<?php
// $Id: purl.module,v 1.1.2.4 2009-04-20 20:52:04 jmiccolis Exp $

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

/**
 * 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'),
    'file' => 'purl.admin.inc',
    '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'),
    'file' => 'purl.admin.inc',
    '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',
    'file' => 'purl.admin.inc',
    'access callback' => 'user_access',
    'access arguments' => array('administer site configuration'),
    'weight' => 5,
  );
  $items['admin/settings/purl/types'] = array(
    'type' => MENU_LOCAL_TASK,
    'title' => t('Types'),
    'page callback' => 'drupal_get_form',
    'page arguments' => array('purl_types_form'),
    'file' => 'purl.admin.inc',
    'access callback' => 'user_access',
    'access arguments' => array('administer site configuration'),
    'weight' => 11,
  );
  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) {
    // Initialize a few things so that we can use them without warnings.
    if (!isset($_GET['q'])) {
      $_GET['q'] = '';
    }
    if (!isset($_REQUEST['q'])) {
      $_REQUEST['q'] = '';
    }

    foreach(_purl_options() as $k => $v) {
      _purl_init($k);
    }
    $once = true;
  }
}

/**
 * Helper function to initialize.
 *
 * @param $method
 *   A string identifier of a purl type/method
 */
function _purl_init($method) {
  $processor = purl_get_processor($method);
  $value = $processor->detect();

  // Parse and cache.
  $parsed = purl_parse($processor, $value);

  if (is_array($parsed)) {
    foreach ($parsed as $element) {
      // Let active modifiers do thier thing.
      purl_set($method, $element);

      // Allow adjustment of page request globals.
      $processor->adjust($value, $element);
    }
  }
}

/**
 * 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);
  }
}

/**
 * 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;
  }
}

/**
 * Rewrites path with the current modifier and removes the modifier if
 * searching for source path.
 *
 * purl extends the $options array in three ways:
 *
 * #1 If $options['purl']['disabled'] is true none of the detected and
 *    removed path modifications will be re-instated. This allows you to
 *    drop all purl modifications
 *
 * #2 $options['purl']['remove'] can be set to an array of providers which
 *    Should be dropped, while others are maintained. Setting this when
 *    $options['purl']['disabled'] is true is redundant.
 *
 * #3 $options['purl']['provider'] and $options['purl']['id'] can be used
 *    together to add a specific modification to the link.
 *
 */
function purl_url_rewrite(&$path, &$options, $original) {
  static $global_elements;

  // Check to see whether url rewriting has been disabled or isn't
  // suitable for this path.
  if (!purl_disable() && !$options['alias'] && !strpos($path, '://')) {
    $elements = array();

    if (!isset($global_elements)) {
      $global_elements = array();
      // Retrieve the path values for the current page that were
      // "stripped out" and write them back into url paths.
      foreach (purl_get() as $method => $items) {
        // Array_pop instead of iterating to preseve order.
        while ($item = array_pop($items)) {
          $global_elements[] = $item;
        }
      }
    }
    $elements = $global_elements;

    // The current url has requested a specific PURL modifier add it.
    if (!empty($options['purl']['provider']) && !empty($options['purl']['id'])) {
      $method = variable_get('purl_method_'. $options['purl']['provider'], PURL_PATH);

      $processor = purl_get_processor($method);
      $local_modifiers = purl_modifiers($method);

      foreach ($local_modifiers as $k => $v) {
        if ($v['provider'] == $options['purl']['provider']) {
          // If an id is NULL it simply indicates that the method doesn't need
          // to cache them, for example PURL_PAIR.
          if ($v['id'] === null) {
            $v['id'] = $options['purl']['id'];
            break;
          }
          elseif ($v['id'] == $options['purl']['id']) {
            break;
          }
        }
      }
      // TODO Allow providers to describe how they should intereact with each 
      // other. For now just assume that an explicitly set provider is the only
      // one to use
      // // Ensure we replace any global ids for this provider.
      // foreach ($elements as $i => $e) {
      //   if ($e->provider == $v['provider']) {
      //     unset($elements[$i]);
      //   }
      // }
      $e = new purl_path_element($processor, $k, $v['provider'], $v['id']);
      $elements = array($e);
    }
    foreach ($elements as $e) {
      $e->processor->rewrite($path, $options, $e);
    }
  }
}

