<?php
// $Id$

/**
 * @file
 * Defines simple link field types.
 */

define('LINK_EXTERNAL', 'external');
define('LINK_INTERNAL', 'internal');
define('LINK_FRONT', 'front');
define('LINK_EMAIL', 'email');
define('LINK_DOMAINS', 'aero|arpa|biz|com|cat|coop|edu|gov|info|int|jobs|mil|museum|name|nato|net|org|pro|travel|mobi|local');

/**
 * Implementation of hook_menu().
 */
function link_menu($may_cache) {
  $items = array();
  if ($may_cache) {
    $items[] = array(
      'path' => 'link/widget/js',
      'callback' => 'link_widget_js',
      'access' => user_access('access content'),
      'type' => MENU_CALLBACK,
    );
  }
  return $items;
}

/**
 * Implementation of hook_field_info().
 */
function link_field_info() {
  return array(
    'link' => array('label' => 'Link'),
  );
}

/**
 * Implementation of hook_field_settings().
 */
function link_field_settings($op, $field) {
  switch ($op) {
    case 'form':
      $form = array(
        '#theme' => 'link_field_settings',
      );

      $form['url'] = array(
        '#type' => 'checkbox',
        '#title' => t('Optional URL'),
        '#default_value' => $field['url'],
        '#return_value' => 'optional',
        '#description' => t('If checked, the URL field is optional and submitting a title alone will be acceptable. If the URL is ommitted, the title will be displayed as plain text.'),
      );

      $title_options = array(
        'optional' => t('Optional Title'),
        'required' => t('Required Title'),
        'value' => t('Static Title: '),
        'none' => t('No Title'),
      );

      $form['title'] = array(
        '#type' => 'radios',
        '#title' => t('Link Title'),
        '#default_value' => isset($field['title']) ? $field['title'] : 'optional',
        '#options' => $title_options,
        '#description' => t('If the link title is optional or required, a field will be displayed to the end user. If the link title is static, the link will always use the same title. If <a href="http://drupal.org/project/token">token module</a> is installed, the static title value may use any other node field as its value. Static and token-based titles may include most inline XHTML tags such as <em>strong</em>, <em>em</em>, <em>img</em>, <em>span</em>, etc.'),
      );

      $form['title_value'] = array(
        '#type' => 'textfield',
        '#default_value' => $field['title_value'],
        '#size' => '46',
      );

      // Add token module replacements if available
      if (module_exists('token')) {
        $form['tokens'] = array(
          '#type' => 'fieldset',
          '#collapsible' => TRUE,
          '#collapsed' => TRUE,
          '#title' => t('Placeholder tokens'),
          '#description' => t("The following placeholder tokens can be used in both paths and titles. When used in a path or title, they will be replaced with the appropriate values."),
        );
        $form['tokens']['help'] = array(
          '#value' => theme('token_help', 'node'),
        );

        $form['enable_tokens'] = array(
          '#type' => 'checkbox',
          '#title' => t('Allow user-entered tokens'),
          '#default_value' => isset($field['enable_tokens']) ? $field['enable_tokens'] : 1,
          '#description' => t('Checking will allow users to enter tokens in URLs and Titles on the node edit form. This does not affect the field settings on this page.'),
        );
      }

      $form['display'] = array(
        '#tree' => true,
      );
      $form['display']['url_cutoff'] = array(
        '#type' => 'textfield',
        '#title' => t('URL Display Cutoff'),
        '#default_value' => isset($field['display']['url_cutoff']) ? $field['display']['url_cutoff'] : '80',
        '#description' => t('If the user does not include a title for this link, the URL will be used as the title. When should the link title be trimmed and finished with an elipsis (&hellip;)? Leave blank for no limit.'),
        '#maxlength' => 3,
        '#size' => 3,
      );

