<?php

namespace App\RSpade\Core\Locks;

use \Redis;
use Exception;
use RuntimeException;

// Ensure helpers are loaded since we run early in bootstrap
$helpers_path = __DIR__ . DIRECTORY_SEPARATOR . '..' . DIRECTORY_SEPARATOR . '..' . DIRECTORY_SEPARATOR . 'helpers.php';
if (file_exists($helpers_path)) {
    require_once $helpers_path;
}

/**
 * Advisory locking system using Redis
 *
 * Implements readers-writer lock pattern:
 * - Multiple readers can hold locks simultaneously
 * - Writers get exclusive access (no readers or other writers)
 * - Writers wait for existing readers to drain
 * - New readers wait if a writer is pending
 *
 * IMPORTANT: This class operates independently of the manifest system
 * and can be used during manifest building itself.
 */
class RsxLocks
{
    // Lock domains
    const SERVER_LOCK = 'server';
    const DATABASE_LOCK = 'database';  // For future extension if needed

    // Lock types
    const READ_LOCK = 'READ';
    const WRITE_LOCK = 'WRITE';

    // System-wide lock names (these are the ONLY locks used in the system)
    const LOCK_APPLICATION = 'APPLICATION';  // Global application lock for all requests
    const LOCK_MANIFEST_BUILD = 'MANIFEST_BUILD';  // Manifest rebuild operations
    const LOCK_BUNDLE_BUILD = 'BUNDLE_BUILD';  // Bundle compilation operations
    const LOCK_MIGRATION = 'MIGRATION';  // Database migration operations
    const LOCK_FILE_WRITE = 'FILE_WRITE';  // File upload/storage operations

    // Site-specific lock prefix (appended with site_id)
    const LOCK_SITE_PREFIX = 'SITE_';  // e.g., SITE_1, SITE_2, etc.

    // Redis configuration
    private static ?\Redis $redis = null;
    private static int $lock_db = 1;  // Database 1 for locks (no eviction)
    private static int $default_timeout = 30;  // Default lock timeout in seconds
    private static float $poll_interval = 0.1;  // 100ms polling interval

    // Track locks held by this process for cleanup
    private static array $held_locks = [];

    // Track lock acquisition counts for reentrant locking
    // Format: ['lock_key' => ['token' => 'xxx', 'count' => 2]]
    private static array $lock_counts = [];

    /**
     * Initialize Redis connection for locking
     * Separate from cache to avoid manifest dependency
     * Returns null in IDE context if Redis extension not available
     */
    private static function _ensure_redis(): ?\Redis
    {
        // Skip Redis in IDE context if extension not available
        if (\is_ide() && !class_exists('\Redis')) {
            return null;
        }

        if (self::$redis === null) {
            if (!class_exists('\Redis')) {
                return null;
            }
            self::$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 locking");
            }

            // Select the lock database (no eviction)
            self::$redis->select(self::$lock_db);

            // Register shutdown handler to release locks on exit
            register_shutdown_function([self::class, '_cleanup_locks']);
        }

        return self::$redis;
    }

    /**
     * Get an advisory lock
     *
     * @param string $domain Lock domain (SERVER_LOCK or DATABASE_LOCK)
     * @param string $name Lock identifier (e.g., MANIFEST_BUILD_LOCK_ID)
     * @param string $type Lock type (READ_LOCK or WRITE_LOCK)
     * @param int $timeout Maximum seconds to wait for lock acquisition
     * @return string Lock token for release
     */
    public static function get_lock(
        string $domain,
        string $name,
        string $type = self::READ_LOCK,
        int $timeout = 30
    ): string {
        if (!in_array($domain, [self::SERVER_LOCK, self::DATABASE_LOCK])) {
            shouldnt_happen("Invalid lock domain: {$domain}");
        }

        if (!in_array($type, [self::READ_LOCK, self::WRITE_LOCK])) {
            shouldnt_happen("Invalid lock type: {$type}");
        }

        // Reentrant locking: Check if we already hold this lock
        $count_key = "{$domain}:{$name}:{$type}";
        if (isset(self::$lock_counts[$count_key])) {
            // Already holding this lock, increment count and return same token
            self::$lock_counts[$count_key]['count']++;
            return self::$lock_counts[$count_key]['token'];
        }

        $redis = self::_ensure_redis();

        // Skip lock in IDE context without Redis
        if ($redis === null) {
            $mock_token = 'ide-mock-token-' . uniqid();
            self::$lock_counts[$count_key] = ['token' => $mock_token, 'count' => 1];
            return $mock_token;
        }

