<?php
// $Id: purl.module,v 1.1 2009-03-08 23:39:24 yhahn Exp $

define('PURL_PATH', 'path');
define('PURL_SUBDOMAIN', 'subdomain');
define('PURL_DOMAIN', 'domain');
define('PURL_PAIR', 'pair');

/**
 * Implementation of hook_theme().
 */
function purl_theme($existing, $type, $theme, $path) {
  return array(
    'purl_settings_form' => array(
      'arguments' => array('form' => NULL),
    ),
  );
}

/**
 * Implementation of hook_menu().
 */
function purl_menu() {
  $items = array();
  $items['admin/settings/purl'] = array(
    'type' => MENU_NORMAL_ITEM,
    'title' => t('Persistent URL'),
    'description' => t('Settings for persistent url.'),
    'page callback' => 'drupal_get_form',
    'page arguments' => array('purl_settings_form'),
    'access callback' => 'user_access',
    'access arguments' => array('administer site configuration'),
    'weight' => 10,
  );
  $items['admin/settings/purl/settings'] = array(
    'type' => MENU_DEFAULT_LOCAL_TASK,
    'title' => t('Settings'),
    'page callback' => 'drupal_get_form',
    'page arguments' => array('purl_settings_form'),
    'access callback' => 'user_access',
    'access arguments' => array('administer site configuration'),
    'weight' => 0,
  );
  $items['admin/settings/purl/list'] = array(
    'type' => MENU_LOCAL_TASK,
    'title' => t('Modifiers'),
    'page callback' => 'purl_admin',
    'access callback' => 'user_access',
    'access arguments' => array('administer site configuration'),
    'weight' => 10,
  );
  return $items;
}

/**
 * Implementation of hook_init()
 * Checks for any valid persistent urls in request string and fire callback appropriately
 */
function purl_init() {
  static $once;
  if (!$once) {
    _purl_init(PURL_PATH);
    _purl_init(PURL_DOMAIN);
    _purl_init(PURL_PAIR);
    $once = true;
  }
}

/**
 * Helper function to initialize.
 */
function _purl_init($method = PURL_PATH) {
  switch ($method) {
    case PURL_PATH:
      $q = isset($_REQUEST["q"]) ? trim($_REQUEST["q"], "/") : '';
      $parsed = purl_parse(PURL_PATH, $q);
      break;
    case PURL_PAIR:
      $q = isset($_REQUEST["q"]) ? trim($_REQUEST["q"], "/") : '';
      $parsed = purl_parse(PURL_PAIR, $q);
      break;
    case PURL_DOMAIN:
      $host = $_SERVER['HTTP_HOST'];
      // We handle sub.domain.com, and nothing more (no sub1.sub2.domain.com).
      $q = str_replace('http://','',$host);
      $parsed = purl_parse(PURL_DOMAIN, $q);
      break;
  }
  
  // Initialize a few things so that we can use them without warnings.
  if (!isset($_GET['q'])) {
    $_GET['q'] = '';
  }
  if (!isset($_REQUEST['q'])) {
    $_REQUEST['q'] = '';
  }
  
  // if $_GET and $_REQUEST are different, the path has NOT been
  // aliased. We may need to rewrite the path.
  if (in_array($method, array(PURL_PATH, PURL_PAIR)) && ($_GET['q'] == trim($_REQUEST['q'], '/'))) {
    $q = purl_remove_modifiers($q, $method);
    // there is nothing beyond the path value -- treat as frontpage
    if ($q == '') {
      $_GET['q'] = variable_get('site_frontpage', 'node');
    }
    // pass the rest of the path onto Drupal cleanly
    else {
      $_REQUEST['q'] = $_GET['q'] = _purl_get_normal_path($q);
    }
  }
  
  if (is_array($parsed)) {
    foreach ($parsed as $value => $info) {
      purl_set($method, $value, $info);
    }
  }
}

/**
 * Check that no one else has implemented the custom_url_rewrite function --
 * if available, use PURL.
 */
if (!function_exists('custom_url_rewrite_outbound')) {
  function custom_url_rewrite_outbound(&$path, &$options, $original) {
    return purl_url_rewrite($path, $options, $original);
  }
}

/**
 * Rewrites path with the current modifier and removes the modifier if searching for source path.
 */
function purl_url_rewrite(&$path, &$options, $original) {
  $working_path = $path; // preserve original path

