<?php

/**
 * @file
 * Honeypot module, for deterring spam bots from completing Drupal forms.
 */

/**
 * Implements hook_menu().
 */
function honeypot_menu() {
  $items['admin/config/content/honeypot'] = array(
    'title' => 'Honeypot configuration',
    'description' => 'Configure Honeypot spam prevention and the forms on which Honeypot will be used.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('honeypot_admin_form'),
    'access arguments' => array('administer honeypot'),
    'file' => 'honeypot.admin.inc',
  );

  return $items;
}

/**
 * Implements hook_permission().
 */
function honeypot_permission() {
  return array(
    'administer honeypot' => array(
      'title' => t('Administer Honeypot'),
      'description' => t('Administer Honeypot-protected forms and settings'),
    ),
    'bypass honeypot protection' => array(
      'title' => t('Bypass Honeypot protection'),
      'description' => t('Bypass Honeypot form protection.'),
    ),
  );
}

/**
 * Implements hook_cron().
 */
function honeypot_cron() {
  // Delete {honeypot_user} entries older than the value of honeypot_expire.
  db_delete('honeypot_user')
    ->condition('timestamp', REQUEST_TIME - variable_get('honeypot_expire', 300), '<')
    ->execute();

  // Regenerate the honeypot css file if it does not exist or is outdated.
  $honeypot_css = honeypot_get_css_file_path();
  $honeypot_element_name = variable_get('honeypot_element_name', 'url');
  if (!file_exists($honeypot_css) || !honeypot_check_css($honeypot_element_name)) {
    honeypot_create_css($honeypot_element_name);
  }
}

/**
 * Implements hook_form_alter().
 *
 * Add Honeypot features to forms enabled in the Honeypot admin interface.
 */
function honeypot_form_alter(&$form, &$form_state, $form_id) {
  // Don't use for maintenance mode forms (install, update, etc.).
  if (defined('MAINTENANCE_MODE')) {
    return;
  }

  $unprotected_forms = array(
    'user_login',
    'user_login_block',
    'search_form',
    'search_block_form',
    'views_exposed_form',
    'honeypot_admin_form',
  );

  // If configured to protect all forms, add protection to every form.
  if (variable_get('honeypot_protect_all_forms', 0) && !in_array($form_id, $unprotected_forms)) {
    // Don't protect system forms - only admins should have access, and system
    // forms may be programmatically submitted by drush and other modules.
    if (strpos($form_id, 'system_') === FALSE && strpos($form_id, 'search_') === FALSE && strpos($form_id, 'views_exposed_form_') === FALSE) {
      honeypot_add_form_protection($form, $form_state, array('honeypot', 'time_restriction'));
    }
  }

  // Otherwise add form protection to admin-configured forms.
  elseif ($forms_to_protect = honeypot_get_protected_forms()) {
    foreach ($forms_to_protect as $protect_form_id) {
      // For most forms, do a straight check on the form ID.
      if ($form_id == $protect_form_id) {
        honeypot_add_form_protection($form, $form_state, array('honeypot', 'time_restriction'));
      }
      // For webforms use a special check for variable form ID.
      elseif ($protect_form_id == 'webforms' && (strpos($form_id, 'webform_client_form') !== FALSE)) {
        honeypot_add_form_protection($form, $form_state, array('honeypot', 'time_restriction'));
      }
    }
  }
}

/**
 * Implements hook_trigger_info().
 */
function honeypot_trigger_info() {
  return array(
    'honeypot' => array(
      'honeypot_reject' => array(
        'label' => t('Honeypot rejection'),
      ),
    ),
  );
}

/**
 * Implements hook_rules_event_info().
 */
function honeypot_rules_event_info() {
  return array(
    'honeypot_reject' => array(
      'label' => t('Honeypot rejection'),
      'group' => t('Honeypot'),
      'variables' => array(
        'form_id' => array(
          'type' => 'text',
          'label' => t('Form ID of the form the user was disallowed from submitting.'),
        ),
        // Don't provide 'uid' in context because it is available as
        // site:current-user:uid.
        'type' => array(
          'type' => 'text',
          'label' => t('String indicating the reason the submission was blocked.'),
        ),
      ),
    ),
  );
}

