import arrayEach from 'lodash/_arrayEach';
import forOwn from 'lodash/_baseForOwn';
import indexOf from 'lodash/_baseIndexOf';
import isArray from 'lodash/isArray';
import okeys from 'lodash/keys';
import noop from 'lodash/noop';
import slice from './internal/slice';
import once from './internal/once';
import onlyOnce from './internal/onlyOnce';
import wrapAsync from './internal/wrapAsync';
/**
* Determines the best order for running the {@link AsyncFunction}s in `tasks`, based on
* their requirements. Each function can optionally depend on other functions
* being completed first, and each function is run as soon as its requirements
* are satisfied.
*
* If any of the {@link AsyncFunction}s pass an error to their callback, the `auto` sequence
* will stop. Further tasks will not execute (so any other functions depending
* on it will not run), and the main `callback` is immediately called with the
* error.
*
* {@link AsyncFunction}s also receive an object containing the results of functions which
* have completed so far as the first argument, if they have dependencies. If a
* task function has no dependencies, it will only be passed a callback.
*
* @name auto
* @static
* @memberOf module:ControlFlow
* @method
* @category Control Flow
* @param {Object} tasks - An object. Each of its properties is either a
* function or an array of requirements, with the {@link AsyncFunction} itself the last item
* in the array. The object's key of a property serves as the name of the task
* defined by that property, i.e. can be used when specifying requirements for
* other tasks. The function receives one or two arguments:
* * a `results` object, containing the results of the previously executed
* functions, only passed if the task has any dependencies,
* * a `callback(err, result)` function, which must be called when finished,
* passing an `error` (which can be `null`) and the result of the function's
* execution.
* @param {number} [concurrency=Infinity] - An optional `integer` for
* determining the maximum number of tasks that can be run in parallel. By
* default, as many as possible.
* @param {Function} [callback] - An optional callback which is called when all
* the tasks have been completed. It receives the `err` argument if any `tasks`
* pass an error to their callback. Results are always returned; however, if an
* error occurs, no further `tasks` will be performed, and the results object
* will only contain partial results. Invoked with (err, results).
* @returns undefined
* @example
*
* async.auto({
* // this function will just be passed a callback
* readData: async.apply(fs.readFile, 'data.txt', 'utf-8'),
* showData: ['readData', function(results, cb) {
* // results.readData is the file's contents
* // ...
* }]
* }, callback);
*
* async.auto({
* get_data: function(callback) {
* console.log('in get_data');
* // async code to get some data
* callback(null, 'data', 'converted to array');
* },
* make_folder: function(callback) {
* console.log('in make_folder');
* // async code to create a directory to store a file in
* // this is run at the same time as getting the data
* callback(null, 'folder');
* },
* write_file: ['get_data', 'make_folder', function(results, callback) {
* console.log('in write_file', JSON.stringify(results));
* // once there is some data and the directory exists,
* // write the data to a file in the directory
* callback(null, 'filename');
* }],
* email_link: ['write_file', function(results, callback) {
* console.log('in email_link', JSON.stringify(results));
* // once the file is written let's email a link to it...
* // results.write_file contains the filename returned by write_file.
* callback(null, {'file':results.write_file, 'email':'user@example.com'});
* }]
* }, function(err, results) {
* console.log('err = ', err);
* console.log('results = ', results);
* });
*/
export default function (tasks, concurrency, callback) {
if (typeof concurrency === 'function') {
// concurrency is optional, shift the args.
callback = concurrency;
concurrency = null;
}
callback = once(callback || noop);
var keys = okeys(tasks);
var numTasks = keys.length;
if (!numTasks) {
return callback(null);
}
if (!concurrency) {
concurrency = numTasks;
}
var results = {};
var runningTasks = 0;
var hasError = false;
var listeners = Object.create(null);
var readyTasks = [];
// for cycle detection:
var readyToCheck = []; // tasks that have been identified as reachable
// without the possibility of returning to an ancestor task
var uncheckedDependencies = {};
forOwn(tasks, function (task, key) {
if (!isArray(task)) {
// no dependencies
enqueueTask(key, [task]);
readyToCheck.push(key);
return;
}
var dependencies = task.slice(0, task.length - 1);
var remainingDependencies = dependencies.length;
if (remainingDependencies === 0) {
enqueueTask(key, task);
readyToCheck.push(key);
return;
}
uncheckedDependencies[key] = remainingDependencies;
arrayEach(dependencies, function (dependencyName) {
if (!tasks[dependencyName]) {
throw new Error('async.auto task `' + key +
'` has a non-existent dependency `' +
dependencyName + '` in ' +
dependencies.join(', '));
}
addListener(dependencyName, function () {
remainingDependencies--;
if (remainingDependencies === 0) {
enqueueTask(key, task);
}
});
});
});
checkForDeadlocks();
processQueue();
function enqueueTask(key, task) {
readyTasks.push(function () {
runTask(key, task);
});
}
function processQueue() {
if (readyTasks.length === 0 && runningTasks === 0) {
return callback(null, results);
}
while(readyTasks.length && runningTasks < concurrency) {
var run = readyTasks.shift();
run();
}
}
function addListener(taskName, fn) {
var taskListeners = listeners[taskName];
if (!taskListeners) {
taskListeners = listeners[taskName] = [];
}
taskListeners.push(fn);
}
function taskComplete(taskName) {
var taskListeners = listeners[taskName] || [];
arrayEach(taskListeners, function (fn) {
fn();
});
processQueue();
}
function runTask(key, task) {
if (hasError) return;
var taskCallback = onlyOnce(function(err, result) {
runningTasks--;
if (arguments.length > 2) {
result = slice(arguments, 1);
}
if (err) {
var safeResults = {};
forOwn(results, function(val, rkey) {
safeResults[rkey] = val;
});
safeResults[key] = result;
hasError = true;
listeners = Object.create(null);
callback(err, safeResults);
} else {
results[key] = result;
taskComplete(key);
}
});
runningTasks++;
var taskFn = wrapAsync(task[task.length - 1]);
if (task.length > 1) {
taskFn(results, taskCallback);
} else {
taskFn(taskCallback);
}
}
function checkForDeadlocks() {
// Kahn's algorithm
// https://en.wikipedia.org/wiki/Topological_sorting#Kahn.27s_algorithm
// http://connalle.blogspot.com/2013/10/topological-sortingkahn-algorithm.html
var currentTask;
var counter = 0;
while (readyToCheck.length) {
currentTask = readyToCheck.pop();
counter++;
arrayEach(getDependents(currentTask), function (dependent) {
if (--uncheckedDependencies[dependent] === 0) {
readyToCheck.push(dependent);
}
});
}
if (counter !== numTasks) {
throw new Error(
'async.auto cannot execute tasks due to a recursive dependency'
);
}
}
function getDependents(taskName) {
var result = [];
forOwn(tasks, function (task, key) {
if (isArray(task) && indexOf(task, taskName, 0) >= 0) {
result.push(key);
}
});
return result;
}
}
