<?php
/**
 * Generic class to handle caching
 *
 * @license    GPL 2 (http://www.gnu.org/licenses/gpl.html)
 * @author     Chris Smith <chris@jalakai.co.uk>
 */

if(!defined('DOKU_INC')) die('meh.');
require_once(DOKU_INC.'inc/io.php');
require_once(DOKU_INC.'inc/pageutils.php');
require_once(DOKU_INC.'inc/parserutils.php');

class cache {
  var $key = '';          // primary identifier for this item
  var $ext = '';          // file ext for cache data, secondary identifier for this item
  var $cache = '';        // cache file name
  var $depends = array(); // array containing cache dependency information,
                          //   used by _useCache to determine cache validity

  var $_event = '';       // event to be triggered during useCache

  function cache($key,$ext) {
    $this->key = $key;
    $this->ext = $ext;
    $this->cache = getCacheName($key,$ext);
  }

  /**
   * public method to determine whether the cache can be used
   *
   * to assist in cetralisation of event triggering and calculation of cache statistics, 
   * don't override this function override _useCache()
   *
   * @param  array   $depends   array of cache dependencies, support dependecies:
   *                            'age'   => max age of the cache in seconds
   *                            'files' => cache must be younger than mtime of each file
   *                                       (nb. dependency passes if file doesn't exist)
   *
   * @return bool    true if cache can be used, false otherwise
   */
  function useCache($depends=array()) {
    $this->depends = $depends;
    $this->_addDependencies();

    if ($this->_event) {
      return $this->_stats(trigger_event($this->_event,$this,array($this,'_useCache')));
    } else {
      return $this->_stats($this->_useCache());
    }
  }

  /**
   * private method containing cache use decision logic
   *
   * this function processes the following keys in the depends array
   *   purge - force a purge on any non empty value
   *   age   - expire cache if older than age (seconds)
   *   files - expire cache if any file in this array was updated more recently than the cache
   *
   * can be overridden
   *
   * @return bool               see useCache()
   */
  function _useCache() {

    if (!empty($this->depends['purge'])) return false;              // purge requested?
    if (!($this->_time = @filemtime($this->cache))) return false;   // cache exists?

    // cache too old?
    if (!empty($this->depends['age']) && ((time() - $this->_time) > $this->depends['age'])) return false;

    if (!empty($this->depends['files'])) {
      foreach ($this->depends['files'] as $file) {
        if ($this->_time < @filemtime($file)) return false;         // cache older than files it depends on?
      }
    }

    return true;
  }

  /**
   * add dependencies to the depends array
   *
   * this method should only add dependencies,
   * it should not remove any existing dependencies and
   * it should only overwrite a dependency when the new value is more stringent than the old
   */
  function _addDependencies() {
    if (isset($_REQUEST['purge'])) $this->depends['purge'] = true;   // purge requested
  }

  /**
   * retrieve the cached data
   *
   * @param   bool   $clean   true to clean line endings, false to leave line endings alone
   * @return  string          cache contents
   */
  function retrieveCache($clean=true) {
    return io_readFile($this->cache, $clean);
  }

  /**
   * cache $data
   *
   * @param   string $data   the data to be cached
   * @return  bool           true on success, false otherwise
   */
  function storeCache($data) {
    return io_savefile($this->cache, $data);
  }

  /**
   * remove any cached data associated with this cache instance
   */
  function removeCache() {
    @unlink($this->cache);
  }

  /**
   * Record cache hits statistics.
   * (Only when debugging allowed, to reduce overhead.)
   *
   * @param    bool   $success   result of this cache use attempt
   * @return   bool              pass-thru $success value
   */
  function _stats($success) {
    global $conf;
    static $stats = NULL;
    static $file;

    if (!$conf['allowdebug']) { return $success; }

    if (is_null($stats)) {
      $file = $conf['cachedir'].'/cache_stats.txt';
      $lines = explode("\n",io_readFile($file));

      foreach ($lines as $line) {
        $i = strpos($line,',');
        $stats[substr($line,0,$i)] = $line;
      }
    }

    if (isset($stats[$this->ext])) {
      list($ext,$count,$hits) = explode(',',$stats[$this->ext]);
    } else {
      $ext = $this->ext;
      $count = 0;
      $hits = 0;
    }