      $target_options = array(
        'default' => t('Default (no target attribute)'),
        '_top' => t('Open link in window root'),
        '_blank' => t('Open link in new window'),
        'user' => t('Allow the user to choose'),
      );
      $form['attributes'] = array(
        '#tree' => true,
      );
      $form['attributes']['target'] = array(
        '#type' => 'radios',
        '#title' => t('Link Target'),
        '#default_value' => empty($field['attributes']['target']) ? 'default' : $field['attributes']['target'],
        '#options' => $target_options,
      );
      $form['attributes']['rel'] = array(
        '#type' => 'textfield',
        '#title' => t('Rel Attribute'),
        '#description' => t('When output, this link will have this rel attribute. The most common usage is <a href="http://en.wikipedia.org/wiki/Nofollow">rel=&quot;nofollow&quot;</a> which prevents some search engines from spidering entered links.'),
        '#default_value' => empty($field['attributes']['rel']) ? '' : $field['attributes']['rel'],
        '#field_prefix' => 'rel = "',
        '#field_suffix' => '"',
        '#size' => 20,
      );
      $form['attributes']['class'] = array(
        '#type' => 'textfield',
        '#title' => t('Additional CSS Class'),
        '#description' => t('When output, this link will have have this class attribute. Multiple classes should be separated by spaces.'),
        '#default_value' => empty($field['attributes']['class']) ? '' : $field['attributes']['class'],
      );
      return $form;

    case 'validate':
      if ($field['title'] == 'value' && empty($field['title_value'])) {
        form_set_error('title_value', t('A default title must be provided if the title is a static value'));
      }
      break;

    case 'save':
      return array('attributes', 'display', 'url', 'title', 'title_value', 'enable_tokens');

    case 'database columns':
      return array(
        'url' => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => "''", 'sortable' => TRUE),
        'title' => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => "''", 'sortable' => TRUE),
        'attributes' => array('type' => 'mediumtext', 'not null' => FALSE),
      );

    case 'filters':
      return array(
        'default' => array(
          'name' => t('URL'),
          'operator' => 'views_handler_operator_like',
          'handler' => 'views_handler_operator_like',
        ),
        'title' => array(
          'name' => t('Title'),
          'operator' => 'views_handler_operator_like',
          'handler' => 'views_handler_operator_like',
        ),
        'protocol' => array(
          'name' => t('Protocol'),
          'list' => drupal_map_assoc(variable_get('filter_allowed_protocols', array('http', 'https', 'ftp', 'news', 'nntp', 'telnet', 'mailto', 'irc', 'ssh', 'sftp', 'webcal'))),
          'operator' => 'views_handler_operator_or',
          'handler' => 'link_views_protocol_filter_handler',
        ),
      );

    case 'arguments':
      return array(
        'content: '. $field['field_name'] .'_title' => array(
          'name' => t('Link Title') .': '. t($field['widget']['label']) .' ('. $field['field_name'] .')',
          'handler' => 'link_views_argument_handler',
        ),
        'content: '. $field['field_name'] .'_target' => array(
          'name' => t('Link Target') .': '. t($field['widget']['label']) .' ('. $field['field_name'] .')',
          'handler' => 'link_views_argument_handler',
        ),
      );

  }
}

/**
 * Theme the settings form for the link field.
 */
function theme_link_field_settings($form) {
  $title_value = drupal_render($form['title_value']);
  $title_checkbox = drupal_render($form['title']['value']);

  // Set Static Title radio option to include the title_value textfield.
  $form['title']['value'] = array('#value' => '<div class="container-inline">'. $title_checkbox . $title_value .'</div>');

  // Reprint the title radio options with the included textfield.
  return drupal_render($form);
}

/**
 * Implementation of hook_field().
 */
function link_field($op, &$node, $field, &$items, $teaser, $page) {
  switch ($op) {
    case 'load':
      foreach ($items as $delta => $item) {
        $items[$delta]['attributes'] = unserialize($item['attributes']);
      }
      break;
    case 'view':
      foreach ($items as $delta => $item) {
        $items[$delta]['view'] = content_format($field, $items[$delta], 'default', $node);
      }
      return theme('field', $node, $field, $items, $teaser, $page);
      break;
  }
}

/**
 * Implementation of hook_widget_info().
 */
function link_widget_info() {
  return array(
    'link' => array(
      'label' => 'Text Fields for Title and URL',
      'field types' => array('link'),
    ),
  );
}

