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import isArray from 'lodash/isArray';
import noop from 'lodash/noop';
import once from './internal/once';
import slice from './internal/slice';
import onlyOnce from './internal/onlyOnce';
import wrapAsync from './internal/wrapAsync';
/**
* Runs the `tasks` array of functions in series, each passing their results to
* the next in the array. However, if any of the `tasks` pass an error to their
* own callback, the next function is not executed, and the main `callback` is
* immediately called with the error.
*
* @name waterfall
* @static
* @memberOf module:ControlFlow
* @method
* @category Control Flow
* @param {Array} tasks - An array of [async functions]{@link AsyncFunction}
* to run.
* Each function should complete with any number of `result` values.
* The `result` values will be passed as arguments, in order, to the next task.
* @param {Function} [callback] - An optional callback to run once all the
* functions have completed. This will be passed the results of the last task's
* callback. Invoked with (err, [results]).
* @returns undefined
* @example
*
* async.waterfall([
* function(callback) {
* callback(null, 'one', 'two');
* },
* function(arg1, arg2, callback) {
* // arg1 now equals 'one' and arg2 now equals 'two'
* callback(null, 'three');
* },
* function(arg1, callback) {
* // arg1 now equals 'three'
* callback(null, 'done');
* }
* ], function (err, result) {
* // result now equals 'done'
* });
*
* // Or, with named functions:
* async.waterfall([
* myFirstFunction,
* mySecondFunction,
* myLastFunction,
* ], function (err, result) {
* // result now equals 'done'
* });
* function myFirstFunction(callback) {
* callback(null, 'one', 'two');
* }
* function mySecondFunction(arg1, arg2, callback) {
* // arg1 now equals 'one' and arg2 now equals 'two'
* callback(null, 'three');
* }
* function myLastFunction(arg1, callback) {
* // arg1 now equals 'three'
* callback(null, 'done');
* }
*/
export default function(tasks, callback) {
callback = once(callback || noop);
if (!isArray(tasks)) return callback(new Error('First argument to waterfall must be an array of functions'));
if (!tasks.length) return callback();
var taskIndex = 0;
function nextTask(args) {
if (taskIndex === tasks.length) {
return callback.apply(null, [null].concat(args));
}
var taskCallback = onlyOnce(function(err/*, cbArgs...*/) {
var cbArgs = slice(arguments, 1);
if (err) {
return callback.apply(null, [err].concat(cbArgs));
}
nextTask(cbArgs);
});
args.push(taskCallback);
var task = wrapAsync(tasks[taskIndex++]);
task.apply(null, args);
}
nextTask([]);
}
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