<?php
require_once __DIR__ . '/Config.php';
class Database {
    private static $instance = null;
    private $config;
    private $connections = [];
    private $inUse = [];
    private $maxConnections = 10;
    private $minConnections = 3;
    private function __construct() {
        $this->config = Config::getInstance();
        $this->maxConnections = $this->config->get('database.max_connections', 10);
        $this->minConnections = $this->config->get('database.min_connections', 3);
        $this->initPool();
    }
    public static function getInstance() {
        if (self::$instance === null) { self::$instance = new self(); }
        return self::$instance;
    }
    private function initPool() {
        for ($i = 0; $i < $this->minConnections; $i++) { $this->connections[] = $this->createConnection(); }
    }
    private function createConnection() {
        $dbConfig = $this->config->get('database');
        $host = $dbConfig['host'];
        $port = $dbConfig['port'];
        $database = $dbConfig['database'];
        $username = $dbConfig['username'];
        $password = $dbConfig['password'];
        $charset = $dbConfig['charset'];
        $dsn = "mysql:host={$host};port={$port};charset={$charset}";
        $options = [
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::ATTR_EMULATE_PREPARES => false,
            PDO::ATTR_PERSISTENT => true
        ];
        $pdo = new PDO($dsn, $username, $password, $options);
        $pdo->exec("CREATE DATABASE IF NOT EXISTS `$database` CHARACTER SET $charset COLLATE {$dbConfig['collation']}");
        $pdo->exec("USE `$database`");
        return $pdo;
    }
    private function getConnection() {
        if (count($this->connections) > 0) {
            $pdo = array_pop($this->connections);
            if (!$this->isValid($pdo)) { $pdo = $this->createConnection(); }
            $this->inUse[] = $pdo;
            return $pdo;
        }
        if (count($this->inUse) < $this->maxConnections) {
            $pdo = $this->createConnection();
            $this->inUse[] = $pdo;
            return $pdo;
        }
        usleep(1000);
        return $this->getConnection();
    }
    private function release($pdo) {
        $key = array_search($pdo, $this->inUse);
        if ($key !== false) {
            unset($this->inUse[$key]);
            if ($this->isValid($pdo)) { $this->connections[] = $pdo; }
        }
    }
    private function isValid($pdo) {
        try { $pdo->query("SELECT 1"); return true; } catch (PDOException $e) { return false; }
    }
    public function fetchAll($sql, $params = []) {
        $pdo = $this->getConnection();
        try { $stmt = $pdo->prepare($sql); $stmt->execute($params); return $stmt->fetchAll(); }
        finally { $this->release($pdo); }
    }
    public function fetchOne($sql, $params = []) {
        $pdo = $this->getConnection();
        try { $stmt = $pdo->prepare($sql); $stmt->execute($params); return $stmt->fetch(); }
        finally { $this->release($pdo); }
    }
    public function query($sql, $params = []) {
        $pdo = $this->getConnection();
        try { $stmt = $pdo->prepare($sql); $stmt->execute($params); return $stmt; }
        finally { $this->release($pdo); }
    }
    public function insert($sql, $params = []) {
        $pdo = $this->getConnection();
        try { $stmt = $pdo->prepare($sql); $stmt->execute($params); return $pdo->lastInsertId(); }
        finally { $this->release($pdo); }
    }
    public function update($sql, $params = []) {
        $pdo = $this->getConnection();
        try { $stmt = $pdo->prepare($sql); $stmt->execute($params); return $stmt->rowCount(); }
        finally { $this->release($pdo); }
    }
    public function delete($sql, $params = []) {
        $pdo = $this->getConnection();
        try { $stmt = $pdo->prepare($sql); $stmt->execute($params); return $stmt->rowCount(); }
        finally { $this->release($pdo); }
    }
    public function beginTransaction() { $pdo = $this->getConnection(); $pdo->beginTransaction(); return $pdo; }
    public function commit($pdo = null) { if ($pdo) { $pdo->commit(); $this->release($pdo); } }
    public function rollback($pdo = null) { if ($pdo) { $pdo->rollBack(); $this->release($pdo); } }
    public function isConnected() {
        $pdo = $this->getConnection();
        try { $pdo->query("SELECT 1"); return true; }
        catch (PDOException $e) { return false; }
        finally { $this->release($pdo); }
    }
    public function getPoolStatus() {
        return [
            'total_connections' => count($this->connections) + count($this->inUse),
            'available_connections' => count($this->connections),
            'in_use_connections' => count($this->inUse),
            'max_connections' => $this->maxConnections
        ];
    }
}