/**
 * 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),
 *    ),
 *  );
 *
 * TODO Figure out a way not to check explicitly for PURL_PAIR as the method.
 *
 * @param $requested_method
 *   A string identifier of a purl type/method
 * @return
 *   Array of modifiers
 */
function purl_modifiers($requested_method) {
  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.
 *
 * @param $processor
 *   Object that implements purl_processor
 * @param $q
 *   The value being parsed.
 * @return
 *   The contents of the cache.
 */
function purl_parse($processor, $q) {
  static $cache;
  if (!isset($cache)) {
    $cache = new purl_cache();
  }
  if ($cache->get($processor->method(), $q) === false) {
    $valid_values = purl_modifiers($processor->method());
    $item = $processor->parse($valid_values, $q);
    $cache->add($processor->method(), array($q => $item));
  }
  return $cache->get($processor->method(), $q);
}

/**
 * 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;
  }
}

/**
 * Static cache function for setting + storing any valued modifiers
 * that are present on this page's request.
 *
 * @param $op
 *   'set' or 'get'
 * @param $type
 *   A string identifier of a purl type/method
 * @param $e
 *   purl_path_element, required for setting.
 */
function _purl_set($op = 'set', $type, $e = null) {
  static $used;
  if (!$used) {
    $used = new purl_cache();
  }
  switch ($op) {
    case 'set':
      // Store value for url rewriting later on in the stack
      $used->add($type, $e, false);

      // Fire the provider callback
      if ($e->provider && $e->id) {
        $providers = purl_providers();
        $callback = $providers[$e->provider]['callback'];
        if (function_exists($callback)) {
          $args = array();
          if (isset($providers[$e->provider]['callback arguments'])) {
            $args = $providers[$e->provider]['callback arguments'];
          }
          $args[] = $e->id;
          call_user_func_array($callback, $args);
        }
      }
      break;
    case 'get':
      if ($type === 'all') {
        return $used->get();
      }
      else {
        return $used->get($type);
      }
  }
}

/**
 * Set wrapper for _purl_set()
 *
 * @param $type
 *   A string identifier of a purl type/method
 * @param $element
 *   purl_path_element
 */
function purl_set($type, $element) {
  return _purl_set('set', $type, $element);
}

/**
 * Get wrapper for _purl_set()
 *
 * @param $type
 *   A string identifier of a purl type/method
 * @return an array of purl_path_element that have been set.
 */
function purl_get($type = 'all') {
  return _purl_set('get', $type);
}

/**
 * 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 = '') {
  $processor = purl_get_processor(variable_get('purl_method_'. $provider, PURL_PATH));

  $form = array(
    '#tree' => TRUE,
    '#element_validate' => array('purl_form_validate'),
  );
  $form['value'] = array(
    '#title' => t('Path value'),
    '#type' => 'textfield',
    '#description' => $processor->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;
  }
}

/**
 * Helper function, returns form options for modifier types.
 *
 * @param $active
 *  only return enabled types. Defaults to true.
 * @return array of options, keys are machine names and values are the human
 *         readable counterparts.
 */
function _purl_options($active = true) {
  static $enabled_options;

  if (isset($enabled_options) && $active) {
    return $enabled_options;
  }

  $options = array(
    PURL_PATH => t('Path'),
    PURL_PAIR => t('Keyed pair'),
    PURL_DOMAIN => t('Full domain'),
    PURL_SUBDOMAIN => t('Subdomain'),
    PURL_EXTENSION => t('File extension'),
  );

  if ($active) {
    $enabled_options = array();
    $enabled = variable_get('purl_types', array(PURL_PATH));
    foreach ($enabled as $v) {
      if (!empty($v)) {
        $enabled_options[$v] = $options[$v];
      }
    }
    return $enabled_options;
  }
  return $options;
}

/**
* Specialized cache for storing modifier information.
*/
class purl_cache {

  protected $cache = array();

  function __construct() {
    foreach (_purl_options() as $k => $v) {
      $this->cache[$k] = 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;
    }
  }
}

/**
 * Factory function to ease instantiation of modifier classes.
 */
function purl_get_processor($method) {
  $modifier = "purl_$method";
  return new $modifier();
}

/**
 * Helper function to determine if a url should be rewritten.
 *
 * @param $e
 *   purl_path_element object
 * @param $o
 *   url optoins array.
 * @return true if processing should be skipped, false otherwise.
 */
function _purl_skip($e, $o) {
  if ($o['purl']['disabled'] == true) {
    return true;
  }
  if (isset($o['purl']['remove'])) {
    return in_array($e->provider, $o['purl']['remove']);
  }
  return false;
}

/**
 * Processors can inspect and manipulate various parts of a request's URI.
 */
interface purl_processor {

  /**
   * Return the method the processor users.
   *
   * @return string, machine name of the method.
   */
   public function method();

  /**
   * Provide a description of processor for the end user
   *
   * @return string description.
   */
  public function description();

  /**
   * Detect the the processor value for the current page request
   *
   * @return value that can be pased to the parse step.
   */
  public function detect();

