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import noop from './internal/noop';
import setImmediate from './setImmediate';
import queue from './queue';
/**
* The same as [async.queue]{@link module:ControlFlow.queue} only tasks are assigned a priority and
* completed in ascending priority order.
*
* @name priorityQueue
* @static
* @memberOf module:ControlFlow
* @method
* @see [async.queue]{@link module:ControlFlow.queue}
* @category Control Flow
* @param {AsyncFunction} worker - An async function for processing a queued task.
* 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 {module:ControlFlow.QueueObject} 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) {
// Start with a normal queue
var q = queue(worker, concurrency);
// Override push to accept second parameter representing priority
q.push = function(data, priority, callback) {
if (callback == null) callback = noop;
if (typeof callback !== 'function') {
throw new Error('task callback must be a function');
}
q.started = true;
if (!Array.isArray(data)) {
data = [data];
}
if (data.length === 0) {
// call drain immediately if there are no tasks
return setImmediate(() => q.drain());
}
priority = priority || 0;
var nextNode = q._tasks.head;
while (nextNode && priority >= nextNode.priority) {
nextNode = nextNode.next;
}
for (var i = 0, l = data.length; i < l; i++) {
var item = {
data: data[i],
priority,
callback
};
if (nextNode) {
q._tasks.insertBefore(nextNode, item);
} else {
q._tasks.push(item);
}
}
setImmediate(q.process);
};
// Remove unshift function
delete q.unshift;
return q;
}
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