A simple API with PHP

.htaccess

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [QSA,L]

ApiTrait.php

<?php

namespace tsu\http;

trait ApiTrait
{
    public function route()
    {
        $httpMethod = strtolower(@$_SERVER['REQUEST_METHOD']);
        $action = ucfirst(
            explode(
                '/',
                str_replace(
                    dirname(@$_SERVER['SCRIPT_NAME']) . '/',
                    '',
                    @$_SERVER['REDIRECT_URL']
                ),
                2
            )[0]
        );

        $method = $httpMethod . $action;

        if (method_exists($this, $method)) {
            $parameters = [];

            if ($httpMethod === 'get') {
                $parameters = $_GET;
            } else {
                parse_str(file_get_contents('php://input'), $parameters);
            }

            $this->$method($parameters);
        } else {
            $route = strtoupper($httpMethod) . '/' . lcfirst($action);

            throw new BadMethodCallException(
                'Route ' . $route . ' not supported'
            );
        }
    }

    public function respond($code, array $data)
    {
        header('Content-Type: application/json', false, $code);

        echo json_encode($data);
    }
}

index.php

<?php

// Usage example
// Set up autoloading e.g. using https://gist.github.com/jwage/221634

use tsu\http\ApiTrait;

class App
{
    use ApiTrait;

    public function run()
    {
        $this->route();
    }

    protected function getTest(array $data)
    {
        $this->respond(200, $data);
    }
}

(new App())->run();