"use strict";

const Promise = require("bluebird");
const pDefer = require("p-defer");
const defaultValue = require("default-value");
const pListen = require("p-listen");

module.exports = function createRequestQueue(options = {}) {
	// FIXME: Validatem, docs
	let requestBuffer = [];
	let responseBuffer = [];
	let seenError;
	let requestDrainListener = pListen();
	let responseDrainListener = pListen();

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

		seenError = error;

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

	function handleOnMatch() {
		return Promise.try(() => {
			if (requestBuffer.length === 0) {
				requestDrainListener.notify();
			}
			
			if (responseBuffer.length === 0) {
				responseDrainListener.notify();
			}

			return maybeCall(options.onMatch);
		}).catch((error) => {
			failAllRequests(error);
		});
	}

	function maybeCall(func, ... args) {
		if (func != null) {
			return func(... args);
		}
	}

	return {
		pushRequest: function (onQueuedRequest) {
			if (responseBuffer.length > 0) {
				let returnValue = Promise.resolve(responseBuffer.shift());
				handleOnMatch();
				return returnValue;
			} else if (seenError !== undefined) {
				return Promise.reject(seenError);
			} else {
				let { resolve, reject, promise } = pDefer();
				requestBuffer.push({ resolve, reject });

				return Promise.try(() => {
					return maybeCall(defaultValue(onQueuedRequest, options.onQueuedRequest));
				}).then(() => {
					return promise;
				});
			}
		},
		pushResponse: function (response, onQueuedResponse) {
			if (requestBuffer.length > 0) {
				let request = requestBuffer.shift();
				request.resolve(response);
				handleOnMatch();
			} else {
				responseBuffer.push(response);
				return maybeCall(defaultValue(onQueuedResponse, options.onQueuedResponse));
			}
		},
		failAllRequests: failAllRequests,
		requestCount: function () {
			return requestBuffer.length;
		},
		responseCount: function () {
			return responseBuffer.length;
		},
		awaitRequestDrain: function () {
			if (this.requestCount() === 0) {
				return Promise.resolve();
			} else {
				return requestDrainListener.listen();
			}
		},
		awaitResponseDrain: function () {
			if (this.responseCount() === 0) {
				return Promise.resolve();
			} else {
				return responseDrainListener.listen();
			}
		}
	};
};