<?php

namespace Drupal\Core\Render\Element;

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Render\BubbleableMetadata;
use Drupal\Core\Url;

/**
 * Provides a base class for form element plugins.
 *
 * Form elements are a subset of render elements, representing elements for
 * HTML forms, which can be referenced in form arrays. See the
 * @link theme_render Render API topic @endlink for an overview of render
 * arrays and render elements, and the @link form_api Form API topic @endlink
 * for an overview of forms and form arrays.
 *
 * The elements of form arrays are divided up into properties (whose keys
 * start with #) and children (whose keys do not start with #). The properties
 * provide data or settings that are used in rendering and form processing.
 * Some properties are specific to a particular type of form/render element,
 * some are available for any render element, and some are available for any
 * form input element. A list of the properties that are available for all form
 * elements follows; see \Drupal\Core\Render\Element\RenderElement for some
 * additional information, as well as a list of properties that are common to
 * all render elements (including form elements). Properties specific to a
 * particular element are documented on that element's class.
 *
 * Here is a list of properties that are used during the rendering and form
 * processing of form elements:
 * - #after_build: (array) Array of callables or function names, which are
 *   called after the element is built. Arguments: $element, $form_state.
 * - #ajax: (array) Array of elements to specify Ajax behavior. See
 *   the @link ajax Ajax API topic @endlink for more information.
 * - #array_parents: (string[], read-only) Array of names of all the element's
 *   parents (including itself) in the render array. See also #parents, #tree.
 * - #default_value: Default value for the element. See also #value.
 * - #description: (string) Help or description text for the element. In an
 *   ideal user interface, the #title should be enough to describe the element,
 *   so most elements should not have a description; if you do need one, make
 *   sure it is translated. If it is not already wrapped in a safe markup
 *   object, it will be filtered for XSS safety.
 * - #disabled: (bool) If TRUE, the element is shown but does not accept
 *   user input.
 * - #element_validate: (array) Array of callables or function names, which
 *   are called to validate the input. Arguments: $element, $form_state, $form.
 * - #field_prefix: (string) Prefix to display before the HTML input element.
 *   Should be translated, normally. If it is not already wrapped in a safe
 *   markup object, will be filtered for XSS safety.
 * - #field_suffix: (string) Suffix to display after the HTML input element.
 *   Should be translated, normally. If it is not already wrapped in a safe
 *   markup object, will be filtered for XSS safety.
 * - #input: (bool, internal) Whether or not the element accepts input.
 * - #parents: (string[], read-only) Array of names of the element's parents
 *   for purposes of getting values out of $form_state. See also
 *   #array_parents, #tree.
 * - #process: (array) Array of callables or function names, which are
 *   called during form building. Arguments: $element, $form_state, $form.
 * - #processed: (bool, internal) Set to TRUE when the element is processed.
 * - #required: (bool) Whether or not input is required on the element.
 * - #states: (array) Information about JavaScript states, such as when to
 *   hide or show the element based on input on other elements.
 *   See \Drupal\Core\Form\FormHelper::processStates() for documentation.
 * - #title: (string) Title of the form element. Should be translated.
 * - #title_display: (string) Where and how to display the #title. Possible
 *   values:
 *   - before: Label goes before the element (default for most elements).
 *   - after: Label goes after the element (default for radio elements).
 *   - invisible: Label is there but is made invisible using CSS.
 *   - attribute: Make it the title attribute (hover tooltip).
 * - #tree: (bool) TRUE if the values of this element and its children should
 *   be hierarchical in $form_state; FALSE if the values should be flat.
 *   See also #parents, #array_parents.
 * - #value_callback: (callable) Callable or function name, which is called
 *   to transform the raw user input to the element's value. Arguments:
 *   $element, $input, $form_state.
 *
 * @see \Drupal\Core\Render\Annotation\FormElement
 * @see \Drupal\Core\Render\Element\FormElementInterface
 * @see \Drupal\Core\Render\ElementInfoManager
 * @see plugin_api
 *
 * @ingroup theme_render
 */
abstract class FormElement extends RenderElement implements FormElementInterface {

