<?php

namespace App\RSpade\Core\Cache;

use Exception;
use Redis;
use App\RSpade\Core\Locks\RsxLocks;
use App\RSpade\Core\Manifest\Manifest;

// Ensure helpers are loaded since we may run early in bootstrap
require_once __DIR__ . '/../../helpers.php';

/**
 * Redis-based caching system with LRU eviction
 *
 * Uses Redis database 0 with LRU eviction policy for general caching.
 * Automatically prefixes all keys with the current manifest build key
 * to ensure cache invalidation when code changes.
 */
class RsxCache
{
    // Redis configuration
    private static ?Redis $_redis = null;

    private static int $cache_db = 0;  // Database 0 for cache (with LRU eviction)

    private static bool $initialized = false;

    // Request-scoped cache (static property storage)
    private static array $_once_cache = [];

    // Default expiration times
    public const NO_EXPIRATION = 0;

    public const HOUR = 3600;

    public const DAY = 86400;

    public const WEEK = 604800;

    /**
     * Initialize the cache system
     * Must be called after manifest is loaded
     */
    public static function _init()
    {
        if (self::$_redis) {
            return self::$_redis;
        }

        // Skip Redis in IDE context if extension not available
        if (self::_redis_bypass()) {
            return null;
        }

        self::$_redis = new Redis();

        // Connect to Redis (will be configured via environment)
        $host = env('REDIS_HOST', '127.0.0.1');
        $port = env('REDIS_PORT', 6379);
        $socket = env('REDIS_SOCKET', null);

        if ($socket && file_exists($socket)) {
            $connected = self::$_redis->connect($socket);
        } else {
            $connected = self::$_redis->connect($host, $port, 2.0);
        }

        if (!$connected) {
            shouldnt_happen('Failed to connect to Redis for caching');
        }

        // Select the cache database (with LRU eviction)
        self::$_redis->select(self::$cache_db);

        return self::$_redis;
    }

    /**
     * Check if we can skip reddis due to special circumstance
     */
    private static function _redis_bypass()
    {
        if (is_ide() && !class_exists('\Redis') && env('APP_ENV') != 'production') {
            return true;
        }

        return false;
    }

    /**
     * Get a value from cache
     *
     * @param string $key Cache key
     * @param mixed $default Default value if key not found
     * @return mixed Cached value or default
     */
    public static function get(string $key, $default = null)
    {
        return self::get_persistent(self::_transform_key_build($key), $default);
    }

    /**
     * Same as ::get but survives changes in the development environment
     *
     * The developer must call this function during manifest build phase, because
     * the build key to determine if the build has been updated is not available
     * until the manifest resccan is complete.  Calling get() during manifest rescan
     * will throw an exception.
     *
     * @param string $key Cache key
     * @param mixed $default Default value if key not found
     * @return mixed Cached value or default
     */
    public static function get_persistent(string $key, $default = null)
    {
        self::_init();

        if (self::_redis_bypass()) {
            return null;
        }

        $full_key = self::_make_key_persistent($key);

        $value = self::$_redis->get($full_key);

        if ($value === false) {
            return $default;
        }

        // Attempt to unserialize
        try {
            return unserialize($value);
        } catch (Exception $e) {
            return $default;
        }
    }

    /**
     * Set a value in cache
     *
     * @param string $key Cache key
     * @param mixed $value Value to cache
     * @param int $expiration Expiration time in seconds (0 = never expire)
     * @return bool Success
     */
    public static function set(string $key, $value, int $expiration = self::NO_EXPIRATION): bool
    {
        return self::set_persistent(self::_transform_key_build($key), $value, $expiration);
    }

    /**
     * Set a ::set but survives a manifest rescan
     * See ::get_persistent
     *
     * @param string $key Cache key
     * @param mixed $value Value to cache
     * @param int $expiration Expiration time in seconds (0 = never expire)
     * @return bool Success
     */
    public static function set_persistent(string $key, $value, int $expiration = self::NO_EXPIRATION): bool
    {
        self::_init();

        if (self::_redis_bypass()) {
            return null;
        }

        $full_key = self::_make_key_persistent($key);

        $value = serialize($value);

        if ($expiration > 0) {
            return self::$_redis->setex($full_key, $expiration, $value);
        }

        return self::$_redis->set($full_key, $value);
    }

    /**
     * Delete a key from cache
     *
     * @param string $key Cache key
     * @return bool Success
     */
    public static function delete(string $key): bool
    {
        self::_init();

        if (self::_redis_bypass()) {
            return null;
        }

        $full_key = self::_make_key_persistent(self::_transform_key_build($key));

        return self::$_redis->del($full_key) > 0;
    }

    /**
     * Check if a key exists in cache
     *
     * @param string $key Cache key
     * @return bool
     */
    public static function exists(string $key): bool
    {
        self::_init();

        if (self::_redis_bypass()) {
            return null;
        }

        $full_key = self::_make_key_persistent(self::_transform_key_build($key));

        return self::$_redis->exists($full_key) > 0;
    }

    /**
     * Clear the entire cache
     * Only clears keys with the current build key prefix
     */
    public static function clear(): void
    {
        self::_init();

