class FileMediaFormatterBase

abstract class FileMediaFormatterBase extends FileFormatterBase implements FileMediaFormatterInterface {
    
    /**
     * Gets the HTML tag for the formatter.
     *
     * @return string
     *   The HTML tag of this formatter.
     */
    protected function getHtmlTag() {
        return static::getMediaType();
    }
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        return [
            'controls' => TRUE,
            'autoplay' => FALSE,
            'loop' => FALSE,
            'multiple_file_display_type' => 'tags',
        ] + parent::defaultSettings();
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        return [
            'controls' => [
                '#title' => $this->t('Show playback controls'),
                '#type' => 'checkbox',
                '#default_value' => $this->getSetting('controls'),
            ],
            'autoplay' => [
                '#title' => $this->t('Autoplay'),
                '#type' => 'checkbox',
                '#default_value' => $this->getSetting('autoplay'),
            ],
            'loop' => [
                '#title' => $this->t('Loop'),
                '#type' => 'checkbox',
                '#default_value' => $this->getSetting('loop'),
            ],
            'multiple_file_display_type' => [
                '#title' => $this->t('Display of multiple files'),
                '#type' => 'radios',
                '#options' => [
                    'tags' => $this->t('Use multiple @tag tags, each with a single source.', [
                        '@tag' => '<' . $this->getHtmlTag() . '>',
                    ]),
                    'sources' => $this->t('Use multiple sources within a single @tag tag.', [
                        '@tag' => '<' . $this->getHtmlTag() . '>',
                    ]),
                ],
                '#default_value' => $this->getSetting('multiple_file_display_type'),
            ],
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public static function isApplicable(FieldDefinitionInterface $field_definition) {
        if (!parent::isApplicable($field_definition)) {
            return FALSE;
        }
        
        /** @var \Symfony\Component\HttpFoundation\File\MimeType\MimeTypeGuesserInterface $extension_mime_type_guesser */
        $extension_mime_type_guesser = \Drupal::service('file.mime_type.guesser.extension');
        $extension_list = array_filter(preg_split('/\\s+/', $field_definition->getSetting('file_extensions')));
        foreach ($extension_list as $extension) {
            $mime_type = $extension_mime_type_guesser->guess('fakedFile.' . $extension);
            if (static::mimeTypeApplies($mime_type)) {
                return TRUE;
            }
        }
        return FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        $summary = [];
        $summary[] = $this->t('Playback controls: %controls', [
            '%controls' => $this->getSetting('controls') ? $this->t('visible') : $this->t('hidden'),
        ]);
        $summary[] = $this->t('Autoplay: %autoplay', [
            '%autoplay' => $this->getSetting('autoplay') ? $this->t('yes') : $this->t('no'),
        ]);
        $summary[] = $this->t('Loop: %loop', [
            '%loop' => $this->getSetting('loop') ? $this->t('yes') : $this->t('no'),
        ]);
        switch ($this->getSetting('multiple_file_display_type')) {
            case 'tags':
                $summary[] = $this->t('Multiple file display: Multiple HTML tags');
                break;
            case 'sources':
                $summary[] = $this->t('Multiple file display: One HTML tag with multiple sources');
                break;
        }
        return $summary;
    }
    
    /**
     * {@inheritdoc}
     */
    public function viewElements(FieldItemListInterface $items, $langcode) {
        $elements = [];
        $source_files = $this->getSourceFiles($items, $langcode);
        if (empty($source_files)) {
            return $elements;
        }
        $attributes = $this->prepareAttributes();
        foreach ($source_files as $delta => $files) {
            $elements[$delta] = [
                '#theme' => $this->getPluginId(),
                '#attributes' => $attributes,
                '#files' => $files,
                '#cache' => [
                    'tags' => [],
                ],
            ];
            $cache_tags = [];
            foreach ($files as $file) {
                $cache_tags = Cache::mergeTags($cache_tags, $file['file']->getCacheTags());
            }
            $elements[$delta]['#cache']['tags'] = $cache_tags;
        }
        return $elements;
    }
    
    /**
     * Prepare the attributes according to the settings.
     *
     * @param string[] $additional_attributes
     *   Additional attributes to be applied to the HTML element. Attribute names
     *   will be used as key and value in the HTML element.
     *
     * @return \Drupal\Core\Template\Attribute
     *   Container with all the attributes for the HTML tag.
     */
    protected function prepareAttributes(array $additional_attributes = []) {
        $attributes = new Attribute();
        foreach (array_merge([
            'controls',
            'autoplay',
            'loop',
        ], $additional_attributes) as $attribute) {
            if ($this->getSetting($attribute)) {
                $attributes->setAttribute($attribute, $attribute);
            }
        }
        return $attributes;
    }
    
    /**
     * Check if given MIME type applies to the media type of the formatter.
     *
     * @param string $mime_type
     *   The complete MIME type.
     *
     * @return bool
     *   TRUE if the MIME type applies, FALSE otherwise.
     */
    protected static function mimeTypeApplies($mime_type) {
        list($type) = explode('/', $mime_type, 2);
        return $type === static::getMediaType();
    }
    
    /**
     * Gets source files with attributes.
     *
     * @param \Drupal\Core\Field\EntityReferenceFieldItemListInterface $items
     *   The item list.
     * @param string $langcode
     *   The language code of the referenced entities to display.
     *
     * @return array
     *   Numerically indexed array, which again contains an associative array with
     *   the following key/values:
     *     - file => \Drupal\file\Entity\File
     *     - source_attributes => \Drupal\Core\Template\Attribute
     */
    protected function getSourceFiles(EntityReferenceFieldItemListInterface $items, $langcode) {
        $source_files = [];
        // Because we can have the files grouped in a single media tag, we do a
        // grouping in case the multiple file behavior is not 'tags'.
        
        /** @var \Drupal\file\Entity\File $file */
        foreach ($this->getEntitiesToView($items, $langcode) as $file) {
            if (static::mimeTypeApplies($file->getMimeType())) {
                $source_attributes = new Attribute();
                $source_attributes->setAttribute('src', $file->createFileUrl())
                    ->setAttribute('type', $file->getMimeType());
                if ($this->getSetting('multiple_file_display_type') === 'tags') {
                    $source_files[] = [
                        [
                            'file' => $file,
                            'source_attributes' => $source_attributes,
                        ],
                    ];
                }
                else {
                    $source_files[0][] = [
                        'file' => $file,
                        'source_attributes' => $source_attributes,
                    ];
                }
            }
        }
        return $source_files;
    }

}