如何用PHP实现微信小程序的电影订票功能？

<?php
// 配置数据库连接
$db_host = "localhost";
$db_user = "root";
$db_password = "123456";
$db_name = "db_ticket";
$conn = new mysqli($db_host, $db_user, $db_password, $db_name);

// 获取电影列表接口
function getMovieList() {
    global $conn;
    $sql = "SELECT * FROM movies";
    $result = $conn->query($sql);
    $movies = [];
    if ($result->num_rows > 0) {
        while($row = $result->fetch_assoc()) {
            array_push($movies, $row);
        }
    }
    echo json_encode($movies);
}

// 创建订单接口
function createOrder($movieId, $seat) {
    global $conn;
    // TODO: 根据传递的参数生成订单并保存到数据库
    echo json_encode(["success" => true, "msg" => "订单创建成功"]);
}

// 查询订单接口
function getOrder($orderId) {
    global $conn;
    // TODO: 根据传递的订单号查询订单信息并返回给小程序
    echo json_encode(["order_id" => $orderId, "status" => "已支付"]);
}

// 完成支付接口
function completePayment($orderId, $payment) {
    global $conn;
    // TODO: 根据传递的订单号和支付凭证，完成支付操作并更新订单状态
    echo json_encode(["success" => true, "msg" => "支付成功"]);
}

// 根据小程序传递的操作类型调用相应的接口
$type = $_POST["type"];
if ($type == "getMovieList") {
    getMovieList();
} elseif ($type == "createOrder") {
    $movieId = $_POST["movieId"];
    $seat = $_POST["seat"];
    createOrder($movieId, $seat);
} elseif ($type == "getOrder") {
    $orderId = $_POST["orderId"];
    getOrder($orderId);
} elseif ($type == "completePayment") {
    $orderId = $_POST["orderId"];
    $payment = $_POST["payment"];
    completePayment($orderId, $payment);
} else {
    echo json_encode(["success" => false, "msg" => "未知操作类型"]);
}