<?php

namespace Amp\Loop;

use Amp\Coroutine;
use Amp\Promise;
use React\Promise\PromiseInterface as ReactPromise;
use function Amp\Promise\rethrow;

class UvDriver extends Driver
{
    /** @var resource|\UVLoop A uv_loop resource created with uv_loop_new() */
    private $handle;

    /** @var resource[] */
    private array $events = [];

    /** @var Watcher[][] */
    private array $watchers = [];

    /** @var resource[] */
    private array $streams = [];

    private \Closure $ioCallback;

    private \Closure $timerCallback;

    private \Closure $signalCallback;

    public function __construct()
    {
        $this->handle = \uv_loop_new();

        /**
         * @param $event
         * @param $status
         * @param $events
         * @param $resource
         *
         * @return void
         */
        $this->ioCallback = function ($event, $status, $events, $resource): void {
            $watchers = $this->watchers[(int) $event];

            switch ($status) {
                case 0: // OK
                    break;

                default: // Invoke the callback on errors, as this matches behavior with other loop back-ends.
                    // Re-enable watcher as libuv disables the watcher on non-zero status.
                    $flags = 0;
                    foreach ($watchers as $watcher) {
                        $flags |= $watcher->enabled ? $watcher->type : 0;
                    }
                    \uv_poll_start($event, $flags, $this->ioCallback);
                    break;
            }

            foreach ($watchers as $watcher) {
                // $events is OR'ed with 4 to trigger watcher if no events are indicated (0) or on UV_DISCONNECT (4).
                // http://docs.libuv.org/en/v1.x/poll.html
                if (!($watcher->enabled && ($watcher->type & $events || ($events | 4) === 4))) {
                    continue;
                }

                try {
                    $result = ($watcher->callback)($watcher->id, $resource, $watcher->data);

                    if ($result === null) {
                        continue;
                    }

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

                    if ($result instanceof Promise || $result instanceof ReactPromise) {
                        rethrow($result);
                    }
                } catch (\Throwable $exception) {
                    $this->error($exception);
                }
            }
        };

        /**
         * @param $event
         *
         * @return void
         */
        $this->timerCallback = function ($event): void {
            $watcher = $this->watchers[(int) $event][0];

            if ($watcher->type & Watcher::DELAY) {
                unset($this->events[$watcher->id], $this->watchers[(int) $event]); // Avoid call to uv_is_active().
                $this->cancel($watcher->id); // Remove reference to watcher in parent.
            } elseif ($watcher->value === 0) {
                // Disable and re-enable so it's not executed repeatedly in the same tick
                // See https://github.com/amphp/amp/issues/131
                $this->disable($watcher->id);
                $this->enable($watcher->id);
            }

            try {
                $result = ($watcher->callback)($watcher->id, $watcher->data);

                if ($result === null) {
                    return;
                }

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

                if ($result instanceof Promise || $result instanceof ReactPromise) {
                    rethrow($result);
                }
            } catch (\Throwable $exception) {
                $this->error($exception);
            }
        };

        /**
         * @param $event
         * @param $signo
         *
         * @return void
         */
        $this->signalCallback = function ($event, $signo): void {
            $watcher = $this->watchers[(int) $event][0];

            try {
                $result = ($watcher->callback)($watcher->id, $signo, $watcher->data);

                if ($result === null) {
                    return;
                }

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

                if ($result instanceof Promise || $result instanceof ReactPromise) {
                    rethrow($result);
                }
            } catch (\Throwable $exception) {
                $this->error($exception);
            }
        };
    }

    /**
     * {@inheritdoc}
     */
    public function cancel(string $watcherId): void
    {
        parent::cancel($watcherId);

        if (!isset($this->events[$watcherId])) {
            return;
        }

        $event = $this->events[$watcherId];
        $eventId = (int) $event;

        if (isset($this->watchers[$eventId][0])) { // All except IO watchers.
            unset($this->watchers[$eventId]);
        } elseif (isset($this->watchers[$eventId][$watcherId])) {
            $watcher = $this->watchers[$eventId][$watcherId];
            unset($this->watchers[$eventId][$watcherId]);

            if (empty($this->watchers[$eventId])) {
                unset($this->watchers[$eventId], $this->streams[(int) $watcher->value]);
            }
        }

        unset($this->events[$watcherId]);
    }

    public static function isSupported(): bool
    {
        return \extension_loaded("uv");
    }

