LukaJCB / ts-mls / 20546274682

import { CodecError } from "../mlsError.js"

import { base64ToBytes, bytesToBase64 } from "../util/byteArray.js"

import { decodeUint64, uint64Encoder } from "./number.js"

import { Decoder, mapDecoder, mapDecoders } from "./tlsDecoder.js"

import { BufferEncoder, contramapBufferEncoder, contramapBufferEncoders } from "./tlsEncoder.js"

export const varLenDataEncoder: BufferEncoder<Uint8Array> = (data) => {

  const [len, write] = lengthEncoder(data.length)

  return [

    len + data.length,

    (offset, buffer) => {

      write(offset, buffer)

      const view = new Uint8Array(buffer)

      view.set(data, offset + len)

    },

  ]

}

export function lengthEncoder(len: number): [number, (offset: number, buffer: ArrayBuffer) => void] {

  if (len < 64) {

    return [

      1,

      (offset, buffer) => {

        const view = new DataView(buffer)

        view.setUint8(offset, len & 0b00111111)

      },

    ]

  } else if (len < 16384) {

    return [

      2,

      (offset, buffer) => {

        const view = new DataView(buffer)

        view.setUint8(offset, ((len >> 8) & 0b00111111) | 0b01000000)

        view.setUint8(offset + 1, len & 0xff)

      },

    ]

  } else if (len < 0x40000000) {

    return [

      4,

      (offset, buffer) => {

        const view = new DataView(buffer)

        view.setUint8(offset, ((len >> 24) & 0b00111111) | 0b10000000)

        view.setUint8(offset + 1, (len >> 16) & 0xff)

        view.setUint8(offset + 2, (len >> 8) & 0xff)

        view.setUint8(offset + 3, len & 0xff)

      },

    ]

  } else {

    throw new CodecError("Length too large to encode (max is 2^30 - 1)")

  }

}

export function determineLength(data: Uint8Array, offset: number = 0): { length: number; lengthFieldSize: number } {

  if (offset >= data.length) {

    throw new CodecError("Offset beyond buffer")

  }

  const firstByte = data[offset] as number

  const prefix = firstByte >> 6

  if (prefix === 0) {

    return { length: firstByte & 0b00111111, lengthFieldSize: 1 }

  } else if (prefix === 1) {

    return { length: ((firstByte & 0b00111111) << 8) | (data[offset + 1] as number), lengthFieldSize: 2 }

  } else if (prefix === 2) {

    return {

      length:

        ((firstByte & 0b00111111) << 24) |

        ((data[offset + 1] as number) << 16) |

        ((data[offset + 2] as number) << 8) |

        (data[offset + 3] as number),

      lengthFieldSize: 4,

    }

  } else {

    throw new CodecError("8-byte length not supported in this implementation")

  }

}

export const decodeVarLenData: Decoder<Uint8Array> = (buf, offset) => {

  if (offset >= buf.length) {

    throw new CodecError("Offset beyond buffer")

  }

  const { length, lengthFieldSize } = determineLength(buf, offset)

  const totalBytes = lengthFieldSize + length

  if (offset + totalBytes > buf.length) {

    throw new CodecError("Data length exceeds buffer")

  }

  const data = buf.subarray(offset + lengthFieldSize, offset + totalBytes)

  return [data, totalBytes]

}

export function varLenTypeEncoder<T>(enc: BufferEncoder<T>): BufferEncoder<T[]> {

  return (data) => {

    let totalLength = 0

    let writeTotal = (_offset: number, _buffer: ArrayBuffer) => {}

    for (let i = 0; i < data.length; i++) {

      const [len, write] = enc(data[i]!)

      const oldFunc = writeTotal

      const currentLen = totalLength

      writeTotal = (offset: number, buffer: ArrayBuffer) => {

        oldFunc(offset, buffer)

        write(offset + currentLen, buffer)

      }

      totalLength += len

    }

    const [headerLength, writeLength] = lengthEncoder(totalLength)

    return [

      headerLength + totalLength,

      (offset, buffer) => {

        writeLength(offset, buffer)

        writeTotal(offset + headerLength, buffer)

      },

    ]

  }

}

export function decodeVarLenType<T>(dec: Decoder<T>): Decoder<T[]> {

  return (b, offset) => {

    const d = decodeVarLenData(b, offset)

    const [totalBytes, totalLength] = d

    let cursor = 0

    const result: T[] = []

    while (cursor < totalBytes.length) {

      const item = dec(totalBytes, cursor)

      if (item === undefined) return undefined

      const [value, len] = item

      result.push(value)

      cursor += len

    }

    return [result, totalLength]

  }

}

export function base64RecordEncoder<V>(valueEncoder: BufferEncoder<V>): BufferEncoder<Record<string, V>> {

  const entryEncoder = contramapBufferEncoders(

    [contramapBufferEncoder(varLenDataEncoder, base64ToBytes), valueEncoder],

    ([key, value]: [string, V]) => [key, value] as const,

  )

  return contramapBufferEncoders([varLenTypeEncoder(entryEncoder)], (record) => [Object.entries(record)] as const)

}

export function decodeBase64Record<V>(decodeValue: Decoder<V>): Decoder<Record<string, V>> {

  return mapDecoder(

    decodeVarLenType(

      mapDecoders([mapDecoder(decodeVarLenData, bytesToBase64), decodeValue], (key, value) => [key, value] as const),

    ),

    (entries) => {

      const record: Record<string, V> = {}

      return record

    },

  )

}

export function numberRecordEncoder<V>(

  numberEncoder: BufferEncoder<number>,

  valueEncoder: BufferEncoder<V>,

): BufferEncoder<Record<number, V>> {

  const entryEncoder = contramapBufferEncoders(

    [numberEncoder, valueEncoder],

    ([key, value]: [number, V]) => [key, value] as const,

  )

  return contramapBufferEncoder(varLenTypeEncoder(entryEncoder), (record) =>

    Object.entries(record).map(([key, value]) => [Number(key), value] as [number, V]),

  )

}

export function decodeNumberRecord<V>(

  decodeNumber: Decoder<number>,

  decodeValue: Decoder<V>,

): Decoder<Record<number, V>> {

  return mapDecoder(

    decodeVarLenType(mapDecoders([decodeNumber, decodeValue], (key, value) => [key, value] as const)),

    (entries) => {

      const record: Record<number, V> = {}

      for (const [key, value] of entries) {

        record[key] = value

      }

      return record

    },

  )

}

export function bigintMapEncoder<V>(valueEncoder: BufferEncoder<V>): BufferEncoder<Map<bigint, V>> {

  const entryEncoder = contramapBufferEncoders(

    [uint64Encoder, valueEncoder],

    ([key, value]: [bigint, V]) => [key, value] as const,

  )

  return contramapBufferEncoder(varLenTypeEncoder(entryEncoder), (map) => Array.from(map.entries()))

}

export function decodeBigintMap<V>(decodeValue: Decoder<V>): Decoder<Map<bigint, V>> {

  return mapDecoder(

    decodeVarLenType(mapDecoders([decodeUint64, decodeValue], (key, value) => [key, value] as const)),

    (entries) => new Map(entries),

  )

}