        $lock_key = "lock:{$domain}:{$name}";
        $lock_token = uniqid(gethostname() . ':' . getmypid() . ':', true);
        $start_time = microtime(true);

        // Use Lua script for atomic operations
        if ($type === self::READ_LOCK) {
            $acquired = self::_acquire_read_lock($redis, $lock_key, $lock_token, $timeout, $start_time);
        } else {
            $acquired = self::_acquire_write_lock($redis, $lock_key, $lock_token, $timeout, $start_time);
        }

        if (!$acquired) {
            throw new RuntimeException(
                "Failed to acquire {$type} lock for {$domain}:{$name} after {$timeout} seconds"
            );
        }

        // Track lock for cleanup
        self::$held_locks[$lock_token] = [
            'domain' => $domain,
            'name' => $name,
            'type' => $type,
            'key' => $lock_key,
            'acquired_at' => time()
        ];

        // Initialize lock count tracking
        self::$lock_counts[$count_key] = ['token' => $lock_token, 'count' => 1];

        return $lock_token;
    }

    /**
     * Release an advisory lock
     *
     * @param string $lock_token Token returned from get_lock
     */
    public static function release_lock(string $lock_token): void
    {
        // Skip mock tokens from IDE context
        if (str_starts_with($lock_token, 'ide-mock-token-')) {
            // Still need to handle reentrant count for IDE mock tokens
            // Find the count_key by matching token in lock_counts
            foreach (self::$lock_counts as $key => $data) {
                if ($data['token'] === $lock_token) {
                    if ($data['count'] > 1) {
                        self::$lock_counts[$key]['count']--;
                    } else {
                        unset(self::$lock_counts[$key]);
                    }
                    return;
                }
            }
            return;
        }

        if (!isset(self::$held_locks[$lock_token])) {
            // Lock already released or not owned by this process
            return;
        }

        $lock_info = self::$held_locks[$lock_token];

        // Build count_key from lock_info for reentrant locking
        $count_key = "{$lock_info['domain']}:{$lock_info['name']}:{$lock_info['type']}";

        // Reentrant locking: Check if count > 1
        if (isset(self::$lock_counts[$count_key]) && self::$lock_counts[$count_key]['count'] > 1) {
            // Decrement count and return without releasing Redis lock
            self::$lock_counts[$count_key]['count']--;
            return;
        }

        $redis = self::_ensure_redis();

        // Skip if Redis not available in IDE
        if ($redis === null) {
            unset(self::$held_locks[$lock_token]);
            unset(self::$lock_counts[$count_key]);
            return;
        }
        $lock_key = $lock_info['key'];

        if ($lock_info['type'] === self::READ_LOCK) {
            self::_release_read_lock($redis, $lock_key, $lock_token);
        } else {
            self::_release_write_lock($redis, $lock_key, $lock_token);
        }

        // Remove from both tracking arrays when count reaches 0
        unset(self::$held_locks[$lock_token]);
        unset(self::$lock_counts[$count_key]);
    }

    /**
     * Upgrade a read lock to a write lock atomically
     *
     * This is used for optimistic concurrency control where we start with a read lock
     * and only upgrade to write if needed. The read lock is NOT released during upgrade.
     *
     * @param string $lock_token Existing read lock token
     * @param int $timeout Maximum seconds to wait for upgrade
     * @return string New write lock token
     * @throws RuntimeException if upgrade fails or token is not a read lock
     */
    public static function upgrade_lock(string $lock_token, int $timeout = 30): string
    {
        // Skip mock tokens from IDE context
        if (str_starts_with($lock_token, 'ide-mock-token-')) {
            $new_token = 'ide-mock-token-' . uniqid();

            // Handle reentrant count for IDE mock tokens
            foreach (self::$lock_counts as $key => $data) {
                if ($data['token'] === $lock_token) {
                    $count = $data['count'];
                    unset(self::$lock_counts[$key]);

                    // Create new count entry with WRITE_LOCK type
                    // Parse the key to get domain and name
                    $parts = explode(':', $key);
                    if (count($parts) === 3) {
                        $new_count_key = "{$parts[0]}:{$parts[1]}:" . self::WRITE_LOCK;
                        self::$lock_counts[$new_count_key] = ['token' => $new_token, 'count' => $count];
                    }
                    break;
                }
            }

            return $new_token;
        }

        if (!isset(self::$held_locks[$lock_token])) {
            throw new RuntimeException("Cannot upgrade lock - token not found or already released");
        }

