<?php

class Proxy {
    protected $allowed = [];

    public function __construct()
    {

        if(!isset($_GET['url'])) {
            header("HTTP/1.0 404 Not Found");
            die('404 - 1');
        }
        

        if (filter_var($_GET['url'], FILTER_VALIDATE_URL) === false) {
            header("HTTP/1.0 404 Not Found");
            die('404 -2');
        }

        if(!$this->isAllowed($_GET['url'])) {
            header("HTTP/1.0 404 Not Found");
            die('404 - 3');
        }
    }

    public function output()
    {
        $ext = pathinfo($this->url, PATHINFO_EXTENSION);
        switch ($ext) {
        case "gif":
            header('Content-Type: image/gif');
            readfile($this->url);
            break;
        case "png":
            header('Content-Type: image/png');
            readfile($this->url);
            break;
        case "jpg":
        default:
            header('Content-Type: image/jpeg');
            readfile($this->url);
            break;
        }
    }

    protected function getHost()
    {
        $result = parse_url($this->url);
        return $result['host'];
    }

    protected function isAllowed($url)
    {
        return in_array($this->getHost($url), $this->allowed);
    }
}

(new Proxy)->output();