case JobState.Failed:
                                batch.FailedCount++;
                                break;
                        case JobState.Cancelled:
                                batch.CancelledCount++;
                                break;
                        case JobState.AwaitingContinuation:
                        case JobState.AwaitingParameters:
                        case JobState.Scheduled:
                        case JobState.Pending:
                        case JobState.Active:
                                throw new ImmediateJobException($"Job '{job.Id}' is not terminal.");
                        default:
                                throw new ArgumentOutOfRangeException(nameof(job), job.State, "Unknown job state.");
                }

                batch.ConcurrencyStamp = Guid.NewGuid();
                if (batch.PendingCount != 0)
                        return;
                batch.State = GetTerminalBatchState(batch.FailedCount, batch.CancelledCount);
                batch.CompletedAt = now;
                parents.Enqueue((
                        ContinuationParentKind.Batch,
                        batch.Id,
                        GetParentOutcome(batch.State)
                ));
        }

        private static async Task EvaluateInitialDependenciesAsync(
                TContext context,
                Dictionary<string, ImmediateJobEntity> jobs,
                ImmediateJobContinuationEntity[] edges,
                DateTimeOffset now,
                CancellationToken cancellationToken
        )
        {
                var externalJobIds = edges
                        .Where(edge => edge.ParentKind == ContinuationParentKind.Job && !jobs.ContainsKey(edge.ParentId))
                        .Select(static edge => edge.ParentId)
                        .Distinct(StringComparer.Ordinal)
                        .Order(StringComparer.Ordinal)
                        .ToArray();
                var externalBatchIds = edges
                        .Where(static edge => edge.ParentKind == ContinuationParentKind.Batch)
                        .Select(static edge => edge.ParentId)
                        .Distinct(StringComparer.Ordinal)
                        .Order(StringComparer.Ordinal)
                        .ToArray();
                var externalJobEntities = externalJobIds.Length == 0
                        ? []
                        : await context.Set<ImmediateJobEntity>()
                                .Where(job => externalJobIds.Contains(job.Id))
                                .OrderBy(static job => job.Id)
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
                var externalBatchEntities = externalBatchIds.Length == 0
                        ? []
                        : await context.Set<ImmediateJobBatchEntity>()
                                .Where(batch => externalBatchIds.Contains(batch.Id))
                                .OrderBy(static batch => batch.Id)
                                .ToListAsync(cancellationToken)
                                .ConfigureAwait(false);
                var externalJobs = externalJobEntities.ToDictionary(job => job.Id, StringComparer.Ordinal);
                var externalBatches = externalBatchEntities.ToDictionary(batch => batch.Id, StringComparer.Ordinal);
                if (externalJobs.Count != externalJobIds.Length || externalBatches.Count != externalBatchIds.Length)
                        throw new ImmediateJobException("A continuation parent does not exist.");
                foreach (var parent in externalJobEntities.Where(parent => !IsTerminal(parent.State)))
                        parent.ConcurrencyStamp = Guid.NewGuid();
                foreach (var parent in externalBatchEntities.Where(parent => parent.State == BatchState.Executing))
                        parent.ConcurrencyStamp = Guid.NewGuid();

                var incoming = edges.ToLookup(static edge => edge.ChildJobId, StringComparer.Ordinal);
                var changed = true;
                while (changed)
                {
                        changed = false;
                        foreach (var job in jobs.Values)
                        {
                                var dependencies = incoming[job.Id];
                                if (!dependencies.Any() || IsTerminal(job.State))
                                        continue;
                                var remaining = 0;
                                var failedDependencies = 0;
                                var requiresFailure = false;
                                var violated = false;
                                foreach (var edge in dependencies)
                                {
                                        var (terminal, parentSucceeded, parentFailed) = GetParentState(
                                                edge,
                                                jobs,
                                                externalJobs,
                                                externalBatches
                                        );
                                        requiresFailure |= edge.Trigger == ContinuationTrigger.Failure;
                                        if (!terminal)
                                        {
                                                remaining++;
                                                continue;
                                        }

                                        edge.ParentOutcome = GetParentOutcome(parentSucceeded, parentFailed);

