@fine-js/channels/src/buffers.js

Bits of Clojure's `core.async` ported to JS

'use strict'

const rename = (func, name, arity = func.length) => Object.defineProperties(func, {
  name: {value: name},
  length: {value: arity},
})

const createBuffer = (name, blocking, impl) => rename((capacity = 1) => {
  const buf = impl(capacity)
  const kind = buf.kind || `${name}(${capacity})`

  return {
    kind,
    load: buf.load,
    capacity,
    blocking,
    readable: buf.readable,
    writable: buf.writable,

    peek: () => {
      if (!buf.readable())
        throw new Error(`${kind} is empty`)

      return buf.peek()
    },

    read: () => {
      if (!buf.readable())
        throw new Error(`${kind} is empty`)

      return buf.read()
    },

    write: (val) => {
      if (!buf.writable())
        throw new Error(`${kind} is full`)

      buf.write(val)
    },

    status: () => ({
      kind,
      load: buf.load(),
      capacity,
      blocking,
      readable: buf.readable(),
      writable: buf.writable(),
    }),
  }
}, name)

const buffer = createBuffer('buffer', true, (capacity) => {
  const buf = []

  return {
    load: () => buf.length,
    peek: () => buf[0],
    read: () => buf.shift(),
    write: (val) => buf.push(val),
    readable: () => buf.length > 0,
    writable: () => buf.length < capacity,
  }
})

const dropping = createBuffer('dropping', false, (capacity) => {
  const buf = []

  return {
    load: () => buf.length,
    peek: () => buf[0],
    read: () => buf.shift(),
    write: (val) => {
      if (capacity > buf.length)
        buf.push(val)
    },
    readable: () => buf.length > 0,
    writable: () => true,
  }
})

const sliding = createBuffer('sliding', false, (capacity) => {
  const buf = []

  return {
    load: () => buf.length,
    peek: () => buf[0],
    read: () => buf.shift(),
    write: (val) => {
      if (buf.push(val) > capacity)
        buf.shift()
    },
    readable: () => buf.length > 0,
    writable: () => true,
  }
})

const unbuffered = () => Object.freeze({
  kind: 'unbuffered()',
  load: () => 0,
  capacity: 0,
  blocking: true,
  readable: () => false,
  writable: () => false,
  peek: () => { throw new Error('peeking into unbuffered()') },
  read: () => { throw new Error('reading from unbuffered()') },
  write: () => { throw new Error('writing to unbuffered()') },
  status: () => null,
})

module.exports = {
  unbuffered,
  buffer,
  dropping,
  sliding,
}