<?php

/**
 * Implements hook_theme().
 */
function multiple_selects_theme() {
  return array(
    'multiple_selects_none' => array(
      'variables' => array('instance' => NULL, 'option' => NULL),
    ),
  );
}

/**
 * Returns HTML for the label for the empty value for options that are not required.
 *
 * The default theme will display N/A for a radio list and '- None -' for a select.
 *
 * @param $variables
 *   An associative array containing:
 *   - instance: An array representing the widget requesting the options.
 *
 * @ingroup themeable
 */
function theme_multiple_selects_none($variables) {
  $instance = $variables['instance'];
  $option = $variables['option'];
  $output = ($option == 'option_none' ? t('- None -') : t('- Select a value -'));
  return $output;
}

/**
 * Implements hook_field_widget_info().
 *
 * Field type modules willing to use those widgets should:
 * - Use hook_field_widget_info_alter() to append their field own types to the
 *   list of types supported by the widgets,
 */
function multiple_selects_field_widget_info() {
  return array(
    'multiple_selects' => array(
      'label' => t('Multiple Selects list'),
      'field types' => array('entityreference', 'node_reference', 'user_reference', 'taxonomy_term_reference', 'list_integer', 'list_float', 'list_text'),
    ),
  );
}

/**
 * Implements hook_field_widget_form().
 */
function multiple_selects_field_widget_form(&$form, &$form_state, $field, $instance, $langcode, $items, $delta, $element) {
  
  // Abstract over the actual field columns, to allow different field types to
  // reuse those widgets.
  $value_key = key($field['columns']);
  $type = "select";
  $multiple = 1;
  $required = $element['#required'];
  $has_value = isset($items[0][$value_key]);
  $properties = _options_properties($type, $multiple, $required, $has_value);

  // Prepare the list of options.
  $options = _multiple_selects_get_options($field, $instance, $properties, NULL, NULL);
  
  $widget = $element;

  $widget += array(
    '#type' => 'select',
    '#default_value' => isset($items[$delta][$value_key]) ? $items[$delta][$value_key] : NULL,
    '#options' => $options,
    '#element_validate' => array('multiple_selects_widget_validate'),
    '#value_key' => $value_key,
    '#properties' => $properties,
  );
  $element[$value_key] = $widget;

  return $element;
}

/**
 * Form element validation handler for options element.
 */
function multiple_selects_widget_validate($element, &$form_state) {
  
  $value_key = $element['#value_key'];
  $properties = $element['#properties'];
  $value = $element['#value'];

  if ($element['#required'] && $element['#value'] == '_none') {
    form_error($element, t('!name field is required.', array('!name' => $element['#title'])));
  }
  
  if ($properties['empty_option']) {
    if ($value == '_none') {
      form_set_value($element, NULL, $form_state);
    }    
  }
  
}

/**
 * Implements hook_field_widget_error().
 */
function multiple_selects_field_widget_error($element, $error, $form, &$form_state) {
  form_error($element, $error['message']);
}

/**
 * Collects the options for a field.
 */
function _multiple_selects_get_options($field, $instance, $properties, $entity_type, $entity) {
  // Get the list of options.
  $options = (array) module_invoke($field['module'], 'options_list', $field, $instance, $entity_type, $entity);

  // Sanitize the options.
  _options_prepare_options($options, $properties);

  if (!$properties['optgroups']) {
    $options = options_array_flatten($options);
  }

  if ($properties['empty_option']) {
    $label = theme('multiple_selects_none', array('instance' => $instance, 'option' => $properties['empty_option']));
    $options = array('_none' => $label) + $options;
  }

  return $options;
}