<?php

namespace Libs;

/**
 * PHP Proxy - DuckBrain
 *
 * Proxy is a library to create a PHP proxy.
 * It allows controlling the headers that will be returned to the client,
 * in addition to placing filters on the resulting HTML code.
 *
 * @author KJ
 * @website https://kj2.me
 * @licence MIT
 */
class Proxy
{
    public static $proxied_headers = [
        'Set-Cookie',
        'Content-Type',
        'Cookie',
        'Location',
    ];
    public static $proxy_base_url_canonical = '/';
    public static ?string $destination_host = null;
    protected static $filters = [];

    /**
     * Host destino efectivo: el asignado explicitamente o la constante
     * SOURCE_URL del proyecto si existe. Se resuelve tarde para que la
     * simple carga de la clase no falle sin configuracion.
     *
     * @return string
     */
    protected static function destinationHost(): string
    {
        if (static::$destination_host !== null) {
            return static::$destination_host;
        }

        return defined('SOURCE_URL') ? (string) SOURCE_URL : '';
    }

    /**
     * Adds a callable (AKA filter) that will receive the content
     * and should return a string.
     *
     * @param callable $cb
     *                     Function that will modify the content.
     *
     * @return void
     */
    public static function add_filter(callable $cb): void
    {
        static::$filters[] = $cb;
    }

    /**
     * Applies the filters configured with add_filter.
     *
     * @param string $content
     *                        Content on which the filters will be applied.
     *
     * @return mixed
     *               It would be correct to return a string, but
     *               since the filters might not return correctly,
     *               to avoid a design error, we specify that it returns mixed.
     */
    protected static function apply_filters(string $content): mixed
    {
        foreach (static::$filters as $filter) {
            $content = call_user_func($filter, $content);
        }
        return $content;
    }

    /**
     * Starts the proxy process.
     *
     * @param string|null $proxy_request_uri
     *                                       The address to which the proxy will be applied.
     *
     * @return void
     */
    public static function run(?string $proxy_request_uri = null): void
    {
        // Get the URI if not defined
        if (is_null($proxy_request_uri)) {
            $proxy_request_uri = substr($_SERVER['REQUEST_URI'], strlen(static::$proxy_base_url_canonical));
        } elseif (substr($proxy_request_uri, 0, 1) == '/') {
            $proxy_request_uri = substr($proxy_request_uri, 1);
        }

        // Generate the final URL
        $proxy_request_url = static::destinationHost() . $proxy_request_uri;

        // cURL initialization
        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, $proxy_request_url);
        curl_setopt($ch, CURLOPT_AUTOREFERER, 1);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
        curl_setopt($ch, CURLOPT_HEADER, 1);
        curl_setopt($ch, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
        curl_setopt($ch, CURLOPT_HTTPHEADER, array('Expect:'));
        curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_0);

        // Capture client cookies
        $hdrs = [];
        if (isset($_SERVER['HTTP_COOKIE'])) {
            $hdrs[] = "Cookie: " . $_SERVER['HTTP_COOKIE'];
        }

        // Capture client browser (User-Agent)
        if (isset($_SERVER['HTTP_USER_AGENT'])) {
            $hdrs[] = "User-Agent: " . $_SERVER['HTTP_USER_AGENT'];
        }

        // Add captured headers
        curl_setopt($ch, CURLOPT_HTTPHEADER, $hdrs);

        // Capture all client headers
        $hdrs = [];
        foreach (\getallheaders() as $name => $value) {
            $hdrs[] = "$name: $value";
        }

        // Add captured headers to the request
        curl_setopt($ch, CURLOPT_HTTPHEADER, $hdrs);

        // Add POST parameters
        if (sizeof($_POST) > 0) {
            curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($_POST));
        }

        // Execute the request
        $res = curl_exec($ch);

        // Parse the response
        list($headers, $body) = explode("\r\n\r\n", $res, 2);
        $headers = str_replace(static::destinationHost(), '/', $headers);

        $headers = explode("\r\n", $headers);
        $hs = [];

        foreach ($headers as $header) {
            if (false !== strpos($header, ': ')) {
                list($h, $v) = explode(': ', $header);
                $hs[$h][] = $v;
            } else {
                $header1  = $header;
            }
        }

        // Define headers in the client
        list($proto, $code, $text) = explode(' ', $header1);
        header($_SERVER['SERVER_PROTOCOL'] . ' ' . $code . ' ' . $text);

        foreach (static::$proxied_headers as $hname) {
            if (isset($hs[$hname])) {
                foreach ($hs[$hname] as $v) {
                    if ($hname === 'Set-Cookie') {
                        header($hname . ": " . $v, false);
                    } else {
                        header($hname . ": " . $v);
                    }
                }
            }
        }

        die(static::apply_filters($body));
    }
}