/**
 * Implementation of hook_widget().
 */
function link_widget($op, &$node, $field, &$items) {
  switch ($op) {
    case 'prepare form values':
      foreach($items as $delta => $value) {
        if (is_numeric($delta)) {
          _link_widget_prepare($items[$delta], $delta);
        }
      }
      if ($_POST[$field['field_name']]) {
        $items = $_POST[$field['field_name']];
        unset($items['count'], $items['more-url'], $items['more']);
      }
      return;
    case 'form':
      $form = array();
      $form[$field['field_name']] = array(
        '#tree' => TRUE,
        '#theme' => 'link_widget_form',
        '#type' => $field['multiple'] ? 'fieldset' : 'markup',
        '#collapsible' => TRUE,
        '#collapsed' => FALSE,
        '#title' => t($field['widget']['label']),
        '#description' => $field['widget']['description'],
      );

      // Add token module replacements if available.
      if (module_exists('token') && $field['enable_tokens']) {
        $tokens_form = array(
          '#type' => 'fieldset',
          '#collapsible' => TRUE,
          '#collapsed' => TRUE,
          '#title' => t('Placeholder tokens'),
          '#description' => t("The following placeholder tokens can be used in both titles and URLs. When used in a URL or title, they will be replaced with the appropriate values."),
          '#weight' => 2,
        );
        $tokens_form['help'] = array(
          '#value' => theme('token_help', 'node'),
        );
      }

      if ($field['multiple']) {
        drupal_add_js(drupal_get_path('module', 'link') .'/link.js');

        $delta = 0;
        // Render link fields for all the entered values.
        foreach ($items as $data) {
          if (is_array($data) && ($data['url'] || $data['title'])) {
            _link_widget_form($form[$field['field_name']][$delta], $field, $data, $delta);
            $delta++;
          }
        }
        // Render two additional new link fields.
        foreach (range($delta, $delta + 1) as $delta) {
          _link_widget_form($form[$field['field_name']][$delta], $field, array(), $delta);
        }

        // Create a wrapper for additional fields.
        $form[$field['field_name']]['wrapper'] = array(
          '#type' => 'markup',
          '#value' => '<div id="' . str_replace('_', '-', $field['field_name']) . '-wrapper" class="clear-block"></div>',
        );

        // Add 'More' Javascript Callback.
        $form[$field['field_name']]['more-url'] = array(
          '#type' => 'hidden',
          '#value' => url('link/widget/js/' . $field['type_name'] . '/' . $field['field_name'], NULL, NULL, TRUE),
          '#attributes' => array('class' => 'more-links'),
          '#id' => str_replace('_', '-', $field['field_name']) . '-more-url',
        );

        // Add Current Field Count.
        $form[$field['field_name']]['count'] = array(
          '#type' => 'hidden',
          '#value' => $delta,
          '#id' => str_replace('_', '-', $field['field_name']) . '-count',
        );

        // Add More Button.
        $form[$field['field_name']]['more'] = array(
          '#type' => 'button',
          '#value' => t('More Links'),
          '#name' => 'more',
          '#id' => str_replace('_', '-', $field['field_name']) . '-more',
          '#weight' => 1,
        );
        if (isset($tokens_form)) {
          $form[$field['field_name']]['tokens'] = $tokens_form;
        }
      } // end if multiple.
      else {
        _link_widget_form($form[$field['field_name']][0], $field, $items[0]);
        if (isset($tokens_form)) {
          $form[$field['field_name']][0]['tokens'] = $tokens_form;
        }
      }
      return $form;

    case 'validate':
      if (!is_object($node)) return;
      unset($items['count']);
      unset($items['more-url']);
      unset($items['more']);
      $optional_field_found = FALSE;
      foreach($items as $delta => $value) {
        _link_widget_validate($items[$delta],$delta, $field, $node, $optional_field_found);
      }

      if ($field['url'] == 'optional' && $field['title'] == 'optional' && $field['required'] && !$optional_field_found) {
        form_set_error($field['field_name'] .'][0][title', t('At least one title or URL must be entered.'));
      }
      return;

    case 'process form values':
      // Remove the JS helper fields.
      unset($items['more-url']);
      unset($items['count']);
      unset($items['more']);
      foreach($items as $delta => $value) {
        if (is_numeric($delta)) {
          _link_widget_process($items[$delta],$delta, $field, $node);
        }
      }
      return;

    case 'submit':
      // Don't save empty fields (beyond the first one).
      $save_field = array();
      unset($items['more-url']);
      unset($items['count']);
      unset($items['more']);
      foreach ($items as $delta => $value) {
        if ($value['url'] !== 'optional' || $delta == 0) {
          $save_items[] = $items[$delta];
        }
      }
      $items = $save_items;
      return;
  }
}

