<?php defined('SYSPATH') OR die('No direct access allowed.');
/**
 * Controls headers that effect client caching of pages
 *
 * $Id: expires.php 4272 2009-04-25 21:47:26Z zombor $
 *
 * @package    Core
 * @author     Kohana Team
 * @copyright  (c) 2007-2008 Kohana Team
 * @license    http://kohanaphp.com/license.html
 */
class expires_Core {

	/**
	 * Sets the amount of time before a page expires
	 *
	 * @param  integer Seconds before the page expires 
	 * @return boolean
	 */
	public static function set($seconds = 60)
	{
		if (expires::check_headers())
		{
			$now = $expires = time();

			// Set the expiration timestamp
			$expires += $seconds;

			// Send headers
			header('Last-Modified: '.gmdate('D, d M Y H:i:s T', $now));
			header('Expires: '.gmdate('D, d M Y H:i:s T', $expires));
			header('Cache-Control: max-age='.$seconds);

			return $expires;
		}

		return FALSE;
	}

	/**
	 * Checks to see if a page should be updated or send Not Modified status
	 *
	 * @param   integer  Seconds added to the modified time received to calculate what should be sent
	 * @return  bool     FALSE when the request needs to be updated
	 */
	public static function check($seconds = 60)
	{
		if ( ! empty($_SERVER['HTTP_IF_MODIFIED_SINCE']) AND expires::check_headers())
		{
			if (($strpos = strpos($_SERVER['HTTP_IF_MODIFIED_SINCE'], ';')) !== FALSE)
			{
				// IE6 and perhaps other IE versions send length too, compensate here
				$mod_time = substr($_SERVER['HTTP_IF_MODIFIED_SINCE'], 0, $strpos);
			}
			else
			{
				$mod_time = $_SERVER['HTTP_IF_MODIFIED_SINCE'];
			}

			$mod_time = strtotime($mod_time);
			$mod_time_diff = $mod_time + $seconds - time();

			if ($mod_time_diff > 0)
			{
				// Re-send headers
				header('Last-Modified: '.gmdate('D, d M Y H:i:s T', $mod_time));
				header('Expires: '.gmdate('D, d M Y H:i:s T', time() + $mod_time_diff));
				header('Cache-Control: max-age='.$mod_time_diff);
				header('Status: 304 Not Modified', TRUE, 304);

				// Prevent any output
				Event::add('system.display', array('expires', 'prevent_output'));

				// Exit to prevent other output
				exit;
			}
		}

		return FALSE;
	}

	/**
	 * Check headers already created to not step on download or Img_lib's feet
	 *
	 * @return boolean
	 */
	public static function check_headers()
	{
		foreach (headers_list() as $header)
		{
			if ((session_cache_limiter() == '' AND stripos($header, 'Last-Modified:') === 0)
			    OR stripos($header, 'Expires:') === 0)
			{
				return FALSE;
			}
		}

		return TRUE;
	}

	/**
	 * Prevent any output from being displayed. Executed during system.display.
	 *
	 * @return  void
	 */
	public static function prevent_output()
	{
		Kohana::$output = '';
	}

} // End expires