  /**
   * Detects processor in the passed 'value'.
   *
   * @param $valid_values
   * @param $value
   * @return an array of purl_path_element objects
   */
  public function parse($valid_values, $value);

  /**
   * Used to provide compatibility with the path alias system.
   *
   * @param $value.
   *   detected value, by reference so that processors that can remove
   *   themselves is a method can have more than on value.
   * @param $element.
   *   purl_path_element
   */
  public function adjust(&$value, $element);

  /**
   * Responsible for rewriting outgoing links. Note: it's this functions
   * job to make sure it doesn't alter a link that has already been
   * treated.
   *
   * This must also check $options['purl']['disabled'] and
   * $optoins['purl']['remove']. The _purl_skip() method is helpful for this.
   *
   * @param $path
   *   string, by-reference the path to modify.
   * @param $options
   *   See url() docs
   * @param $element
   *   The element to add to the path.
   */
  public function rewrite(&$path, &$options, $element);
}

/**
 * Path prefixer.
 */
class purl_path implements purl_processor {

  public function method() {
    return PURL_PATH;
  }

  /**
   * Detect a default value for 'q' when created.
   */
  public function detect() {
    return isset($_REQUEST["q"]) ? trim($_REQUEST["q"], "/") : '';
  }

  public function description() {
    return t('Choose a value path. May contain only lowercase letters, numbers, dashes and underscores. e.g. "my-value"');
  }

  /**
   * Tear apart the path and iterate thought it looking for valid values.
   */
  public function parse($valid_values, $q) {
    $parsed = array();
    $args = explode('/', $q);
    $arg = $args[0];
    while (isset($valid_values[$arg])) {
      $parsed[$arg] = $valid_values[$arg];
      array_shift($args);
      $arg = $args[0];
      if (in_array($arg, $parsed)) {
        break;
      }
    }
    return purl_path_elements($this, $parsed);
  }

  /**
   * if $_GET and $_REQUEST are different, the path has NOT been
   * aliased. We may need to rewrite the path.
   */
  public function adjust(&$q, $item) {
    if ($_GET['q'] == trim($_REQUEST['q'], '/')) {
      $q = $this->remove($q, $item);
      // there is nothing beyond the path value -- treat as frontpage
      if ($q == '') {
        $_GET['q'] = variable_get('site_frontpage', 'node');
      }
      // pass the rest of the path onto Drupal cleanly
      else {
        $q = $_REQUEST['q'] = $_GET['q'] = _purl_get_normal_path($q);
      }
    }
  }

  /**
   * Removes specific modifier from a query string.
   *
   * @param $q
   *   The current path.
   * @param $element
   *   a purl_path_element object
   * @return path string with the modifier removed.
   */
  function remove($q, $element) {
    $args = explode('/', $q);

    // Remove the first occurrence of each value value from the query string
    $k = array_search($element->value, $args);
    if ($k !== FALSE) {
      unset($args[$k]);
    }
    return implode('/', $args);
  }

  /**
   * Just need to add the value to the front of the path.
   */
  public function rewrite(&$path, &$options, $element) {
    if (!_purl_skip($element, $options)) {
      $items = explode('/', $path);
      array_unshift($items, $element->value);
      $path = implode('/', $items);
    }
  }
}

/**
 * Pair pair prefixer.
 */
class purl_pair extends purl_path {

  public function method() {
    return PURL_PAIR;
  }

  public function parse($valid_values, $q) {
    $parsed = array();
    $args = explode('/', $q);
    $arg = $args[0];
    while (isset($valid_values[$arg])) {
      $parsed[$arg] = $valid_values[$arg];
      array_shift($args);
      $parsed[$arg]['id'] = array_shift($args);

      $arg = $args[0];
      if (in_array($arg, $parsed)) {
        break;
      }
    }
    return purl_path_elements($this, $parsed);
  }

  /**
   * Removes specific modifier pair from a query string.
   *
   * @param $q
   *   The current path.
   * @param $element
   *   a purl_path_element object
   * @return path string with the pair removed.
   */
  function remove($q, $element) {
    $args = explode('/', $q);
    array_splice($args, array_search($element->value, $args), 2);
    return implode('/', $args);
  }

  public function rewrite(&$path, &$options, $element) {
    if (!_purl_skip($element, $options)) {
      $items = explode('/', $path);
      array_unshift($items, "{$element->value}/{$element->id}");
      $path = implode('/', $items);
    }
  }
}

/**
 *  Full domain handling.
 */
class purl_domain implements purl_processor {

  function detect() {
    return str_replace('http://','',$_SERVER['HTTP_HOST']);
  }

  public function method() {
    return PURL_DOMAIN;
  }

  public function description() {
    return t('Enter a domain registered for this context, such as "www.example.com".  Do not include http://');
  }