/**
 * Helper function renders the link widget in both single and multiple value cases.
 */

function _link_widget_form(&$form_item, $field, $item, $delta = 0) {
  $form_item = array(
    '#tree' => TRUE,
    '#theme' => 'link_widget_form_row',
  );

  $default_url = "";
  if (isset($field['widget']['default_value'][$delta]['url'])) {
    $default_url = $field['widget']['default_value'][$delta]['url'];
  }

  $form_item['url'] = array(
    '#type' => 'textfield',
    '#maxlength' => '255',
    '#title' => $delta == 0 ? t('URL') : NULL,
    '#default_value' => ($item['url']) ? $item['url'] : $default_url,
    '#required' => ($delta == 0) ? ($field['required'] && empty($field['url'])) : FALSE,
  );
  if ($field['title'] != 'value' && $field['title'] != 'none') {
    $default_title = "";
    if (isset($field['widget']['default_value'][$delta]['title'])) {
      $default_title = $field['widget']['default_value'][$delta]['title'];
    }
    $form_item['title'] = array(
      '#type' => 'textfield',
      '#maxlength' => '255',
      '#title' => $delta == 0 ? t('Title') : NULL,
      '#default_value' => ($item['title']) ? $item['title'] : $default_title,
      '#required' => ($delta == 0 && $field['title'] == 'required') ? $field['required'] : FALSE,
    );
  }
  if (!empty($field['attributes']['target']) && $field['attributes']['target'] == 'user') {
    $form_item['attributes']['target'] = array(
      '#type' => 'checkbox',
      '#title' => t('Open URL in a New Window'),
      '#default_value' => $item['attributes']['target'],
      '#return_value' => "_blank",
    );
  }
}

function _link_widget_prepare(&$item, $delta = 0) {
  // Unserialize the attributes array.
  $item['attributes'] = unserialize($item['attributes']);
}

function _link_widget_process(&$item, $delta = 0, $field, $node) {
  // Remove the target attribute if not selected.
  if (!$item['attributes']['target'] || $item['attributes']['target'] == "default") {
    unset($item['attributes']['target']);
  }
  // Trim whitespace from URL.
  $item['url'] = trim($item['url']);
  // Serialize the attributes array.
  $item['attributes'] = serialize($item['attributes']);

  // Don't save an invalid default value (e.g. 'http://').
  if ((isset($field['widget']['default_value'][$delta]['url']) && $item['url'] == $field['widget']['default_value'][$delta]['url']) && is_object($node)) {
    if (!link_validate_url($item['url'])) {
      unset($item['url']);
    }
  }
}

function _link_widget_validate(&$item, $delta, $field, $node, &$optional_field_found) {
  if ($item['url'] && !(isset($field['widget']['default_value'][$delta]['url']) && $item['url'] == $field['widget']['default_value'][$delta]['url'] && !$field['required'])) {
    // Validate the link.
    if (link_validate_url(trim($item['url'])) == FALSE) {
      form_set_error($field['field_name'] .']['. $delta. '][url', t('Not a valid URL.'));
    }
    // Require a title for the link if necessary.
    if ($field['title'] == 'required' && strlen(trim($item['title'])) == 0) {
      form_set_error($field['field_name'] .']['. $delta. '][title', t('Titles are required for all links.'));
    }
  }
  // Require a link if we have a title.
  if ($field['url'] !== 'optional' && strlen($item['title']) > 0 && strlen(trim($item['url'])) == 0) {
    form_set_error($field['field_name'] .']['. $delta. '][url', t('You cannot enter a title without a link url.'));
  }
  // In a totally bizzaro case, where URLs and titles are optional but the field is required, ensure there is at least one link.
  if ($field['url'] == 'optional' && $field['title'] == 'optional' && (strlen(trim($item['url'])) != 0 || strlen(trim($item['title'])) != 0)) {
    $optional_field_found = TRUE;
  }
}

function link_widget_js($type_name, $field_name) {
  $field = content_fields($field_name, $type_name);
  $type = content_types($type);
  $delta = $_POST[$field_name]['count'];
  $form = array();
  $node_field = array();