  /**
   * TODO: we need to abstract this base_url dissection into a
   * handler, and in there, we'll abstract out for
   * protocol handling, and handling the site's base_url like www.
   *
   * TODO: we need to make sure that other valued contexts don't
   * get dropped. e.g. if you are on 'en/node/43' and you
   * purl_goto('spaces', 'mygroup'), you should end up
   * at 'en/mygroup', not 'mygroup'
   *
   */

  // Check to see whether url rewriting has been disabled.
  if (empty($options['purl']['disabled']) || !purl_disable()) {
    $args = 
    $active_path_values = array();

    // The current url has requested a specific PURL modifier use it only
    if (!empty($options['purl']['provider']) && !empty($options['purl']['id'])) {
      $method = variable_get('purl_method_'. $options['purl']['provider'], PURL_PATH);
      $modifiers = purl_modifiers($method);
      switch ($method) {
        case PURL_PATH:
          foreach ($modifiers as $key => $modifier) {
            if ($modifier['id'] == $options['purl']['id'] && $modifier['provider'] == $options['purl']['provider']) {
              $active_path_values[] = $key;
              break;
            }
          }
          break;
        case PURL_PAIR:
          // @TODO: this ($values[0]) is really sketchy -- does it work?
          $modifiers = array_keys($modifiers);
          $active_path_values[] = "{$modifiers[0]}/{$options['purl']['id']}";
          break;
        case PURL_DOMAIN:
          foreach ($modifiers as $key => $info) {
            if ($modifier['id'] == $options['purl']['id'] && $modifier['provider'] == $options['purl']['provider']) {
              $options['absolute'] = TRUE;
              $active_path_values = array();
              $path = "http://{$key}/{$path}";
              break;
            }
          }
          break;
      }
    }
    else {
      // Retrieve the path values for the current page that were
      // "stripped out" and write them back into url paths.
      foreach (purl_get(PURL_PAIR) as $modifier) {
        $active_path_values[] = "{$modifier['value']}/{$modifier['id']}";
      }
      foreach (purl_get(PURL_PATH) as $modifier) {
        $active_path_values[] = $modifier['value'];
      }
    }

    if (count($active_path_values)) {
      $parsed = purl_parse(PURL_PATH, $working_path) + purl_parse(PURL_PAIR, $working_path);
      // A "normal" url was requested -- value the path
      if (!$options['alias'] && !strpos($path, '://') && !count($parsed) && count($active_path_values)) {
        $args = $args + $active_path_values;
      }
    }

    if (!empty($working_path)) {
      $args[] = $working_path;
    }

    $path = is_array($args) ? implode('/', $args) : '';
  }
  else {
    // Handle domains -- need to force domain onto the path and push through as absolute url
    $options['absolute'] = TRUE;
    if ($path == '<front>') {
      $path = variable_get('site_frontpage', 'node');
    }
    if ($domain = variable_get('purl_base_domain', '')) {
      $path = $domain .'/'. $path; // REPLACE BASE_URL with the hub domain.
    }  
  }

}

/**
 * Queries the database & modules for valid values based on modifing method.
 *
 * Modules that wish to provide in-code values should implement the 
 * hook_purl_modifiers(). Which should return an array of values by
 * by provider. 
 * 
 * For example:
 *
 *  return array(
 *    'my_module => array(
 *      array('value' => 'foo', 'id' => 1),
 *      array('value' => 'bar', 'id' => 2),
 *    ),
 *  );
 */
function purl_modifiers($requested_method = PURL_PATH) {
  static $values;
  if (!isset($values)) {
    $values = array();

    // Invoke purl_modifiers() and gather all values
    // provided "in code" (or stored by their respective modules)
    $providers = module_invoke_all('purl_modifiers');

    foreach ($providers as $provider => $items) {
      // Store providers for use when retrieving db values
      $method = variable_get('purl_method_'. $provider, PURL_PATH);

      // If using a value pair we don't need to cache the valid values.
      if ($method == PURL_PAIR) {
        $value = variable_get('purl_method_'. $provider .'_key', false);
        if ($value != false) {
          $values[$method][$value] = array(
            'provider' => $provider,
            'id' => null,
          );
        }
      }
      else {
        foreach ($items as $item) {
          if ($item['value'] && $item['id']) {
            $values[$method][$item['value']] = array(
              'provider' => $provider,
              'id' => $item['id'],
            );
          }
        }
      }
    }

