<?php
/**
 * Database Connection Manager
 * 
 * Enterprise-level connection management, pooling, and optimization
 *
 * @package CareBook\Ultimate\Database
 * @since 1.0.0
 */

declare(strict_types=1);

namespace CareBook\Ultimate\Database;

/**
 * Advanced database connection management
 * 
 * @since 1.0.0
 */
class ConnectionManager
{
    private static ?self $instance = null;
    private \wpdb $wpdb;
    private array $connections = [];
    private array $connectionConfig;
    private array $performanceMetrics = [];
    private int $maxConnections = 10;
    private int $connectionTimeout = 30;
    private bool $enablePersistentConnections = true;
    private array $queryLog = [];
    private bool $enableQueryLogging = false;
    private int $slowQueryThreshold = 1000; // milliseconds
    
    /**
     * Private constructor for singleton
     * 
     * @since 1.0.0
     */
    private function __construct()
    {
        global $wpdb;
        $this->wpdb = $wpdb;
        
        $this->connectionConfig = [
            'charset' => $this->wpdb->charset,
            'collate' => $this->wpdb->collate,
            'host' => DB_HOST,
            'database' => DB_NAME,
            'username' => DB_USER,
            'password' => DB_PASSWORD
        ];
        
        $this->initializePerformanceMetrics();
        $this->setupQueryLogging();
    }
    
    /**
     * Get singleton instance
     * 
     * @return self
     * @since 1.0.0
     */
    public static function getInstance(): self
    {
        if (self::$instance === null) {
            self::$instance = new self();
        }
        
        return self::$instance;
    }
    
    /**
     * Initialize performance metrics tracking
     * 
     * @return void
     * @since 1.0.0
     */
    private function initializePerformanceMetrics(): void
    {
        $this->performanceMetrics = [
            'total_queries' => 0,
            'slow_queries' => 0,
            'failed_queries' => 0,
            'total_execution_time' => 0.0,
            'connection_count' => 0,
            'active_connections' => 0,
            'connection_errors' => 0,
            'query_cache_hits' => 0,
            'query_cache_misses' => 0,
            'last_reset' => time()
        ];
    }
    
    /**
     * Setup query logging if enabled
     * 
     * @return void
     * @since 1.0.0
     */
    private function setupQueryLogging(): void
    {
        if ($this->enableQueryLogging) {
            add_filter('query', [$this, 'logQuery'], 10, 1);
        }
    }
    
    /**
     * Get primary database connection
     * 
     * @return \wpdb
     * @since 1.0.0
     */
    public function getConnection(): \wpdb
    {
        return $this->wpdb;
    }
    
    /**
     * Get or create read-only connection for read replicas
     * 
     * @return \wpdb
     * @since 1.0.0
     */
    public function getReadConnection(): \wpdb
    {
        // In a real environment, this would connect to read replicas
        // For now, return the main connection
        return $this->getConnection();
    }
    
    /**
     * Get or create write connection for master database
     * 
     * @return \wpdb
     * @since 1.0.0
     */
    public function getWriteConnection(): \wpdb
    {
        return $this->getConnection();
    }
    
    /**
     * Execute query with connection management
     * 
     * @param string $sql
     * @param array<mixed> $parameters
     * @param string $connectionType
     * @return mixed
     * @since 1.0.0
     */
    public function query(string $sql, array $parameters = [], string $connectionType = 'read')
    {
        $startTime = microtime(true);
        $connection = $connectionType === 'write' ? $this->getWriteConnection() : $this->getReadConnection();
        
        try {
            // Prepare query if parameters provided
            if (!empty($parameters)) {
                $sql = $connection->prepare($sql, ...$parameters);
            }
            
            // Execute query
            $result = $connection->get_results($sql, ARRAY_A);
            
            // Track performance metrics
            $executionTime = (microtime(true) - $startTime) * 1000; // Convert to milliseconds
            $this->trackQueryExecution($sql, $executionTime, true);
            
            return $result;
            
        } catch (\Exception $e) {
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution($sql, $executionTime, false, $e->getMessage());
            
            throw $e;
        }
    }
    
    /**
     * Execute single row query
     * 
     * @param string $sql
     * @param array<mixed> $parameters
     * @param string $connectionType
     * @return mixed
     * @since 1.0.0
     */
    public function queryRow(string $sql, array $parameters = [], string $connectionType = 'read')
    {
        $startTime = microtime(true);
        $connection = $connectionType === 'write' ? $this->getWriteConnection() : $this->getReadConnection();
        
        try {
            if (!empty($parameters)) {
                $sql = $connection->prepare($sql, ...$parameters);
            }
            
            $result = $connection->get_row($sql, ARRAY_A);
            
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution($sql, $executionTime, true);
            
            return $result;
            
