如何设计和开发RESTful API以实现PHP应用的数据交互

<?php
require_once 'db.php';

function respond_json($data) {
    header('Content-Type: application/json');
    echo json_encode($data);
}

// 获取所有用户信息
function get_users() {
    $users = db_get_all();
    respond_json($users);
}

// 获取指定用户信息
function get_user($id) {
    $user = db_get_user($id);
    respond_json($user);
}

// 创建用户
function create_user() {
    $data = json_decode(file_get_contents('php://input'), true);
    $user = db_create_user($data);
    respond_json($user);
}

// 更新用户信息
function update_user($id) {
    $data = json_decode(file_get_contents('php://input'), true);
    $user = db_update_user($id, $data);
    respond_json($user);
}

// 删除用户
function delete_user($id) {
    $user = db_delete_user($id);
    respond_json($user);
}

// 根据请求路由调用相应的处理函数
switch ($_SERVER['REQUEST_METHOD']) {
    case 'GET': {
        if ($_SERVER['REQUEST_URI'] == '/users') {
            get_users();
        } else {
            preg_match('/^/users/(d+)$/', $_SERVER['REQUEST_URI'], $matches);
            if (count($matches) == 2) {
                get_user($matches[1]);
            }
        }
        break;
    }

    case 'POST': {
        if ($_SERVER['REQUEST_URI'] == '/users') {
            create_user();
        }
        break;
    }

    case 'PUT': {
        preg_match('/^/users/(d+)$/', $_SERVER['REQUEST_URI'], $matches);
        if (count($matches) == 2) {
            update_user($matches[1]);
        }
        break;
    }

    case 'DELETE': {
        preg_match('/^/users/(d+)$/', $_SERVER['REQUEST_URI'], $matches);
        if (count($matches) == 2) {
            delete_user($matches[1]);
        }
        break;
    }
}