        if (self::_redis_bypass()) {
            return;
        }

        self::$_redis->flushDb();
    }

    /**
     * Increment a numeric value
     *
     * @param string $key Cache key
     * @param int $amount Amount to increment by
     * @return int New value
     */
    public static function increment(string $key, int $amount = 1): int
    {
        self::_init();

        if (self::_redis_bypass()) {
            return 0;
        }

        $full_key = self::_make_key_persistent(self::_transform_key_build($key));

        if ($amount === 1) {
            return self::$_redis->incr($full_key);
        }

        return self::$_redis->incrBy($full_key, $amount);
    }

    /**
     * Decrement a numeric value
     *
     * @param string $key Cache key
     * @param int $amount Amount to decrement by
     * @return int New value
     */
    public static function decrement(string $key, int $amount = 1): int
    {
        self::_init();

        if (self::_redis_bypass()) {
            return 0;
        }

        $full_key = self::_make_key_persistent(self::_transform_key_build($key));

        if ($amount === 1) {
            return self::$_redis->decr($full_key);
        }

        returnself::$_redis->decrBy($full_key, $amount);
    }

    /**
     * Get cache statistics
     *
     * @return array Cache statistics
     */
    public static function stats(): array
    {
        self::_init();

        if (self::_redis_bypass()) {
            return 0;
        }

        $_redis = self::$_redis;

        // Return empty stats if Redis not available in IDE
        if ($_redis === null) {
            return [
                'total_keys' => 0,
                'used_memory' => 'N/A (IDE context)',
                'used_memory_peak' => 'N/A (IDE context)',
                'maxmemory' => '0',
                'maxmemory_policy' => 'noeviction',
            ];
        }

        // Get info from Redis
        $info = $_redis->info('memory');
        $db_info = $_redis->info('keyspace');

        // Parse keyspace info for current database
        $db_key = 'db' . self::$cache_db;
        $key_count = 0;
        if (isset($db_info[$db_key])) {
            $match_result = preg_match('/keys=(\d+)/', $db_info[$db_key], $matches);
            if ($match_result) {
                $key_count = (int)$matches[1];
            }
        }

        // Count keys with our build prefix
        $pattern = self::_make_key('*');

        return [
            'total_keys' => $key_count,
            'used_memory' => $info['used_memory_human'] ?? 'unknown',
            'used_memory_peak' => $info['used_memory_peak_human'] ?? 'unknown',
            'maxmemory' => $_redis->config('GET', 'maxmemory')['maxmemory'] ?? '0',
            'maxmemory_policy' => $_redis->config('GET', 'maxmemory-policy')['maxmemory-policy'] ?? 'noeviction',
        ];
    }

    // Document me
    private static function _transform_key_build(string $key): string
    {
        return Manifest::get_build_key() . '_' . $key;
    }

    /**
     * Create a full cache key with build prefix
     *
     * @param string $key User-provided key
     * @return string Full cache key
     */
    private static function _make_key_persistent(string $key): string
    {
        return 'cache:' . sha1($key);
    }

    /**
     * Request-scoped cache - stores value in static property for request duration
     *
     * Simplest caching - no Redis, no locks, just memory. Perfect for expensive
     * calculations that might be called multiple times in a single request.
     *
     * @param string $key Cache key (request-scoped)
     * @param callable $callback Callback to generate value if not cached
     * @return mixed Cached or generated value
     */
    public static function once(string $key, callable $callback)
    {
        if (array_key_exists($key, self::$_once_cache)) {
            return self::$_once_cache[$key];
        }

        $value = $callback();
        self::$_once_cache[$key] = $value;

        return $value;
    }

    /**
     * Build-scoped cache with advisory locking
     *
     * Caches value in Redis with build key prefix. Uses advisory write lock
     * during cache building to prevent stampede (multiple processes building
     * same cache simultaneously). Cache survives until manifest rebuild.
     *
     * @param string $key Cache key (build-scoped)
     * @param callable $callback Callback to generate value if not cached
     * @param int|null $seconds Expiration in seconds (null = never expire)
     * @return mixed Cached or generated value
     */
    public static function remember(string $key, callable $callback, ?int $seconds = null)
    {
        self::_init();

        // Check cache first (fast path - no lock needed)
        $value = self::get($key);
        if ($value !== null) {
            return $value;
        }

        // Cache miss - acquire write lock to build cache
        // This prevents multiple processes from building the same cache
        $lock_key = 'cache_build:' . $key;
        $lock_token = RsxLocks::get_lock(
            RsxLocks::SERVER_LOCK,
            $lock_key,
            RsxLocks::WRITE_LOCK,
            30  // 30 second timeout for cache building
        );

        try {
            // Check cache again after acquiring lock
            // Another process may have built it while we were waiting
            $value = self::get($key);
            if ($value !== null) {
                return $value;
            }

            // Build the cache
            $value = $callback();

            // Store in cache
            $expiration = $seconds ?? self::NO_EXPIRATION;
            self::set($key, $value, $expiration);

            return $value;
        } finally {
            RsxLocks::release_lock($lock_token);
        }
    }
}