class NegotiationBrowserForm

class NegotiationBrowserForm extends ConfigFormBase {
    
    /**
     * The configurable language manager.
     *
     * @var \Drupal\language\ConfigurableLanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * {@inheritdoc}
     */
    public function __construct(ConfigFactoryInterface $config_factory, ConfigurableLanguageManagerInterface $language_manager) {
        parent::__construct($config_factory);
        $this->languageManager = $language_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('config.factory'), $container->get('language_manager'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'language_negotiation_configure_browser_form';
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getEditableConfigNames() {
        return [
            'language.mappings',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form = [];
        // Initialize a language list to the ones available, including English.
        $languages = $this->languageManager
            ->getLanguages();
        $existing_languages = [];
        foreach ($languages as $langcode => $language) {
            $existing_languages[$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();
        }
        else {
            $language_options = [
                (string) $this->t('Existing languages') => $existing_languages,
                (string) $this->t('Languages not yet added') => $this->languageManager
                    ->getStandardLanguageListWithoutConfigured(),
            ];
        }
        $form['mappings'] = [
            '#type' => 'table',
            '#header' => [
                $this->t('Browser language code'),
                $this->t('Site language'),
                $this->t('Operations'),
            ],
            '#attributes' => [
                'id' => 'language-negotiation-browser',
            ],
            '#empty' => $this->t('No browser language mappings available.'),
        ];
        $mappings = $this->language_get_browser_drupal_langcode_mappings();
        foreach ($mappings as $browser_langcode => $drupal_langcode) {
            $form['mappings'][$browser_langcode] = [
                'browser_langcode' => [
                    '#title' => $this->t('Browser language code'),
                    '#title_display' => 'invisible',
                    '#type' => 'textfield',
                    '#default_value' => $browser_langcode,
                    '#size' => 20,
                    '#required' => TRUE,
                ],
                'drupal_langcode' => [
                    '#title' => $this->t('Site language'),
                    '#title_display' => 'invisible',
                    '#type' => 'select',
                    '#options' => $language_options,
                    '#default_value' => $drupal_langcode,
                    '#required' => TRUE,
                ],
            ];
            // Operations column.
            $form['mappings'][$browser_langcode]['operations'] = [
                '#type' => 'operations',
                '#links' => [],
            ];
            $form['mappings'][$browser_langcode]['operations']['#links']['delete'] = [
                'title' => $this->t('Delete'),
                'url' => Url::fromRoute('language.negotiation_browser_delete', [
                    'browser_langcode' => $browser_langcode,
                ]),
            ];
        }
        // Add empty row.
        $form['new_mapping'] = [
            '#type' => 'details',
            '#title' => $this->t('Add a new mapping'),
            '#tree' => TRUE,
        ];
        $form['new_mapping']['browser_langcode'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Browser language code'),
            '#description' => $this->t('Use language codes as <a href=":w3ctags">defined by the W3C</a> for interoperability. <em>Examples: "en", "en-gb" and "zh-hant".</em>', [
                ':w3ctags' => 'http://www.w3.org/International/articles/language-tags/',
            ]),
            '#size' => 20,
        ];
        $form['new_mapping']['drupal_langcode'] = [
            '#type' => 'select',
            '#title' => $this->t('Site language'),
            '#options' => $language_options,
        ];
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        // Array to check if all browser language codes are unique.
        $unique_values = [];
        // Check all mappings.
        if ($form_state->hasValue('mappings')) {
            $mappings = $form_state->getValue('mappings');
            foreach ($mappings as $key => $data) {
                // Make sure browser_langcode is unique.
                if (array_key_exists($data['browser_langcode'], $unique_values)) {
                    $form_state->setErrorByName('mappings][new_mapping][browser_langcode', $this->t('Browser language codes must be unique.'));
                }
                elseif (preg_match('/[^a-z\\-]/', $data['browser_langcode'])) {
                    $form_state->setErrorByName('mappings][new_mapping][browser_langcode', $this->t('Browser language codes can only contain lowercase letters and a hyphen(-).'));
                }
                $unique_values[$data['browser_langcode']] = $data['drupal_langcode'];
            }
        }
        // Check new mapping.
        $data = $form_state->getValue('new_mapping');
        if (!empty($data['browser_langcode'])) {
            // Make sure browser_langcode is unique.
            if (array_key_exists($data['browser_langcode'], $unique_values)) {
                $form_state->setErrorByName('mappings][' . $key . '][browser_langcode', $this->t('Browser language codes must be unique.'));
            }
            elseif (preg_match('/[^a-z\\-]/', $data['browser_langcode'])) {
                $form_state->setErrorByName('mappings][' . $key . '][browser_langcode', $this->t('Browser language codes can only contain lowercase letters and a hyphen(-).'));
            }
            $unique_values[$data['browser_langcode']] = $data['drupal_langcode'];
        }
        $form_state->set('mappings', $unique_values);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $mappings = $form_state->get('mappings');
        if (!empty($mappings)) {
            $config = $this->config('language.mappings');
            $config->setData([
                'map' => $mappings,
            ]);
            $config->save();
        }
        parent::submitForm($form, $form_state);
    }
    
    /**
     * Retrieves the browser's langcode mapping configuration array.
     *
     * @return array
     *   The browser's langcode mapping configuration array.
     */
    protected function language_get_browser_drupal_langcode_mappings() {
        $config = $this->config('language.mappings');
        if ($config->isNew()) {
            return [];
        }
        return $config->get('map');
    }

}