    /**
     * {@inheritdoc}
     */
    public function now(): int
    {
        \uv_update_time($this->handle);

        /** @psalm-suppress TooManyArguments */
        return \uv_now($this->handle);
    }

    /**
     * {@inheritdoc}
     */
    public function getHandle()
    {
        return $this->handle;
    }

    /**
     * {@inheritdoc}
     *
     * @return void
     */
    protected function dispatch(bool $blocking): void
    {
        /** @psalm-suppress TooManyArguments */
        \uv_run($this->handle, $blocking ? \UV::RUN_ONCE : \UV::RUN_NOWAIT);
    }

    /**
     * {@inheritdoc}
     *
     * @return void
     */
    protected function activate(array $watchers): void
    {
        $now = $this->now();

        foreach ($watchers as $watcher) {
            $id = $watcher->id;

            switch ($watcher->type) {
                case Watcher::READABLE:
                case Watcher::WRITABLE:
                    \assert(\is_resource($watcher->value));

                    $streamId = (int) $watcher->value;

                    if (isset($this->streams[$streamId])) {
                        $event = $this->streams[$streamId];
                    } elseif (isset($this->events[$id])) {
                        $event = $this->streams[$streamId] = $this->events[$id];
                    } else {
                        /** @psalm-suppress UndefinedFunction */
                        $event = $this->streams[$streamId] = \uv_poll_init_socket($this->handle, $watcher->value);
                    }

                    $eventId = (int) $event;
                    $this->events[$id] = $event;
                    $this->watchers[$eventId][$id] = $watcher;

                    $flags = 0;
                    foreach ($this->watchers[$eventId] as $w) {
                        $flags |= $w->enabled ? $w->type : 0;
                    }
                    \uv_poll_start($event, $flags, $this->ioCallback);
                    break;

                case Watcher::DELAY:
                case Watcher::REPEAT:
                    \assert(\is_int($watcher->value));

                    if (isset($this->events[$id])) {
                        $event = $this->events[$id];
                    } else {
                        $event = $this->events[$id] = \uv_timer_init($this->handle);
                    }

                    $this->watchers[(int) $event] = [$watcher];

                    \uv_timer_start(
                        $event,
                        \max(0, $watcher->expiration - $now),
                        ($watcher->type & Watcher::REPEAT) ? $watcher->value : 0,
                        $this->timerCallback
                    );
                    break;

                case Watcher::SIGNAL:
                    \assert(\is_int($watcher->value));

                    if (isset($this->events[$id])) {
                        $event = $this->events[$id];
                    } else {
                        /** @psalm-suppress UndefinedFunction */
                        $event = $this->events[$id] = \uv_signal_init($this->handle);
                    }

                    $this->watchers[(int) $event] = [$watcher];

                    /** @psalm-suppress UndefinedFunction */
                    \uv_signal_start($event, $this->signalCallback, $watcher->value);
                    break;

                default:
                    // @codeCoverageIgnoreStart
                    throw new \Error("Unknown watcher type");
                // @codeCoverageIgnoreEnd
            }
        }
    }

    /**
     * {@inheritdoc}
     *
     * @return void
     */
    protected function deactivate(Watcher $watcher): void
    {
        $id = $watcher->id;

        if (!isset($this->events[$id])) {
            return;
        }

        $event = $this->events[$id];

        if (!\uv_is_active($event)) {
            return;
        }

        switch ($watcher->type) {
            case Watcher::READABLE:
            case Watcher::WRITABLE:
                $flags = 0;
                foreach ($this->watchers[(int) $event] as $w) {
                    $flags |= $w->enabled ? $w->type : 0;
                }

                if ($flags) {
                    \uv_poll_start($event, $flags, $this->ioCallback);
                } else {
                    \uv_poll_stop($event);
                }
                break;

            case Watcher::DELAY:
            case Watcher::REPEAT:
                \uv_timer_stop($event);
                break;

            case Watcher::SIGNAL:
                \uv_signal_stop($event);
                break;

            default:
                // @codeCoverageIgnoreStart
                throw new \Error("Unknown watcher type");
            // @codeCoverageIgnoreEnd
        }
    }
}