    // Gather database values -- we exclude providers that we have
    // already collected values for through code.
    $providers = array_diff_key(purl_providers(), $providers);

    foreach ($providers as $provider => $info) {
      $method = variable_get('purl_method_'. $provider, PURL_PATH);
      // Don't load all data base values for keyed pairs.
      if ($method == PURL_PAIR) {
        $value = variable_get('purl_method_'. $provider .'_key', false);
        if ($value != false) {
          $values[$method][$value] = array(
            'provider' => $provider,
            'id' => null,
          );
        }
      }
      else {
        $result = db_query("SELECT * FROM {purl} WHERE provider = '%s'", $provider);
        while ($row = db_fetch_object($result)) {
          $values[$method][$row->value] = array(
            'provider' => $row->provider,
            'id' => $row->id,
          );
        }
      }
    }
  }

  return (isset($values[$requested_method]) ? $values[$requested_method] : array());
}

/**
 * Parses a query string of various types (url, domain, etc.) and
 * returns an array of any found values and their respective
 * providers/id values.
 */
function purl_parse($method = PURL_PATH, $q) {
  static $cache;
  if (!isset($cache)) {
    $cache = new purl_cache();
  }
  if ($cache->get($method, $q) === false) {
    $valid_values = purl_modifiers($method);

    // Parse the provided query string and provide an array of any values found
    switch ($method) {
      case PURL_PATH:
      case PURL_PAIR:      
        $parsed = array();
        $args = explode('/', $q);
        $arg = $args[0];
        while (isset($valid_values[$arg])) {
          $parsed[$arg] = $valid_values[$arg];
          array_shift($args);
          if ($method == PURL_PAIR) {
            $parsed[$arg]['id'] = array_shift($args);
          }

          $arg = $args[0];
          if (in_array($arg, $parsed)) {
            break;
          }
        }
        $cache->add($method, array($q => $parsed));
        break;
      case PURL_DOMAIN:
        $parsed = array();
        if (isset($valid_values[$q])) {
          $parsed[$q] = $valid_values[$q];
        }
        $cache->add($method, array($q => $parsed));
        break;
    }
  }
  return $cache->get($method, $q);
}

/**
 * Removes any modifiers from a query string. For path values only.
 */
function purl_remove_modifiers($q, $method, $providers = array()) {
  $parsed = purl_parse($method, $q);
  if (is_array($providers) && count($providers)) {
    foreach ($parsed as $value => $info) {
      if (!in_array($info['provider'], $providers)) {
        unset($parsed[$value]);
      }
    }
  }
  $parsed = array_keys($parsed);
  $args = explode('/', $q);
  switch ($method) {
    case PURL_PATH:
      // Remove the first occurrence of each value value from the query string
      foreach ($parsed as $value) {
        $k = array_search($value, $args);
        if ($k !== FALSE) {
          unset($args[$k]);
        }
      }
      break;
    case PURL_PAIR:
      foreach ($parsed as $v) {
        array_splice($args, array_search($v, $args), 2);
      }
      break;
  }
  return implode('/', $args);
}

/**
 * Invokes hook_purl_provider() to gather all providers.
 *
 * Modules that implement hook_purl_provider need to return an
 * array of value definitions. Each definition should have the following 
 * keys:
 *  - name
 *  - description
 *  - callback
 *  - example 
 *
 * See the spaces module for an usage example.
 */
function purl_providers($by_method = FALSE) {
  static $providers;
  if (!is_array($providers)) {
    $providers = array();
    $providers = module_invoke_all('purl_provider');
  }
  if ($by_method) {
    static $methods;
    if (!isset($methods)) {
      $methods = new purl_cache();

      foreach ($providers AS $id => $provider) {
        $methods->add(variable_get('purl_method_'. $id, PURL_PATH), array($id => $provider));
      }
    }
    return $methods->get();
  }
  else {
    return $providers;
  }
}

/**
 * Taken from i18n
 */
function _purl_get_normal_path($path) {
  // If bootstrap, drupal_lookup_path is not defined
  if (!function_exists('drupal_get_headers')) {
    return $path;
  }
  // Check alias without lang
  elseif ($alias = drupal_lookup_path('source', $path)) {
    return $alias;
  }
  else {
    return $path;
  }
}

