class ExposedFormPluginBase

abstract class ExposedFormPluginBase extends PluginBase implements CacheableDependencyInterface, ExposedFormPluginInterface {
    
    /**
     * {@inheritdoc}
     */
    protected $usesOptions = TRUE;
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['submit_button'] = [
            'default' => $this->t('Apply'),
        ];
        $options['reset_button'] = [
            'default' => FALSE,
        ];
        $options['reset_button_label'] = [
            'default' => $this->t('Reset'),
        ];
        $options['exposed_sorts_label'] = [
            'default' => $this->t('Sort by'),
        ];
        $options['expose_sort_order'] = [
            'default' => TRUE,
        ];
        $options['sort_asc_label'] = [
            'default' => $this->t('Asc'),
        ];
        $options['sort_desc_label'] = [
            'default' => $this->t('Desc'),
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        $form['submit_button'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Submit button text'),
            '#default_value' => $this->options['submit_button'],
            '#required' => TRUE,
        ];
        $form['reset_button'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Include reset button (resets all applied exposed filters)'),
            '#default_value' => $this->options['reset_button'],
        ];
        $form['reset_button_label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Reset button label'),
            '#description' => $this->t('Text to display in the reset button of the exposed form.'),
            '#default_value' => $this->options['reset_button_label'],
            '#required' => TRUE,
            '#states' => [
                'invisible' => [
                    'input[name="exposed_form_options[reset_button]"]' => [
                        'checked' => FALSE,
                    ],
                ],
            ],
        ];
        $form['exposed_sorts_label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Exposed sorts label'),
            '#default_value' => $this->options['exposed_sorts_label'],
            '#required' => TRUE,
        ];
        $form['expose_sort_order'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Allow people to choose the sort order'),
            '#description' => $this->t('If sort order is not exposed, the sort criteria settings for each sort will determine its order.'),
            '#default_value' => $this->options['expose_sort_order'],
        ];
        $form['sort_asc_label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Label for ascending sort'),
            '#default_value' => $this->options['sort_asc_label'],
            '#required' => TRUE,
            '#states' => [
                'visible' => [
                    'input[name="exposed_form_options[expose_sort_order]"]' => [
                        'checked' => TRUE,
                    ],
                ],
            ],
        ];
        $form['sort_desc_label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Label for descending sort'),
            '#default_value' => $this->options['sort_desc_label'],
            '#required' => TRUE,
            '#states' => [
                'visible' => [
                    'input[name="exposed_form_options[expose_sort_order]"]' => [
                        'checked' => TRUE,
                    ],
                ],
            ],
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function renderExposedForm($block = FALSE) {
        // Deal with any exposed filters we may have, before building.
        $form_state = (new FormState())->setStorage([
            'view' => $this->view,
            'display' => &$this->view->display_handler->display,
            'rerender' => TRUE,
        ])
            ->setMethod('get')
            ->setAlwaysProcess()
            ->disableRedirect();
        // Some types of displays (eg. attachments) may wish to use the exposed
        // filters of their parent displays instead of showing an additional
        // exposed filter form for the attachment as well as that for the parent.
        if (!$this->view->display_handler
            ->displaysExposed() || !$block && $this->view->display_handler
            ->getOption('exposed_block')) {
            $form_state->set('rerender', NULL);
        }
        if (!empty($this->ajax)) {
            $form_state->set('ajax', TRUE);
        }
        $form = \Drupal::formBuilder()->buildForm('\\Drupal\\views\\Form\\ViewsExposedForm', $form_state);
        $errors = $form_state->getErrors();
        // If the exposed form had errors, do not build the view.
        if (!empty($errors)) {
            $this->view->build_info['abort'] = TRUE;
        }
        if (!$this->view->display_handler
            ->displaysExposed() || !$block && $this->view->display_handler
            ->getOption('exposed_block')) {
            return [];
        }
        else {
            return $form;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        $view = $this->view;
        $exposed_data = $view->exposed_data ?? [];
        $sort_by = $exposed_data['sort_by'] ?? NULL;
        if (!empty($sort_by)) {
            // Make sure the original order of sorts is preserved
            // (e.g. a sticky sort is often first)
            $view->query->orderby = [];
            foreach ($view->sort as $sort) {
                if (!$sort->isExposed()) {
                    $sort->query();
                }
                elseif (!empty($sort->options['expose']['field_identifier']) && $sort->options['expose']['field_identifier'] === $sort_by) {
                    if (isset($exposed_data['sort_order']) && in_array($exposed_data['sort_order'], [
                        'ASC',
                        'DESC',
                    ], TRUE)) {
                        $sort->options['order'] = $exposed_data['sort_order'];
                    }
                    $sort->setRelationship();
                    $sort->query();
                }
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function preRender($values) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function postRender(&$output) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function preExecute() {
    }
    
