<?php

namespace React\Promise;

class CancellationQueue
{
private $started = false;
private $queue = [];

public function __invoke()
{
if ($this->started) {
return;
}

$this->started = true;
$this->drain();
}

public function enqueue($cancellable)
{
if (!\is_object($cancellable) || !\method_exists($cancellable, 'then') || !\method_exists($cancellable, 'cancel')) {
return;
}

$length = \array_push($this->queue, $cancellable);

if ($this->started && 1 === $length) {
$this->drain();
}
}

private function drain()
{
for ($i = key($this->queue); isset($this->queue[$i]); $i++) {
$cancellable = $this->queue[$i];

$exception = null;

try {
$cancellable->cancel();
} catch (\Throwable $exception) {
} catch (\Exception $exception) {
}

unset($this->queue[$i]);

if ($exception) {
throw $exception;
}
}

$this->queue = [];
}
}