<?php
/**
 * Database Connection Factory
 *
 * Centralizes database connection creation and management.
 * Provides a singleton connection for the request lifecycle.
 */
class Database {
    private static ?mysqli $connection = null;

    /**
     * Get database connection (singleton pattern)
     *
     * @return mysqli Database connection
     * @throws Exception If connection fails
     */
    public static function getConnection(): mysqli {
        if (self::$connection === null) {
            self::$connection = self::createConnection();
        }

        // Check if connection is still alive
        if (!self::$connection->ping()) {
            self::$connection = self::createConnection();
        }

        return self::$connection;
    }

    /**
     * Create a new database connection
     *
     * @return mysqli Database connection
     * @throws Exception If connection fails
     */
    private static function createConnection(): mysqli {
        // Ensure config is loaded
        if (!isset($GLOBALS['config'])) {
            require_once dirname(__DIR__) . '/config/config.php';
        }

        $conn = new mysqli(
            $GLOBALS['config']['DB_HOST'],
            $GLOBALS['config']['DB_USER'],
            $GLOBALS['config']['DB_PASS'],
            $GLOBALS['config']['DB_NAME']
        );

        if ($conn->connect_error) {
            throw new Exception("Database connection failed: " . $conn->connect_error);
        }

        // Set charset to utf8mb4 for proper Unicode support
        $conn->set_charset('utf8mb4');

        return $conn;
    }

    /**
     * Close the database connection
     */
    public static function close(): void {
        if (self::$connection !== null) {
            self::$connection->close();
            self::$connection = null;
        }
    }

    /**
     * Begin a transaction
     *
     * @return bool Success
     */
    public static function beginTransaction(): bool {
        return self::getConnection()->begin_transaction();
    }

    /**
     * Commit a transaction
     *
     * @return bool Success
     */
    public static function commit(): bool {
        return self::getConnection()->commit();
    }

    /**
     * Rollback a transaction
     *
     * @return bool Success
     */
    public static function rollback(): bool {
        return self::getConnection()->rollback();
    }

    /**
     * Execute a query and return results
     *
     * @param string $sql SQL query with placeholders
     * @param string $types Parameter types (i=int, s=string, d=double, b=blob)
     * @param array $params Parameters to bind
     * @return mysqli_result|bool Query result
     */
    public static function query(string $sql, string $types = '', array $params = []) {
        $conn = self::getConnection();

        if (empty($types) || empty($params)) {
            return $conn->query($sql);
        }

        $stmt = $conn->prepare($sql);
        if (!$stmt) {
            throw new Exception("Query preparation failed: " . $conn->error);
        }

        $stmt->bind_param($types, ...$params);
        $stmt->execute();

        $result = $stmt->get_result();
        $stmt->close();

        return $result;
    }

    /**
     * Execute an INSERT/UPDATE/DELETE and return affected rows
     *
     * @param string $sql SQL query with placeholders
     * @param string $types Parameter types
     * @param array $params Parameters to bind
     * @return int Affected rows (-1 on failure)
     */
    public static function execute(string $sql, string $types = '', array $params = []): int {
        $conn = self::getConnection();

        $stmt = $conn->prepare($sql);
        if (!$stmt) {
            throw new Exception("Query preparation failed: " . $conn->error);
        }

        if (!empty($types) && !empty($params)) {
            $stmt->bind_param($types, ...$params);
        }

        if ($stmt->execute()) {
            $affected = $stmt->affected_rows;
            $stmt->close();
            return $affected;
        }

        $error = $stmt->error;
        $stmt->close();
        throw new Exception("Query execution failed: " . $error);
    }

    /**
     * Get the last insert ID
     *
     * @return int Last insert ID
     */
    public static function lastInsertId(): int {
        return self::getConnection()->insert_id;
    }

    /**
     * Escape a string for use in queries (prefer prepared statements)
     *
     * @param string $string String to escape
     * @return string Escaped string
     */
    public static function escape(string $string): string {
        return self::getConnection()->real_escape_string($string);
    }
}