<?php
require_once __DIR__ . '/db/config.php';

header('Content-Type: application/json');

$response = ['success' => false, 'message' => 'An unknown error occurred.'];

if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
    http_response_code(405);
    $response['message'] = 'Invalid request method.';
    echo json_encode($response);
    exit;
}

$data = json_decode(file_get_contents('php://input'), true);
$cart = $data['cart'] ?? [];
$paymentMethod = $data['payment_method'] ?? 'Cash';

if (empty($cart)) {
    http_response_code(400);
    $response['message'] = 'Cart is empty.';
    echo json_encode($response);
    exit;
}

$pdo = db();
try {
    $pdo->beginTransaction();

    $totalAmount = 0;
    foreach ($cart as $item) {
        $totalAmount += $item['price'] * $item['quantity'];
    }

    $transactionId = 'TXN-' . strtoupper(uniqid());
    $stmt = $pdo->prepare("INSERT INTO sales (transaction_id, total_amount, payment_method) VALUES (?, ?, ?)");
    $stmt->execute([$transactionId, $totalAmount, $paymentMethod]);
    $saleId = $pdo->lastInsertId();

    $itemStmt = $pdo->prepare("INSERT INTO sale_items (sale_id, product_id, quantity, price) VALUES (?, ?, ?, ?)");
    $stockStmt = $pdo->prepare("UPDATE products SET stock = stock - ? WHERE id = ?");

    foreach ($cart as $item) {
        $productId = $item['id'];
        $quantity = $item['quantity'];
        $price = $item['price'];

        $itemStmt->execute([$saleId, $productId, $quantity, $price]);
        $stockStmt->execute([$quantity, $productId]);
    }

    $pdo->commit();

    $response['success'] = true;
    $response['message'] = 'Checkout successful!';
    $response['transaction_id'] = $transactionId;
    http_response_code(200);

} catch (Exception $e) {
    if ($pdo->inTransaction()) {
        $pdo->rollBack();
    }
    http_response_code(500);
    $response['message'] = 'Checkout failed: ' . $e->getMessage();
}

echo json_encode($response);