<?php

/**
 * @file
 * Menu item limit enables the limitation of items per menu.
 */

/**
 * Implements hook_form_alter().
 */
function menu_item_limit_form_alter(&$form, &$form_state, $form_id) {
  switch ($form_id) {
    case 'menu_edit_menu':
      // Extend menu_edit_menu with the limit form.
      $form['menu_item_limit'] = menu_item_limit_config_menu($form, $form_state);
      $form['#validate'][] = 'menu_item_limit_config_menu_validate';
      $form['#submit'][] = 'menu_item_limit_config_menu_submit';
      break;

    case 'menu_edit_item':
      // Add a validation to form menu_edit_item.
      array_unshift($form['#validate'], 'menu_item_limit_menu_validate');
      break;

    default:
      break;
  }
}

/**
 * Add a form element to configure the item limitation of a menu.
 *
 * @param array $form
 *   The current menu edit form.
 * @param array $form_state
 *   The current state of the menu edit form.
 *
 * @return array
 *   The prefilled form element.
 */
function menu_item_limit_config_menu($form, &$form_state) {
  $menu_name = empty($form_state['build_info']['args'][1]['menu_name']) ? 'new' : $form_state['build_info']['args'][1]['menu_name'];
  // Try to get the current limit of the menu.
  $limit = variable_get('menu_item_limit-' . $menu_name, '0');
  $config_item = array(
    '#type' => 'textfield',
    '#description' => t('Set the amount of items allowed in this menu. Set 0 to allow unlimited items.'),
    '#title' => t('Item Limitation'),
    '#default_value' => $limit,
  );
  return $config_item;
}

/**
 * Validate the user input for the item limitation.
 *
 * @param array $form
 *   The current menu edit form.
 * @param array $form_state
 *   The current state of the menu edit form.
 */
function menu_item_limit_config_menu_validate($form, &$form_state) {
  // Check if the entered limit is set to a value of 0 or higher.
  $limit = check_plain($form_state['values']['menu_item_limit']);
  if ((!is_numeric($limit)) || ($limit < 0)) {
    form_set_error('menu_item_limit', t('The Item Limitation has to be set to 0 or higher.'));
  }
}

/**
 * Set the new value for the item limitation of the menu.
 *
 * @param array $form
 *   The current menu edit form.
 * @param array $form_state
 *   The current state of the menu edit form.
 */
function menu_item_limit_config_menu_submit($form, &$form_state) {
  // Set the limit for the menu.
  $limit = check_plain($form_state['values']['menu_item_limit']);
  $menu_name = $form_state['values']['menu_name'];
  variable_set('menu_item_limit-' . $menu_name, $limit);
}

/**
 * Validate an item within limit settings.
 *
 * @param array $form
 *   The current menu item edit form.
 * @param array $form_state
 *   The current state of the menu item edit form.
 *
 * @return bool
 *   TRUE when the item can be created and the limit hasn't been reached.
 */
function menu_item_limit_menu_validate($form, &$form_state) {
  // Check if menu item already exists and validate then.
  if (!empty($form_state['values']['original_item']['mlid'])) {
    return TRUE;
  }
  $menu_name = explode(':', $form_state['values']['parent']);
  $menu_name = $menu_name[0];
  // Get the item limitation, default to 0.
  $limit = variable_get('menu_item_limit-' . $menu_name, 0);
  // If the limit is set to unlimited, validate the form.
  if ($limit == 0) {
    return TRUE;
  }
  // Get the current amount of items and check if the count is within limits.
  else {
    $item_count = _menu_item_limitation_get_item_count($menu_name);
    if ($item_count >= $limit) {
      form_set_error('parent', t('The chosen menu already has the maximum number of items.'));
    }
  }
}

/**
 * This function takes a menu name and returns the number of menu items in it.
 *
 * @param string $menu_name
 *   The name of the menu.
 *
 * @return int
 *   The amount of items in the menu.
 */
function _menu_item_limitation_get_item_count($menu_name) {
  $menu = menu_tree_all_data($menu_name);
  if (!empty($menu)) {
    return count($menu);
  }
  else {
    return 0;
  }
}