        $lock_info = self::$held_locks[$lock_token];

        if ($lock_info['type'] !== self::READ_LOCK) {
            throw new RuntimeException("Can only upgrade READ locks to WRITE locks");
        }

        // Handle reentrant lock count transfer from READ to WRITE
        $old_count_key = "{$lock_info['domain']}:{$lock_info['name']}:" . self::READ_LOCK;
        $new_count_key = "{$lock_info['domain']}:{$lock_info['name']}:" . self::WRITE_LOCK;
        $current_count = self::$lock_counts[$old_count_key]['count'] ?? 1;

        $redis = self::_ensure_redis();

        // Skip if Redis not available in IDE
        if ($redis === null) {
            $new_token = 'ide-mock-token-' . uniqid();
            unset(self::$lock_counts[$old_count_key]);
            self::$lock_counts[$new_count_key] = ['token' => $new_token, 'count' => $current_count];
            unset(self::$held_locks[$lock_token]);
            self::$held_locks[$new_token] = [
                'domain' => $lock_info['domain'],
                'name' => $lock_info['name'],
                'type' => self::WRITE_LOCK,
                'key' => $lock_info['key'],
                'acquired_at' => time(),
                'upgraded_from' => $lock_token
            ];
            return $new_token;
        }
        $lock_key = $lock_info['key'];
        $new_token = uniqid(gethostname() . ':' . getmypid() . ':write:', true);
        $start_time = microtime(true);

        // Attempt atomic upgrade
        $upgraded = self::_upgrade_read_to_write_lock(
            $redis,
            $lock_key,
            $lock_token,
            $new_token,
            $timeout,
            $start_time
        );

        if (!$upgraded) {
            throw new RuntimeException(
                "Failed to upgrade read lock to write lock for {$lock_info['domain']}:{$lock_info['name']} after {$timeout} seconds"
            );
        }

        // Remove old read lock from tracking
        unset(self::$held_locks[$lock_token]);
        unset(self::$lock_counts[$old_count_key]);

        // Add new write lock to tracking with preserved count
        self::$held_locks[$new_token] = [
            'domain' => $lock_info['domain'],
            'name' => $lock_info['name'],
            'type' => self::WRITE_LOCK,
            'key' => $lock_key,
            'acquired_at' => time(),
            'upgraded_from' => $lock_token
        ];
        self::$lock_counts[$new_count_key] = ['token' => $new_token, 'count' => $current_count];

        return $new_token;
    }

    /**
     * Acquire a read lock
     */
    private static function _acquire_read_lock(
        Redis $redis,
        string $lock_key,
        string $lock_token,
        int $timeout,
        float $start_time
    ): bool {
        $writer_queue_key = "{$lock_key}:writer_queue";
        $readers_key = "{$lock_key}:readers";
        $writer_active_key = "{$lock_key}:writer_active";

        while ((microtime(true) - $start_time) < $timeout) {
            // Lua script for atomic read lock acquisition
            $lua = <<<'LUA'
                local lock_key = KEYS[1]
                local writer_queue_key = KEYS[2]
                local readers_key = KEYS[3]
                local writer_active_key = KEYS[4]
                local lock_token = ARGV[1]
                local ttl = ARGV[2]

                -- Check if a writer is active
                local writer_active = redis.call('EXISTS', writer_active_key)
                if writer_active == 1 then
                    return 0  -- Writer is active, cannot acquire read lock
                end

                -- Check if writers are waiting
                local writers_waiting = redis.call('LLEN', writer_queue_key)
                if writers_waiting > 0 then
                    return 0  -- Writers are waiting, new readers must wait
                end

                -- Add this reader
                redis.call('HSET', readers_key, lock_token, '1')
                redis.call('EXPIRE', readers_key, ttl)
                return 1  -- Successfully acquired read lock
LUA;

            $result = $redis->eval(
                $lua,
                [$lock_key, $writer_queue_key, $readers_key, $writer_active_key, $lock_token, self::$default_timeout],
                4
            );

            if ($result === 1) {
                return true;
            }

            // Wait before retrying
            usleep(self::$poll_interval * 1000000);
        }

        return false;
    }

    /**
     * Acquire a write lock
     */
    private static function _acquire_write_lock(
        Redis $redis,
        string $lock_key,
        string $lock_token,
        int $timeout,
        float $start_time
    ): bool {
        $writer_queue_key = "{$lock_key}:writer_queue";
        $readers_key = "{$lock_key}:readers";
        $writer_active_key = "{$lock_key}:writer_active";

