How to write RESTful APIs in "Vanilla" PHP?

PHP supports them native. In a certain PHP, I have to code in "pure PHP", no RESTful APIs library/engine provided. So I decided to write a file called api.php to handle all API request. I used this pattern

if ($grabber->method() === 'GET') {
    // define your APIs here
    echo json_encode(array('Appl RESTful APIs'), JSON_UNESCAPED_UNICODE);
    exit(0);

} else if ($grabber->method() === 'POST') {
    // define your APIs here

} else if ($grabber->method() === 'PUT') {
    // define your APIs here

} else if ($grabber->method() === 'DELETE') {
    // define your APIs here

}

You can see the api.php at Github