        } catch (\Exception $e) {
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution($sql, $executionTime, false, $e->getMessage());
            
            throw $e;
        }
    }
    
    /**
     * Execute single value query
     * 
     * @param string $sql
     * @param array<mixed> $parameters
     * @param string $connectionType
     * @return mixed
     * @since 1.0.0
     */
    public function queryValue(string $sql, array $parameters = [], string $connectionType = 'read')
    {
        $startTime = microtime(true);
        $connection = $connectionType === 'write' ? $this->getWriteConnection() : $this->getReadConnection();
        
        try {
            if (!empty($parameters)) {
                $sql = $connection->prepare($sql, ...$parameters);
            }
            
            $result = $connection->get_var($sql);
            
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution($sql, $executionTime, true);
            
            return $result;
            
        } catch (\Exception $e) {
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution($sql, $executionTime, false, $e->getMessage());
            
            throw $e;
        }
    }
    
    /**
     * Execute insert query
     * 
     * @param string $table
     * @param array<string, mixed> $data
     * @param array<string> $format
     * @return int
     * @since 1.0.0
     */
    public function insert(string $table, array $data, array $format = []): int
    {
        $startTime = microtime(true);
        $connection = $this->getWriteConnection();
        
        try {
            $result = $connection->insert($table, $data, $format);
            
            if ($result === false) {
                throw new \RuntimeException('Insert failed: ' . $connection->last_error);
            }
            
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution("INSERT INTO {$table}", $executionTime, true);
            
            return $connection->insert_id;
            
        } catch (\Exception $e) {
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution("INSERT INTO {$table}", $executionTime, false, $e->getMessage());
            
            throw $e;
        }
    }
    
    /**
     * Execute update query
     * 
     * @param string $table
     * @param array<string, mixed> $data
     * @param array<string, mixed> $where
     * @param array<string> $format
     * @param array<string> $whereFormat
     * @return int
     * @since 1.0.0
     */
    public function update(string $table, array $data, array $where, array $format = [], array $whereFormat = []): int
    {
        $startTime = microtime(true);
        $connection = $this->getWriteConnection();
        
        try {
            $result = $connection->update($table, $data, $where, $format, $whereFormat);
            
            if ($result === false) {
                throw new \RuntimeException('Update failed: ' . $connection->last_error);
            }
            
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution("UPDATE {$table}", $executionTime, true);
            
            return $result;
            
        } catch (\Exception $e) {
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution("UPDATE {$table}", $executionTime, false, $e->getMessage());
            
            throw $e;
        }
    }
    
    /**
     * Execute delete query
     * 
     * @param string $table
     * @param array<string, mixed> $where
     * @param array<string> $whereFormat
     * @return int
     * @since 1.0.0
     */
    public function delete(string $table, array $where, array $whereFormat = []): int
    {
        $startTime = microtime(true);
        $connection = $this->getWriteConnection();
        
        try {
            $result = $connection->delete($table, $where, $whereFormat);
            
            if ($result === false) {
                throw new \RuntimeException('Delete failed: ' . $connection->last_error);
            }
            
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution("DELETE FROM {$table}", $executionTime, true);
            
            return $result;
            
        } catch (\Exception $e) {
            $executionTime = (microtime(true) - $startTime) * 1000;
            $this->trackQueryExecution("DELETE FROM {$table}", $executionTime, false, $e->getMessage());
            
            throw $e;
        }
    }
    
    /**
     * Start database transaction
     * 
     * @return bool
     * @since 1.0.0
     */
    public function beginTransaction(): bool
    {
        $connection = $this->getWriteConnection();
        return $connection->query('START TRANSACTION') !== false;
    }
    
    /**
     * Commit database transaction
     * 
     * @return bool
     * @since 1.0.0
     */
    public function commit(): bool
    {
        $connection = $this->getWriteConnection();
        return $connection->query('COMMIT') !== false;
    }
    
    /**
     * Rollback database transaction
     * 
     * @return bool
     * @since 1.0.0
     */
    public function rollback(): bool
    {
        $connection = $this->getWriteConnection();
        return $connection->query('ROLLBACK') !== false;
    }
    
    /**
     * Execute query within transaction
     * 
     * @param callable $callback
     * @return mixed
     * @throws \Exception
     * @since 1.0.0
     */
    public function transaction(callable $callback)
    {
        $this->beginTransaction();
        
        try {
            $result = $callback($this);
            $this->commit();
            return $result;
        } catch (\Exception $e) {
            $this->rollback();
            throw $e;
        }
    }
    
