<?php
    /**
     * HTTPCache found here.
     * This file is a part of FeedMagick.
     *
     * @author l.m.orchard <l.m.orchard@pobox.com>
     * @license http://opensource.org/licenses/gpl-license.php GNU Public License
     * @copyright Š2006 l.m.orchard
     * @link http://decafbad.com/trac/wiki/FeedMagick
     * @version 0.0
     */
     
    /**
     * Required classes
     */
    require_once('Snoopy.class.php');

    /* 
     * CONSTANTS - redefine these in your config.
     *
     * HTTP_CACHE_ROOT - Root path where all cached HTTP requests go.
     *
     */
    if ( !defined('HTTP_CACHE_ROOT') ) {
        define('HTTP_CACHE_ROOT', 'http-cache');
    }
    if ( !defined('HTTP_CACHE_USE_CACHE') ) {
        define('HTTP_CACHE_USE_CACHE', true);
    }
    if ( !defined('HTTP_CACHE_USE_GZIP') ) {
        define('HTTP_CACHE_USE_GZIP', true);
    }
    if ( !defined('HTTP_CACHE_USER_AGENT') ) {
        $ua = 'FeedMagick/0.0 (+http://decafbad.com/trac/wiki/FeedMagick)';
        define('HTTP_CACHE_USER_AGENT', $ua);
    }
    if ( !defined('HTTP_CACHE_MAX_AGE') ) {
        define('HTTP_CACHE_MAX_AGE', 3600);
    }
    
    /**
     * HTTPCache implements an HTTP cache for feeds using conditional GET
     * 
     * This class is a bit inspired by Joe Gregorio's httpcache.py [1] in
     * Python and uses bits stolen from MagpieRSS [2].
     *
     * [1]: http://bitworking.org/projects/httpcache/
     * [2]: http://magpierss.sourceforge.net/
     *
     * Synopsis:
     *
     *     $cache =& new HTTPCache('http://example.com');
     *     $data  =  $cache->fetch();
     *     if ($cache->fresh) {
     *         print "The data hasn't changed!";
     *     }
     *
     */
    class HTTPCache {
        
        var $client;
        var $content;
        var $fresh;
        var $url;
        var $headers;
        var $cache_id;
        var $cache_path;
        var $cache_entry;
        var $cache_root = HTTP_CACHE_ROOT;
        
        function HTTPCache($url) {
            $this->content     = null;
            $this->fresh       = null;
            $this->url         = $url;
            $this->cache_entry = array();
            $this->headers     = array();
            $this->max_age     = HTTP_CACHE_MAX_AGE;
        }

        function fetch() {
            global $log;
            
            // If USE_CACHE is false, circumvent caching altogether.
            if (!HTTP_CACHE_USE_CACHE) {
                $log->debug("Disabled cache fetch of ".$this->url);
                $this->_fetchURL();
                return $this->content;
            }
            
            $this->cache_id    = md5($this->url);
            $this->cache_path  = $this->cache_root."/".$this->cache_id;

            if ($this->_loadCacheEntry()) {
                if (array_key_exists('etag', $this->cache_entry)) {
                    $this->headers['If-None-Match']    = $this->cache_entry['etag'];
                }
                if (array_key_exists('last_modified', $this->cache_entry)) {
                    $this->headers['If-Last-Modified'] = $this->cache_entry['last_modified'];
                }
                
                // TODO: Streamline this age check into the 304 check below?
                // Check cache entry age
                $mtime = filemtime($this->cache_path);
                $age = time() - $mtime;
                if ( $age < $this->max_age ) {
                    $log->debug("Still-fresh cache hit of ".$this->url);
                    $this->fresh   = true;
                    $this->content = $this->cache_entry['content'];
                    return $this->content;
                }
            }
            
            $log->debug("Cache miss and fetch of ".$this->url);
            $this->_fetchURL();

            if ( ('304' == $this->client->status) && (array_key_exists('content', $this->cache_entry)) ) {
                $this->fresh   = true;
                $this->content = $this->cache_entry['content'];
            } elseif ($this->is_success($this->client->status)) {
                $this->fresh   = false;
                $this->content = $this->client->results;
                $this->_cacheResponseHeaders();
            } // elseif ($this->is_error($this->client->status)) {  }
            
            $this->_saveCacheEntry();

            return $this->content;
        }

        function _cacheResponseHeaders() {
            // find Etag, and Last-Modified
            foreach($this->client->headers as $h) {
                // 2003-03-02 - Nicola Asuni (www.tecnick.com) - fixed bug "Undefined offset: 1"
                if (strpos($h, ": ")) {
                    list($field, $val) = explode(": ", $h, 2);
                }
                else {
                    $field = $h;
                    $val = "";
                }
                
                if ( $field == 'ETag' ) {
                    $this->cache_entry['etag'] = $val;
                }
                
                if ( $field == 'Last-Modified' ) {
                    $this->cache_entry['last_modified'] = $val;
                }
            }

        }
        
        function _loadCacheEntry() {
            $fn = $this->cache_path;
            if ( file_exists($fn) && ($fin = fopen($fn,'r')) ) {
                $data = fread($fin, filesize($fn));
                $this->cache_entry = unserialize($data);
                fclose($fin);
                return true;
            }
            return false;
        }

        function _saveCacheEntry() {
            // TODO: Report error if HTTPCache cache file not writable
            /*
            if (!is_writable($this->cache_path)) {
                error_log("Cache entry not writeable: ".$this->cache_path);
                return;
            }
            */
            if ($fout = fopen($this->cache_path,'w')) {
                $this->cache_entry['content'] = $this->content;
                fwrite($fout, serialize($this->cache_entry));
                fclose($fout);
            }
        }

        function _fetchURL() {
            // Snoopy is an HTTP client in PHP
            $this->client = new Snoopy();
            $this->client->agent    = HTTP_CACHE_USER_AGENT;
            $this->client->use_gzip = HTTP_CACHE_USE_GZIP;
            if (is_array($this->headers) ) {
                $this->client->rawheaders = $this->headers;
            }
            
            @$this->client->fetch($this->url);

            return $this->client;
        }
        
        function is_success ($sc) { 
            return $sc >= 200 && $sc < 300; 
        }
        
        function is_error ($sc) { 
            return $sc >= 400 && $sc < 600; 
        }
        
        function is_info ($sc) { 
            return $sc >= 100 && $sc < 200; 
        }

        function is_redirect ($sc) { 
            return $sc >= 300 && $sc < 400; 
        }

        function is_client_error ($sc) { 
            return $sc >= 400 && $sc < 500; 
        }

        function is_server_error ($sc) { 
            return $sc >= 500 && $sc < 600; 
        }

    }

?>