<?php
/**
 * @file views_dependent_filters.module
 * Provides a Views exposed filter which makes other filters depend on values
 * in yet further filters for their visiblity and processing.
 * For example: if the 'node type' filter is set to 'article', show a filter for
 * a field that is only present on articles.
 */

/**
 * Implements hook_views_api().
 */
function views_dependent_filters_views_api() {
  return array(
    'api' => '3.0-alpha1',
    'path' => drupal_get_path('module', 'views_dependent_filters'),
  );
}

/**
 * After build form processor for the views exposed form.
 *
 * This is added by the exposed filter handler so that we can add a CTools
 * visiblity dependency.
 * We don't use Drupal core #states because as far as I can tell they don't
 * work here.
 * See also merlinofchaos's comment here: http://drupal.org/node/1406470
 */
function views_dependent_filters_exposed_form_after_build($form, $form_state) {
  // We may have multiple dependency info arrays from more than one copies
  // of the views_dependent_filters_handler_filter_dependent handler.
  foreach ($form_state['dependent_exposed_filters'] as $dependency_info) {
    // Build up the CTools #dependency item to put onto each dependent element.
    $form_dependency = array();
    foreach ($dependency_info['controllers'] as $filter_id => $controller_values) {
      $identifier = $dependency_info['identifiers'][$filter_id];
      // Regular form.
      $filter_html_id = views_dependent_filters_recreate_html_id($identifier);
      $form_dependency['edit-' . $filter_html_id] = $controller_values;
      // better_exposed_filters form.
      foreach ($controller_values as $value) {
        $value = views_dependent_filters_recreate_html_id($value);
        $key = 'edit-' . $filter_html_id . '-' . $value;
        $form_dependency[$key] = array(TRUE);
      }
    }

    // Set the dependency on each form element as required.
    foreach ($dependency_info['dependents'] as $dependent_filter_id) {
      $identifier = $dependency_info['identifiers'][$dependent_filter_id];
      $form[$identifier]['#process'][] = 'ctools_dependent_process';
      if (!isset($form[$identifier]['#dependency'])) {
        $form[$identifier]['#dependency'] = array();
      }
      $form[$identifier]['#dependency'] += $form_dependency;
    }
  }

  return $form;
}

/**
 * Convert a string to an HTML id matching one made with drupal_html_id().
 *
 * We can't simply call drupal_html_id() because that only returns unique
 * ids; this is intended for when the ID already exists and we want to recreate
 * it from the original input.
 */
function views_dependent_filters_recreate_html_id($id) {
  $id = strtr(drupal_strtolower($id), array(' ' => '-', '_' => '-', '[' => '-', ']' => ''));

  // As defined in http://www.w3.org/TR/html4/types.html#type-name, HTML IDs can
  // only contain letters, digits ([0-9]), hyphens ("-"), underscores ("_"),
  // colons (":"), and periods ("."). We strip out any character not in that
  // list. Note that the CSS spec doesn't allow colons or periods in identifiers
  // (http://www.w3.org/TR/CSS21/syndata.html#characters), so we strip those two
  // characters as well.
  $id = preg_replace('/[^A-Za-z0-9\-_]/', '', $id);

  // Removing multiple consecutive hyphens.
  $id = preg_replace('/\-+/', '-', $id);

  return $id;
}