place_order.php

<?php
include("header.php");

if ($_SERVER["REQUEST_METHOD"] === "POST") {
    $user_id = $_SESSION['id'];
    $productIds = isset($_POST['product_id']) ? explode(",", $_POST['product_id']) : [];
    $quantities = isset($_POST['quantity']) ? explode(",", $_POST['quantity']) : [];
    $selected_address = $_POST['selected_address'];
    $payment_method = isset($_POST['payment_method']) ? $_POST['payment_method'] : null;

    if (empty($payment_method)) {
        echo "<script>alert('Please select a payment method!'); window.location.href='checkout.php';</script>";
        exit();
    }

    if (empty($selected_address)) {
        echo "<script>alert('Please select a shipping address!'); window.location.href='shipping_address.php';</script>";
        exit();
    }

    $order_total = 0;
    $order_details = [];

    foreach ($productIds as $index => $product_id) {
        $quantity = isset($quantities[$index]) ? $quantities[$index] : 1;

        // Fetch stock details for the product
        $query = "SELECT price, stocks_count FROM product WHERE p_id = '$product_id'";
        $result = mysqli_query($conn, $query);

        if ($result && mysqli_num_rows($result) > 0) {
            $product = mysqli_fetch_assoc($result);
            $price = $product['price'];
            $stock = $product['stocks_count'];

            // Check if stock is sufficient
            if ($quantity > $stock) {
                echo "<script>alert('Insufficient stock for product ID $product_id. Please adjust the quantity.'); window.location.href='show_cart.php';</script>";
                exit();
            }

            $order_details[] = [
                'product_id' => $product_id,
                'quantity' => $quantity,
                'price' => $price,
            ];
        } else {
            echo "<script>alert('Invalid product selected!'); window.location.href='cart.php';</script>";
            exit();
        }
    }

    // Insert order into the `orders` table
    $order_query = "INSERT INTO orders(u_id, order_date, status, payment_method, address_id) VALUES ('$user_id', NOW(), 'Pending', '$payment_method', '$selected_address')";
    if (mysqli_query($conn, $order_query)) {
        $order_id = mysqli_insert_id($conn);

        foreach ($order_details as $detail) {
            $product_id = $detail['product_id'];
            $quantity = $detail['quantity'];
            $price = $detail['price'];
            $order_total = $price * $quantity;

            $detail_query = "INSERT INTO order_details (order_id, p_id, quantity, price) VALUES ('$order_id', '$product_id', '$quantity', '$order_total')";
            mysqli_query($conn, $detail_query);

            $update_stock_query = "UPDATE product SET stocks_count = stocks_count - $quantity WHERE p_id = '$product_id'";
            mysqli_query($conn, $update_stock_query);

            $adminOrderRequestQuery = "INSERT INTO admin_order_request (order_id, u_id, status) VALUES ($order_id, $user_id, 'Pending')";
            mysqli_query($conn, $adminOrderRequestQuery);
        }

        $clear_cart_query = "DELETE FROM cart WHERE u_id = '$user_id'";
        mysqli_query($conn, $clear_cart_query);

        echo "<script>window.location.href='order_success.php?order_id=$order_id';</script>";
    } 
    else {
        echo "<script>alert('Failed to place the order. Please try again later.'); window.location.href='cart.php';</script>";
    }
} else {
    echo "<script>alert('Invalid request!'); window.location.href='cart.php';</script>";
}

?>