    /**
     * {@inheritdoc}
     */
    public function postExecute() {
    }
    
    /**
     * {@inheritdoc}
     */
    public function exposedFormAlter(&$form, FormStateInterface $form_state) {
        if (!empty($this->options['submit_button'])) {
            $form['actions']['submit']['#value'] = $this->options['submit_button'];
        }
        // Check if there is exposed sorts for this view
        $exposed_sorts = [];
        $exposed_sorts_options = [];
        foreach ($this->view->sort as $id => $handler) {
            if ($handler->canExpose() && $handler->isExposed() && !empty($handler->options['expose']['field_identifier'])) {
                $exposed_sorts[$handler->options['expose']['field_identifier']] = $id;
                $exposed_sorts_options[$handler->options['expose']['field_identifier']] = $handler->options['expose']['label'];
            }
        }
        if (count($exposed_sorts)) {
            $form['sort_by'] = [
                '#type' => 'select',
                '#options' => $exposed_sorts_options,
                '#title' => $this->options['exposed_sorts_label'],
            ];
            $sort_order = [
                'ASC' => $this->options['sort_asc_label'],
                'DESC' => $this->options['sort_desc_label'],
            ];
            $user_input = $form_state->getUserInput();
            if (isset($user_input['sort_by']) && isset($exposed_sorts[$user_input['sort_by']]) && isset($this->view->sort[$exposed_sorts[$user_input['sort_by']]])) {
                $default_sort_order = $this->view->sort[$exposed_sorts[$user_input['sort_by']]]->options['order'];
            }
            else {
                $first_sort = reset($this->view->sort);
                $default_sort_order = $first_sort->options['order'];
            }
            if (!isset($user_input['sort_by'])) {
                $keys = array_keys($exposed_sorts);
                $user_input['sort_by'] = array_shift($keys);
                $form_state->setUserInput($user_input);
            }
            if ($this->options['expose_sort_order']) {
                $form['sort_order'] = [
                    '#type' => 'select',
                    '#options' => $sort_order,
                    '#title' => $this->t('Order', [], [
                        'context' => 'Sort order',
                    ]),
                    '#default_value' => $default_sort_order,
                ];
            }
        }
        if (!empty($this->options['reset_button'])) {
            $form['actions']['reset'] = [
                '#value' => $this->options['reset_button_label'],
                '#type' => 'submit',
                '#weight' => 10,
            ];
            // Get an array of exposed filters, keyed by identifier option.
            $exposed_filters = [];
            foreach ($this->view->filter as $id => $handler) {
                if ($handler->canExpose() && $handler->isExposed() && !empty($handler->options['expose']['identifier'])) {
                    $exposed_filters[$handler->options['expose']['identifier']] = $id;
                }
            }
            $all_exposed = array_merge($exposed_sorts, $exposed_filters);
            // Set the access to FALSE if there is no exposed input.
            if (!array_intersect_key($all_exposed, $this->view
                ->getExposedInput())) {
                $form['actions']['reset']['#access'] = FALSE;
            }
        }
        $pager = $this->view->display_handler
            ->getPlugin('pager');
        if ($pager) {
            $pager->exposedFormAlter($form, $form_state);
            $form_state->set('pager_plugin', $pager);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function exposedFormValidate(&$form, FormStateInterface $form_state) {
        if ($pager_plugin = $form_state->get('pager_plugin')) {
            $pager_plugin->exposedFormValidate($form, $form_state);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function exposedFormSubmit(&$form, FormStateInterface $form_state, &$exclude) {
        if (!$form_state->isValueEmpty('op') && $form_state->getValue('op') == $this->options['reset_button_label']) {
            $this->resetForm($form, $form_state);
        }
        if ($pager_plugin = $form_state->get('pager_plugin')) {
            $pager_plugin->exposedFormSubmit($form, $form_state, $exclude);
            $exclude[] = 'pager_plugin';
        }
    }
    
    /**
     * Resets all the states of the exposed form.
     *
     * This method is called when the "Reset" button is triggered. Clears
     * user inputs, stored session, and the form state.
     *
     * @param array $form
     *   An associative array containing the structure of the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    public function resetForm(&$form, FormStateInterface $form_state) {
        // _SESSION is not defined for users who are not logged in.
        // If filters are not overridden, store the 'remember' settings on the
        // default display. If they are, store them on this display. This way,
        // multiple displays in the same view can share the same filters and
        // remember settings.
        $display_id = $this->view->display_handler
            ->isDefaulted('filters') ? 'default' : $this->view->current_display;
        $session = $this->view
            ->getRequest()
            ->getSession();
        $views_session = $session->get('views', []);
        if (isset($views_session[$this->view->storage
            ->id()][$display_id])) {
            unset($views_session[$this->view->storage
                ->id()][$display_id]);
        }
        $session->set('views', $views_session);
        // Set the form to allow redirect.
        if (empty($this->view->live_preview) && !\Drupal::request()->isXmlHttpRequest()) {
            $form_state->disableRedirect(FALSE);
        }
        else {
            $form_state->setRebuild();
            $this->view->exposed_data = [];
        }
        $form_state->setRedirect('<current>');
        $form_state->setValues([]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheMaxAge() {
        return Cache::PERMANENT;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheContexts() {
        $contexts = [];
        if ($this->options['expose_sort_order']) {
            // The sort order query arg is just important in case there is an exposed
            // sort order.
            $has_exposed_sort_handler = FALSE;
            
            /** @var \Drupal\views\Plugin\views\sort\SortPluginBase $sort_handler */
            foreach ($this->displayHandler
                ->getHandlers('sort') as $sort_handler) {
                if ($sort_handler->isExposed()) {
                    $has_exposed_sort_handler = TRUE;
                }
            }
            if ($has_exposed_sort_handler) {
                $contexts[] = 'url.query_args:sort_order';
            }
        }
        // Merge in cache contexts for all exposed filters to prevent display of
        // cached forms.
        foreach ($this->displayHandler
            ->getHandlers('filter') as $filter_handler) {
            if ($filter_handler->isExposed()) {
                $contexts = Cache::mergeContexts($contexts, $filter_handler->getCacheContexts());
            }
        }
        return $contexts;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheTags() {
        return [];
    }

}