<?php

namespace Drupal\Core\Form;

use Drupal\Component\Utility\Crypt;
use Drupal\Core\Access\CsrfTokenGenerator;
use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\KeyValueStore\KeyValueExpirableFactoryInterface;
use Drupal\Core\PageCache\RequestPolicyInterface;
use Drupal\Core\Session\AccountInterface;
use Drupal\Core\Site\Settings;
use Psr\Log\LoggerInterface;
use Symfony\Component\HttpFoundation\RequestStack;

/**
 * Encapsulates the caching of a form and its form state.
 *
 * @ingroup form_api
 */
class FormCache implements FormCacheInterface {

  /**
   * The factory for expirable key value stores used by form cache.
   *
   * @var \Drupal\Core\KeyValueStore\KeyValueExpirableFactoryInterface
   */
  protected $keyValueExpirableFactory;

  /**
   * The CSRF token generator to validate the form token.
   *
   * @var \Drupal\Core\Access\CsrfTokenGenerator
   */
  protected $csrfToken;

  /**
   * The current user.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $currentUser;

  /**
   * The module handler.
   *
   * @var \Drupal\Core\Extension\ModuleHandlerInterface
   */
  protected $moduleHandler;

  /**
   * Logger channel.
   *
   * @var \Drupal\Core\Logger\LoggerChannelInterface
   */
  protected $logger;

  /**
   * The config factory.
   *
   * @var \Drupal\Core\Config\ConfigFactoryInterface
   */
  protected $configFactory;

  /**
   * The request stack.
   *
   * @var \Symfony\Component\HttpFoundation\RequestStack
   */
  protected $requestStack;

  /**
   * A policy rule determining the cacheability of a request.
   *
   * @var \Drupal\Core\PageCache\RequestPolicyInterface
   */
  protected $requestPolicy;

  /**
   * The app root.
   *
   * @var string
   */
  protected $root;

  /**
   * Constructs a new FormCache.
   *
   * @param string $root
   *   The app root.
   * @param \Drupal\Core\KeyValueStore\KeyValueExpirableFactoryInterface $key_value_expirable_factory
   *   The key value expirable factory, used to create key value expirable
   *   stores for the form cache and form state cache.
   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
   *   The module handler.
   * @param \Drupal\Core\Session\AccountInterface $current_user
   *   The current user.
   * @param \Drupal\Core\Access\CsrfTokenGenerator $csrf_token
   *   The CSRF token generator.
   * @param \Psr\Log\LoggerInterface $logger
   *   A logger instance.
   * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
   *   The request stack.
   * @param \Drupal\Core\PageCache\RequestPolicyInterface $request_policy
   *   A policy rule determining the cacheability of a request.
   */
  public function __construct($root, KeyValueExpirableFactoryInterface $key_value_expirable_factory, ModuleHandlerInterface $module_handler, AccountInterface $current_user, CsrfTokenGenerator $csrf_token, LoggerInterface $logger, RequestStack $request_stack, RequestPolicyInterface $request_policy) {
    $this->root = $root;
    $this->keyValueExpirableFactory = $key_value_expirable_factory;
    $this->moduleHandler = $module_handler;
    $this->currentUser = $current_user;
    $this->logger = $logger;
    $this->csrfToken = $csrf_token;
    $this->requestStack = $request_stack;
    $this->requestPolicy = $request_policy;
  }

  /**
   * {@inheritdoc}
   */
  public function getCache($form_build_id, FormStateInterface $form_state) {
    if ($form = $this->keyValueExpirableFactory->get('form')->get($form_build_id)) {
      if ((isset($form['#cache_token']) && $this->csrfToken->validate($form['#cache_token'])) || (!isset($form['#cache_token']) && $this->currentUser->isAnonymous())) {
        $this->loadCachedFormState($form_build_id, $form_state);

        // Generate a new #build_id if the cached form was rendered on a
        // cacheable page.
        $build_info = $form_state->getBuildInfo();
        if (!empty($build_info['immutable'])) {
          $form['#build_id_old'] = $form['#build_id'];
          $form['#build_id'] = 'form-' . Crypt::randomBytesBase64();
          $form['form_build_id']['#value'] = $form['#build_id'];
          $form['form_build_id']['#id'] = $form['#build_id'];
          unset($build_info['immutable']);
          $form_state->setBuildInfo($build_info);
        }
        return $form;
      }
    }
  }

  /**
   * Loads the cached form state.
   *
   * @param string $form_build_id
   *   The unique form build ID.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  protected function loadCachedFormState($form_build_id, FormStateInterface $form_state) {
    if ($stored_form_state = $this->keyValueExpirableFactory->get('form_state')->get($form_build_id)) {
      // Re-populate $form_state for subsequent rebuilds.
      $form_state->setFormState($stored_form_state);

      // If the original form is contained in include files, load the files.
      // @see \Drupal\Core\Form\FormStateInterface::loadInclude()
      $build_info = $form_state->getBuildInfo();
      $build_info += ['files' => []];
      foreach ($build_info['files'] as $file) {
        if (is_array($file)) {
          $file += ['type' => 'inc', 'name' => $file['module']];
          $this->moduleHandler->loadInclude($file['module'], $file['type'], $file['name']);
        }
        elseif (file_exists($file)) {
          require_once $this->root . '/' . $file;
        }
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public function setCache($form_build_id, $form, FormStateInterface $form_state) {
    // Cache forms for 6 hours by default.
    $expire = Settings::get('form_cache_expiration', 21600);

    // Ensure that the form build_id embedded in the form structure is the same
    // as the one passed in as a parameter. This is an additional safety measure
    // to prevent legacy code operating directly with
    // \Drupal::formBuilder()->getCache() and \Drupal::formBuilder()->setCache()
    // from accidentally overwriting immutable form state.
    if (isset($form['#build_id']) && $form['#build_id'] != $form_build_id) {
      $this->logger->error('Form build-id mismatch detected while attempting to store a form in the cache.');
      return;
    }

    // Cache form structure.
    if (isset($form)) {
      if ($this->currentUser->isAuthenticated()) {
        $form['#cache_token'] = $this->csrfToken->get();
      }
      unset($form['#build_id_old']);
      $this->keyValueExpirableFactory->get('form')->setWithExpire($form_build_id, $form, $expire);
    }

    if ($data = $form_state->getCacheableArray()) {
      $this->keyValueExpirableFactory->get('form_state')->setWithExpire($form_build_id, $data, $expire);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function deleteCache($form_build_id) {
    $this->keyValueExpirableFactory->get('form')->delete($form_build_id);
    $this->keyValueExpirableFactory->get('form_state')->delete($form_build_id);
  }

}