<?php
class cachefile
{
  /** Where to store the cached informations */
  public $directory = "./cache";
  /** If TRUE : no information is cached */
  public $nocache = false;

  /** Check if there is some garbage to clean */
  public function garbage ()
  {
    try
    {
      $this->cachedir ();
    }
    catch (Exception $e)
    {
      throw new Exception ($e->getMessage(), $e->getCode());
    }

    $res = $this->read ("CACHE-Garbage");
    if ($res === false)
    {
      $this->write ("CACHE-Garbage", "Let's go, garbage !", 24*60*60);
      $files = glob ($this->directory."/*", GLOB_NOSORT);
      foreach ($files as $fileCache)
      {
        $datas = file_get_contents ($fileCache);
        if ($datas === false)
        {
          unlink ($fileCache);
          continue;
        }

        $datas = unserialize ($datas);
        if (! isset ($datas["ttl"]) || ! isset ($datas["data"]) ||
            ! isset ($datas["createTime"]))
        {
          unlink ($fileCache);
          continue;
        }

        if (($datas["createTime"] + $datas["ttl"]) >= time ())
        {
          unlink ($fileCache);
        }
      }
    }
  }

  /** This function check if the cachedir exists and create it if it is not the
      case.
      Check if the cache dir is writable and readable */
  public function cachedir ()
  {
    if (! isset ($this->directory) || $this->directory === "")
      throw new Exception (_("No cache directory defined"), 500);
    if (! file_exists ($this->directory))
    {
      // Need to create the cache dir
      $parent = realpath (dirname ($this->directory));
      if (! is_writeable (dirname ($this->directory)))
        throw new Exception (sprintf (_(
               "Directory %s is not writable : can not create cache directory"),
                $parent), 500);
      if (!mkdir ($this->directory))
        throw new Exception (sprintf (_("Can not create cache directory %s"),
                             $this->directory), 500);
      chmod ($this->directory, 0777);
    }
    if (! is_writable ($this->directory))
      throw new Exception (sprintf (_("Cache directory %s is not writable"), 
                                    $this->directory), 500);
    if (! is_readable ($this->directory))
      throw new Exception (sprintf (_("Cache directory %s is not readable"),
                                    $this->directory), 500);
    if (!file_exists ($this->directory."/.htaccess"))
      file_put_contents ($this->directory."/.htaccess", "deny from all\n");
    return true;
  }

  /** This function write data in cache
      The cache system can not save FALSE value
      @param string $id Cache identifier (add the authentication, the METHOD...)
      @param string $data The data to save
      @param integer|null $ttl The cache Time to Leave in seconds (3600s by
                               default)*/
  public function write ($id, $data, $ttl = 3600)
  {
    if ($this->nocache !== false)
      return false;
    if ($data === false)
      throw new Exception (_("Can not store FALSE in cache"), 500);
    try
    {
      $this->cachedir ();
    }
    catch (Exception $e)
    {
      throw new Exception ($e->getMessage(), $e->getCode());
    }

    $fileCache = $this->directory."/".sha1 ($id);
    touch ($fileCache.".lock");
    $datas = array ("ttl"=>$ttl,
                    "createTime"=>time(),
                    "data"=>$data);
    file_put_contents ($fileCache, serialize ($datas));
    unlink ($fileCache.".lock");
    chmod ($fileCache, 0666);
    return true;
  }

  /** This function read data from cache. Return FALSE in case of empty or too
      older cache
      @param string $id Cache identifier (add the authentication, the METHOD) */
  public function read ($id)
  {
    if ($this->nocache !== false)
      return false;
    try
    {
      $this->cachedir ();
    }
    catch (Exception $e)
    {
      throw new Exception ($e->getMessage(), $e->getCode());
    }

    $fileCache = $this->directory."/".sha1 ($id);
    if (!file_exists ($fileCache))
      return false;
    if (!is_readable ($fileCache))
      throw new Exception (sprintf (_("File cache %s is not readable"),
                                    $fileCache), 500);
    if (!is_writable ($fileCache))
      throw new Exception (sprintf (_("File cache %s is not writable"),
                                    $fileCache), 500);
    // Lock : waiting the reconstruction of the cache by another process
    // Waiting 10s maximum to re-create the cache file
    $startTime = time ();
    while (file_exists ($fileCache.".lock") && time () < $startTime + 10)
    {
      usleep (100000);
    }

    // The lock is pending 10s (stale) : removing it to read the datas quicker
    // next time
    if (file_exists ($fileCache.".lock"))
      unlink ($fileCache.".lock");

    $datas = file_get_contents ($fileCache);
    if ($datas === false)
    {
      unlink ($fileCache);
      return false;
    }

    $datas = unserialize ($datas);
    if (! isset ($datas["ttl"]) || ! isset ($datas["data"]) ||
        ! isset ($datas["createTime"]))
    {
      unlink ($fileCache);
      return false;
    }

    if (($datas["createTime"] + $datas["ttl"]) >= time ())
    {
      if (file_exists ($fileCache.".lock"))
        unlink ($fileCache.".lock");
      return $datas["data"];
    }

    return false;
  }

  /** This function delete an id in cache
      @param string $id Cache identifier (add the authentication, the METHOD...)
    */
  public function delete ($id)
  {
    $fileCache = $this->directory."/".sha1 ($id);
    if (!file_exists ($fileCache))
      return false;
    unlink ($fileCache);
    return true;
  }
}