class Alignment

class Alignment extends CKEditor5PluginDefault implements CKEditor5PluginConfigurableInterface, CKEditor5PluginElementsSubsetInterface {
    use CKEditor5PluginConfigurableTrait;
    
    /**
     * The default configuration for this plugin.
     *
     * @var string[][]
     */
    const DEFAULT_CONFIGURATION = [
        'enabled_alignments' => [
            'left',
            'center',
            'right',
            'justify',
        ],
    ];
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return static::DEFAULT_CONFIGURATION;
    }
    
    /**
     * {@inheritdoc}
     *
     * Form for choosing which alignment types are available.
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $form['enabled_alignments'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Enabled Alignments'),
            '#description' => $this->t('These are the alignment types that will appear in the alignment dropdown.'),
        ];
        foreach ($this->getPluginDefinition()
            ->getCKEditor5Config()['alignment']['options'] as $alignment_option) {
            $name = $alignment_option['name'];
            $form['enabled_alignments'][$name] = [
                '#type' => 'checkbox',
                '#title' => $this->t($name),
                '#return_value' => $name,
                '#default_value' => in_array($name, $this->configuration['enabled_alignments'], TRUE) ? $name : NULL,
            ];
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
        // Match the config schema structure at ckeditor5.plugin.ckeditor5_alignment.
        $form_value = $form_state->getValue('enabled_alignments');
        $config_value = array_values(array_filter($form_value));
        $form_state->setValue('enabled_alignments', $config_value);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
        $this->configuration['enabled_alignments'] = $form_state->getValue('enabled_alignments');
    }
    
    /**
     * {@inheritdoc}
     *
     * Filters the alignment options to those chosen in editor config.
     */
    public function getDynamicPluginConfig(array $static_plugin_config, EditorInterface $editor) : array {
        $enabled_alignments = $this->configuration['enabled_alignments'];
        $all_alignment_options = $static_plugin_config['alignment']['options'];
        $configured_alignment_options = array_filter($all_alignment_options, function ($option) use ($enabled_alignments) {
            return in_array($option['name'], $enabled_alignments, TRUE);
        });
        return [
            'alignment' => [
                'options' => array_values($configured_alignment_options),
            ],
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getElementsSubset() : array {
        $enabled_alignments = $this->configuration['enabled_alignments'];
        $plugin_definition = $this->getPluginDefinition();
        $all_elements = $plugin_definition->getElements();
        $subset = HTMLRestrictions::fromString(implode($all_elements));
        foreach ($plugin_definition->getCKEditor5Config()['alignment']['options'] as $configured_alignment) {
            if (!in_array($configured_alignment['name'], $enabled_alignments, TRUE)) {
                $element_string = '<$text-container class=' . '"' . $configured_alignment["className"] . '"' . '>';
                $subset = $subset->diff(HTMLRestrictions::fromString($element_string));
            }
        }
        return $subset->toCKEditor5ElementsArray();
    }

}