        // First, add ourselves to the writer queue
        $redis->rPush($writer_queue_key, $lock_token);
        $redis->expire($writer_queue_key, self::$default_timeout);

        try {
            while ((microtime(true) - $start_time) < $timeout) {
                // Lua script for atomic write lock acquisition
                $lua = <<<'LUA'
                    local lock_key = KEYS[1]
                    local writer_queue_key = KEYS[2]
                    local readers_key = KEYS[3]
                    local writer_active_key = KEYS[4]
                    local lock_token = ARGV[1]
                    local ttl = ARGV[2]

                    -- Check if we're next in the writer queue
                    local next_writer = redis.call('LINDEX', writer_queue_key, 0)
                    if next_writer ~= lock_token then
                        return 0  -- Not our turn yet
                    end

                    -- Check if any readers are active
                    local reader_count = redis.call('HLEN', readers_key)
                    if reader_count > 0 then
                        return 0  -- Readers still active, must wait
                    end

                    -- Check if another writer is active
                    local writer_active = redis.call('EXISTS', writer_active_key)
                    if writer_active == 1 then
                        return 0  -- Another writer is active
                    end

                    -- Acquire the write lock
                    redis.call('SET', writer_active_key, lock_token, 'EX', ttl)
                    redis.call('LPOP', writer_queue_key)  -- Remove ourselves from queue
                    return 1  -- Successfully acquired write lock
LUA;

                $result = $redis->eval(
                    $lua,
                    [$lock_key, $writer_queue_key, $readers_key, $writer_active_key, $lock_token, self::$default_timeout],
                    4
                );

                if ($result === 1) {
                    return true;
                }

                // Wait before retrying
                usleep(self::$poll_interval * 1000000);
            }
        } catch (Exception $e) {
            // Remove from queue on error
            $redis->lRem($writer_queue_key, $lock_token, 0);
            throw $e;
        }

        // Timeout - remove from queue
        $redis->lRem($writer_queue_key, $lock_token, 0);
        return false;
    }

    /**
     * Upgrade a read lock to a write lock atomically
     *
     * IMPORTANT: To prevent deadlock, readers that are upgrading to writers
     * are NOT counted as blocking readers. This allows multiple readers to
     * upgrade without deadlocking each other.
     */
    private static function _upgrade_read_to_write_lock(
        Redis $redis,
        string $lock_key,
        string $old_token,
        string $new_token,
        int $timeout,
        float $start_time
    ): bool {
        $writer_queue_key = "{$lock_key}:writer_queue";
        $readers_key = "{$lock_key}:readers";
        $writer_active_key = "{$lock_key}:writer_active";
        $upgrading_readers_key = "{$lock_key}:upgrading_readers";

        // Mark ourselves as an upgrading reader (not blocking other upgrades)
        $redis->sAdd($upgrading_readers_key, $old_token);
        $redis->expire($upgrading_readers_key, self::$default_timeout);

        // Add ourselves to the writer queue
        $redis->rPush($writer_queue_key, $new_token); // Normal queue order
        $redis->expire($writer_queue_key, self::$default_timeout);

        try {
            while ((microtime(true) - $start_time) < $timeout) {
                // Lua script for atomic lock upgrade (deadlock-safe)
                $lua = <<<'LUA'
                    local lock_key = KEYS[1]
                    local writer_queue_key = KEYS[2]
                    local readers_key = KEYS[3]
                    local writer_active_key = KEYS[4]
                    local upgrading_readers_key = KEYS[5]
                    local old_token = ARGV[1]
                    local new_token = ARGV[2]
                    local ttl = ARGV[3]

                    -- Verify we still hold the read lock
                    local has_read_lock = redis.call('HEXISTS', readers_key, old_token)
                    if has_read_lock == 0 then
                        return -1  -- Lost our read lock somehow
                    end

                    -- Check if we're next in the writer queue
                    local next_writer = redis.call('LINDEX', writer_queue_key, 0)
                    if next_writer ~= new_token then
                        return 0  -- Not our turn yet
                    end

                    -- Check if any OTHER readers are active (excluding upgrading readers)
                    -- This prevents deadlock where multiple readers wait for each other
                    local all_readers = redis.call('HKEYS', readers_key)
                    local upgrading = redis.call('SMEMBERS', upgrading_readers_key)
                    local upgrading_set = {}
                    for i, token in ipairs(upgrading) do
                        upgrading_set[token] = true
                    end

                    local blocking_readers = 0
                    for i, reader_token in ipairs(all_readers) do
                        -- Don't count ourselves or other upgrading readers as blockers
                        if reader_token ~= old_token and not upgrading_set[reader_token] then
                            blocking_readers = blocking_readers + 1
                        end
                    end

                    if blocking_readers > 0 then
                        return 0  -- Non-upgrading readers still active, must wait
                    end