  _link_widget_form($form, $field, $node_field, $delta);

  // Assign parents matching the original form.
  foreach (element_children($form) as $key) {
    $form[$key]['#parents'] = array($field_name, $delta, $key);
  }

  // Add names, ids, and other form properties.
  foreach (module_implements('form_alter') as $module) {
    $function = $module .'_form_alter';
    $function('link_widget_js', $form);
  }
  $form = form_builder('link_widget_js', $form);

  $output = drupal_render($form);

  print drupal_to_js(array('status' => TRUE, 'data' => $output));
  exit;
}

/**
 * Theme the display of the entire link set
 */
function theme_link_widget_form($element) {
  drupal_add_css(drupal_get_path('module', 'link') .'/link.css');
  // Check for multiple (output normally).
  if (isset($element[1])) {
    $output = drupal_render($element);
  }
  // Add the field label to the 'Title' and 'URL' labels.
  else {
    if (isset($element[0]['title'])) {
      $element[0]['title']['#title'] = $element['#title'] . ' ' . $element[0]['title']['#title'];
      $element[0]['title']['#description'] = $element['#description'];
      $element[0]['url']['#title'] = $element['#title'] . ' ' . $element[0]['url']['#title'];
    }
    else {
      $element[0]['url']['#title'] = $element['#title'];
      $element[0]['url']['#description'] = $element['#description'];
    }
    $output = drupal_render($element);
  }

  return $output;
}

/**
 * Theme the display of a single form row
 */
function theme_link_widget_form_row($element) {
  $output = '';
  $output .= '<div class="link-field-row clear-block"><div class="link-field-subrow clear-block">';
  if ($element['title']) {
    $output .= '<div class="link-field-title link-field-column">' . drupal_render($element['title']) . '</div>';
  }
  $output .= '<div class="link-field-url' . ($element['title'] ? ' link-field-column' : '') . '">' . drupal_render($element['url']) . '</div>';
  $output .= '</div>';
  if ($element['attributes']) {
    $output .= '<div class="link-attributes">' . drupal_render($element['attributes']) . '</div>';
  }
  $output .= drupal_render($element);
  $output .= '</div>';
  return $output;
}

/**
 * Implementation of hook_field_formatter_info().
 */
function link_field_formatter_info() {
  return array(
    'default' => array(
      'label' => t('Title, as link (default)'),
      'field types' => array('link'),
    ),
    'url' => array(
      'label' => t('URL, as link'),
      'field types' => array('link'),
    ),
    'plain' => array(
      'label' => t('URL, plain text'),
      'field types' => array('link'),
    ),
    'short' => array(
      'label' => t('Short, as link with title "Link"'),
      'field types' => array('link'),
    ),
    'label' => array(
      'label' => t('Label, as link with label as title'),
      'field types' => array('link'),
    ),
    'separate' => array(
      'label' => t('Separate title and URL'),
      'field types' => array('link'),
    ),
  );
}

/**
 * Implementation of hook_field_formatter().
 */
function link_field_formatter($field, $item, $formatter, $node) {
  if (empty($item['url']) && ($field['url'] != 'optional' || empty($item['title']))) {
    return '';
  }

  if ($formatter == 'plain') {
    return empty($item['url']) ? check_plain($item['title']) : check_plain(link_cleanup_url($item['url']));
  }

  // Replace URL tokens.
  if (module_exists('token') && $field['enable_tokens']) {
    // Load the node if necessary for nodes in views.
    $token_node = isset($node->nid) ? node_load($node->nid) : $node;
    $item['url'] = token_replace($item['url'], 'node', $token_node);
  }

