/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the Source EULA. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

'use strict';

import assert = require('assert');

/**
 * Executes the given function (fn) over the given array of items (list) in parallel and returns the resulting errors and results as
 * array to the callback (callback). The resulting errors and results are evaluated by calling the provided callback function.
 */
export function parallel<T, E>(list: T[], fn: (item: T, callback: (err: Error, result: E) => void) => void, callback: (err: Error[], result: E[]) => void): void {
	let results = new Array(list.length);
	let errors = new Array<Error>(list.length);
	let didErrorOccur = false;
	let doneCount = 0;

	if (list.length === 0) {
		return callback(null, []);
	}

	list.forEach((item, index) => {
		fn(item, (error, result) => {
			if (error) {
				didErrorOccur = true;
				results[index] = null;
				errors[index] = error;
			} else {
				results[index] = result;
				errors[index] = null;
			}

			if (++doneCount === list.length) {
				return callback(didErrorOccur ? errors : null, results);
			}
		});
	});
}

/**
 * Executes the given function (fn) over the given array of items (param) in sequential order and returns the first occurred error or the result as
 * array to the callback (callback). The resulting errors and results are evaluated by calling the provided callback function. The first param can
 * either be a function that returns an array of results to loop in async fashion or be an array of items already.
 */
export function loop<T, E>(param: (callback: (error: Error, result: T[]) => void) => void, fn: (item: T, callback: (error: Error, result: E) => void, index: number, total: number) => void, callback: (error: Error, result: E[]) => void): void;
export function loop<T, E>(param: T[], fn: (item: T, callback: (error: Error, result: E) => void, index: number, total: number) => void, callback: (error: Error, result: E[]) => void): void;
export function loop<E>(param: any, fn: (item: any, callback: (error: Error, result: E) => void, index: number, total: number) => void, callback: (error: Error, result: E[]) => void): void {

	// Assert
	assert.ok(param, 'Missing first parameter');
	assert.ok(typeof (fn) === 'function', 'Second parameter must be a function that is called for each element');
	assert.ok(typeof (callback) === 'function', 'Third parameter must be a function that is called on error and success');

	// Param is function, execute to retrieve array
	if (typeof (param) === 'function') {
		try {
			param((error: Error, result: E[]) => {
				if (error) {
					callback(error, null);
				} else {
					loop(result, fn, callback);
				}
			});
		} catch (error) {
			callback(error, null);
		}
	}

	// Expect the param to be an array and loop over it
	else {
		let results: E[] = [];

		let looper: (i: number) => void = function (i: number): void {

			// Still work to do
			if (i < param.length) {

				// Execute function on array element
				try {
					fn(param[i], (error: any, result: E) => {

						// A method might only send a boolean value as return value (e.g. fs.exists), support this case gracefully
						if (error === true || error === false) {
							result = error;
							error = null;
						}

						// Quit looping on error
						if (error) {
							callback(error, null);
						}

						// Otherwise push result on stack and continue looping
						else {
							if (result) { //Could be that provided function is not returning a result
								results.push(result);
							}

							process.nextTick(() => {
								looper(i + 1);
							});
						}
					}, i, param.length);
				} catch (error) {
					callback(error, null);
				}
			}

			// Done looping, pass back results too callback function
			else {
				callback(null, results);
			}
		};

		// Start looping with first element in array
		looper(0);
	}
}

function Sequence(sequences: { (...param: any[]): void; }[]): void {

	// Assert
	assert.ok(sequences.length > 1, 'Need at least one error handler and one function to process sequence');
	sequences.forEach((sequence) => {
		assert.ok(typeof (sequence) === 'function');
	});

	// Execute in Loop
	let errorHandler = sequences.splice(0, 1)[0]; //Remove error handler
	let sequenceResult: any = null;

	loop(sequences, (sequence, clb) => {
		let sequenceFunction = function (error: any, result: any): void {

			// A method might only send a boolean value as return value (e.g. fs.exists), support this case gracefully
			if (error === true || error === false) {
				result = error;
				error = null;
			}

			// Handle Error and Result
			if (error) {
				clb(error, null);
			} else {
				sequenceResult = result; //Remember result of sequence
				clb(null, null); //Don't pass on result to Looper as we are not aggregating it
			}
		};

		// We call the sequence function setting "this" to be the callback we define here
		// and we pass in the "sequenceResult" as first argument. Doing all this avoids having
		// to pass in a callback to the sequence because the callback is already "this".
		try {
			sequence.call(sequenceFunction, sequenceResult);
		} catch (error) {
			clb(error, null);
		}
	}, (error, result) => {
		if (error) {
			errorHandler(error);
		}
	});
}

/**
 * Takes a variable list of functions to execute in sequence. The first function must be the error handler and the
 * following functions can do arbitrary work. "this" must be used as callback value for async functions to continue
 * through the sequence:
 * 	sequence(
 * 		function errorHandler(error) {
 * 			clb(error, null);
 * 		},
 *
 * 		function doSomethingAsync() {
 * 			fs.doAsync(path, this);
 * 		},
 *
 * 		function done(result) {
 * 			clb(null, result);
 * 		}
 * 	);
 */
export function sequence(errorHandler: (error: Error) => void, ...sequences: Function[]): void;
export function sequence(sequences: Function[]): void;
export function sequence(sequences: any): void {
	Sequence((Array.isArray(sequences)) ? sequences : Array.prototype.slice.call(arguments));
}