<?php

/**
 * @file
 * Contains the admin form and callback functions for datastream manipulations.
 */

/**
 * Callback to download the given datastream to the users computer.
 *
 * @param AbstractDatastream $datastream
 *   The datastream to download.
 */
function islandora_download_datastream(AbstractDatastream $datastream) {
  islandora_view_datastream($datastream, TRUE);
}

/**
 * Callback function to view or download a datastream.
 *
 * @note
 *  This function calls exit().
 *
 * @param AbstractDatastream $datastream
 *   The datastream to view/download.
 * @param bool $download
 *   If TRUE the file is download to the user computer for viewing otherwise it
 *   will attempt to display in the browser natively.
 * @param int $version
 *   The version of the datastream to display
 */
function islandora_view_datastream(AbstractDatastream $datastream, $download = FALSE, $version = NULL) {
  module_load_include('inc', 'islandora', 'includes/mimetype.utils');
  // XXX: Certain features of the Devel module rely on the use of "shutdown
  // handlers", such as query logging... The problem is that they might blindly
  // add additional output which will break things if what is actually being
  // output is anything but a webpage... like an image or video or audio or
  // whatever the datastream is here.
  $GLOBALS['devel_shutdown'] = FALSE;

  if ($version !== NULL) {
    if (isset($datastream[$version])) {
      $datastream = $datastream[$version];
    }
    else {
      return drupal_not_found();
    }
  }
  header('Content-type: ' . $datastream->mimetype);
  if ($datastream->controlGroup == 'M' || $datastream->controlGroup == 'X') {
    header('Content-length: ' . $datastream->size);
  }
  if ($download) {
    // Browsers will not append all extensions.
    $extension = '.' . islandora_get_extension_for_mimetype($datastream->mimetype);
    // Prevent adding on a duplicate extension.
    $label = $datastream->label;
    $extension_length = strlen($extension);
    $duplicate_extension_position = strlen($label) > $extension_length ?
      strripos($label, $extension, -$extension_length) :
      FALSE;
    $filename = $label;
    if ($duplicate_extension_position === FALSE) {
      $filename .= $extension;
    }

    // Allow other modules to modify or replace the filename.
    drupal_alter('islandora_datastream_filename', $filename, $datastream);

    header("Content-Disposition: attachment; filename=\"$filename\"");
  }

  $cache_check = islandora_view_datastream_cache_check($datastream);
  if ($cache_check !== 200) {
    if ($cache_check === 304) {
      header('HTTP/1.1 304 Not Modified');
    }
    elseif ($cache_check === 412) {
      header('HTTP/1.0 412 Precondition Failed');
    }
  }
  islandora_view_datastream_set_cache_headers($datastream);

  drupal_page_is_cacheable(FALSE);

  // New content needed.
  if ($cache_check === 200) {
    // We need to see if the chunking is being requested. This will mainly
    // happen with iOS video requests as they do not support any other way
    // to receive content for playback.
    $chunk_headers = FALSE;
    if (isset($_SERVER['HTTP_RANGE'])) {
      // XXX: Can't make assertions on byte ranging of redirect datastreams.
      // @see https://jira.duraspace.org/browse/ISLANDORA-2084.
      if (!$download && $datastream->controlGroup == 'R') {
        drupal_goto($datastream->url);
      }
      // Set headers specific to chunking.
      $chunk_headers = islandora_view_datastream_set_chunk_headers($datastream);
    }
    // Try not to load the file into PHP memory!
    // Close and flush ALL the output buffers!
    while (@ob_end_flush()) {
    };

    if (isset($_SERVER['HTTP_RANGE'])) {
      if ($chunk_headers) {
        islandora_view_datastream_deliver_chunks($datastream, $chunk_headers);
      }
    }
    else {
      $datastream->getContent('php://output');
    }
  }
  exit();
}

/**
 * Parse "etags" from HTTP If-Match or If-None-Match headers.
 *
 * Parses from the CSV-like struture supported by HTTP headers into an array,
 * so `"asdf", "fdsa", W/"2132"` should become an array containing the strings:
 * - asdf
 * - fdsa
 * - 2132
 *
 * @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.24
 * @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26
 *
 * @param string $header_value
 *   The value from the headers.
 *
 * @return array
 *   An array containing all the etags present.
 */
function islandora_parse_http_match_headers($header_value) {
  $matches = array();
  // Match the CSV-like structure supported by the HTTP headers.
  $count = preg_match_all('/(((W\/)?("?)(\*|.+?)\4)(, +)?)/', $header_value, $matches);
  // The fifth sub-expression/group is which will contain the etags.
  return $matches[5];
}