                                        if (parentFailed)
                                                failedDependencies++;
                                        if (edge.Trigger == ContinuationTrigger.Success && !parentSucceeded)
                                                violated = true;
                                }

                                job.FailedDependencies = failedDependencies;
                                if (violated || (remaining == 0 && requiresFailure && failedDependencies == 0))
                                {
                                        job.State = JobState.Cancelled;
                                        job.RemainingDependencies = 0;
                                        job.CompletedAt = now;
                                        changed = true;
                                }
                                else if (remaining == 0)
                                {
                                        job.State = job.DueAt <= now ? JobState.Pending : JobState.Scheduled;
                                        job.RemainingDependencies = 0;
                                }
                                else
                                {
                                        job.State = JobState.AwaitingContinuation;
                                        job.RemainingDependencies = remaining;
                                }
                        }
                }
        }

        private static (bool Terminal, bool Succeeded, bool Failed) GetParentState(
                ImmediateJobContinuationEntity edge,
                Dictionary<string, ImmediateJobEntity> jobs,
                Dictionary<string, ImmediateJobEntity> externalJobs,
                Dictionary<string, ImmediateJobBatchEntity> externalBatches
        )
        {
                if (edge.ParentKind == ContinuationParentKind.Batch)
                {
                        var state = externalBatches[edge.ParentId].State;
                        return (state != BatchState.Executing, state == BatchState.Succeeded, state == BatchState.Failed);
                }

                var jobState = jobs.TryGetValue(edge.ParentId, out var job) ? job.State : externalJobs[edge.ParentId].State;
                return (IsTerminal(jobState), jobState == JobState.Succeeded, jobState == JobState.Failed);
        }

        private static void ThrowIfCyclic(
                HashSet<string> jobIds,
                IReadOnlyList<ImmediateJobContinuationEntity> edges
        )
        {
                var indegree = jobIds.ToDictionary(static id => id, static _ => 0, StringComparer.Ordinal);
                var children = new Dictionary<string, List<string>>(StringComparer.Ordinal);
                foreach (var edge in edges.Where(edge =>
                        edge.ParentKind == ContinuationParentKind.Job && jobIds.Contains(edge.ParentId)))
                {
                        indegree[edge.ChildJobId]++;
                        if (!children.TryGetValue(edge.ParentId, out var values))
                                children[edge.ParentId] = values = [];
                        values.Add(edge.ChildJobId);
                }

                var ready = new Queue<string>(indegree.Where(static pair => pair.Value == 0).Select(static pair => pair.Key));
                var visited = 0;
                while (ready.TryDequeue(out var parent))
                {
                        visited++;
                        if (!children.TryGetValue(parent, out var values))
                                continue;
                        foreach (var child in values)
                        {
                                if (--indegree[child] == 0)
                                        ready.Enqueue(child);
                        }
                }

                if (visited != jobIds.Count)
                        throw new ImmediateJobException("The continuation graph contains a dependency cycle.");
        }

        private static bool IsTerminal(JobState state) =>
                state is JobState.Succeeded or JobState.Failed or JobState.Cancelled;

        private static ContinuationParentOutcome GetParentOutcome(JobState state) => state switch
        {
                JobState.Succeeded => ContinuationParentOutcome.Succeeded,
                JobState.Failed => ContinuationParentOutcome.Failed,
                JobState.AwaitingContinuation or
                JobState.AwaitingParameters or
                JobState.Scheduled or
                JobState.Pending or
                JobState.Active or
                JobState.Cancelled => ContinuationParentOutcome.Other,
                _ => throw new ArgumentOutOfRangeException(nameof(state), state, "Unknown job state."),
        };

        private static ContinuationParentOutcome GetParentOutcome(BatchState state) => state switch
        {
                BatchState.Succeeded => ContinuationParentOutcome.Succeeded,
                BatchState.Failed => ContinuationParentOutcome.Failed,
                BatchState.Executing or BatchState.Cancelled => ContinuationParentOutcome.Other,
                _ => throw new ArgumentOutOfRangeException(nameof(state), state, "Unknown batch state."),
        };

