<?php

namespace GuzzleHttp\Promise;

/**
* A task queue that executes tasks in a FIFO order.
*
* This task queue class is used to settle promises asynchronously and
* maintains a constant stack size. You can use the task queue asynchronously
* by calling the `run()` function of the global task queue in an event loop.
*
* GuzzleHttp\Promise\Utils::queue()->run();
*/
class TaskQueue implements TaskQueueInterface
{
private $enableShutdown = true;
private $queue = [];

public function __construct($withShutdown = true)
{
if ($withShutdown) {
register_shutdown_function(function () {
if ($this->enableShutdown) {
// Only run the tasks if an E_ERROR didn't occur.
$err = error_get_last();
if (!$err || ($err['type'] ^ E_ERROR)) {
$this->run();
}
}
});
}
}

public function isEmpty()
{
return !$this->queue;
}

public function add(callable $task)
{
$this->queue[] = $task;
}

public function run()
{
while ($task = array_shift($this->queue)) {
/** @var callable $task */
$task();
}
}

/**
* The task queue will be run and exhausted by default when the process
* exits IFF the exit is not the result of a PHP E_ERROR error.
*
* You can disable running the automatic shutdown of the queue by calling
* this function. If you disable the task queue shutdown process, then you
* MUST either run the task queue (as a result of running your event loop
* or manually using the run() method) or wait on each outstanding promise.
*
* Note: This shutdown will occur before any destructors are triggered.
*/
public function disableShutdown()
{
$this->enableShutdown = false;
}
}