<?php

namespace BetterMessages\React\EventLoop;

use BadMethodCallException;
use Event;
use EventBase;
use BetterMessages\React\EventLoop\Tick\FutureTickQueue;
use BetterMessages\React\EventLoop\Timer\Timer;
use SplObjectStorage;

/**
 * [Deprecated] An `ext-libevent` based event loop.
 *
 * This uses the [`libevent` PECL extension](https://pecl.php.net/package/libevent),
 * that provides an interface to `libevent` library.
 * `libevent` itself supports a number of system-specific backends (epoll, kqueue).
 *
 * This event loop does only work with PHP 5.
 * An [unofficial update](https://github.com/php/pecl-event-libevent/pull/2) for
 * PHP 7 does exist, but it is known to cause regular crashes due to `SEGFAULT`s.
 * To reiterate: Using this event loop on PHP 7 is not recommended.
 * Accordingly, neither the [`Loop` class](#loop) nor the deprecated
 * [`Factory` class](#factory) will try to use this event loop on PHP 7.
 *
 * This event loop is known to trigger a readable listener only if
 * the stream *becomes* readable (edge-triggered) and may not trigger if the
 * stream has already been readable from the beginning.
 * This also implies that a stream may not be recognized as readable when data
 * is still left in PHP's internal stream buffers.
 * As such, it's recommended to use `stream_set_read_buffer($stream, 0);`
 * to disable PHP's internal read buffer in this case.
 * See also [`addReadStream()`](#addreadstream) for more details.
 *
 * @link https://pecl.php.net/package/libevent
 * @deprecated 1.2.0, use [`ExtEventLoop`](#exteventloop) instead.
 */
final class ExtLibeventLoop implements LoopInterface
{
    /** @internal */
    const MICROSECONDS_PER_SECOND = 1000000;

    private $eventBase;
    private $futureTickQueue;
    private $timerCallback;
    private $timerEvents;
    private $streamCallback;
    private $readEvents = array();
    private $writeEvents = array();
    private $readListeners = array();
    private $writeListeners = array();
    private $running;
    private $signals;
    private $signalEvents = array();

    public function __construct()
    {
        if (!\function_exists('event_base_new')) {
            throw new BadMethodCallException('Cannot create ExtLibeventLoop, ext-libevent extension missing');
        }

        $this->eventBase = \event_base_new();
        $this->futureTickQueue = new FutureTickQueue();
        $this->timerEvents = new SplObjectStorage();
        $this->signals = new SignalsHandler();

        $this->createTimerCallback();
        $this->createStreamCallback();
    }

    public function addReadStream($stream, $listener)
    {
        $key = (int) $stream;
        if (isset($this->readListeners[$key])) {
            return;
        }

        $event = \event_new();
        \event_set($event, $stream, \EV_PERSIST | \EV_READ, $this->streamCallback);
        \event_base_set($event, $this->eventBase);
        \event_add($event);

        $this->readEvents[$key] = $event;
        $this->readListeners[$key] = $listener;
    }

    public function addWriteStream($stream, $listener)
    {
        $key = (int) $stream;
        if (isset($this->writeListeners[$key])) {
            return;
        }

        $event = \event_new();
        \event_set($event, $stream, \EV_PERSIST | \EV_WRITE, $this->streamCallback);
        \event_base_set($event, $this->eventBase);
        \event_add($event);

        $this->writeEvents[$key] = $event;
        $this->writeListeners[$key] = $listener;
    }

    public function removeReadStream($stream)
    {
        $key = (int) $stream;

        if (isset($this->readListeners[$key])) {
            $event = $this->readEvents[$key];
            \event_del($event);
            \event_free($event);

            unset(
                $this->readEvents[$key],
                $this->readListeners[$key]
            );
        }
    }

    public function removeWriteStream($stream)
    {
        $key = (int) $stream;

        if (isset($this->writeListeners[$key])) {
            $event = $this->writeEvents[$key];
            \event_del($event);
            \event_free($event);

            unset(
                $this->writeEvents[$key],
                $this->writeListeners[$key]
            );
        }
    }

    public function addTimer($interval, $callback)
    {
        $timer = new Timer($interval, $callback, false);