                    -- Check if another writer is active
                    local writer_active = redis.call('EXISTS', writer_active_key)
                    if writer_active == 1 then
                        return 0  -- Another writer is active
                    end

                    -- Upgrade to write lock atomically
                    -- 1. Remove our read lock
                    redis.call('HDEL', readers_key, old_token)
                    -- 2. Remove from upgrading readers set
                    redis.call('SREM', upgrading_readers_key, old_token)
                    -- 3. Set write lock
                    redis.call('SET', writer_active_key, new_token, 'EX', ttl)
                    -- 4. Remove from writer queue
                    redis.call('LPOP', writer_queue_key)

                    return 1  -- Successfully upgraded
LUA;

                $result = $redis->eval(
                    $lua,
                    [$lock_key, $writer_queue_key, $readers_key, $writer_active_key, $upgrading_readers_key, $old_token, $new_token, self::$default_timeout],
                    5
                );

                if ($result === 1) {
                    return true;
                } elseif ($result === -1) {
                    // Lost our read lock - this shouldn't happen
                    $redis->lRem($writer_queue_key, $new_token, 0);
                    $redis->sRem($upgrading_readers_key, $old_token);
                    throw new RuntimeException("Lost read lock during upgrade attempt");
                }

                // Wait before retrying
                usleep(self::$poll_interval * 1000000);
            }
        } catch (Exception $e) {
            // Remove from queues on error
            $redis->lRem($writer_queue_key, $new_token, 0);
            $redis->sRem($upgrading_readers_key, $old_token);
            throw $e;
        }

        // Timeout - remove from queues
        $redis->lRem($writer_queue_key, $new_token, 0);
        $redis->sRem($upgrading_readers_key, $old_token);
        return false;
    }

    /**
     * Release a read lock
     */
    private static function _release_read_lock(Redis $redis, string $lock_key, string $lock_token): void
    {
        $readers_key = "{$lock_key}:readers";
        $redis->hDel($readers_key, $lock_token);
    }

    /**
     * Release a write lock
     */
    private static function _release_write_lock(Redis $redis, string $lock_key, string $lock_token): void
    {
        $writer_active_key = "{$lock_key}:writer_active";

        // Only delete if we own it
        $lua = <<<'LUA'
            local writer_active_key = KEYS[1]
            local lock_token = ARGV[1]

            local current_writer = redis.call('GET', writer_active_key)
            if current_writer == lock_token then
                redis.call('DEL', writer_active_key)
                return 1
            end
            return 0
LUA;

        $redis->eval($lua, [$writer_active_key, $lock_token], 1);
    }

    /**
     * Cleanup locks on process exit
     * Called by shutdown handler
     */
    public static function _cleanup_locks(): void
    {
        foreach (array_keys(self::$held_locks) as $lock_token) {
            try {
                self::release_lock($lock_token);
            } catch (Exception $e) {
                // Ignore errors during cleanup
            }
        }
    }

    /**
     * Force clear all locks for a given name (emergency use only)
     *
     * @param string $domain Lock domain
     * @param string $name Lock name
     */
    public static function force_clear_lock(string $domain, string $name): void
    {
        $redis = self::_ensure_redis();

        // Skip if Redis not available in IDE
        if ($redis === null) {
            return;
        }
        $lock_key = "lock:{$domain}:{$name}";

        $redis->del([
            $lock_key,
            "{$lock_key}:writer_queue",
            "{$lock_key}:readers",
            "{$lock_key}:writer_active"
        ]);
    }

    /**
     * Get lock statistics for monitoring
     *
     * @param string $domain Lock domain
     * @param string $name Lock name
     * @return array Lock statistics
     */
    public static function get_lock_stats(string $domain, string $name): array
    {
        $redis = self::_ensure_redis();

        // Skip if Redis not available in IDE
        if ($redis === null) {
            return [
                'readers_active' => 0,
                'writers_waiting' => 0,
                'writer_active' => false,
                'writer_token' => null
            ];
        }
        $lock_key = "lock:{$domain}:{$name}";

        $writer_queue = $redis->lLen("{$lock_key}:writer_queue");
        $reader_count = $redis->hLen("{$lock_key}:readers");
        $writer_active = $redis->get("{$lock_key}:writer_active");

        return [
            'readers_active' => $reader_count,
            'writers_waiting' => $writer_queue,
            'writer_active' => $writer_active !== false,
            'writer_token' => $writer_active ?: null
        ];
    }
}