  $type = link_validate_url($item['url']);
  $url = link_cleanup_url($item['url']);

  // Separate out the anchor if any.
  if (strpos($url, '#') !== FALSE) {
    $fragment = substr($url, strpos($url, '#') + 1);
    $url = substr($url, 0, strpos($url, '#'));
  }
  // Separate out the query string if any.
  if (strpos($url, '?') !== FALSE) {
    $query = substr($url, strpos($url, '?') + 1);
    $url = substr($url, 0, strpos($url, '?'));
  }

  // Create a display URL.
  $display_url = $type == LINK_EMAIL ? str_replace('mailto:', '', $url) : url($url, $query, $fragment, TRUE);
  if ($field['display']['url_cutoff'] && strlen($display_url) > $field['display']['url_cutoff']) {
    $display_url = substr($display_url, 0, $field['display']['url_cutoff']) . "...";
  }

  // Build a list of attributes.
  $attributes = array();
  $item['attributes'] = unserialize($item['attributes']);
  // Add attributes defined at the widget level.
  if (!empty($item['attributes']) && is_array($item['attributes'])) {
    foreach($item['attributes'] as $attribute => $attbvalue) {
      if (isset($item['attributes'][$attribute]) && $field['attributes'][$attribute] == 'user') {
        $attributes[$attribute] = $attbvalue;
      }
    }
  }
  // Add attributes defined at the field level.
  if (is_array($field['attributes'])) {
    foreach($field['attributes'] as $attribute => $attbvalue) {
      if (!empty($attbvalue) && $attbvalue != 'default' && $attbvalue != 'user') {
        $attributes[$attribute] = $attbvalue;
      }
    }
  }
  // Remove the rel=nofollow for internal links.
  if ($type != LINK_EXTERNAL && isset($attributes['rel']) && strpos($attributes['rel'], 'nofollow') !== FALSE) {
    $attributes['rel'] = str_replace('nofollow', '', $attributes['rel']);
    if (empty($attributes['rel'])) {
      unset($attributes['rel']);
    }
  }

  // Give the link the title 'Link'.
  if ($formatter == 'short') {
    $output = l(t('Link'), $url, $attributes, $query, $fragment);
  }
  // Build the link using the widget label.
  elseif ($formatter == 'label') {
    $output = l(t($field['widget']['label']), $url, $attributes, $query, $fragment);
  }
  // Build the link using the URL as title
  elseif ($formatter == 'url') {
    $output = l($display_url, $url, $attributes, $query, $fragment);
  }
  // Build the link using the widget label as separate title.
  elseif ($formatter == 'separate') {
    $title = check_plain(_link_field_formatter_title($field, $item, $node));
    $class = empty($field['attributes']['class']) ? '' : ' '. $field['attributes']['class'];
    unset($field['attributes']['class']);

    $output = '';
    $output .= '<div class="link-item'. $class .'">';
    $output .= '<div class="link-title">'. $title .'</div>';
    $output .= '<div class="link-url">'. l($display_url, $url, $attributes, $query, $fragment, FALSE, $item['html']) .'</div>';
    $output .= '</div>';
  }
  // Build the link with a title.
  elseif (strlen(trim($item['title'])) || ($field['title'] == 'value' && strlen(trim($field['title_value'])))) {
    $title = _link_field_formatter_title($field, $item, $node);
    if (empty($url) && !empty($title)) {
      $output = check_plain($title);
    }
    else {
      $output = l($title, $url, $attributes, $query, $fragment, FALSE, $item['html']);
    }
  }
  // Build the link with the URL or email address as the title (max 80 characters).
  else {
    $output = l($display_url, $url, $attributes, $query, $fragment);
  }
  return $output;
}

/**
 * Helper function for link_field_formatter().
 */
function _link_field_formatter_title(&$field, &$item, &$node) {
  // Use the title defined at the field level.
  if ($field['title'] == 'value' && trim($field['title_value'])) {
    $title = $field['title_value'];
  }
  // Use the title defined by the user at the widget level.
  else {
    $title = $item['title'];
  }
  // Replace tokens.
  $item['html'] = FALSE;
  if (module_exists('token') && ($field['title'] == 'value' || $field['enable_tokens'])) {
    // Load the node if necessary for nodes in views.
    $token_node = isset($node->nid) ? node_load($node->nid) : $node;
    $title = filter_xss(token_replace($title, 'node', $token_node), array('b', 'br', 'code', 'em', 'i', 'img', 'span', 'strong', 'sub', 'sup', 'tt', 'u'));
    $item['html'] = TRUE;
  }
  return $title;
}