/**
 * Validate cache headers.
 *
 * @param AbstractDatastream $datastream
 *   The datastream for which to check the request headers against.
 *
 * @return int
 *   An integer representing the HTTP response code. One of:
 *   - 200: Proceed as normal. (Full download).
 *   - 304: Resource hasn't changed; pass cache validation.
 *   - 412: Resource has changed; fail cache validation.
 *
 * @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
 */
function islandora_view_datastream_cache_check(AbstractDatastream $datastream) {
  if (!variable_get('islandora_use_datastream_cache_headers', TRUE)) {
    return 200;
  }

  // Let's assume that if we get here, we'll be able to complete the request.
  $return = 200;

  if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
    $modified_since = DateTime::createFromFormat('D, d M Y H:i:s e', $_SERVER['HTTP_IF_MODIFIED_SINCE']);
    if ($modified_since === FALSE) {
      return $return;
    }
    else {
      if ($datastream->createdDate->getTimestamp() - $modified_since->getTimestamp() > 0) {
        // Changed!
        return $return;
      }
      else {
        $return = 304;
      }
    }
  }
  if ($return === 200 && isset($_SERVER['HTTP_IF_UNMODIFIED_SINCE'])) {
    $unmodified_since = DateTime::createFromFormat('D, d M Y H:i:s e', $_SERVER['HTTP_IF_UNMODIFIED_SINCE']);
    if ($unmodified_since === FALSE) {
      return $return;
    }
    else {
      if ($datastream->createdDate->getTimestamp() !== $unmodified_since->getTimestamp()) {
        // Changed!
        $return = 412;
      }
      else {
        return $return;
      }
    }
  }

  // Only consider Etags we have provided.
  if (isset($datastream->checksum)) {
    $tags = array();
    foreach ($datastream as $offset => $version) {
      if (isset($version->checksum)) {
        $tags[$offset] = $version->checksum;
      }
    }

    if ($return === 200 && isset($_SERVER['HTTP_IF_MATCH'])) {
      $request_tags = islandora_parse_http_match_headers($_SERVER['HTTP_IF_MATCH']);
      if (in_array('*', $request_tags) || count(array_intersect($tags, $request_tags)) > 0) {
        // There's a match... Let things go ahead.
        return $return;
      }
      else {
        $return = 412;
      }
    }
    if (in_array($return, array(200, 304), TRUE) && isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
      $request_tags = islandora_parse_http_match_headers($_SERVER['HTTP_IF_NONE_MATCH']);
      if (in_array('*', $request_tags) || count(array_intersect($tags, $request_tags)) > 0) {
        $return = 304;
      }
      else {
        $return = 200;
      }
    }
  }

  return $return;
}

/**
 * Set various HTTP headers for caching.
 *
 * @param AbstractDatastream $datastream
 *   The datastream being viewed/downloaded.
 */
function islandora_view_datastream_set_cache_headers(AbstractDatastream $datastream) {
  if (variable_get('islandora_use_datastream_cache_headers', TRUE)) {
    // Force cache revalidation.
    header('Expires: Sun, 19 Nov 1978 05:00:00 GMT');
    $cache_control = array();
    if ($datastream->parent->repository->api->connection->username == 'anonymous') {
      $cache_control[] = 'public';
    }
    else {
      $cache_control[] = 'private';
    }
    $cache_control[] = 'must-revalidate';
    $cache_control[] = 'max-age=0';
    header('Cache-Control: ' . implode(', ', $cache_control));
    header('Last-Modified: ' . $datastream->createdDate->format('D, d M Y H:i:s \G\M\T'));
    if (isset($datastream->checksum)) {
      header("Etag: \"{$datastream->checksum}\"");
    }
  }
  else {
    header_remove('Cache-Control');
    header_remove('Expires');
  }
}

/**
 * Get the human readable size of the given datastream.
 *
 * @param AbstractDatastream $datastream
 *   The datastream to check.
 *
 * @return string
 *   A human readable size of the given datastream, or '-' if the size could not
 *   be determined.
 */
function islandora_datastream_get_human_readable_size(AbstractDatastream $datastream) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  $size_is_calculatable = $datastream->controlGroup == 'M' || $datastream->controlGroup == 'X';
  return $size_is_calculatable ? islandora_convert_bytes_to_human_readable($datastream->size) : '-';
}

