class TranslateFilterForm

class TranslateFilterForm extends TranslateFormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'locale_translate_filter_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $filters = $this->translateFilters();
        $filter_values = $this->translateFilterValues();
        $form['#attached']['library'][] = 'locale/drupal.locale.admin';
        $form['filters'] = [
            '#type' => 'details',
            '#title' => $this->t('Filter translatable strings'),
            '#open' => TRUE,
        ];
        foreach ($filters as $key => $filter) {
            // Special case for 'string' filter.
            if ($key == 'string') {
                $form['filters']['status']['string'] = [
                    '#type' => 'search',
                    '#title' => $filter['title'],
                    '#description' => $filter['description'],
                    '#default_value' => $filter_values[$key],
                ];
            }
            else {
                $empty_option = isset($filter['options'][$filter['default']]) ? $filter['options'][$filter['default']] : '- None -';
                $form['filters']['status'][$key] = [
                    '#title' => $filter['title'],
                    '#type' => 'select',
                    '#empty_value' => $filter['default'],
                    '#empty_option' => $empty_option,
                    '#size' => 0,
                    '#options' => $filter['options'],
                    '#default_value' => $filter_values[$key],
                ];
                if (isset($filter['states'])) {
                    $form['filters']['status'][$key]['#states'] = $filter['states'];
                }
            }
        }
        $form['filters']['actions'] = [
            '#type' => 'actions',
            '#attributes' => [
                'class' => [
                    'container-inline',
                ],
            ],
        ];
        $form['filters']['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Filter'),
        ];
        if (!empty($_SESSION['locale_translate_filter'])) {
            $form['filters']['actions']['reset'] = [
                '#type' => 'submit',
                '#value' => $this->t('Reset'),
                '#submit' => [
                    '::resetForm',
                ],
            ];
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $filters = $this->translateFilters();
        foreach ($filters as $name => $filter) {
            if ($form_state->hasValue($name)) {
                $_SESSION['locale_translate_filter'][$name] = $form_state->getValue($name);
            }
        }
        $form_state->setRedirect('locale.translate_page');
    }
    
    /**
     * Provides a submit handler for the reset button.
     */
    public function resetForm(array &$form, FormStateInterface $form_state) {
        $_SESSION['locale_translate_filter'] = [];
        $form_state->setRedirect('locale.translate_page');
    }

}