<?php

namespace App\Http\Controllers;

use App\Http\Resources\MessageResource;
use App\Models\Message;
use App\Services\ChatService;
use Illuminate\Http\Request;
use Illuminate\Http\Response;
use Illuminate\Support\Facades\Redis;
use Symfony\Component\HttpFoundation\StreamedResponse;

class ChatSessionSseController extends Controller
{
    public function __construct(private readonly ChatService $service)
    {
    }

    public function stream(Request $request, string $sessionId): Response|StreamedResponse
    {
        set_time_limit(360);
        $this->service->getSession($sessionId); // ensure exists

        $lastEventId = $request->header('Last-Event-ID');
        $afterSeq = is_numeric($lastEventId) ? (int) $lastEventId : (int) $request->query('after_seq', 0);
        $limit = (int) $request->query('limit', 200);
        $limit = $limit > 0 && $limit <= 500 ? $limit : 200;

        $useBacklogOnly = app()->runningUnitTests()
            || app()->environment('testing')
            || defined('PHPUNIT_COMPOSER_INSTALL')
            || ! class_exists(\Redis::class);

        if ($useBacklogOnly) {
            $lastSentSeq = $afterSeq;
            ob_start();
            $this->sendBacklog($sessionId, $lastSentSeq, $limit, false);
            $content = ob_get_clean() ?: '';

            return response($content, 200, [
                'Content-Type' => 'text/event-stream',
                'Cache-Control' => 'no-cache',
                'X-Accel-Buffering' => 'no',
            ]);
        }

        $response = new StreamedResponse(function () use ($sessionId, $afterSeq, $limit) {
            $lastSentSeq = $afterSeq;
            $lastHeartbeat = microtime(true);

            $this->sendBacklog($sessionId, $lastSentSeq, $limit);
            $this->sendHeartbeat($lastHeartbeat);

            try {
                $redis = Redis::connection()->client();
                if (method_exists($redis, 'setOption')) {
                    $redis->setOption(\Redis::OPT_READ_TIMEOUT, 360);
                }

                $channel = "session:{$sessionId}:messages";
                logger('sse open');
                // Fallback for Redis drivers without pubSubLoop (older phpredis)
                $redis->subscribe([$channel], function ($redisInstance, $chan, $payload) use (&$lastSentSeq, $sessionId, $limit, &$lastHeartbeat) {
                    if (connection_aborted()) {
                        logger('sse aborted');
                        $redisInstance->unsubscribe([$chan]);
                        return;
                    }

                    $this->sendHeartbeat($lastHeartbeat);

                    if (! $payload) {
                        return;
                    }

                    $msg = json_decode($payload, true, 512, JSON_THROW_ON_ERROR);
                    $msg = new Message($msg);

                    // message.delta 不持久化，seq=0，直接推送
                    if ($msg && $msg->type === 'message.delta') {
                        $this->emitMessage($msg, true);
                        return;
                    }

                    if ($msg && $msg->seq > $lastSentSeq) {
                        if ($msg->seq > $lastSentSeq + 1) {
                            $this->sendBacklog($sessionId, $lastSentSeq, $limit);
                        }

                        if ($msg->seq > $lastSentSeq) {
                            $this->emitMessage($msg);
                            $lastSentSeq = $msg->seq;
                        }
                    }
                });
            } catch (\RedisException $exception) {
                logger()->warning('SSE redis subscription failed', [
                    'session_id' => $sessionId,
                    'message' => $exception->getMessage(),
                    'code' => $exception->getCode(),
                ]);
                echo ": redis-error\n\n";
                @ob_flush();
                @flush();
            }
        });

        $response->headers->set('Content-Type', 'text/event-stream');
        $response->headers->set('Cache-Control', 'no-cache');
        $response->headers->set('X-Accel-Buffering', 'no');

        return $response;
    }

    private function sendBacklog(string $sessionId, int &$lastSentSeq, int $limit, bool $flush = true): void
    {
        $backlog = $this->service->listMessagesBySeq($sessionId, $lastSentSeq, $limit);
        foreach ($backlog as $message) {
            $this->emitMessage($message, $flush);
            $lastSentSeq = $message->seq;
        }
    }

    private function emitMessage($message, bool $flush = true): void
    {
        $payload = (new MessageResource($message))->resolve();
        echo 'id: '.$message->seq."\n";
        echo "event: message\n";
        echo 'data: '.json_encode($payload, JSON_UNESCAPED_UNICODE)."\n\n";
        if ($flush) {
            @ob_flush();
            @flush();
        }
    }

    private function sendHeartbeat(float &$lastHeartbeat, int $intervalSeconds = 15): void
    {
        if ((microtime(true) - $lastHeartbeat) < $intervalSeconds) {
            return;
        }

        echo ": ping\n\n";
        @ob_flush();
        @flush();
        $lastHeartbeat = microtime(true);
    }
}