/**
 * Get either the 'view' or 'download' url for the given datastream if possible.
 *
 * @param AbstractDatastream $datastream
 *   The datastream to generated the url to.
 * @param string $type
 *   One of:
 *   - download
 *   - view
 * @param int $version
 *   (Optional) The version of the datastream to get a URL for.
 *
 * @return string
 *   either the 'view' or 'download' url for the given datastream.
 */
function islandora_datastream_get_url(AbstractDatastream $datastream, $type = 'download', $version = NULL) {
  if ($version === NULL) {
    $link = "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/$type";
  }
  else {
    $link = "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/version/$version/$type";
    $datastream = $datastream[$version];
  }

  if ($datastream->controlGroup == 'R') {
    return $datastream->url;
  }
  else {
    return $link;
  }
}

/**
 * Display the edit datastream page.
 *
 * @param AbstractDatastream $datastream
 *   The datastream to edit.
 */
function islandora_edit_datastream(AbstractDatastream $datastream) {
  module_load_include('inc', 'islandora', 'includes/utilities');

  $edit_registry = islandora_build_datastream_edit_registry($datastream);
  $edit_count = count($edit_registry);
  switch ($edit_count) {
    case 0:
      // No edit implementations.
      drupal_set_message(t('There are no edit methods specified for this datastream.'));
      drupal_goto("islandora/object/{$datastream->parent->id}/manage/datastreams");
      break;

    case 1:
      // One registry implementation, go there.
      $entry = reset($edit_registry);
      drupal_goto($entry['url']);
      break;

    default:
      // Multiple edit routes registered.
      return islandora_edit_datastream_registry_render($edit_registry);
  }
}

/**
 * Displays links to all the edit datastream registry items.
 *
 * @param array $edit_registry
 *   A list of 'islandora_edit_datastream_registry' values.
 *
 * @return array
 *   A Drupal renderable array containing the "edit" markup.
 */
function islandora_edit_datastream_registry_render(array $edit_registry) {
  $markup = '';
  foreach ($edit_registry as $edit_route) {
    $markup .= l($edit_route['name'], $edit_route['url']) . '<br/>';
  }
  return array(
    '#type' => 'markup',
    '#markup' => $markup,
  );
}

/**
 * Set the headers for the chunking of our content.
 *
 * @param AbstractDatastream $datastream
 *   An AbstractDatastream representing a datastream on a Fedora object.
 *
 * @return bool
 *   TRUE if there are chunks to be returned, FALSE otherwise.
 */
function islandora_view_datastream_set_chunk_headers(AbstractDatastream $datastream) {
  $file_uri = islandora_view_datastream_retrieve_file_uri($datastream);
  // The meat of this has been taken from:
  // http://mobiforge.com/design-development/content-delivery-mobile-devices.
  $size   = filesize($file_uri);
  $length = $size;
  $start  = 0;
  $end    = $size - 1;

  header("Accept-Ranges: 0-$length");
  if (isset($_SERVER['HTTP_RANGE'])) {
    $c_start = $start;
    $c_end   = $end;
    // Extract the range string.
    list(, $range) = explode('=', $_SERVER['HTTP_RANGE'], 2);
    // Make sure the client hasn't sent us a multibyte range.
    if (strpos($range, ',') !== FALSE) {
      // Not a valid range, notify the client.
      header('HTTP/1.1 416 Requested Range Not Satisfiable');
      header("Content-Range: bytes $start-$end/$size");
      exit;
    }
    // If the range starts with an '-' we start from the beginning. If not, we
    // forward the file pointer and make sure to get the end byte if specified.
    if (strpos($range, '-') === 0) {
      // The n-number of the last bytes is requested.
      $c_start = $size - substr($range, 1);
    }
    else {
      $range  = explode('-', $range);
      $c_start = $range[0];
      $c_end   = (isset($range[1]) && is_numeric($range[1])) ? $range[1] : $size;
    }
    /* Check the range and make sure it's treated according to the specs.
     * http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
     */
    // End bytes can not be larger than $end.
    $c_end = ($c_end > $end) ? $end : $c_end;
    // Validate the requested range and return an error if it's not correct.
    if ($c_start > $c_end || $c_start > $size - 1 || $c_end >= $size) {
      header('HTTP/1.1 416 Requested Range Not Satisfiable');
      header("Content-Range: bytes $start-$end/$size");
      exit;
    }
    $start  = $c_start;
    $end    = $c_end;
    // Calculate new content length.
    $length = $end - $start + 1;
    header('HTTP/1.1 206 Partial Content');
  }
  // Notify the client the byte range we'll be outputting.
  header("Content-Range: bytes $start-$end/$size");
  header("Content-Length: $length");
  return array(
    'start' => $start,
    'end' => $end,
  );
}

