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'use strict';
import arrayEach from 'lodash/_arrayEach';
import isArray from 'lodash/isArray';
import noop from 'lodash/noop';
import setImmediate from './setImmediate';
import queue from './queue';
/**
* The same as {@link async.queue} only tasks are assigned a priority and
* completed in ascending priority order.
*
* @name priorityQueue
* @static
* @memberOf async
* @see async.queue
* @category Control Flow
* @param {Function} worker - An asynchronous function for processing a queued
* task, which must call its `callback(err)` argument when finished, with an
* optional `error` as an argument. If you want to handle errors from an
* individual task, pass a callback to `q.push()`. Invoked with
* (task, callback).
* @param {number} concurrency - An `integer` for determining how many `worker`
* functions should be run in parallel. If omitted, the concurrency defaults to
* `1`. If the concurrency is `0`, an error is thrown.
* @returns {queue} A priorityQueue object to manage the tasks. There are two
* differences between `queue` and `priorityQueue` objects:
* * `push(task, priority, [callback])` - `priority` should be a number. If an
* array of `tasks` is given, all tasks will be assigned the same priority.
* * The `unshift` method was removed.
*/
export default function(worker, concurrency) {
function _compareTasks(a, b) {
return a.priority - b.priority;
}
function _binarySearch(sequence, item, compare) {
var beg = -1,
end = sequence.length - 1;
while (beg < end) {
var mid = beg + ((end - beg + 1) >>> 1);
if (compare(item, sequence[mid]) >= 0) {
beg = mid;
} else {
end = mid - 1;
}
}
return beg;
}
function _insert(q, data, priority, callback) {
if (callback != null && typeof callback !== 'function') {
throw new Error('task callback must be a function');
}
q.started = true;
if (!isArray(data)) {
data = [data];
}
if (data.length === 0) {
// call drain immediately if there are no tasks
return setImmediate(function() {
q.drain();
});
}
arrayEach(data, function(task) {
var item = {
data: task,
priority: priority,
callback: typeof callback === 'function' ? callback : noop
};
q.tasks.splice(_binarySearch(q.tasks, item, _compareTasks) + 1, 0, item);
setImmediate(q.process);
});
}
// Start with a normal queue
var q = queue(worker, concurrency);
// Override push to accept second parameter representing priority
q.push = function(data, priority, callback) {
_insert(q, data, priority, callback);
};
// Remove unshift function
delete q.unshift;
return q;
}
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