UsersController.php

<?php

class UsersController {

    private $requestMethod;

    public function __construct($requestMethod)
    {
        $this->requestMethod = $requestMethod;
    }

    public function processRequest()
    {
        switch ($this->requestMethod) {
            case 'GET':
                $response = $this->getAllUsers();
                break;
            default:
                $response = $this->notFoundResponse();
                break;
        }
        header($response['status_code_header']);
        if ($response['body']) {
            echo $response['body'];
        }
    }

    private function getAllUsers()
    {
        $tab_users = UserModel::getAllUsers();
        $response['status_code_header'] = http_response_code(200);
        $response['body'] = json_encode($tab_users);
        return $response;
    }

    private function notFoundResponse()
    {
        $response['status_code_header'] = 'HTTP/1.1 404 Not Found';
        $response['body'] = null;
        return $response;
    }
}