<?php
session_start();
require_once 'db/config.php';

if (!isset($_GET['action'])) {
    header('Location: index.php');
    exit;
}

$action = $_GET['action'];
$user_id = $_SESSION['user_id'] ?? null;
$session_id = session_id();
$pdoconnection = db();

if ($action == 'add') {
    if (!isset($_POST['menu_item_id']) || !isset($_POST['quantity'])) {
        header('Location: cart.php');
        exit;
    }

    $menu_item_id = $_POST['menu_item_id'];
    $quantity = $_POST['quantity'];

    // Check if item is already in cart
    if ($user_id) {
        $stmt = $pdoconnection->prepare("SELECT * FROM cart WHERE user_id = :user_id AND menu_item_id = :menu_item_id");
        $stmt->execute([':user_id' => $user_id, ':menu_item_id' => $menu_item_id]);
    } else {
        $stmt = $pdoconnection->prepare("SELECT * FROM cart WHERE session_id = :session_id AND menu_item_id = :menu_item_id");
        $stmt->execute([':session_id' => $session_id, ':menu_item_id' => $menu_item_id]);
    }
    $existing_item = $stmt->fetch();

    if ($existing_item) {
        // Update quantity
        $new_quantity = $existing_item['quantity'] + $quantity;
        $stmt = $pdoconnection->prepare("UPDATE cart SET quantity = :quantity WHERE id = :id");
        $stmt->execute([':quantity' => $new_quantity, ':id' => $existing_item['id']]);
    } else {
        // Insert new item
        $stmt = $pdoconnection->prepare("INSERT INTO cart (user_id, session_id, menu_item_id, quantity) VALUES (:user_id, :session_id, :menu_item_id, :quantity)");
        $stmt->execute([
            ':user_id' => $user_id,
            ':session_id' => $user_id ? null : $session_id,
            ':menu_item_id' => $menu_item_id,
            ':quantity' => $quantity
        ]);
    }

    header('Location: cart.php');
    exit;
}