class ViewsFormMainForm

class ViewsFormMainForm implements FormInterface, TrustedCallbackInterface {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
    }
    
    /**
     * Replaces views substitution placeholders.
     *
     * @param array $element
     *   An associative array containing the properties of the element.
     *   Properties used: #substitutions, #children.
     *
     * @return array
     *   The $element with prepared variables ready for #theme 'form'
     *   in views_form_views_form.
     */
    public static function preRenderViewsForm(array $element) {
        // Placeholders and their substitutions (usually rendered form elements).
        $search = [];
        $replace = [];
        // Add in substitutions provided by the form.
        foreach ($element['#substitutions']['#value'] as $substitution) {
            $field_name = $substitution['field_name'];
            $row_id = $substitution['row_id'];
            $search[] = $substitution['placeholder'];
            $replace[] = isset($element[$field_name][$row_id]) ? \Drupal::service('renderer')->render($element[$field_name][$row_id]) : '';
        }
        // Add in substitutions from hook_views_form_substitutions().
        $substitutions = \Drupal::moduleHandler()->invokeAll('views_form_substitutions');
        foreach ($substitutions as $placeholder => $substitution) {
            $search[] = Html::escape($placeholder);
            // Ensure that any replacements made are safe to make.
            if (!$substitution instanceof MarkupInterface) {
                $substitution = Html::escape($substitution);
            }
            $replace[] = $substitution;
        }
        // Apply substitutions to the rendered output.
        $output = str_replace($search, $replace, \Drupal::service('renderer')->render($element['output']));
        $element['output'] = [
            '#markup' => ViewsRenderPipelineMarkup::create($output),
        ];
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function trustedCallbacks() {
        return [
            'preRenderViewsForm',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state, ViewExecutable $view = NULL, $output = []) {
        $form['#prefix'] = '<div class="views-form">';
        $form['#suffix'] = '</div>';
        $form['#pre_render'][] = [
            static::class,
            'preRenderViewsForm',
        ];
        // Add the output markup to the form array so that it's included when the form
        // array is passed to the theme function.
        $form['output'] = $output;
        // This way any additional form elements will go before the view
        // (below the exposed widgets).
        $form['output']['#weight'] = 50;
        $form['actions'] = [
            '#type' => 'actions',
        ];
        $form['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => t('Save'),
        ];
        $substitutions = [];
        foreach ($view->field as $field_name => $field) {
            $form_element_name = $field_name;
            if (method_exists($field, 'form_element_name')) {
                $form_element_name = $field->form_element_name();
            }
            $method_form_element_row_id_exists = FALSE;
            if (method_exists($field, 'form_element_row_id')) {
                $method_form_element_row_id_exists = TRUE;
            }
            // If the field provides a views form, allow it to modify the $form array.
            $has_form = FALSE;
            if (property_exists($field, 'views_form_callback')) {
                $callback = $field->views_form_callback;
                $callback($view, $field, $form, $form_state);
                $has_form = TRUE;
            }
            elseif (method_exists($field, 'viewsForm')) {
                $field->viewsForm($form, $form_state);
                $has_form = TRUE;
            }
            // Build the substitutions array for use in the theme function.
            if ($has_form) {
                foreach ($view->result as $row_id => $row) {
                    if ($method_form_element_row_id_exists) {
                        $form_element_row_id = $field->form_element_row_id($row_id);
                    }
                    else {
                        $form_element_row_id = $row_id;
                    }
                    $substitutions[] = [
                        'placeholder' => '<!--form-item-' . $form_element_name . '--' . $form_element_row_id . '-->',
                        'field_name' => $form_element_name,
                        'row_id' => $form_element_row_id,
                    ];
                }
            }
        }
        // Give the area handlers a chance to extend the form.
        $area_handlers = array_merge(array_values($view->header), array_values($view->footer));
        $empty = empty($view->result);
        foreach ($area_handlers as $area) {
            if (method_exists($area, 'viewsForm') && !$area->viewsFormEmpty($empty)) {
                $area->viewsForm($form, $form_state);
            }
        }
        $form['#substitutions'] = [
            '#type' => 'value',
            '#value' => $substitutions,
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        $view = $form_state->getBuildInfo()['args'][0];
        // Call the validation method on every field handler that has it.
        foreach ($view->field as $field) {
            if (method_exists($field, 'viewsFormValidate')) {
                $field->viewsFormValidate($form, $form_state);
            }
        }
        // Call the validate method on every area handler that has it.
        foreach ([
            'header',
            'footer',
        ] as $area) {
            foreach ($view->{$area} as $area_handler) {
                if (method_exists($area_handler, 'viewsFormValidate')) {
                    $area_handler->viewsFormValidate($form, $form_state);
                }
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $view = $form_state->getBuildInfo()['args'][0];
        // Call the submit method on every field handler that has it.
        foreach ($view->field as $field) {
            if (method_exists($field, 'viewsFormSubmit')) {
                $field->viewsFormSubmit($form, $form_state);
            }
        }
        // Call the submit method on every area handler that has it.
        foreach ([
            'header',
            'footer',
        ] as $area) {
            foreach ($view->{$area} as $area_handler) {
                if (method_exists($area_handler, 'viewsFormSubmit')) {
                    $area_handler->viewsFormSubmit($form, $form_state);
                }
            }
        }
    }

}