'use strict';

const none = Symbol.for('object-stream.none');
const stop = Symbol.for('object-stream.stop');

const finalSymbol = Symbol.for('object-stream.final');
const manySymbol = Symbol.for('object-stream.many');
const flushSymbol = Symbol.for('object-stream.flush');

const finalValue = value => ({[finalSymbol]: 1, value});
const many = values => ({[manySymbol]: 1, values});

const isFinalValue = o => o && o[finalSymbol] === 1;
const isMany = o => o && o[manySymbol] === 1;
const isFlushable = o => o && o[flushSymbol] === 1;

const getFinalValue = value => value.value;
const getManyValues = value => value.values;

const flushable = (write, final = null) => {
  const fn = final ? value => (value === none ? final() : write(value)) : write;
  fn[flushSymbol] = 1;
  return fn;
};

class Stop extends Error {}

// old aliases
const final = finalValue;

module.exports = {
  none,
  stop,
  Stop,
  finalSymbol,
  manySymbol,
  flushSymbol,
  finalValue,
  many,
  flushable,
  isFinalValue,
  isMany,
  isFlushable,
  getFinalValue,
  getManyValues,
  final
};