class ImportForm

class ImportForm extends FormBase {
    
    /**
     * Uploaded file entity.
     *
     * @var \Drupal\file\Entity\File
     */
    protected $file;
    
    /**
     * The module handler service.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * The configurable language manager.
     *
     * @var \Drupal\language\ConfigurableLanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('module_handler'), $container->get('language_manager'));
    }
    
    /**
     * Constructs a form for language import.
     *
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler service.
     * @param \Drupal\language\ConfigurableLanguageManagerInterface $language_manager
     *   The configurable language manager.
     */
    public function __construct(ModuleHandlerInterface $module_handler, ConfigurableLanguageManagerInterface $language_manager) {
        $this->moduleHandler = $module_handler;
        $this->languageManager = $language_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'locale_translate_import_form';
    }
    
    /**
     * Form constructor for the translation import screen.
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $languages = $this->languageManager
            ->getLanguages();
        // Initialize a language list to the ones available, including English if we
        // are to translate Drupal to English as well.
        $existing_languages = [];
        foreach ($languages as $langcode => $language) {
            if (locale_is_translatable($langcode)) {
                $existing_languages[$langcode] = $language->getName();
            }
        }
        // If we have no languages available, present the list of predefined
        // languages only. If we do have already added languages, set up two option
        // groups with the list of existing and then predefined languages.
        if (empty($existing_languages)) {
            $language_options = $this->languageManager
                ->getStandardLanguageListWithoutConfigured();
            $default = key($language_options);
        }
        else {
            $default = key($existing_languages);
            $language_options = [
                (string) $this->t('Existing languages') => $existing_languages,
                (string) $this->t('Languages not yet added') => $this->languageManager
                    ->getStandardLanguageListWithoutConfigured(),
            ];
        }
        $validators = [
            'FileExtension' => [
                'extensions' => 'po',
            ],
            'FileSizeLimit' => [
                'fileLimit' => Environment::getUploadMaxSize(),
            ],
        ];
        $form['file'] = [
            '#type' => 'file',
            '#title' => $this->t('Translation file'),
            '#description' => [
                '#theme' => 'file_upload_help',
                '#description' => $this->t('A Gettext Portable Object file.'),
                '#upload_validators' => $validators,
            ],
            '#size' => 50,
            '#upload_validators' => $validators,
            '#upload_location' => 'translations://',
            '#attributes' => [
                'class' => [
                    'file-import-input',
                ],
            ],
        ];
        $form['langcode'] = [
            '#type' => 'select',
            '#title' => $this->t('Language'),
            '#options' => $language_options,
            '#default_value' => $default,
            '#attributes' => [
                'class' => [
                    'langcode-input',
                ],
            ],
        ];
        $form['customized'] = [
            '#title' => $this->t('Treat imported strings as custom translations'),
            '#type' => 'checkbox',
        ];
        $form['overwrite_options'] = [
            '#type' => 'container',
            '#tree' => TRUE,
        ];
        $form['overwrite_options']['not_customized'] = [
            '#title' => $this->t('Overwrite non-customized translations'),
            '#type' => 'checkbox',
            '#states' => [
                'checked' => [
                    ':input[name="customized"]' => [
                        'checked' => TRUE,
                    ],
                ],
            ],
        ];
        $form['overwrite_options']['customized'] = [
            '#title' => $this->t('Overwrite existing customized translations'),
            '#type' => 'checkbox',
        ];
        $form['actions'] = [
            '#type' => 'actions',
        ];
        $form['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Import'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        $this->file = _file_save_upload_from_form($form['file'], $form_state, 0);
        // Ensure we have the file uploaded.
        if (!$this->file) {
            $form_state->setErrorByName('file', $this->t('File to import not found.'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->moduleHandler
            ->loadInclude('locale', 'translation.inc');
        // Add language, if not yet supported.
        $language = $this->languageManager
            ->getLanguage($form_state->getValue('langcode'));
        if (empty($language)) {
            $language = ConfigurableLanguage::createFromLangcode($form_state->getValue('langcode'));
            $language->save();
            $this->messenger()
                ->addStatus($this->t('The language %language has been created.', [
                '%language' => $this->t($language->label()),
            ]));
        }
        $options = array_merge(_locale_translation_default_update_options(), [
            'langcode' => $form_state->getValue('langcode'),
            'overwrite_options' => $form_state->getValue('overwrite_options'),
            'customized' => $form_state->getValue('customized') ? LOCALE_CUSTOMIZED : LOCALE_NOT_CUSTOMIZED,
        ]);
        $this->moduleHandler
            ->loadInclude('locale', 'bulk.inc');
        $file = locale_translate_file_attach_properties($this->file, $options);
        $batch = locale_translate_batch_build([
            $file->uri => $file,
        ], $options);
        batch_set($batch);
        // Create or update all configuration translations for this language.
        if ($batch = locale_config_batch_update_components($options, [
            $form_state->getValue('langcode'),
        ])) {
            batch_set($batch);
        }
        $form_state->setRedirect('locale.translate_page');
    }

}