        $this->scheduleTimer($timer);

        return $timer;
    }

    public function addPeriodicTimer($interval, $callback)
    {
        $timer = new Timer($interval, $callback, true);

        $this->scheduleTimer($timer);

        return $timer;
    }

    public function cancelTimer(TimerInterface $timer)
    {
        if ($this->timerEvents->contains($timer)) {
            $event = $this->timerEvents[$timer];
            \event_del($event);
            \event_free($event);

            $this->timerEvents->detach($timer);
        }
    }

    public function futureTick($listener)
    {
        $this->futureTickQueue->add($listener);
    }

    public function addSignal($signal, $listener)
    {
        $this->signals->add($signal, $listener);

        if (!isset($this->signalEvents[$signal])) {
            $this->signalEvents[$signal] = \event_new();
            \event_set($this->signalEvents[$signal], $signal, \EV_PERSIST | \EV_SIGNAL, array($this->signals, 'call'));
            \event_base_set($this->signalEvents[$signal], $this->eventBase);
            \event_add($this->signalEvents[$signal]);
        }
    }

    public function removeSignal($signal, $listener)
    {
        $this->signals->remove($signal, $listener);

        if (isset($this->signalEvents[$signal]) && $this->signals->count($signal) === 0) {
            \event_del($this->signalEvents[$signal]);
            \event_free($this->signalEvents[$signal]);
            unset($this->signalEvents[$signal]);
        }
    }

    public function run()
    {
        $this->running = true;

        while ($this->running) {
            $this->futureTickQueue->tick();

            $flags = \EVLOOP_ONCE;
            if (!$this->running || !$this->futureTickQueue->isEmpty()) {
                $flags |= \EVLOOP_NONBLOCK;
            } elseif (!$this->readEvents && !$this->writeEvents && !$this->timerEvents->count() && $this->signals->isEmpty()) {
                break;
            }

            \event_base_loop($this->eventBase, $flags);
        }
    }

    public function stop()
    {
        $this->running = false;
    }

    /**
     * Schedule a timer for execution.
     *
     * @param TimerInterface $timer
     */
    private function scheduleTimer(TimerInterface $timer)
    {
        $this->timerEvents[$timer] = $event = \event_timer_new();

        \event_timer_set($event, $this->timerCallback, $timer);
        \event_base_set($event, $this->eventBase);
        \event_add($event, $timer->getInterval() * self::MICROSECONDS_PER_SECOND);
    }

    /**
     * Create a callback used as the target of timer events.
     *
     * A reference is kept to the callback for the lifetime of the loop
     * to prevent "Cannot destroy active lambda function" fatal error from
     * the event extension.
     */
    private function createTimerCallback()
    {
        $that = $this;
        $timers = $this->timerEvents;
        $this->timerCallback = function ($_, $__, $timer) use ($timers, $that) {
            \call_user_func($timer->getCallback(), $timer);

            // Timer already cancelled ...
            if (!$timers->contains($timer)) {
                return;
            }

            // Reschedule periodic timers ...
            if ($timer->isPeriodic()) {
                \event_add(
                    $timers[$timer],
                    $timer->getInterval() * ExtLibeventLoop::MICROSECONDS_PER_SECOND
                );

            // Clean-up one shot timers ...
            } else {
                $that->cancelTimer($timer);
            }
        };
    }

    /**
     * Create a callback used as the target of stream events.
     *
     * A reference is kept to the callback for the lifetime of the loop
     * to prevent "Cannot destroy active lambda function" fatal error from
     * the event extension.
     */
    private function createStreamCallback()
    {
        $read =& $this->readListeners;
        $write =& $this->writeListeners;
        $this->streamCallback = function ($stream, $flags) use (&$read, &$write) {
            $key = (int) $stream;

            if (\EV_READ === (\EV_READ & $flags) && isset($read[$key])) {
                \call_user_func($read[$key], $stream);
            }

            if (\EV_WRITE === (\EV_WRITE & $flags) && isset($write[$key])) {
                \call_user_func($write[$key], $stream);
            }
        };
    }
}
