parallelize/request-queue.js

"use strict";

const Promise = require("bluebird");
const pDefer = require("p-defer");

module.exports = function createRequestQueue(options = {}) {
	let requestBuffer = [];
	let responseBuffer = [];
	let seenError;

	function failAllRequests(error) {
		let failedRequests = requestBuffer;
		requestBuffer = [];

		seenError = error;

		for (let request of failedRequests) {
			request.reject(error);
		}
	}

	function maybeOnMatch() {
		if (options.onMatch != null) {
			return Promise.try(() => {
				return options.onMatch();
			}).catch((error) => {
				failAllRequests(error);
			});
		}
	}

	return {
		pushRequest: function () {
			if (responseBuffer.length > 0) {
				let returnValue = Promise.resolve(responseBuffer.shift());
				maybeOnMatch();
				return returnValue;
			} else if (seenError !== undefined) {
				return Promise.reject(seenError);
			} else {
				let { resolve, reject, promise } = pDefer();
				requestBuffer.push({ resolve, reject });
				return promise;
			}
		},
		pushResponse: function (response) {
			if (requestBuffer.length > 0) {
				let request = requestBuffer.shift();
				request.resolve(response);
				maybeOnMatch();
			} else {
				responseBuffer.push(response);
			}
		},
		failAllRequests: failAllRequests,
		requestCount: function () {
			return requestBuffer.length;
		},
		responseCount: function () {
			return responseBuffer.length;
		}
	};
};