  /**
   * Simply match our 'q' (aka domain) against an allowed value.
   */
  public function parse($valid_values, $q) {
    $parsed = array();
    if (isset($valid_values[$q])) {
      $parsed[$q] = $valid_values[$q];
    }
    return purl_path_elements($this, $parsed);
  }

  public function adjust(&$value, $item) { return; }

  /**
   * Either force the url, or set it back to the base.
   */
  public function rewrite(&$path, &$options, $element) {
    $options['absolute'] = TRUE;
    if (!_purl_skip($element, $options)) {
      $options['base_url'] = "http://{$element->value}";
    }
    else {
      $options['base_url'] = variable_get('purl_base_domain', $base_url);
    }
  }
}

/**
 * Subdomain prefixing.
 */
class purl_subdomain implements purl_processor {

  function detect() {
    $parts = explode('.', str_replace('http://','',$_SERVER['HTTP_HOST']));
    return array_shift($parts);
  }

  public function method() {
    return PURL_SUBDOMAIN;
  }

  public function description() {
    return t('Enter a sub-domain for this context, such as "mygroup".  Do not include http://');
  }

  public function parse($valid_values, $q) {
    $parsed = array();
    if (isset($valid_values[$q])) {
      $parsed[$q] = $valid_values[$q];
    }
    return purl_path_elements($this, $parsed);
  }

  public function adjust(&$value, $item) { return; }

  public function rewrite(&$path, &$options, $element) {
    $options['absolute'] = TRUE;
    if (!_purl_skip($element, $options)) {
      // Check to see if the link has already been treated.
      $parts = explode('.', str_replace('http://','', $options['base_url']));
      $possible = array_shift($parts);
      $matches = purl_parse($this, $possible);

      // If not add our subdomain.
      if (!count($matches)) {
        // ...but replace what we checked first.
        array_unshift($parts, $possible);
        array_unshift($parts, $element->value);

        $options['absolute'] = TRUE;
        $options['base_url'] = "http://". implode('.', $parts);
      }
    }
    else {
      $options['base_url'] = variable_get('purl_base_domain', $base_url);
    }
  }
}

/**
 * File extension style. Like ".csv"
 */
class purl_extension implements purl_processor {

  public function detect(){
    $q = isset($_REQUEST["q"]) ? trim($_REQUEST["q"], "/") : '';
    $last = explode('.', array_pop(explode('/', $q)));
    if (count($last) > 1) {
      return array_pop($last);
    }
    return '';
  }

  public function method() {
    return PURL_EXTENSION;
  }

  public function description() {
    return t('Enter a extension for this context, such as "csv".');
  }

  public function parse($valid_values, $q) {
    $parsed = array();
    $parsed = array();
    if (isset($valid_values[$q])) {
      $parsed[$q] = $valid_values[$q];
    }
    return purl_path_elements($this, $parsed);
  }

  /**
   * if $_GET and $_REQUEST are different, the path has NOT been
   * aliased. We may need to rewrite the path.
   */
  public function adjust(&$value, $item) {
    if ($_GET['q'] == trim($_REQUEST['q'], '/')) {
      $q = $this->remove($_GET['q'], $item);
      // pass the rest of the path onto Drupal cleanly
      $_REQUEST['q'] = $_GET['q'] = _purl_get_normal_path($q);
    }
  }

  /**
   * Remove our extension from the tail end of the path.
   *
   * @param $q
   *   The current path.
   * @param $element
   *   a purl_path_element object
   * @return path string with the extension removed.
   */
  public function remove($q, $element ) {
    $args = explode('.', $q);
    if (count($args > 1)) {
      $extension = array_pop($args);
      if ($element->value == $extension) {
        return implode('.', $args);
      }
    }
    return $q;
  }

  /**
   * Because of the expected usage of the files extensions we don't provide
   * a rewrite.
   */
  public function rewrite(&$path, &$options, $element) {}
}

/**
 * Generate a array of purl_path_elements objects from parsed values.
 *
 * @param $processor
 *   The processor used to parse the string.
 * @param $values
 *    Array or values which were detected.
 * @return an array of purl_path_elements
 */
function purl_path_elements($processor, $values) {
  $return = array();
  foreach ($values as $v => $i) {
    $return[$v] = new purl_path_element($processor, $v, $i['provider'], $i['id']);
  }
  return $return;
}

class purl_path_element {
  public $processor;
  public $value;
  public $provider;
  public $id;

  function __construct($processor, $value, $provider, $id) {
    $this->processor = $processor;
    $this->value = $value;
    $this->provider = $provider;
    $this->id = $id;
  }
}