<?php
// core/Database.php

class Database {
    private static ?Database $instance = null;
    private PDO $pdo;

    private function __construct() {
        $dsn = 'mysql:host=' . DB_HOST . ';dbname=' . DB_NAME . ';charset=' . DB_CHARSET;
        $options = [
            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::ATTR_EMULATE_PREPARES   => false,
            PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES utf8mb4"
        ];
        try {
            $this->pdo = new PDO($dsn, DB_USER, DB_PASS, $options);
        } catch (PDOException $e) {
            die(json_encode(['error' => 'Database connection failed: ' . $e->getMessage()]));
        }
    }

    public static function getInstance(): Database {
        if (self::$instance === null) {
            self::$instance = new Database();
        }
        return self::$instance;
    }

    public function getConnection(): PDO {
        return $this->pdo;
    }

    // Shorthand query
    public function query(string $sql, array $params = []): PDOStatement {
        $stmt = $this->pdo->prepare($sql);
        $stmt->execute($params);
        return $stmt;
    }

    public function fetchAll(string $sql, array $params = []): array {
        return $this->query($sql, $params)->fetchAll();
    }

    public function fetchOne(string $sql, array $params = []): ?array {
        $row = $this->query($sql, $params)->fetch();
        return $row ?: null;
    }

    public function insert(string $table, array $data): int {
        $cols = implode(', ', array_keys($data));
        $placeholders = implode(', ', array_fill(0, count($data), '?'));
        $sql = "INSERT INTO `$table` ($cols) VALUES ($placeholders)";
        $this->query($sql, array_values($data));
        return (int)$this->pdo->lastInsertId();
    }

    public function update(string $table, array $data, string $where, array $whereParams = []): int {
        $sets = implode(', ', array_map(fn($k) => "`$k` = ?", array_keys($data)));
        $sql = "UPDATE `$table` SET $sets WHERE $where";
        $stmt = $this->query($sql, array_merge(array_values($data), $whereParams));
        return $stmt->rowCount();
    }

    public function delete(string $table, string $where, array $params = []): int {
        $stmt = $this->query("DELETE FROM `$table` WHERE $where", $params);
        return $stmt->rowCount();
    }

    public function lastInsertId(): string {
        return $this->pdo->lastInsertId();
    }

    // Prevent cloning
    private function __clone() {}
}