AddToCart.php

<?php
header("Access-Control-Allow-Origin: *");
header("Content-Type: application/json; charset=UTF-8");
header("Access-Control-Allow-Methods: POST");
header("Access-Control-Allow-Headers: Content-Type, Access-Control-Allow-Headers, Authorization, X-Requested-With");

include "conx.php"; // Include your database connection

$data = json_decode(file_get_contents("php://input"), true);

// Debug: Log incoming data
file_put_contents("debug.log", print_r($data, true));

// Validate input
if (!empty($data['user_id']) && !empty($data['id']) && !empty($data['price']) && !empty($data['quantity']) && !empty($data['image'])) {
    $user_id = $data['user_id'];
    $product_id = $data['id'];
    $price = $data['price'];
    $quantity = $data['quantity'];
    $image = $data['image'];

    // Check if quantity is greater than available stock
    $stockQuery = "SELECT quantity FROM products WHERE id = ?";
    $stmt = $conn->prepare($stockQuery);
    $stmt->bind_param("i", $product_id);
    $stmt->execute();
    $result = $stmt->get_result();
    $product = $result->fetch_assoc();
    
    if ($product) {
        $availableStock = $product['quantity'];

        // Check if the quantity to add exceeds available stock
        if ($quantity > $availableStock) {
            echo json_encode(["success" => false, "message" => "Cannot add more than {$availableStock} items to the cart."]);
            $stmt->close();
            $conn->close();
            exit();
        }
    } else {
        echo json_encode(["success" => false, "message" => "Product not found."]);
        $stmt->close();
        $conn->close();
        exit();
    }

    $totalPrice = $price * $quantity;

    // Check if the product already exists in the cart
    $checkQuery = "SELECT * FROM cart WHERE user_id = ? AND product = ?";
    $stmt = $conn->prepare($checkQuery);
    $stmt->bind_param("ii", $user_id, $product_id);
    $stmt->execute();
    $result = $stmt->get_result();

    if ($result->num_rows > 0) {
        // Update existing cart item
        $existingProduct = $result->fetch_assoc();
        $newQuantity = $existingProduct['quantity'] + $quantity;

        // Check again if the updated quantity exceeds available stock
        if ($newQuantity > $availableStock) {
            echo json_encode(["success" => false, "message" => "Cannot update the cart. The new quantity exceeds available stock."]);
            $stmt->close();
            $conn->close();
            exit();
        }

        $newTotalPrice = $price * $newQuantity;
        $updateQuery = "UPDATE cart SET quantity = ?, totalPrice = ?, image = ? WHERE user_id = ? AND product = ?";
        $stmt = $conn->prepare($updateQuery);
        $stmt->bind_param("idisi", $newQuantity, $newTotalPrice, $image, $user_id, $product_id);

        if ($stmt->execute()) {
            echo json_encode(["success" => true, "message" => "Product quantity updated in cart"]);
        } else {
            echo json_encode(["success" => false, "message" => "Failed to update product in cart"]);
        }
    } else {
        // Insert new cart item
        $insertQuery = "INSERT INTO cart (user_id, product, price, quantity, totalPrice, image) VALUES (?, ?, ?, ?, ?, ?)";
        $stmt = $conn->prepare($insertQuery);
        $stmt->bind_param("iidids", $user_id, $product_id, $price, $quantity, $totalPrice, $image);

        if ($stmt->execute()) {
            echo json_encode(["success" => true, "message" => "Product added to cart successfully"]);
        } else {
            echo json_encode(["success" => false, "message" => "Failed to add product to cart"]);
        }
    }

    $stmt->close();
} else {
    echo json_encode(["success" => false, "message" => "Invalid product data"]);
}

$conn->close();
?>