class FormTestSelectForm

class FormTestSelectForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_select';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $base = [
            '#type' => 'select',
            '#options' => [
                'one' => 'one',
                'two' => 'two',
                'three' => 'three',
                'four' => '<strong>four</strong>',
            ],
        ];
        $form['select'] = $base + [
            '#title' => '#default_value one',
            '#default_value' => 'one',
        ];
        $form['select_required'] = $base + [
            '#title' => '#default_value one, #required',
            '#required' => TRUE,
            '#default_value' => 'one',
        ];
        $form['select_optional'] = $base + [
            '#title' => '#default_value one, not #required',
            '#required' => FALSE,
            '#default_value' => 'one',
        ];
        $form['empty_value'] = $base + [
            '#title' => '#default_value one, #required, #empty_value 0',
            '#required' => TRUE,
            '#default_value' => 'one',
            '#empty_value' => 0,
        ];
        $form['empty_value_one'] = $base + [
            '#title' => '#default_value = #empty_value, #required',
            '#required' => TRUE,
            '#default_value' => 'one',
            '#empty_value' => 'one',
        ];
        $form['no_default'] = $base + [
            '#title' => 'No #default_value, #required',
            '#required' => TRUE,
        ];
        $form['no_default_optional'] = $base + [
            '#title' => 'No #default_value, not #required',
            '#required' => FALSE,
            '#description' => 'Should result in "one" because it is not required and there is no #empty_value requested, so default browser behavior of preselecting first option is in effect.',
        ];
        $form['no_default_optional_empty_value'] = $base + [
            '#title' => 'No #default_value, not #required, #empty_value empty string',
            '#empty_value' => '',
            '#required' => FALSE,
            '#description' => 'Should result in an empty string (due to #empty_value) because it is optional.',
        ];
        $form['no_default_empty_option'] = $base + [
            '#title' => 'No #default_value, #required, #empty_option',
            '#required' => TRUE,
            '#empty_option' => '- Choose -',
        ];
        $form['no_default_empty_option_optional'] = $base + [
            '#title' => 'No #default_value, not #required, #empty_option',
            '#empty_option' => '- Dismiss -',
            '#description' => 'Should result in an empty string (default of #empty_value) because it is optional.',
        ];
        $form['no_default_empty_value'] = $base + [
            '#title' => 'No #default_value, #required, #empty_value 0',
            '#required' => TRUE,
            '#empty_value' => 0,
            '#description' => 'Should never result in 0.',
        ];
        $form['no_default_empty_value_one'] = $base + [
            '#title' => 'No #default_value, #required, #empty_value one',
            '#required' => TRUE,
            '#empty_value' => 'one',
            '#description' => 'A mistakenly assigned #empty_value contained in #options should not be valid.',
        ];
        $form['no_default_empty_value_optional'] = $base + [
            '#title' => 'No #default_value, not #required, #empty_value 0',
            '#required' => FALSE,
            '#empty_value' => 0,
            '#description' => 'Should result in 0 because it is optional.',
        ];
        $form['multiple'] = $base + [
            '#title' => '#multiple, #default_value two',
            '#default_value' => [
                'two',
            ],
            '#multiple' => TRUE,
        ];
        $form['multiple_no_default'] = $base + [
            '#title' => '#multiple, no #default_value',
            '#multiple' => TRUE,
        ];
        $form['multiple_no_default_required'] = $base + [
            '#title' => '#multiple, #required, no #default_value',
            '#required' => TRUE,
            '#multiple' => TRUE,
        ];
        $form['opt_groups'] = [
            '#type' => 'select',
            '#options' => [
                'optgroup_one' => [
                    'one' => 'one',
                    'two' => 'two',
                    'three' => 'three',
                    'four' => '<strong>four</strong>',
                ],
                'optgroup_two' => [
                    'five' => 'five',
                    'six' => 'six',
                ],
            ],
        ];
        // Add a select that should have its options left alone.
        $form['unsorted'] = [
            '#type' => 'select',
            '#options' => $this->makeSortableOptions('uso'),
        ];
        // Add a select to test sorting at the top level, and with some of the
        // option groups sorted, some left alone, and at least one with #sort_start
        // set to a non-default value.
        $sortable_options = $this->makeSortableOptions('sso');
        $sortable_options['sso_zz_group']['#sort_options'] = TRUE;
        $sortable_options['sso_xx_group']['#sort_options'] = TRUE;
        $sortable_options['sso_xx_group']['#sort_start'] = 1;
        // Do not use a sort start on this one.
        $form['sorted'] = [
            '#type' => 'select',
            '#options' => $sortable_options,
            '#sort_options' => TRUE,
        ];
        // Add a select to test sorting with a -NONE- option included,
        // and #sort_start set.
        $sortable_none_options = $this->makeSortableOptions('sno');
        $sortable_none_options['sno_zz_group']['#sort_options'] = TRUE;
        $form['sorted_none'] = [
            '#type' => 'select',
            '#options' => $sortable_none_options,
            '#sort_options' => TRUE,
            '#sort_start' => 4,
            '#empty_value' => 'sno_empty',
        ];
        // Add a select to test sorting with a -NONE- option included,
        // and #sort_start not set.
        $sortable_none_no_start_options = $this->makeSortableOptions('snn');
        $sortable_none_no_start_options['snn_zz_group']['#sort_options'] = TRUE;
        $form['sorted_none_no_start'] = [
            '#type' => 'select',
            '#options' => $sortable_none_no_start_options,
            '#sort_options' => TRUE,
            '#empty_value' => 'snn_empty',
        ];
        $form['submit'] = [
            '#type' => 'submit',
            '#value' => 'Submit',
        ];
        return $form;
    }
    
    /**
     * Makes and returns a set of options to test sorting on.
     *
     * @param string $prefix
     *   Prefix for the keys of the options.
     *
     * @return array
     *   Options array, including option groups, for testing.
     */
    protected function makeSortableOptions($prefix) {
        return [
            // Don't use $this->t() here, to avoid adding strings to
            // localize.drupal.org. Do use TranslatableMarkup in places, to test
            // that labels are cast to strings before sorting.
$prefix . '_first_element' => new TranslatableMarkup('first element'),
            $prefix . '_second' => new TranslatableMarkup('second element'),
            $prefix . '_zz_group' => [
                $prefix . '_gc' => new TranslatableMarkup('group c'),
                $prefix . '_ga' => new TranslatableMarkup('group a'),
                $prefix . '_gb' => 'group b',
            ],
            $prefix . '_yy_group' => [
                $prefix . '_ge' => new TranslatableMarkup('group e'),
                $prefix . '_gd' => new TranslatableMarkup('group d'),
                $prefix . '_gf' => new TranslatableMarkup('group f'),
            ],
            $prefix . '_xx_group' => [
                $prefix . '_gz' => new TranslatableMarkup('group z'),
                $prefix . '_gi' => new TranslatableMarkup('group i'),
                $prefix . '_gh' => new TranslatableMarkup('group h'),
            ],
            $prefix . '_d' => 'd',
            $prefix . '_c' => new TranslatableMarkup('main c'),
            $prefix . '_b' => new TranslatableMarkup('main b'),
            $prefix . '_a' => 'a',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $form_state->setResponse(new JsonResponse($form_state->getValues()));
    }

}