<?php

namespace Amp\Parallel\Threading\Internal;

use Amp\Coroutine;
use Amp\Parallel\{ ChannelException, SerializationException };
use Amp\Parallel\Sync\{ Channel, ChannelledSocket, Internal\ExitFailure, Internal\ExitSuccess };
use AsyncInterop\{ Loop, Promise };

/**
 * An internal thread that executes a given function concurrently.
 *
 * @internal
 */
class Thread extends \Thread {
    const KILL_CHECK_FREQUENCY = 250;

    /** @var callable The function to execute in the thread. */
    private $function;

    /** @var mixed[] Arguments to pass to the function. */
    private $args;

    /** @var resource */
    private $socket;

    /** @var bool */
    private $killed = false;

    /**
     * Creates a new thread object.
     *
     * @param resource $socket   IPC communication socket.
     * @param callable $function The function to execute in the thread.
     * @param mixed[]  $args     Arguments to pass to the function.
     */
    public function __construct($socket, callable $function, array $args = []) {
        $this->function = $function;
        $this->args = $args;
        $this->socket = $socket;
    }

    /**
     * Runs the thread code and the initialized function.
     *
     * @codeCoverageIgnore Only executed in thread.
     */
    public function run() {
        /* First thing we need to do is re-initialize the class autoloader. If
         * we don't do this first, any object of a class that was loaded after
         * the thread started will just be garbage data and unserializable
         * values (like resources) will be lost. This happens even with
         * thread-safe objects.
         */
        $paths = [
            \dirname(__DIR__, 3) . '/vendor/autoload.php',
            \dirname(__DIR__, 5) . '/autoload.php',
        ];

        $autoloadPath = null;
        foreach ($paths as $path) {
            if (\file_exists($path)) {
                $autoloadPath = $path;
                break;
            }
        }

        if ($autoloadPath === null) {
            throw new \Error('Could not locate autoload.php');
        }

        // Protect scope by using a static closure.
        (static function () use ($autoloadPath) { require $autoloadPath; })();

        // At this point, the thread environment has been prepared so begin using the thread.

        try {
            Loop::execute(\Amp\wrap(function () {
                $channel = new ChannelledSocket($this->socket, $this->socket, false);

                $watcher = Loop::repeat(self::KILL_CHECK_FREQUENCY, function () {
                    if ($this->killed) {
                        Loop::stop();
                    }
                });

                Loop::unreference($watcher);

                return $this->execute($channel);
            }));
        } catch (\Throwable $exception) {
            return 1;
        }

        return 0;
    }

    /**
     * Sets a local variable to true so the running event loop can check for a kill signal.
     */
    public function kill() {
        return $this->killed = true;
    }

    /**
     * @coroutine
     *
     * @param \Amp\Parallel\Sync\Channel $channel
     *
     * @return \Generator
     *
     * @codeCoverageIgnore Only executed in thread.
     */
    private function execute(Channel $channel): \Generator {
        try {
            if ($this->function instanceof \Closure) {
                $function = $this->function->bindTo($channel, Channel::class);
            }

            if (empty($function)) {
                $function = $this->function;
            }

            $result = $function(...$this->args);

            if ($result instanceof \Generator) {
                $result = new Coroutine($result);
            }

            if ($result instanceof Promise) {
                $result = yield $result;
            }

            $result = new ExitSuccess($result);
        } catch (\Throwable $exception) {
            $result = new ExitFailure($exception);
        }

        // Attempt to return the result.
        try {
            try {
                return yield $channel->send($result);
            } catch (SerializationException $exception) {
                // Serializing the result failed. Send the reason why.
                return yield $channel->send(new ExitFailure($exception));
            }
        } catch (ChannelException $exception) {
            // The result was not sendable! The parent context must have died or killed the context.
            return 0;
        }
    }
}