/**
 * Static cache function for setting + storing any valued modifiers
 * that are present on this page's request.
 */
function _purl_set($op = 'set', $type = PURL_PATH, $value = '', $info = array()) {
  static $used;
  if (!$used) {
    $used = new purl_cache();
  }
  switch ($op) {
    case 'set':
      // Store value for url rewriting later on in the stack
      $info['value'] = $value;
      $used->add($type, $info, false);
      
      // Fire the provider callback
      if ($info['provider'] && $info['id']) {
        $providers = purl_providers();
        $callback = $providers[$info['provider']]['callback'];
        $args = isset($providers[$info['provider']]['callback arguments']) ? $providers[$info['provider']]['callback arguments'] : array();
        $args[] = $info['id'];
        if (function_exists($callback)) {
          call_user_func_array($callback, $args);
        }
      }
      break;
    case 'get':
      if ($type === 'all') {
        return $used->get();
      }
      else {
        return $used->get($type);
      }
  }
}

/**
 * Set wrapper for _purl_set()
 */
function purl_set($type = PURL_PATH, $value = '', $info = array()) {
  return _purl_set('set', $type, $value, $info);
}

/**
 * Get wrapper for _purl_set()
 */
function purl_get($type = PURL_PATH) {
  return _purl_set('get', $type);
}

/**
 * PAGE CALLBACKS =====================================================
 */

/**
 * Page callback for the purl administration page.
 */
function purl_admin() {
  global $pager_page_array, $pager_total, $pager_total_items;
  $page = isset($_GET['page']) ? $_GET['page'] : 0;
  $element = 0;
  $limit = 20;
  $providers = purl_providers();

  // Convert $page to an array, used by other functions.
  $pager_page_array = array($page);

  $methods = _purl_options();
  
  $merged = array();
  foreach(array_keys($methods) as $method) {
    foreach(purl_modifiers($method) as $value => $info) {
      $info['value'] = $value;
      $merged[] = $info;
    }
  }

  $rows = array();
  for ($i = $page * $limit; $i < ($page+1) * $limit && $i < count($merged); $i++) {
    $rows[] = array(
      $providers[$merged[$i]['provider']]['name'],
      $merged[$i]['value'],
      $merged[$i]['id'],
      $methods[variable_get('purl_method_'. $merged[$i]['provider'], PURL_PATH)],
    );
  }

  // We calculate the total of pages as ceil(items / limit).
  $pager_total_items[$element] = count($merged);
  $pager_total[$element] = ceil($pager_total_items[$element] / $limit);
  $pager_page_array[$element] = max(0, min((int)$pager_page_array[$element], ((int)$pager_total[$element]) - 1));

  if ($rows) {
    $output = theme('table', array(t('Provider'), t('Modifier'), t('ID'), t('Method')), $rows);
    $output .= theme('pager');
  }
  else {
    $output = "<p>". t('No persistent urls have been registered.') ."</p>";
  }
  return $output;
}

/**
 * Settings form for choosing the operating mode of purl
 */
function purl_settings_form() {
  global $base_url;
  $form = array();

  $options = _purl_options();

  foreach (purl_providers() as $id => $provider) {
    // Check to see whether provider has limited the available valueing methods
    if (isset($provider['methods']) && count($provider['methods'])) {
      $provider_options = array();
      foreach ($provider['methods'] as $method) {
        $provider_options[$method] = $options[$method];
      }
    }
    else {
      $provider_options = $options;
    }

    $form[$id] = array(
      '#fieldset' => true,
      '#provider' => true,
      '#title' => $provider['name'],
      '#description' => $provider['description'],
    );
    $form[$id]['purl_method_'. $id] = array(
      '#title' => t('Method'),
      '#type' => 'select',
      '#options' => $provider_options,
      '#default_value' => variable_get('purl_method_'. $id, PURL_PATH),
    );
    $form[$id]['purl_method_'. $id .'_key'] = array(
      '#title' => t('Key'),
      '#type' => 'textfield',
      '#size' => 12,
      '#default_value' => variable_get('purl_method_'. $id .'_key', ''),
    );
  }

  $form['purl_location'] = array(
    '#type' => 'fieldset',
    // '#title' => t(''),
  );
  $form['purl_location']['purl_base_domain'] = array(
    '#type' => 'textfield',
    '#title' => t('Default domain'),
    '#description' => t('Enter the default domain if you are using domain modifiers.'),
    '#required' => FALSE,
    '#default_value' => variable_get('purl_base_domain', $base_url),
  );
  $form = system_settings_form($form);
  $form['#theme'] = 'purl_settings_form';
  return $form;
}

