cart.js

const express = require('express');
const router = express.Router();
const pool = require('../config/database');

// ฟังก์ชันช่วยคำนวณราคารวม
async function calculateTotal(sessionId) {
    const [cartItems] = await pool.query(
        `SELECT cart_items.*, products.price 
         FROM cart_items 
         JOIN products ON cart_items.product_id = products.id 
         WHERE cart_items.session_id = ?`,
        [sessionId]
    );
    return cartItems.reduce((sum, item) => sum + (item.price * item.quantity), 0);
}

// แสดงตะกร้าสินค้า
router.get('/', async (req, res) => {
    try {
        const [cartItems] = await pool.query(
            `SELECT cart_items.*, products.name, products.price, products.stock
             FROM cart_items 
             JOIN products ON cart_items.product_id = products.id 
             WHERE session_id = ?`,
            [req.session.id]
        );
        const total = await calculateTotal(req.session.id);
        res.render('cart', { cartItems, total });
    } catch (error) {
        console.error(error);
        res.status(500).send('Error fetching cart');
    }
});

// เพิ่มสินค้าลงตะกร้า
router.post('/add', async (req, res) => {
    const { productId, quantity } = req.body;
    try {
        const [[product]] = await pool.query(
            'SELECT stock FROM products WHERE id = ?', [productId]
        );

        if (!product) {
            return res.status(404).send('Product not found');
        }

        if (quantity > product.stock) {
            return res.status(400).send('สินค้ามีจำนวนไม่เพียงพอ');
        }

        // ตรวจสอบว่าสินค้านี้มีอยู่ในตะกร้าหรือยัง
        const [[existingItem]] = await pool.query(
            'SELECT id, quantity FROM cart_items WHERE session_id = ? AND product_id = ?',
            [req.session.id, productId]
        );

        if (existingItem) {
            // อัปเดตจำนวนสินค้า
            const newQuantity = existingItem.quantity + parseInt(quantity);
            if (newQuantity > product.stock) {
                return res.status(400).send('สินค้ามีจำนวนไม่เพียงพอ');
            }
            await pool.query(
                'UPDATE cart_items SET quantity = ? WHERE id = ?',
                [newQuantity, existingItem.id]
            );
        } else {
            // เพิ่มสินค้าใหม่
            await pool.query(
                'INSERT INTO cart_items (session_id, product_id, quantity) VALUES (?, ?, ?)',