/**
 * Build an array of all the protected forms on the site, by form_id.
 *
 * @todo - Add in API call/hook to allow modules to add to this array.
 */
function honeypot_get_protected_forms() {
  $forms = &drupal_static(__FUNCTION__);

  // If the data isn't already in memory, get from cache or look it up fresh.
  if (!isset($forms)) {
    if ($cache = cache_get('honeypot_protected_forms')) {
      $forms = $cache->data;
    }
    else {
      $forms = array();
      // Look up all the honeypot forms in the variables table.
      $result = db_query("SELECT name FROM {variable} WHERE name LIKE 'honeypot_form_%'")->fetchCol();
      // Add each form that's enabled to the $forms array.
      foreach ($result as $variable) {
        if (variable_get($variable, 0)) {
          $forms[] = substr($variable, 14);
        }
      }

      // Save the cached data.
      cache_set('honeypot_protected_forms', $forms, 'cache');
    }
  }

  return $forms;
}

/**
 * Form builder function to add different types of protection to forms.
 *
 * @param array $options
 *   Array of options to be added to form. Currently accepts 'honeypot' and
 *   'time_restriction'.
 *
 * @return array
 *   Returns elements to be placed in a form's elements array to prevent spam.
 */
function honeypot_add_form_protection(&$form, &$form_state, $options = array()) {
  global $user;

  // Allow other modules to alter the protections applied to this form.
  drupal_alter('honeypot_form_protections', $options, $form);

  // Don't add any protections if the user can bypass the Honeypot.
  if (user_access('bypass honeypot protection')) {
    return;
  }

  // Build the honeypot element.
  if (in_array('honeypot', $options)) {
    // Get the element name (default is generic 'url').
    $honeypot_element = variable_get('honeypot_element_name', 'url');

    // Add 'autocomplete="off"' if configured.
    $attributes = array();
    if (variable_get('honeypot_autocomplete_attribute', 1)) {
      $attributes = array('autocomplete' => 'off');
    }

    // Get the path to the honeypot css file.
    $honeypot_css = honeypot_get_css_file_path();

    // Build the honeypot element.
    $honeypot_class = $honeypot_element . '-textfield';
    $form[$honeypot_element] = array(
      '#type' => 'textfield',
      '#title' => t('Leave this field blank'),
      '#size' => 20,
      '#weight' => 100,
      '#attributes' => $attributes,
      '#element_validate' => array('_honeypot_honeypot_validate'),
      '#prefix' => '<div class="' . $honeypot_class . '">',
      '#suffix' => '</div>',
      // Hide honeypot using CSS.
      '#attached' => array(
        'css' => array(
          'data' => $honeypot_css,
        ),
      ),
    );
  }

  // Build the time restriction element (if it's not disabled).
  if (in_array('time_restriction', $options) && variable_get('honeypot_time_limit', 5) != 0) {
    // Set the current time in a hidden value to be checked later.
    $form['honeypot_time'] = array(
      '#type' => 'hidden',
      '#title' => t('Timestamp'),
      '#default_value' => honeypot_get_signed_timestamp(REQUEST_TIME),
      '#element_validate' => array('_honeypot_time_restriction_validate'),
    );

    // Disable page caching to make sure timestamp isn't cached.
    if (user_is_anonymous()) {
      drupal_page_is_cacheable(FALSE);
    }
  }

  // Allow other modules to react to addition of form protection.
  if (!empty($options)) {
    module_invoke_all('honeypot_add_form_protection', $options, $form);
  }
}

/**
 * Validate honeypot field.
 */
function _honeypot_honeypot_validate($element, &$form_state) {
  // Get the honeypot field value.
  $honeypot_value = $element['#value'];