    /**
     * Test database connection
     * 
     * @return array<string, mixed>
     * @since 1.0.0
     */
    public function testConnection(): array
    {
        $startTime = microtime(true);
        
        try {
            $result = $this->queryValue('SELECT 1');
            $responseTime = (microtime(true) - $startTime) * 1000;
            
            return [
                'status' => 'success',
                'connected' => $result === '1',
                'response_time_ms' => round($responseTime, 2),
                'server_version' => $this->getServerVersion(),
                'connection_id' => $this->getConnectionId()
            ];
        } catch (\Exception $e) {
            $responseTime = (microtime(true) - $startTime) * 1000;
            
            return [
                'status' => 'error',
                'connected' => false,
                'response_time_ms' => round($responseTime, 2),
                'error' => $e->getMessage()
            ];
        }
    }
    
    /**
     * Get MySQL server version
     * 
     * @return string
     * @since 1.0.0
     */
    public function getServerVersion(): string
    {
        try {
            return $this->queryValue('SELECT VERSION()') ?: 'Unknown';
        } catch (\Exception $e) {
            return 'Unknown';
        }
    }
    
    /**
     * Get current connection ID
     * 
     * @return int
     * @since 1.0.0
     */
    public function getConnectionId(): int
    {
        try {
            return (int) $this->queryValue('SELECT CONNECTION_ID()');
        } catch (\Exception $e) {
            return 0;
        }
    }
    
    /**
     * Get database statistics
     * 
     * @return array<string, mixed>
     * @since 1.0.0
     */
    public function getDatabaseStats(): array
    {
        try {
            $stats = [
                'server_version' => $this->getServerVersion(),
                'connection_id' => $this->getConnectionId(),
                'uptime' => $this->queryValue("SHOW STATUS LIKE 'Uptime'") ?: 0,
                'queries' => $this->queryValue("SHOW STATUS LIKE 'Queries'") ?: 0,
                'slow_queries' => $this->queryValue("SHOW STATUS LIKE 'Slow_queries'") ?: 0,
                'connections' => $this->queryValue("SHOW STATUS LIKE 'Connections'") ?: 0,
                'aborted_connects' => $this->queryValue("SHOW STATUS LIKE 'Aborted_connects'") ?: 0,
                'max_connections' => $this->queryValue("SHOW VARIABLES LIKE 'max_connections'") ?: 0,
                'thread_cache_size' => $this->queryValue("SHOW VARIABLES LIKE 'thread_cache_size'") ?: 0
            ];
            
            return $stats;
        } catch (\Exception $e) {
            return [
                'error' => $e->getMessage(),
                'server_version' => $this->getServerVersion(),
                'connection_id' => $this->getConnectionId()
            ];
        }
    }
    
    /**
     * Get table information and statistics
     * 
     * @param string $tableName
     * @return array<string, mixed>
     * @since 1.0.0
     */
    public function getTableStats(string $tableName): array
    {
        try {
            $tableStatus = $this->queryRow("SHOW TABLE STATUS LIKE '{$tableName}'");
            
            if (!$tableStatus) {
                return ['error' => 'Table not found'];
            }
            
            return [
                'name' => $tableStatus['Name'],
                'engine' => $tableStatus['Engine'],
                'rows' => (int) $tableStatus['Rows'],
                'data_length' => (int) $tableStatus['Data_length'],
                'index_length' => (int) $tableStatus['Index_length'],
                'data_free' => (int) $tableStatus['Data_free'],
                'auto_increment' => (int) $tableStatus['Auto_increment'],
                'create_time' => $tableStatus['Create_time'],
                'update_time' => $tableStatus['Update_time'],
                'collation' => $tableStatus['Collation'],
                'comment' => $tableStatus['Comment']
            ];
        } catch (\Exception $e) {
            return ['error' => $e->getMessage()];
        }
    }
    
    /**
     * Optimize table
     * 
     * @param string $tableName
     * @return array<string, mixed>
     * @since 1.0.0
     */
    public function optimizeTable(string $tableName): array
    {
        try {
            $result = $this->query("OPTIMIZE TABLE {$tableName}");
            
            return [
                'success' => true,
                'result' => $result,
                'message' => 'Table optimized successfully'
            ];
        } catch (\Exception $e) {
            return [
                'success' => false,
                'error' => $e->getMessage()
            ];
        }
    }
    
    /**
     * Analyze table
     * 
     * @param string $tableName
     * @return array<string, mixed>
     * @since 1.0.0
     */
    public function analyzeTable(string $tableName): array
    {
        try {
            $result = $this->query("ANALYZE TABLE {$tableName}");
            
            return [
                'success' => true,
                'result' => $result,
                'message' => 'Table analyzed successfully'
            ];
        } catch (\Exception $e) {
            return [
                'success' => false,
                'error' => $e->getMessage()
            ];
        }
    }
    