/**
 * Deliver back the specified chunks of a file.
 *
 * @param AbstractDatastream $datastream
 *   An AbstractDatastream representing a datastream on a Fedora object.
 * @param array $params
 *   An associate array containing the start and ending chunk bytes.
 */
function islandora_view_datastream_deliver_chunks(AbstractDatastream $datastream, $params) {
  $file_uri = islandora_view_datastream_retrieve_file_uri($datastream);
  // The meat of this has been taken from:
  // http://mobiforge.com/design-development/content-delivery-mobile-devices.
  $fp = @fopen($file_uri, 'rb');
  fseek($fp, $params['start']);
  // Start buffered download.
  $buffer = 1024 * 8;
  while (!feof($fp) && ($p = ftell($fp)) <= $params['end']) {
    if ($p + $buffer > $params['end']) {
      // In case we're only outputting a chunk, make sure we don't read past the
      // length.
      $buffer = $params['end'] - $p + 1;
    }
    // Reset time limit for big files.
    set_time_limit(0);
    echo fread($fp, $buffer);
  }
  fclose($fp);
}

/**
 * Creates/returns the file URI for the content of a datastream for chunking.
 *
 * File locks are used to ensure the datastream is completely downloaded before
 * attempting to serve up chunks from the file.
 *
 * @throws RepositoryException|Exception
 *   Exceptions may be thrown if the file was unable to be reliably acquired.
 *
 * @param AbstractDatastream $datastream
 *   An AbstractDatastream representing a datastream on a Fedora object.
 *
 * @return string
 *   The URI of the file.
 */
function islandora_view_datastream_retrieve_file_uri(AbstractDatastream $datastream) {
  module_load_include('inc', 'islandora', 'includes/mimetype.utils');
  module_load_include('inc', 'islandora', 'includes/utilities');

  $extension = islandora_get_extension_for_mimetype($datastream->mimetype);
  $file_uri = 'temporary://chunk_' . $datastream->parent->id . '_' . $datastream->id . '_' . $datastream->createdDate->getTimestamp() . '.' . $extension;
  touch(drupal_realpath($file_uri));
  $fp = fopen($file_uri, 'r+b');
  if (flock($fp, LOCK_SH)) {
    try {
      fseek($fp, 0, SEEK_END);
      if (ftell($fp) === 0 && $datastream->size > 0) {
        // Just opened at beginning of file, if beginning == EOF, need to grab
        // it.
        if (!flock($fp, LOCK_EX | LOCK_NB)) {
          // Hypothetically, two threads could have a "shared" lock with an
          // unpopulated file, so to avoid deadlock on the "exclusive" lock,
          // drop the "shared" lock before blocking to obtain the "exclusive"
          // lock.
          flock($fp, LOCK_UN);
        }
        if (flock($fp, LOCK_EX)) {
          // Get exclusive lock, write file.
          $file = islandora_temp_file_entry($file_uri, $datastream->mimeType);
          if ($file->filesize == $datastream->size) {
            // Populated in another thread while we were waiting for the
            // "exclusive" lock; drop lock and return.
            flock($fp, LOCK_UN);
            fclose($fp);
            return $file_uri;
          }

          try {
            $datastream->getContent($file->uri);
            clearstatcache($file->uri);
            $file = file_save($file);
            if ($file->filesize != $datastream->size) {
              throw new RepositoryException(t('Size of file downloaded for chunking does not match: Got @apparent bytes when expecting @actual.', array(
                '@apparent' => $file->filesize,
                '@actual' => $datastream->size,
              )));
            }
          }
          catch (RepositoryException $e) {
            file_delete($file);
            throw $e;
          }
        }
        else {
          throw new Exception(t('Failed to acquire write lock when downloading @pid/@dsid for chunking.', array(
            '@pid' => $datastream->parent->id,
            '@dsid' => $datastream->id,
          )));
        }
      }
      flock($fp, LOCK_UN);
      fclose($fp);
      return $file_uri;
    }
    catch (Exception $e) {
      flock($fp, LOCK_UN);
      fclose($fp);
      throw $e;
    }
  }
  throw new Exception(t('Failed to acquire shared lock when chunking @pid/@dsid.', array(
    '@pid' => $datastream->parent->id,
    '@dsid' => $datastream->id,
  )));
}