class LanguageAddForm

class LanguageAddForm extends LanguageFormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        // @todo Remove in favor of base method.
        return 'language_admin_add_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $form['#title'] = $this->t('Add language');
        $predefined_languages = $this->languageManager
            ->getStandardLanguageListWithoutConfigured();
        $predefined_languages['custom'] = $this->t('Custom language...');
        $predefined_default = $form_state->getValue('predefined_langcode', key($predefined_languages));
        $form['predefined_langcode'] = [
            '#type' => 'select',
            '#title' => $this->t('Language name'),
            '#default_value' => $predefined_default,
            '#options' => $predefined_languages,
        ];
        $form['predefined_submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Add language'),
            '#name' => 'add_language',
            '#limit_validation_errors' => [
                [
                    'predefined_langcode',
                ],
                [
                    'predefined_submit',
                ],
            ],
            '#states' => [
                'invisible' => [
                    'select#edit-predefined-langcode' => [
                        'value' => 'custom',
                    ],
                ],
            ],
            '#validate' => [
                '::validatePredefined',
            ],
            '#submit' => [
                '::submitForm',
                '::save',
            ],
            '#button_type' => 'primary',
        ];
        $custom_language_states_conditions = [
            'select#edit-predefined-langcode' => [
                'value' => 'custom',
            ],
        ];
        $form['custom_language'] = [
            '#type' => 'container',
            '#states' => [
                'visible' => $custom_language_states_conditions,
            ],
        ];
        $this->commonForm($form['custom_language']);
        $form['custom_language']['langcode']['#states'] = [
            'required' => $custom_language_states_conditions,
        ];
        $form['custom_language']['label']['#states'] = [
            'required' => $custom_language_states_conditions,
        ];
        $form['custom_language']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Add custom language'),
            '#name' => 'add_custom_language',
            '#validate' => [
                '::validateCustom',
            ],
            '#submit' => [
                '::submitForm',
                '::save',
            ],
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function save(array $form, FormStateInterface $form_state) {
        parent::save($form, $form_state);
        $t_args = [
            '%language' => $this->entity
                ->label(),
            '%langcode' => $this->entity
                ->id(),
        ];
        $this->logger('language')
            ->notice('The %language (%langcode) language has been created.', $t_args);
        $this->messenger()
            ->addStatus($this->t('The language %language has been created and can now be used.', $t_args));
        if ($this->moduleHandler
            ->moduleExists('block')) {
            // Tell the user they have the option to add a language switcher block
            // to their theme so they can switch between the languages.
            $this->messenger()
                ->addStatus($this->t('Use one of the language switcher blocks to allow site visitors to switch between languages. You can enable these blocks on the <a href=":block-admin">block administration page</a>.', [
                ':block-admin' => Url::fromRoute('block.admin_display')->toString(),
            ]));
        }
        $form_state->setRedirectUrl($this->entity
            ->toUrl('collection'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function actions(array $form, FormStateInterface $form_state) {
        // No actions needed.
        return [];
    }
    
    /**
     * Validates the language addition form on custom language button.
     */
    public function validateCustom(array $form, FormStateInterface $form_state) {
        if ($form_state->getValue('predefined_langcode') == 'custom') {
            $langcode = $form_state->getValue('langcode');
            // Reuse the editing form validation routine if we add a custom language.
            $this->validateCommon($form['custom_language'], $form_state);
            if ($language = $this->languageManager
                ->getLanguage($langcode)) {
                $form_state->setErrorByName('langcode', $this->t('The language %language (%langcode) already exists.', [
                    '%language' => $language->getName(),
                    '%langcode' => $langcode,
                ]));
            }
        }
        else {
            $form_state->setErrorByName('predefined_langcode', $this->t('Use the <em>Add language</em> button to save a predefined language.'));
        }
    }
    
    /**
     * Element specific validator for the Add language button.
     */
    public function validatePredefined($form, FormStateInterface $form_state) {
        $langcode = $form_state->getValue('predefined_langcode');
        if ($langcode == 'custom') {
            $form_state->setErrorByName('predefined_langcode', $this->t('Fill in the language details and save the language with <em>Add custom language</em>.'));
        }
        else {
            if ($language = $this->languageManager
                ->getLanguage($langcode)) {
                $form_state->setErrorByName('predefined_langcode', $this->t('The language %language (%langcode) already exists.', [
                    '%language' => $language->getName(),
                    '%langcode' => $langcode,
                ]));
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
        $langcode = $form_state->getValue('predefined_langcode');
        if ($langcode == 'custom') {
            $langcode = $form_state->getValue('langcode');
            $label = $form_state->getValue('label');
            $direction = $form_state->getValue('direction');
        }
        else {
            $standard_languages = LanguageManager::getStandardLanguageList();
            $label = $standard_languages[$langcode][0];
            $direction = $standard_languages[$langcode][2] ?? ConfigurableLanguage::DIRECTION_LTR;
        }
        $entity->set('id', $langcode);
        $entity->set('label', $label);
        $entity->set('direction', $direction);
        // There is no weight on the edit form. Fetch all configurable languages
        // ordered by weight and set the new language to be placed after them.
        $languages = \Drupal::languageManager()->getLanguages(ConfigurableLanguage::STATE_CONFIGURABLE);
        $last_language = end($languages);
        $entity->setWeight($last_language->getWeight() + 1);
    }

}