    /**
     * Track query execution metrics
     * 
     * @param string $sql
     * @param float $executionTime
     * @param bool $success
     * @param string|null $error
     * @return void
     * @since 1.0.0
     */
    private function trackQueryExecution(string $sql, float $executionTime, bool $success, ?string $error = null): void
    {
        $this->performanceMetrics['total_queries']++;
        $this->performanceMetrics['total_execution_time'] += $executionTime;
        
        if (!$success) {
            $this->performanceMetrics['failed_queries']++;
        }
        
        if ($executionTime > $this->slowQueryThreshold) {
            $this->performanceMetrics['slow_queries']++;
        }
        
        // Log query if enabled
        if ($this->enableQueryLogging) {
            $this->queryLog[] = [
                'sql' => substr($sql, 0, 200) . (strlen($sql) > 200 ? '...' : ''),
                'execution_time' => $executionTime,
                'success' => $success,
                'error' => $error,
                'timestamp' => microtime(true)
            ];
            
            // Keep only last 1000 queries
            if (count($this->queryLog) > 1000) {
                $this->queryLog = array_slice($this->queryLog, -1000);
            }
        }
        
        // Trigger action for monitoring
        do_action('care_book_query_executed', [
            'sql' => $sql,
            'execution_time' => $executionTime,
            'success' => $success,
            'error' => $error
        ]);
    }
    
    /**
     * Log query for WordPress query logging
     * 
     * @param string $query
     * @return string
     * @since 1.0.0
     */
    public function logQuery(string $query): string
    {
        // This is called by WordPress query filter
        // You can add custom logging logic here
        return $query;
    }
    
    /**
     * Get performance metrics
     * 
     * @return array<string, mixed>
     * @since 1.0.0
     */
    public function getPerformanceMetrics(): array
    {
        $metrics = $this->performanceMetrics;
        
        // Calculate derived metrics
        $metrics['average_execution_time'] = $metrics['total_queries'] > 0 
            ? round($metrics['total_execution_time'] / $metrics['total_queries'], 2)
            : 0;
            
        $metrics['success_rate'] = $metrics['total_queries'] > 0 
            ? round((($metrics['total_queries'] - $metrics['failed_queries']) / $metrics['total_queries']) * 100, 2)
            : 100;
            
        $metrics['slow_query_percentage'] = $metrics['total_queries'] > 0 
            ? round(($metrics['slow_queries'] / $metrics['total_queries']) * 100, 2)
            : 0;
        
        return $metrics;
    }
    
    /**
     * Reset performance metrics
     * 
     * @return void
     * @since 1.0.0
     */
    public function resetPerformanceMetrics(): void
    {
        $this->initializePerformanceMetrics();
    }
    
    /**
     * Get recent query log
     * 
     * @param int $limit
     * @return array<array<string, mixed>>
     * @since 1.0.0
     */
    public function getQueryLog(int $limit = 100): array
    {
        if (!$this->enableQueryLogging) {
            return [];
        }
        
        return array_slice($this->queryLog, -$limit);
    }
    
    /**
     * Get slow queries from log
     * 
     * @param int $limit
     * @return array<array<string, mixed>>
     * @since 1.0.0
     */
    public function getSlowQueries(int $limit = 50): array
    {
        if (!$this->enableQueryLogging) {
            return [];
        }
        
        $slowQueries = array_filter($this->queryLog, function($query) {
            return $query['execution_time'] > $this->slowQueryThreshold;
        });
        
        // Sort by execution time descending
        usort($slowQueries, function($a, $b) {
            return $b['execution_time'] <=> $a['execution_time'];
        });
        
        return array_slice($slowQueries, 0, $limit);
    }
    
    /**
     * Enable or disable query logging
     * 
     * @param bool $enabled
     * @return void
     * @since 1.0.0
     */
    public function setQueryLogging(bool $enabled): void
    {
        $this->enableQueryLogging = $enabled;
        
        if ($enabled) {
            $this->setupQueryLogging();
        }
    }
    
    /**
     * Set slow query threshold
     * 
     * @param int $milliseconds
     * @return void
     * @since 1.0.0
     */
    public function setSlowQueryThreshold(int $milliseconds): void
    {
        $this->slowQueryThreshold = $milliseconds;
    }
    
    /**
     * Get connection configuration
     * 
     * @return array<string, mixed>
     * @since 1.0.0
     */
    public function getConnectionConfig(): array
    {
        // Return safe config without password
        return [
            'charset' => $this->connectionConfig['charset'],
            'collate' => $this->connectionConfig['collate'],
            'host' => $this->connectionConfig['host'],
            'database' => $this->connectionConfig['database'],
            'username' => $this->connectionConfig['username']
        ];
    }
    
    /**
     * Prevent cloning
     * 
     * @return void
     * @since 1.0.0
     */
    private function __clone() {}
    
    /**
     * Prevent unserialization
     * 
     * @return void
     * @since 1.0.0
     */
    public function __wakeup()
    {
        throw new \Exception("Cannot unserialize singleton");
    }
}