  // Make sure it's empty.
  if (!empty($honeypot_value)) {
    _honeypot_log($form_state['values']['form_id'], 'honeypot');
    form_set_error('', t('There was a problem with your form submission. Please refresh the page and try again.'));
  }
}

/**
 * Validate honeypot's time restriction field.
 */
function _honeypot_time_restriction_validate($element, &$form_state) {
  if (!empty($form_state['programmed'])) {
    // Don't do anything if the form was submitted programmatically.
    return;
  }

  // Don't do anything if the triggering element is a preview button.
  if ($form_state['triggering_element']['#value'] == t('Preview')) {
    return;
  }

  // Get the time value.
  $honeypot_time = honeypot_get_time_from_signed_timestamp($form_state['values']['honeypot_time']);

  // Get the honeypot_time_limit.
  $time_limit = honeypot_get_time_limit($form_state['values']);

  // Make sure current time - (time_limit + form time value) is greater than 0.
  // If not, throw an error.
  if (!$honeypot_time || REQUEST_TIME < ($honeypot_time + $time_limit)) {
    _honeypot_log($form_state['values']['form_id'], 'honeypot_time');
    // Get the time limit again, since it increases after first failure.
    $time_limit = honeypot_get_time_limit($form_state['values']);
    $form_state['values']['honeypot_time'] = honeypot_get_signed_timestamp(REQUEST_TIME);
    form_set_error('', t('There was a problem with your form submission. Please wait @limit seconds and try again.', array('@limit' => $time_limit)));
  }
}

/**
 * Log blocked form submissions.
 *
 * @param string $form_id
 *   Form ID for the form on which submission was blocked.
 * @param string $type
 *   String indicating the reason the submission was blocked. Allowed values:
 *     - honeypot: If honeypot field was filled in.
 *     - honeypot_time: If form was completed before the configured time limit.
 */
function _honeypot_log($form_id, $type) {
  honeypot_log_failure($form_id, $type);
  if (variable_get('honeypot_log', 0)) {
    $variables = array(
      '%form'  => $form_id,
      '@cause' => ($type == 'honeypot') ? t('submission of a value in the honeypot field') : t('submission of the form in less than minimum required time'),
    );
    watchdog('honeypot', 'Blocked submission of %form due to @cause.', $variables);
  }
}

/**
 * Look up the time limit for the current user.
 *
 * @param array $form_values
 *   Array of form values (optional).
 */
function honeypot_get_time_limit($form_values = array()) {
  global $user;
  $honeypot_time_limit = variable_get('honeypot_time_limit', 5);

  // Only calculate time limit if honeypot_time_limit has a value > 0.
  if ($honeypot_time_limit) {
    $expire_time = variable_get('honeypot_expire', 300);
    // Query the {honeypot_user} table to determine the number of failed
    // submissions for the current user.
    $query = db_select('honeypot_user', 'hs')
      ->condition('uid', $user->uid)
      ->condition('timestamp', REQUEST_TIME - $expire_time, '>');

    // For anonymous users, take the hostname into account.
    if ($user->uid === 0) {
      $query->condition('hostname', ip_address());
    }
    $number = $query->countQuery()->execute()->fetchField();

    // Don't add more than 30 days' worth of extra time.
    $honeypot_time_limit = (int) min($honeypot_time_limit + exp($number) - 1, 2592000);
    $additions = module_invoke_all('honeypot_time_limit', $honeypot_time_limit, $form_values, $number);
    if (count($additions)) {
      $honeypot_time_limit += array_sum($additions);
    }
  }

  return $honeypot_time_limit;
}

/**
 * Log the failed submision with timestamp and hostname.
 *
 * @param string $form_id
 *   Form ID for the rejected form submission.
 * @param string $type
 *   String indicating the reason the submission was blocked. Allowed values:
 *     - honeypot: If honeypot field was filled in.
 *     - honeypot_time: If form was completed before the configured time limit.
 */
function honeypot_log_failure($form_id, $type) {
  global $user;

  db_insert('honeypot_user')
    ->fields(array(
      'uid' => $user->uid,
      'hostname' => ip_address(),
      'timestamp' => REQUEST_TIME,
    ))
    ->execute();