/**
 * Theme function for purl_settings_form()
 */
function theme_purl_settings_form($form) {
  $output = '';
  $rows = array();
  foreach (element_children($form) as $id) {
    $row = array();
    if (isset($form[$id]['#provider'])) {
      $name = $form[$id]['#title'];
      $description = $form[$id]['#description'];
      unset($form[$id]['#title']);
      unset($form[$id]['#description']);
      $row[] = "<strong>$name</strong><div class='description'>$description</div>";

      $cell = '';
      foreach (element_children($form[$id]) as $item) {
        unset($form[$id][$item]['#title']);
        $cell .= drupal_render($form[$id][$item]);
      }
      $row[] = $cell;
    }
    $rows[] = $row;
  }
  $output .= theme('table', array(t('Provider'), t('Modifier type')), $rows);
  $output .= drupal_render($form);
  drupal_add_js(drupal_get_path("module", "purl") ."/purl.admin.js");
  return $output;
}

/**
 * API Functions ======================================================
 */

/**
 * Load a modifier from the database by provider or value.
 */
function purl_load($modifier) {
  if (isset($modifier['provider'])) {
    if ($modifier['id']) {
      $modifier = db_fetch_array(db_query("SELECT * FROM {purl} WHERE id = '%s' AND provider = '%s'", $modifier['id'], $modifier['provider']));
      if ($modifier) {
        return $modifier;
      }
    }
    else if ($modifier['value']) {
      $modifier = db_fetch_array(db_query("SELECT * FROM {purl} WHERE value = '%s' AND provider = '%s'", $modifier['value'], $modifier['provider']));
      if ($modifier) {
        return $modifier;
      }
    }
  }
  return false;
}

/**
 * Validation for modifiers.
 */
function purl_validate($modifier) {
  // Check that the value is valid
  if (check_plain($modifier['provider']) && !empty($modifier['value']) && preg_match('!^[a-z0-9_-]+$!', $modifier['value']) && !menu_get_item($modifier['value'])) {
    $id = db_result(db_query("SELECT id FROM {purl} WHERE value = '%s'", $modifier['value']));
    if (!$id) {
      return true;
    }
    else if (isset($modifier['id']) && ($id == $modifier['id'])) {
      return true;
    }
  }
  return false;
}

/**
 * Save modifier to database. Will insert new entry if no ID is provided and update an existing one otherwise.
 */
function purl_save($modifier) {
  if (purl_validate($modifier)) {
    $id = db_result(db_query("SELECT id FROM {purl} WHERE id = '%s'", $modifier['id']));
    if (!empty($id)) {
      $status = drupal_write_record('purl', $modifier, array('provider', 'id'));
    }
    else {
      $status = drupal_write_record('purl', $modifier);
    }
    return $status;
  }
  return false;
}

/**
 * Delete a modifier entry from the database.
 */
function purl_delete($modifier) {
  if ($modifier['value']) {
    $param = 'value';
    $where = $modifier['value'];
  }
  else if ($modifier['id']) {
    $param = 'id';
    $where = $modifier['id'];
  }
  $check = db_result(db_query("SELECT id FROM {purl} WHERE provider = '%s' AND $param = '%s'", $modifier['provider'], $where));
  if ($check) {
    $status = db_query("DELETE FROM {purl} WHERE provider = '%s' AND $param = '%s'", $modifier['provider'], $where);
    return $status;
  }
  return false;
}

/**
 * An alternative implementation of drupal_goto() that allows PURL modifiers to
 * be added or removed from the destination URL. You provide a drupal path ('node/43')
 * and a persistent url modifier (provider/id pair) and purl_goto will determine the
 * correct location to use. The 'disable' flag may also be used to drop any
 * purl modifiers from the redirect.
 *
 * The code below is nearly identical to drupal_goto(), except that it passes an
 * $options array to url().
 */
function purl_goto($path = '', $options = array(), $http_response_code = 302) {

  $options = !is_array($options) ? array() : $options;
  $options['absolute'] = TRUE;

  if (isset($_REQUEST['destination'])) {
    extract(parse_url(urldecode($_REQUEST['destination'])));
  }
  else if (isset($_REQUEST['edit']['destination'])) {
    extract(parse_url(urldecode($_REQUEST['edit']['destination'])));
  }

  $url = url($path, $options);
  // Remove newlines from the URL to avoid header injection attacks.
  $url = str_replace(array("\n", "\r"), '', $url);

