when/lib/decorators/iterate.js

/** @license MIT License (c) copyright 2010-2014 original author or authors */
/** @author Brian Cavalier */
/** @author John Hann */

(function(define) { 'use strict';
define(function() {

	return function generate(Promise) {

		var resolve = Promise.resolve;

		Promise.iterate = iterate;
		Promise.unfold = unfold;

		return Promise;

		/**
		 * @deprecated Use github.com/cujojs/most streams and most.iterate
		 * Generate a (potentially infinite) stream of promised values:
		 * x, f(x), f(f(x)), etc. until condition(x) returns true
		 * @param {function} f function to generate a new x from the previous x
		 * @param {function} condition function that, given the current x, returns
		 *  truthy when the iterate should stop
		 * @param {function} handler function to handle the value produced by f
		 * @param {*|Promise} x starting value, may be a promise
		 * @return {Promise} the result of the last call to f before
		 *  condition returns true
		 */
		function iterate(f, condition, handler, x) {
			return unfold(function(x) {
				return [x, f(x)];
			}, condition, handler, x);
		}

		/**
		 * @deprecated Use github.com/cujojs/most streams and most.unfold
		 * Generate a (potentially infinite) stream of promised values
		 * by applying handler(generator(seed)) iteratively until
		 * condition(seed) returns true.
		 * @param {function} unspool function that generates a [value, newSeed]
		 *  given a seed.
		 * @param {function} condition function that, given the current seed, returns
		 *  truthy when the unfold should stop
		 * @param {function} handler function to handle the value produced by unspool
		 * @param x {*|Promise} starting value, may be a promise
		 * @return {Promise} the result of the last value produced by unspool before
		 *  condition returns true
		 */
		function unfold(unspool, condition, handler, x) {
			return resolve(x).then(function(seed) {
				return resolve(condition(seed)).then(function(done) {
					return done ? seed : resolve(unspool(seed)).spread(next);
				});
			});

			function next(item, newSeed) {
				return resolve(handler(item)).then(function() {
					return unfold(unspool, condition, handler, newSeed);
				});
			}
		}
	};

});
}(typeof define === 'function' && define.amd ? define : function(factory) { module.exports = factory(); }));