        private static ContinuationParentOutcome GetParentOutcome(bool succeeded, bool failed) =>
                (succeeded, failed) switch
                {
                        (true, _) => ContinuationParentOutcome.Succeeded,
                        (_, true) => ContinuationParentOutcome.Failed,
                        _ => ContinuationParentOutcome.Other,
                };

        private static BatchState GetTerminalBatchState(int failed, int cancelled) =>
                failed != 0 ? BatchState.Failed : cancelled != 0 ? BatchState.Cancelled : BatchState.Succeeded;

        private async ValueTask MutateRecurringAsync(string name, Action<ImmediateRecurringJobEntity> mutate, CancellationToken cancellationToken)
        {
                ArgumentException.ThrowIfNullOrWhiteSpace(name);
                await using var context = await contextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
                var schedule = await context.Set<ImmediateRecurringJobEntity>().FindAsync([name], cancellationToken).ConfigureAwait(false);
                if (schedule is null)
                        return;
                mutate(schedule);
                schedule.ConcurrencyStamp = Guid.NewGuid();
                _ = await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
        }

        private static Task<int> UpdateRecurringAsync(
                TContext context,
                RecurringJobSchedule schedule,
                CancellationToken cancellationToken
        )
        {
                var concurrencyStamp = Guid.NewGuid();
                return context.Set<ImmediateRecurringJobEntity>()
                        .Where(entity => entity.Name == schedule.Name && (schedule.IsCodeDefined || !entity.IsCodeDefined))
                        .ExecuteUpdateAsync(setters => setters
                                .SetProperty(entity => entity.JobName, schedule.JobName)
                                .SetProperty(entity => entity.Cron, schedule.Cron)
                                .SetProperty(entity => entity.TimeZone, schedule.TimeZone)
                                .SetProperty(entity => entity.IsCodeDefined, schedule.IsCodeDefined)
                                .SetProperty(entity => entity.NextRunAt, schedule.NextRunAt)
                                .SetProperty(entity => entity.ConcurrencyStamp, concurrencyStamp),
                                cancellationToken);
        }

        private static async Task ThrowIfReplacingCodeDefinedScheduleAsync(
                TContext context,
                RecurringJobSchedule schedule,
                CancellationToken cancellationToken
        )
        {
                if (!schedule.IsCodeDefined && await context.Set<ImmediateRecurringJobEntity>()
                        .AnyAsync(entity => entity.Name == schedule.Name && entity.IsCodeDefined, cancellationToken)
                        .ConfigureAwait(false))
                {
                        throw new ImmediateJobException("Code-defined recurring schedules cannot be replaced by dynamic schedules.");
                }
        }

        private static ImmediateJobEntity ToEntity(JobRecord job) => new()
        {
                Id = job.Id,
                QueueName = job.QueueName,
                JobName = job.JobName,
                GroupId = job.GroupId,
                Payload = job.Payload,
                Context = job.Context,
                State = job.State,
                DueAt = job.DueAt,
                CreatedAt = job.CreatedAt,
                Attempt = job.Attempt,
                WorkerId = job.WorkerId,
                LeaseExpiresAt = job.LeaseExpiresAt,
                LastError = job.LastError,
                CompletedAt = job.CompletedAt,
                RecurringKey = job.RecurringKey,
                TraceParent = job.TraceParent,
                TraceState = job.TraceState,
                ExecutionTraceId = job.ExecutionTraceId,
                ExecutionSpanId = job.ExecutionSpanId,
                ExecutionStartedAt = job.ExecutionStartedAt,
                BatchId = job.BatchId,
                RemainingDependencies = job.RemainingDependencies,
                FailedDependencies = job.FailedDependencies,
                ConcurrencyStamp = Guid.NewGuid(),
        };

        private static ImmediateJobContinuationEntity ToEntity(JobContinuationEdge edge)
        {
                var hasJobParent = edge.ParentJobId is not null;
                var hasBatchParent = edge.ParentBatchId is not null;
                if (hasJobParent == hasBatchParent)
                        throw new ImmediateJobException("A continuation edge must identify exactly one parent job or batch.");
                return new()
                {
                        ChildJobId = edge.ChildJobId,
                        ParentKind = hasJobParent ? ContinuationParentKind.Job : ContinuationParentKind.Batch,
                        ParentId = edge.ParentJobId ?? edge.ParentBatchId!,
                        Trigger = edge.Trigger,
                };
        }