  // Allow modules to react to the end of the page request before redirecting.
  // We do not want this while running update.php.
  if (!defined('MAINTENANCE_MODE') || MAINTENANCE_MODE != 'update') {
    module_invoke_all('exit', $url);
  }

  // Even though session_write_close() is registered as a shutdown function, we
  // need all session data written to the database before redirecting.
  session_write_close();

  header('Location: '. $url, TRUE, $http_response_code);

  // The "Location" header sends a redirect status code to the HTTP daemon. In
  // some cases this can be wrong, so we make sure none of the code below the
  // drupal_goto() call gets executed upon redirection.
  exit();
}

/**
 * Returns whether the current l/url call should use context rewriting or not
 */
function purl_disable($set = FALSE) {
  static $drop;
  if (!isset($drop)) {
    $drop = FALSE;
  }
  if ($set) {
    $drop = TRUE;
  }
  return $drop;
}

/**
 * Generates a persistent url form element that can be dropped into a
 * FormAPI form array. Includes validation, but nsert/update must be
 * handled by the implementing submit handler.
 */
function purl_form($provider, $id, $value = '') {
  switch (variable_get('purl_method_'. $provider, PURL_PATH)) {
    case PURL_PATH:
    case PURL_PAIR:
      $description = t('Choose a value path. May contain only lowercase letters, numbers, dashes and underscores. e.g. "my-value"');
      break;
    case PURL_SUBDOMAIN:
      $description = t('Enter a domain registered for this context, such as "mygroup".  Do not include http://');
      break;
    case PURL_DOMAIN:
      $description = t('Enter a domain registered for this context, such as "www.example.com".  Do not include http://');
      break;
  }

  $form = array(
    '#tree' => TRUE,
    '#element_validate' => array('purl_form_validate'),
  );
  $form['value'] = array(
    '#title' => t('Path value'),
    '#type' => 'textfield',
    '#description' => $description,
    '#maxlength' => 255,
    '#required' => true,
    '#default_value' => $value,
  );
  $form['provider'] = array(
    '#type' => 'value',
    '#value' => $provider,
  );
  $form['id'] = array(
    '#type' => 'value',
    '#value' => $id,
  );
  return $form;
}

/**
 * Validation handler for purl_form().
 */
function purl_form_validate($form) {
  $modifier = array(
    'provider' => $form['provider']['#value'],
    'value' => $form['value']['#value'],
    'id' => $form['id']['#value'],
  );
  if (!purl_validate($modifier)) {
    form_set_error($form['#parents'][0], t('There was an error registering the value "@value". It is either invalid or is already taken. Please choose another.', array('@value' => $form['value']['#value'])));
    return false;
  }
  else {
    return true;
  }
}

/**
* Specialized cache for storing modifier information.
*/
class purl_cache {
  
  protected $cache = array();
  
  function __construct() {
    $this->cache[PURL_PATH] = array();
    $this->cache[PURL_PAIR] = array();
    $this->cache[PURL_SUBDOMAIN] = array();
    $this->cache[PURL_DOMAIN] = array();
  }
  
  /**
   * @param $method
   *   The method to add to the cache for
   * @param $item
   *   Either a integer|string, or keyed array to add
   * @param $merge
   *   Preserve keys and merge into cache for method.
   */
  public function add($method, $item, $merge = true) {
    if (is_array($item) && $merge) {
      // Need to preserve keys so we use the '+' array operator.
      $this->cache[$method] = $this->cache[$method] + $item;
    }
    else {
      $this->cache[$method][] = $item;
    }
  }
  
  /**
   * @param $method
   *   The method to retrieve from the cache for.
   * @param $item
   *   Optionally and key of the required info.
   *
   * @return the desired info or false if an id doesn't exist.
   */
  public function get($method = false, $id = false) {
    if ($method !== false && $id !== false) {
      return (isset($this->cache[$method][$id]) ? $this->cache[$method][$id] : false);
    }
    elseif ($method !== false) {
      return $this->cache[$method];
    }
    else {
      return $this->cache;
    }
  }
}

/**
 * Helper function, returns form options for modifier types.
 */
function _purl_options() {
  return array(
    PURL_PATH => t('Path'),
    PURL_PAIR => t('Keyed pair'),
    PURL_DOMAIN => t('Full domain'),
    // PURL_SUBDOMAIN => t('Subdomain'),
  );
}