Calculate and output the estimated time remaining on a large number of batched promises and asynchronous tasks

estimated_time_remaining.js

var NUM_COUNT = 1000;
var _nums;


function _everyFiveWaitASecond() {
	var chunk = function(i, results) {
		results = results || [];
		console.log('chunk(', i, ')');

		if (!_nums.length) {
			return Promise.resolve();
		}

		var pair = _nums.pop();
		var a = pair[0];
		var b = pair[1];
		return addAsync(a, b).then(function(res) {
			results.push(res);
			return delay(
				i % 5 === 0 ? 1000 : 0
			).then(function() {
				return chunk(++i, results);
			})
		});
	};

	chunk(0).then(console.log);
}

function _init() {
	_nums = [];
	for (var i = 0; i < NUM_COUNT; i++) {
		_nums.push([i, i + 1]);
	}
}


function addAsync(a, b) {
	return new Promise(function(resolve) {
		var sum = a + b;
		var time = Math.floor(Math.random() * 1000);
		delay(time).then(function() {
			resolve(sum);
		});
	});
}

function delay(t) {
	return new Promise(function(resolve) {
		setTimeout(function() {
			resolve();
		}, t);
	});
}

function $q(promises) {
	return Promise.all(promises);
}

function main() {
	_init();
	// _everyFiveWaitASecond();

	var chunkSize = 5;
	var tasks = [];
	var results = [];

	for (var i = 0; i < _nums.length; i += chunkSize) {
		var fn = function(j) {
			var chunk = _nums.slice(j, j + chunkSize);
			return function() {
				return $q(chunk.map(function(pair) {
					var a = pair[0];
					var b = pair[1];
					return addAsync(a, b);
				})).then(function(sums) {
					results = results.concat(sums);
					console.log(sums);
				});
			};
		};
		tasks.push(fn(i));
	}

	var toTimeString = function(ms) {
		var seconds = Math.floor(ms / 1000);
		var minutes = Math.floor(ms / (1000 * 60));
		var hours = Math.floor(ms / (1000 * 60 * 60));
		var days = Math.floor(ms / (1000 * 60 * 60 * 24));
		var intervals = [];

		if (days > 0) {
			intervals.push(days, 'days');
		}

		if (hours > 0) {
			intervals.push(hours % 24, 'hours');
		}

		if (minutes > 0) {
			intervals.push(minutes % 60, 'minutes');
		}

		if (seconds > 0) {
			intervals.push(seconds % 60, 'seconds');
		}
		var str = intervals.join(' ');
		return str;
	};

	var times = [];
	var before = Date.now();
	var p = tasks.reduce(function(p, task, index) {
		return p.then(task).then(function() {
			times.push(Date.now());
			if (times.length < 2) {
				return;
			}
			var diff = 0;
			for (var i = 0; i < times.length - 1; i++) {
				var a = times[i];
				var b = times[i + 1];
				diff += b - a;
			}
			var avg = diff / times.length;
			var ms = avg * (tasks.length - index);
			var calculated = toTimeString(ms);
			var actual = toTimeString(Date.now() - before);
			console.log('Calculated: ', calculated);
			console.log('Actual:     ', actual);
		});
	}, Promise.resolve());

	p.then(function() {
		console.log(results.join(','));
	});
}


if (require.main === module) {
	main();
}