        private static ImmediateJobEntity Copy(ImmediateJobEntity job) => new()
        {
                Id = job.Id,
                QueueName = job.QueueName,
                JobName = job.JobName,
                GroupId = job.GroupId,
                Payload = job.Payload,
                Context = job.Context,
                State = job.State,
                DueAt = job.DueAt,
                CreatedAt = job.CreatedAt,
                Attempt = job.Attempt,
                WorkerId = job.WorkerId,
                LeaseExpiresAt = job.LeaseExpiresAt,
                LastError = job.LastError,
                CompletedAt = job.CompletedAt,
                RecurringKey = job.RecurringKey,
                TraceParent = job.TraceParent,
                TraceState = job.TraceState,
                ExecutionTraceId = job.ExecutionTraceId,
                ExecutionSpanId = job.ExecutionSpanId,
                ExecutionStartedAt = job.ExecutionStartedAt,
                BatchId = job.BatchId,
                RemainingDependencies = job.RemainingDependencies,
                FailedDependencies = job.FailedDependencies,
                ConcurrencyStamp = job.ConcurrencyStamp,
        };

        private static JobRecord ToRecord(ImmediateJobEntity job) => new()
        {
                Id = job.Id,
                QueueName = job.QueueName,
                JobName = job.JobName,
                GroupId = job.GroupId,
                Payload = job.Payload,
                Context = job.Context,
                State = job.State,
                DueAt = job.DueAt,
                CreatedAt = job.CreatedAt,
                Attempt = job.Attempt,
                WorkerId = job.WorkerId,
                LeaseExpiresAt = job.LeaseExpiresAt,
                LastError = job.LastError,
                CompletedAt = job.CompletedAt,
                RecurringKey = job.RecurringKey,
                TraceParent = job.TraceParent,
                TraceState = job.TraceState,
                ExecutionTraceId = job.ExecutionTraceId,
                ExecutionSpanId = job.ExecutionSpanId,
                ExecutionStartedAt = job.ExecutionStartedAt,
                BatchId = job.BatchId,
                RemainingDependencies = job.RemainingDependencies,
                FailedDependencies = job.FailedDependencies,
        };

        private static BatchStatus ToStatus(ImmediateJobBatchEntity batch) => new(
                batch.Id,
                batch.State,
                batch.TotalJobs,
                batch.SucceededCount,
                batch.FailedCount,
                batch.CancelledCount,
                batch.PendingCount,
                batch.CreatedAt,
                batch.StartedAt,
                batch.CompletedAt,
                BatchStatus.CalculateFractionSettled(batch.TotalJobs, batch.PendingCount)
        );

        private static JobContinuationEdge ToContinuationEdge(ImmediateJobContinuationEntity edge) => new()
        {
                ChildJobId = edge.ChildJobId,
                ParentJobId = edge.ParentKind == ContinuationParentKind.Job ? edge.ParentId : null,
                ParentBatchId = edge.ParentKind == ContinuationParentKind.Batch ? edge.ParentId : null,
                Trigger = edge.Trigger,
        };

        private static BatchGraphEdge ToGraphEdge(ImmediateJobContinuationEntity edge) => new(
                edge.ChildJobId,
                edge.ParentKind == ContinuationParentKind.Job ? edge.ParentId : null,
                edge.ParentKind == ContinuationParentKind.Batch ? edge.ParentId : null,
                edge.Trigger
        );

        private static ImmediateRecurringJobEntity ToEntity(RecurringJobSchedule schedule) => new()
        {
                Name = schedule.Name,
                JobName = schedule.JobName,
                Cron = schedule.Cron,
                TimeZone = schedule.TimeZone,
                IsCodeDefined = schedule.IsCodeDefined,
                IsPaused = schedule.IsPaused,
                NextRunAt = schedule.NextRunAt,
                LastRunAt = schedule.LastRunAt,
                ConcurrencyStamp = Guid.NewGuid(),
        };
}

ImmediatePlatform / Immediate.Jobs / 30589302714

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