  // Allow other modules to react to honeypot rejections.
  module_invoke_all('honeypot_reject', $form_id, $user->uid, $type);

  // Trigger honeypot_reject action.
  if (module_exists('trigger')) {
    $aids = trigger_get_assigned_actions('honeypot_reject');
    $context = array(
      'group' => 'honeypot',
      'hook' => 'honeypot_reject',
      'form_id' => $form_id,
      // Do not provide $user in context because it is available as a global.
      'type' => $type,
    );
    // Honeypot does not act on any specific object.
    $object = NULL;
    actions_do(array_keys($aids), $object, $context);
  }

  // Trigger rules honeypot_reject event.
  if (module_exists('rules')) {
    rules_invoke_event('honeypot_reject', $form_id, $type);
  }
}

/**
 * Retrieve the location of the Honeypot CSS file.
 *
 * @return string
 *   The path to the honeypot.css file.
 */
function honeypot_get_css_file_path() {
  return variable_get('file_public_path', conf_path() . '/files') . '/honeypot/honeypot.css';
}

/**
 * Create CSS file to hide the Honeypot field.
 *
 * @param string $element_name
 *   The honeypot element class name (e.g. 'url').
 */
function honeypot_create_css($element_name) {
  $path = 'public://honeypot';

  if (!file_prepare_directory($path, FILE_CREATE_DIRECTORY)) {
    drupal_set_message(t('Unable to create Honeypot CSS directory, %path. Check the permissions on your files directory.', array('%path' => file_uri_target($path))), 'error');
  }
  else {
    $filename = $path . '/honeypot.css';
    $data = '.' . $element_name . '-textfield { display: none !important; }';
    file_unmanaged_save_data($data, $filename, FILE_EXISTS_REPLACE);
  }
}

/**
 * Check Honeypot's CSS file for a given Honeypot element name.
 *
 * This function assumes the Honeypot CSS file already exists.
 *
 * @param string $element_name
 *   The honeypot element class name (e.g. 'url').
 *
 * @return bool
 *   TRUE if CSS is has element class name, FALSE if not.
 */
function honeypot_check_css($element_name) {
  $path = honeypot_get_css_file_path();
  $handle = fopen($path, 'r');
  $contents = fread($handle, filesize($path));
  fclose($handle);

  if (strpos($contents, $element_name) === 1) {
    return TRUE;
  }

  return FALSE;
}

/**
 * Sign the timestamp $time.
 *
 * @param mixed $time
 *   The timestamp to sign.
 *
 * @return string
 *   A signed timestamp in the form timestamp|HMAC.
 */
function honeypot_get_signed_timestamp($time) {
  return $time . '|' . drupal_hmac_base64($time, drupal_get_private_key());
}

/**
 * Validate a signed timestamp.
 *
 * @param string $signed_timestamp
 *   A timestamp concateneted with the signature
 *
 * @return int
 *   The timestamp if the signature is correct, 0 otherwise.
 */
function honeypot_get_time_from_signed_timestamp($signed_timestamp) {
  $honeypot_time = 0;

  // Fail fast if timestamp was forged or saved with an older Honeypot version.
  if (strpos($signed_timestamp, '|') === FALSE) {
    return $honeypot_time;
  }

  list($timestamp, $received_hmac) = explode('|', $signed_timestamp);

  if ($timestamp && $received_hmac) {
    $calculated_hmac = drupal_hmac_base64($timestamp, drupal_get_private_key());
    // Prevent leaking timing information, compare second order hmacs.
    $random_key = drupal_random_bytes(32);
    if (drupal_hmac_base64($calculated_hmac, $random_key) === drupal_hmac_base64($received_hmac, $random_key)) {
      $honeypot_time = $timestamp;
    }
  }

  return $honeypot_time;
}