    $count++;
    if ($success) $hits++;
    $stats[$this->ext] = "$ext,$count,$hits";

    io_saveFile($file,join("\n",$stats));

    return $success;
  }
}

class cache_parser extends cache {

  var $file = '';       // source file for cache
  var $mode = '';       // input mode (represents the processing the input file will undergo)

  var $_event = 'PARSER_CACHE_USE';

  function cache_parser($id, $file, $mode) {
    if ($id) $this->page = $id;
    $this->file = $file;
    $this->mode = $mode;

    parent::cache($file.$_SERVER['HTTP_HOST'].$_SERVER['SERVER_PORT'],'.'.$mode);
  }

  function _useCache() {

    if (!@file_exists($this->file)) return false;                   // source exists?
    return parent::_useCache();
  }

  function _addDependencies() {
    global $conf, $config_cascade;

    $this->depends['age'] = isset($this->depends['age']) ? 
                   min($this->depends['age'],$conf['cachetime']) : $conf['cachetime'];

    // parser cache file dependencies ...
    $files = array($this->file,                                     // ... source
                   DOKU_INC.'inc/parser/parser.php',                // ... parser
                   DOKU_INC.'inc/parser/handler.php',               // ... handler
             );
    $files = array_merge($files, getConfigFiles('main'));           // ... wiki settings

    $this->depends['files'] = !empty($this->depends['files']) ? array_merge($files, $this->depends['files']) : $files;
    parent::_addDependencies();
  }

}

class cache_renderer extends cache_parser {

  function useCache($depends=array()) {
    $use = parent::useCache($depends);

    // meta data needs to be kept in step with the cache
    if (!$use && isset($this->page)) {
      p_set_metadata($this->page,array(),true);
    }

    return $use;
  }

  function _useCache() {
    global $conf;

    if (!parent::_useCache()) return false;

    // for wiki pages, check metadata dependencies
    if (isset($this->page)) {
      $metadata = p_get_metadata($this->page);

      // check currnent link existence is consistent with cache version
      // first check the purgefile
      // - if the cache is more recent that the purgefile we know no links can have been updated
      if ($this->_time < @filemtime($conf['cachedir'].'/purgefile')) {

#       $links = p_get_metadata($this->page,"relation references");
        $links = $metadata['relation']['references'];

        if (!empty($links)) {
          foreach ($links as $id => $exists) {
            if ($exists != page_exists($id,'',false)) return false;
          }
        }
      }
    }

    return true;
  }

  function _addDependencies() {

    // renderer cache file dependencies ...
    $files = array(
                   DOKU_INC.'inc/parser/'.$this->mode.'.php',       // ... the renderer
             );

    // page implies metadata and possibly some other dependencies
    if (isset($this->page)) {

      $metafile = metaFN($this->page,'.meta');
      if (@file_exists($metafile)) {
        $files[] = $metafile;                                       // ... the page's own metadata
        $files[] = DOKU_INC.'inc/parser/metadata.php';              // ... the metadata renderer

        $valid = p_get_metadata($this->page, 'date valid');
        if (!empty($valid['age'])) {
          $this->depends['age'] = isset($this->depends['age']) ?
                   min($this->depends['age'],$valid['age']) : $valid['age'];
        }

      } else {
        $this->depends['purge'] = true;                             // ... purging cache will generate metadata
        return;
      }
    }

    $this->depends['files'] = !empty($this->depends['files']) ? array_merge($files, $this->depends['files']) : $files;
    parent::_addDependencies();
  }
}

class cache_instructions extends cache_parser {

  function cache_instructions($id, $file) {
    parent::cache_parser($id, $file, 'i');
  }

  function retrieveCache() {
    $contents = io_readFile($this->cache, false);
    return !empty($contents) ? unserialize($contents) : array();
  }

  function storeCache($instructions) {
    return io_savefile($this->cache,serialize($instructions));
  }
}
