pnpm/lib/node_modules/most/src/source/iterate.js

Fast, disk space efficient package manager

/** @license MIT License (c) copyright 2010-2016 original author or authors */
/** @author Brian Cavalier */
/** @author John Hann */

import Stream from '../Stream'

/**
 * Compute a stream by iteratively calling f to produce values
 * Event times may be controlled by returning a Promise from f
 * @param {function(x:*):*|Promise<*>} f
 * @param {*} x initial value
 * @returns {Stream}
 */
export function iterate (f, x) {
  return new Stream(new IterateSource(f, x))
}

function IterateSource (f, x) {
  this.f = f
  this.value = x
}

IterateSource.prototype.run = function (sink, scheduler) {
  return new Iterate(this.f, this.value, sink, scheduler)
}

function Iterate (f, initial, sink, scheduler) {
  this.f = f
  this.sink = sink
  this.scheduler = scheduler
  this.active = true

  var x = initial

  var self = this
  function err (e) {
    self.sink.error(self.scheduler.now(), e)
  }

  function start (iterate) {
    return stepIterate(iterate, x)
  }

  Promise.resolve(this).then(start).catch(err)
}

Iterate.prototype.dispose = function () {
  this.active = false
}

function stepIterate (iterate, x) {
  iterate.sink.event(iterate.scheduler.now(), x)

  if (!iterate.active) {
    return x
  }

  var f = iterate.f
  return Promise.resolve(f(x)).then(function (y) {
    return continueIterate(iterate, y)
  })
}

function continueIterate (iterate, x) {
  return !iterate.active ? iterate.value : stepIterate(iterate, x)
}