/**
 * Views module argument handler for link fields
 */
function link_views_argument_handler($op, &$query, $argtype, $arg = '') {
  if ($op == 'filter') {
    $field_name = substr($argtype['type'], 9, strrpos($argtype['type'], '_') - 9);
    $column = substr($argtype['type'], strrpos($argtype['type'], '_') + 1);
  }
  else {
    $field_name = substr($argtype, 9, strrpos($argtype, '_') - 9);
    $column = substr($argtype, strrpos($argtype, '_') + 1);
  }

  // Right now the only attribute we support in views in 'target', but
  // other attributes of the href tag could be added later.
  if ($column == 'target') {
    $attribute = $column;
    $column = 'attributes';
  }

  $field = content_fields($field_name);
  $db_info = content_database_info($field);
  $main_column = $db_info['columns'][$column];

  // The table name used here is the Views alias for the table, not the actual
  // table name.
  $table = 'node_data_'. $field['field_name'];

  switch ($op) {
    case 'summary':
      $query->ensure_table($table);
      $query->add_field($main_column['column'], $table);
      return array('field' => $table .'.'. $main_column['column']);
      break;

    case 'filter':
      $query->ensure_table($table);
      if ($column == 'attributes') {
        // Because attributes are stored serialized, our only option is to also
        // serialize the data we're searching for and use LIKE to find similar data.
        $query->add_where($table .'.'. $main_column['column'] ." LIKE '%%%s%'", serialize($attribute) . serialize($arg));
      }
      else {
        $query->add_where($table .'.'. $main_column['column'] ." = '%s'", $arg);
      }
      break;

    case 'link':
      $item = array();
      foreach ($db_info['columns'] as $column => $attributes) {
        $view_column_name = $attributes['column'];
        $item[$column] = $query->$view_column_name;
      }

      return l(content_format($field, $item, 'plain'), $arg .'/'. $query->$main_column['column'], array(), NULL, NULL, FALSE, TRUE);

    case 'sort':
      break;

    case 'title':
      $item = array(key($db_info['columns']) => $query);
      return content_format($field, $item);
      break;
  }
}

/**
 * Views modules filter handler for link protocol filtering
 */
function link_views_protocol_filter_handler($op, $filter, $filterinfo, &$query) {
  global $db_type;

  $protocols = $filter['value'];
  $field = $filterinfo['field'];
  // $table is not the real table name but the views alias.
  $table = 'node_data_'. $filterinfo['content_field']['field_name'];

  foreach ($protocols as $protocol) {
    // Simple case, the URL begins with the specified protocol.
    $condition = $table .'.'. $field .' LIKE \''. $protocol .'%\'';

    // More complex case, no protocol specified but is automatically cleaned up
    // by link_cleanup_url(). RegEx is required for this search operation.
    if ($protocol == 'http') {
      if ($db_type == 'pgsql') {
        // PostGreSQL code has NOT been tested. Please report any problems to the link issue queue.
        // pgSQL requires all slashes to be double escaped in regular expressions.
        // See http://www.postgresql.org/docs/8.1/static/functions-matching.html#FUNCTIONS-POSIX-REGEXP
        $condition .= ' OR '. $table .'.'. $field .' ~* \''. '^(([a-z0-9]([a-z0-9\\-_]*\\.)+)('. LINK_DOMAINS .'|[a-z][a-z]))' .'\'';
      }
      else {
        // mySQL requires backslashes to be double (triple?) escaped within character classes.
        // See http://dev.mysql.com/doc/refman/5.0/en/string-comparison-functions.html#operator_regexp
        $condition .= ' OR '. $table .'.'. $field .' REGEXP \''. '^(([a-z0-9]([a-z0-9\\\-_]*\.)+)('. LINK_DOMAINS .'|[a-z][a-z]))' .'\'';
      }
    }

