<?php

namespace App\RSpade\Core\Realtime;

use Illuminate\Support\Facades\Redis;
use App\RSpade\Core\Manifest\Manifest;
use App\RSpade\Core\Realtime\Realtime_Topic_Abstract;
use App\RSpade\Core\Session\Session;

/**
 * Realtime
 *
 * Static API for the WebSocket realtime notification system.
 *
 * PHP is the authority — it issues auth tokens, checks permissions,
 * and publishes events. The Node.js WebSocket server is a dumb relay
 * that validates HMAC signatures and routes messages.
 *
 * Usage:
 *     // Publish after saving a record
 *     Realtime::publish('Contact_Updated_Topic', ['id' => $contact->id]);
 *
 *     // Generate tokens (called by Realtime_Controller)
 *     $token = Realtime::connection_token();
 *     $token = Realtime::subscribe_token('Contact_Updated_Topic', ['id' => 5]);
 */
class Realtime
{
    /**
     * Token expiry in seconds
     */
    private const TOKEN_EXPIRY = 60;

    /**
     * Redis channel prefix for realtime messages
     */
    private const REDIS_PREFIX = 'rsx_rt';

    /**
     * Check if realtime is enabled
     */
    public static function is_enabled(): bool
    {
        return env('REALTIME_ENABLED', false);
    }

    /**
     * Generate a connection token for WebSocket authentication
     *
     * Contains user_id, site_id, session_id, and expiry.
     * Signed with APP_KEY via HMAC-SHA256.
     * Short-lived (60 seconds) — only valid for initial handshake.
     *
     * @return string Signed token
     */
    public static function connection_token(): string
    {
        $payload = [
            'user_id' => Session::get_user_id(),
            'site_id' => Session::get_site_id(),
            'session_id' => Session::get_session_id(),
            'exp' => time() + self::TOKEN_EXPIRY,
        ];

        return self::_sign_token($payload);
    }

    /**
     * Generate a subscribe token for a specific topic
     *
     * Checks the topic's can_subscribe() method first.
     * Contains topic name, filter, site_id, and expiry.
     *
     * @param string $topic_class Topic class name (e.g., 'Contact_Updated_Topic')
     * @param array $filter Subscription filter (e.g., ['id' => 5])
     * @return string Signed token
     * @throws \RuntimeException If topic class not found or permission denied
     */
    public static function subscribe_token(string $topic_class, array $filter = []): string
    {
        // Resolve topic class
        $fqcn = Manifest::resolve_class($topic_class);

        if (!$fqcn) {
            throw new \RuntimeException("Realtime topic class not found: {$topic_class}");
        }

        if (!is_subclass_of($fqcn, Realtime_Topic_Abstract::class)) {
            throw new \RuntimeException("Class {$topic_class} is not a Realtime_Topic_Abstract");
        }

        // Check permission
        if (!$fqcn::can_subscribe($filter)) {
            throw new \RuntimeException("Permission denied for topic: {$topic_class}");
        }

        $payload = [
            'topic' => $topic_class,
            'filter' => $filter,
            'site_id' => Session::get_site_id(),
            'exp' => time() + self::TOKEN_EXPIRY,
        ];

        return self::_sign_token($payload);
    }

    /**
     * Publish a message to all subscribers of a topic
     *
     * Sends via Redis pub/sub to the Node.js WebSocket server.
     * Messages are scoped to the current site_id automatically.
     *
     * IMPORTANT: Never include confidential data in the payload.
     * Messages are notifications only — clients fetch fresh data
     * through normal Ajax after receiving a notification.
     *
     * @param string $topic_class Topic class name (e.g., 'Contact_Updated_Topic')
     * @param array $data Notification payload (e.g., ['id' => 5, 'updated_by' => 3])
     */
    public static function publish(string $topic_class, array $data = []): void
    {
        if (!self::is_enabled()) {
            return;
        }

        $site_id = Session::get_site_id();

        $message = json_encode([
            'topic' => $topic_class,
            'data' => $data,
            'site_id' => $site_id,
            'ts' => time(),
        ]);

        $channel = self::REDIS_PREFIX . ':' . $site_id;

        Redis::publish($channel, $message);
    }

    /**
     * Sign a payload with HMAC-SHA256
     *
     * Token format: base64(json_payload).base64(hmac_signature)
     *
     * @param array $payload Data to sign
     * @return string Signed token
     */
    private static function _sign_token(array $payload): string
    {
        $json = json_encode($payload);
        $signature = hash_hmac('sha256', $json, config('app.key'));

        return base64_encode($json) . '.' . $signature;
    }
}