<?php
/*
 * Limb PHP Framework
 *
 * @link http://limb-project.com
 * @copyright  Copyright &copy; 2004-2009 BIT(http://bit-creative.com)
 * @license    LGPL http://www.gnu.org/copyleft/lesser.html
 */
//inspired by http://alexandre.alapetite.net/doc-alex/php-http-304/

/**
 * class lmbHttpCache.
 *
 * @package net
 * @version $Id: lmbHttpCache.class.php 7486 2009-01-26 19:13:20Z pachanga $
 */
class lmbHttpCache
{
  protected $etag;
  protected $last_modified_time;
  protected $cache_time;
  protected $cache_type;

  const TYPE_PRIVATE = 0;
  const TYPE_PUBLIC = 1;

  function __construct()
  {
    $this->reset();
  }

  function reset()
  {
    $this->last_modified_time = time();
    $this->etag = null;
    $this->cache_time = 0;
    $this->cache_type = self::TYPE_PRIVATE;
  }

  function checkAndWrite($response)
  {
    if($this->is412())
    {
      $this->_write412Response($response);
      return true;
    }
    elseif($this->is304())
    {
      $this->_write304Response($response);
      return true;
    }
    else
    {
      $this->_writeCachingResponse($response);

      return isset($_SERVER['REQUEST_METHOD']) && $_SERVER['REQUEST_METHOD'] == 'HEAD'; //rfc2616-sec9.html#sec9.4
    }
  }

  function is412()
  {
    if (isset($_SERVER['HTTP_IF_MATCH'])) //rfc2616-sec14.html#sec14.24
    {
      $etag_client = stripslashes($_SERVER['HTTP_IF_MATCH']);
      return (($etag_client != '*') &&  (strpos($etag_client, $this->getEtag()) === false));
    }

    if (isset($_SERVER['HTTP_IF_UNMODIFIED_SINCE'])) //http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.28
    {
      return (strcasecmp($_SERVER['HTTP_IF_UNMODIFIED_SINCE'], $this->formatLastModifiedTime()) != 0);
    }

    return false;
  }

  function is304()
  {
    if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) //rfc2616-sec14.html#sec14.25 //rfc1945.txt
    {
      return ($_SERVER['HTTP_IF_MODIFIED_SINCE'] == $this->formatLastModifiedTime());
    }

    if (isset($_SERVER['HTTP_IF_NONE_MATCH'])) //rfc2616-sec14.html#sec14.26
    {
      $etag_client = stripslashes($_SERVER['HTTP_IF_NONE_MATCH']);
      return (($etag_client == $this->getEtag()) ||  ($etag_client == '*'));
    }

    return false;
  }

  protected function _write412Response($response)
  {
    $response->addHeader('HTTP/1.1 412 Precondition Failed');
    $response->addHeader('Cache-Control: protected, max-age=0, must-revalidate');
    $response->addHeader('Content-Type: text/plain');

    $response->write("HTTP/1.1 Error 412 Precondition Failed: Precondition request failed positive evaluation\n");
  }

  protected function _write304Response($response)
  {
    $response->addHeader('HTTP/1.0 304 Not Modified');
    $response->addHeader('Etag: ' . $this->getEtag());
    $response->addHeader('Pragma: ');
    $response->addHeader('Cache-Control: ');
    $response->addHeader('Last-Modified: ');
    $response->addHeader('Expires: ');
  }

  protected function _writeCachingResponse($response)
  {
    $response->addHeader('Cache-Control: ' . $this->_getCacheControl()); //rfc2616-sec14.html#sec14.9
    $response->addHeader('Last-Modified: ' . $this->formatLastModifiedTime());
    $response->addHeader('Etag: ' . $this->getEtag());
    $response->addHeader('Pragma: ');
    $response->addHeader('Expires: ');
  }

  protected function _getCacheControl()
  {
    if ($this->cache_time == 0)
      $cache = 'protected, must-revalidate, ';
    elseif ($this->cache_type == self::TYPE_PRIVATE)
      $cache = 'protected, ';
    elseif ($this->cache_type == self::TYPE_PUBLIC)
      $cache = 'public, ';
    else
      $cache = '';
    $cache .= 'max-age=' . floor($this->cache_time);
    return $cache;
  }

  function formatLastModifiedTime()
  {
    return $this->_formatGmtTime($this->last_modified_time);
  }

  protected function _formatGmtTime($time)
  {
    return gmdate('D, d M Y H:i:s \G\M\T', $time);
  }

  function setLastModifiedTime($last_modified_time)
  {
    $this->last_modified_time = $last_modified_time;
  }

  function getLastModifiedTime()
  {
    return $this->last_modified_time;
  }

  function setEtag($etag)
  {
    $this->etag = $etag;
  }

  function getEtag()
  {
    if($this->etag)
      return $this->etag;

    //rfc2616-sec14.html#sec14.19 //='"0123456789abcdef0123456789abcdef"'
    if (isset($_SERVER['QUERY_STRING']))
      $query = '?' . $_SERVER['QUERY_STRING'];
    else
      $query = '';

    $this->etag = '"' . md5($this->_getScriptName() . $query . '#' . $this->last_modified_time ) . '"';

    return $this->etag;
  }

  protected function _getScriptName()
  {
    if (isset($_SERVER['SCRIPT_FILENAME']))
      return $_SERVER['SCRIPT_FILENAME'];
    elseif (isset($_SERVER['PATH_TRANSLATED']))
      return $_SERVER['PATH_TRANSLATED'];
    else
      return '';
  }

  function setCacheTime($cache_time)
  {
    $this->cache_time = $cache_time;
  }

  function getCacheTime()
  {
    return $this->cache_time;
  }

  function setCacheType($cache_type)
  {
    $this->cache_type = $cache_type;
  }

  function getCacheType()
  {
    return $this->cache_type;
  }
}