    $where_conditions[] = $condition;
  }

  $query->ensure_table($table);
  $query->add_where(implode(' '. $filter['operator'] .' ', $where_conditions));
}

/**
 * Forms a valid URL if possible from an entered address.
 * Trims whitespace and automatically adds an http:// to addresses without a protocol specified
 *
 * @param string $url
 * @param string $protocol The protocol to be prepended to the url if one is not specified
 */
function link_cleanup_url($url, $protocol = "http") {
  $url = trim($url);
  $type = link_validate_url($url);

  if ($type == LINK_EXTERNAL) {
    // Check if there is no protocol specified.
    $protocol_match = preg_match("/^([a-z0-9][a-z0-9\.\-_]*:\/\/)/i",$url);
    if (empty($protocol_match)) {
      // But should there be? Add an automatic http:// if it starts with a domain name.
      $domain_match = preg_match('/^(([a-z0-9]([a-z0-9\-_]*\.)+)('. LINK_DOMAINS .'|[a-z]{2}))/i',$url);
      if (!empty($domain_match)) {
        $url = $protocol."://".$url;
      }
    }
  }

  return $url;
}

/**
 * A lenient verification for URLs. Accepts all URLs following RFC 1738 standard
 * for URL formation and all email addresses following the RFC 2368 standard for
 * mailto address formation.
 *
 * @param string $text
 * @return mixed Returns boolean FALSE if the URL is not valid. On success, returns an object with
 * the following attributes: protocol, hostname, ip, and port.
 */
function link_validate_url($text) {

  $allowed_protocols = variable_get('filter_allowed_protocols', array('http', 'https', 'ftp', 'news', 'nntp', 'telnet', 'mailto', 'irc', 'ssh', 'sftp', 'webcal'));

  $protocol = '((' . implode("|", $allowed_protocols) . '):\/\/)';
  $authentication = '([a-z0-9]+(:[a-z0-9]+)?@)';
  $domain = '(([a-z0-9]([a-z0-9\-_\[\]])*)(\.(([a-z0-9\-_\[\]])+\.)*('. LINK_DOMAINS .'|[a-z]{2}))?)';
  $ipv4 = '([0-9]{1,3}(\.[0-9]{1,3}){3})';
  $ipv6 = '([0-9a-fA-F]{1,4}(\:[0-9a-fA-F]{1,4}){7})';
  $port = '(:([0-9]{1,5}))';

  // Pattern specific to eternal links.
  $external_pattern = '/^' . $protocol . '?' . $authentication . '?' . '(' . $domain . '|' . $ipv4 . '|' . $ipv6 . ' |localhost)' . $port . '?';

  // Pattern specific to internal links.
  $internal_pattern = "/^([a-z0-9_\-+\[\]]+)";

  $directories = "(\/[a-z0-9_\-\.~+%=&,$'():;*@\[\]]*)*";
   // Yes, four backslashes == a single backslash.
  $query = "(\/?\?([?a-z0-9+_|\-\.\/\\\\%=&,$'():;*@\[\]]*))";
  $anchor = "(#[a-z0-9_\-\.~+%=&,$'():;*@\[\]]*)";

  // The rest of the path for a standard URL.
  $end = $directories . '?' . $query . '?' . $anchor . '?' . '$/i';

  $user = '[a-zA-Z0-9_\-\.\+\^!#\$%&*+\/\=\?\`\|\{\}~\'\[\]]+';
  $email_pattern = '/^mailto:' . $user . '@' . '(' . $domain . '|' . $ipv4 .'|'. $ipv6 . '|localhost)' . $query . '?$/';

  if (strpos($text, '<front>') === 0) {
    return LINK_FRONT;
  }
  if (in_array('mailto', $allowed_protocols) && preg_match($email_pattern, $text)) {
    return LINK_EMAIL;
  }
  if (preg_match($internal_pattern . $end, $text)) {
    return LINK_INTERNAL;
  }
  if (preg_match($external_pattern . $end, $text)) {
    return LINK_EXTERNAL;
  }

  return FALSE;
}