  /**
   * {@inheritdoc}
   */
  public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
    return NULL;
  }

  /**
   * #process callback for #pattern form element property.
   *
   * @param array $element
   *   An associative array containing the properties and children of the
   *   generic input element.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   * @param array $complete_form
   *   The complete form structure.
   *
   * @return array
   *   The processed element.
   */
  public static function processPattern(&$element, FormStateInterface $form_state, &$complete_form) {
    if (isset($element['#pattern']) && !isset($element['#attributes']['pattern'])) {
      $element['#attributes']['pattern'] = $element['#pattern'];
      $element['#element_validate'][] = [get_called_class(), 'validatePattern'];
    }

    return $element;
  }

  /**
   * #element_validate callback for #pattern form element property.
   *
   * @param $element
   *   An associative array containing the properties and children of the
   *   generic form element.
   * @param $form_state
   *   The current state of the form.
   * @param array $complete_form
   *   The complete form structure.
   */
  public static function validatePattern(&$element, FormStateInterface $form_state, &$complete_form) {
    if ($element['#value'] !== '') {
      // The pattern must match the entire string and should have the same
      // behavior as the RegExp object in ECMA 262.
      // - Use bracket-style delimiters to avoid introducing a special delimiter
      //   character like '/' that would have to be escaped.
      // - Put in brackets so that the pattern can't interfere with what's
      //   prepended and appended.
      $pattern = '{^(?:' . $element['#pattern'] . ')$}';

      if (!preg_match($pattern, $element['#value'])) {
        $form_state->setError($element, t('%name field is not in the right format.', ['%name' => $element['#title']]));
      }
    }
  }

  /**
   * Adds autocomplete functionality to elements.
   *
   * This sets up autocomplete functionality for elements with an
   * #autocomplete_route_name property, using the #autocomplete_route_parameters
   * property if present.
   *
   * For example, suppose your autocomplete route name is
   * 'mymodule.autocomplete' and its path is
   * '/mymodule/autocomplete/{a}/{b}'. In a form array, you would create a text
   * field with properties:
   * @code
   * '#autocomplete_route_name' => 'mymodule.autocomplete',
   * '#autocomplete_route_parameters' => array('a' => $some_key, 'b' => $some_id),
   * @endcode
   * If the user types "keywords" in that field, the full path called would be:
   * 'mymodule_autocomplete/$some_key/$some_id?q=keywords'
   *
   * @param array $element
   *   The form element to process. Properties used:
   *   - #autocomplete_route_name: A route to be used as callback URL by the
   *     autocomplete JavaScript library.
   *   - #autocomplete_route_parameters: The parameters to be used in
   *     conjunction with the route name.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   * @param array $complete_form
   *   The complete form structure.
   *
   * @return array
   *   The form element.
   */
  public static function processAutocomplete(&$element, FormStateInterface $form_state, &$complete_form) {
    $url = NULL;
    $access = FALSE;

    if (!empty($element['#autocomplete_route_name'])) {
      $parameters = isset($element['#autocomplete_route_parameters']) ? $element['#autocomplete_route_parameters'] : [];
      $url = Url::fromRoute($element['#autocomplete_route_name'], $parameters)->toString(TRUE);
      /** @var \Drupal\Core\Access\AccessManagerInterface $access_manager */
      $access_manager = \Drupal::service('access_manager');
      $access = $access_manager->checkNamedRoute($element['#autocomplete_route_name'], $parameters, \Drupal::currentUser(), TRUE);
    }

    if ($access) {
      $metadata = BubbleableMetadata::createFromRenderArray($element);
      if ($access->isAllowed()) {
        $element['#attributes']['class'][] = 'form-autocomplete';
        $metadata->addAttachments(['library' => ['core/drupal.autocomplete']]);
        // Provide a data attribute for the JavaScript behavior to bind to.
        $element['#attributes']['data-autocomplete-path'] = $url->getGeneratedUrl();
        $metadata = $metadata->merge($url);
      }
      $metadata
        ->merge(BubbleableMetadata::createFromObject($access))
        ->applyTo($element);
    }

    return $element;
  }

}
