class MediaSourceBase

abstract class MediaSourceBase extends PluginBase implements MediaSourceInterface, ContainerFactoryPluginInterface {
    
    /**
     * Plugin label.
     *
     * @var string
     */
    protected $label;
    
    /**
     * The entity type manager service.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The entity field manager service.
     *
     * @var \Drupal\Core\Entity\EntityFieldManagerInterface
     */
    protected $entityFieldManager;
    
    /**
     * The field type plugin manager service.
     *
     * @var \Drupal\Core\Field\FieldTypePluginManagerInterface
     */
    protected $fieldTypeManager;
    
    /**
     * The config factory service.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * Constructs a new class instance.
     *
     * @param array $configuration
     *   A configuration array containing information about the plugin instance.
     * @param string $plugin_id
     *   The plugin_id for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   Entity type manager service.
     * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
     *   Entity field manager service.
     * @param \Drupal\Core\Field\FieldTypePluginManagerInterface $field_type_manager
     *   The field type plugin manager service.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory service.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, EntityFieldManagerInterface $entity_field_manager, FieldTypePluginManagerInterface $field_type_manager, ConfigFactoryInterface $config_factory) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->entityTypeManager = $entity_type_manager;
        $this->entityFieldManager = $entity_field_manager;
        $this->fieldTypeManager = $field_type_manager;
        $this->configFactory = $config_factory;
        // Add the default configuration of the media source to the plugin.
        $this->setConfiguration($configuration);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('entity_type.manager'), $container->get('entity_field.manager'), $container->get('plugin.manager.field.field_type'), $container->get('config.factory'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function setConfiguration(array $configuration) {
        $this->configuration = NestedArray::mergeDeep($this->defaultConfiguration(), $configuration);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConfiguration() {
        return $this->configuration;
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'source_field' => '',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMetadata(MediaInterface $media, $attribute_name) {
        switch ($attribute_name) {
            case 'default_name':
                return 'media:' . $media->bundle() . ':' . $media->uuid();
            case 'thumbnail_uri':
                $default_thumbnail_filename = $this->pluginDefinition['default_thumbnail_filename'];
                return $this->configFactory
                    ->get('media.settings')
                    ->get('icon_base_uri') . '/' . $default_thumbnail_filename;
        }
        return NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function calculateDependencies() {
        return [];
    }
    
    /**
     * Get the source field options for the media type form.
     *
     * This returns all fields related to media entities, filtered by the allowed
     * field types in the media source annotation.
     *
     * @return string[]
     *   A list of source field options for the media type form.
     */
    protected function getSourceFieldOptions() {
        // If there are existing fields to choose from, allow the user to reuse one.
        $options = [];
        foreach ($this->entityFieldManager
            ->getFieldStorageDefinitions('media') as $field_name => $field) {
            $allowed_type = in_array($field->getType(), $this->pluginDefinition['allowed_field_types'], TRUE);
            if ($allowed_type && !$field->isBaseField()) {
                $options[$field_name] = $field->getLabel();
            }
        }
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $options = $this->getSourceFieldOptions();
        $form['source_field'] = [
            '#type' => 'select',
            '#title' => $this->t('Field with source information'),
            '#default_value' => $this->configuration['source_field'],
            '#empty_option' => $this->t('- Create -'),
            '#options' => $options,
            '#description' => $this->t('Select the field that will store essential information about the media item. If "Create" is selected a new field will be automatically created.'),
        ];
        if (!$options && $form_state->get('operation') === 'add') {
            $form['source_field']['#access'] = FALSE;
            $field_definition = $this->fieldTypeManager
                ->getDefinition(reset($this->pluginDefinition['allowed_field_types']));
            $form['source_field_message'] = [
                '#markup' => $this->t('%field_type field will be automatically created on this type to store the essential information about the media item.', [
                    '%field_type' => $field_definition['label'],
                ]),
            ];
        }
        elseif ($form_state->get('operation') === 'edit') {
            $form['source_field']['#access'] = FALSE;
            $fields = $this->entityFieldManager
                ->getFieldDefinitions('media', $form_state->get('type')
                ->id());
            $form['source_field_message'] = [
                '#markup' => $this->t('%field_name field is used to store the essential information about the media item.', [
                    '%field_name' => $fields[$this->configuration['source_field']]
                        ->getLabel(),
                ]),
            ];
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
        foreach (array_intersect_key($form_state->getValues(), $this->configuration) as $config_key => $config_value) {
            $this->configuration[$config_key] = $config_value;
        }
        // If no source field is explicitly set, create it now.
        if (empty($this->configuration['source_field'])) {
            $field_storage = $this->createSourceFieldStorage();
            $field_storage->save();
            $this->configuration['source_field'] = $field_storage->getName();
        }
    }
    
    /**
     * Creates the source field storage definition.
     *
     * By default, the first field type listed in the plugin definition's
     * allowed_field_types array will be the generated field's type.
     *
     * @return \Drupal\field\FieldStorageConfigInterface
     *   The unsaved field storage definition.
     */
    protected function createSourceFieldStorage() {
        return $this->entityTypeManager
            ->getStorage('field_storage_config')
            ->create([
            'entity_type' => 'media',
            'field_name' => $this->getSourceFieldName(),
            'type' => reset($this->pluginDefinition['allowed_field_types']),
        ]);
    }
    
    /**
     * Returns the source field storage definition.
     *
     * @return \Drupal\Core\Field\FieldStorageDefinitionInterface|null
     *   The field storage definition or NULL if it doesn't exists.
     */
    protected function getSourceFieldStorage() {
        // Nothing to do if no source field is configured yet.
        $field = $this->configuration['source_field'];
        if ($field) {
            // Even if we do know the name of the source field, there's no
            // guarantee that it exists.
            $fields = $this->entityFieldManager
                ->getFieldStorageDefinitions('media');
            return isset($fields[$field]) ? $fields[$field] : NULL;
        }
        return NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getSourceFieldDefinition(MediaTypeInterface $type) {
        // Nothing to do if no source field is configured yet.
        $field = $this->configuration['source_field'];
        if ($field) {
            // Even if we do know the name of the source field, there is no
            // guarantee that it already exists.
            $fields = $this->entityFieldManager
                ->getFieldDefinitions('media', $type->id());
            return isset($fields[$field]) ? $fields[$field] : NULL;
        }
        return NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function createSourceField(MediaTypeInterface $type) {
        $storage = $this->getSourceFieldStorage() ?: $this->createSourceFieldStorage();
        return $this->entityTypeManager
            ->getStorage('field_config')
            ->create([
            'field_storage' => $storage,
            'bundle' => $type->id(),
            'label' => $this->pluginDefinition['label'],
            'required' => TRUE,
        ]);
    }
    
    /**
     * Determine the name of the source field.
     *
     * @return string
     *   The source field name. If one is already stored in configuration, it is
     *   returned. Otherwise, a new, unused one is generated.
     */
    protected function getSourceFieldName() {
        // Some media sources are using a deriver, so their plugin IDs may contain
        // a separator (usually ':') which is not allowed in field names.
        $base_id = 'field_media_' . str_replace(static::DERIVATIVE_SEPARATOR, '_', $this->getPluginId());
        $tries = 0;
        $storage = $this->entityTypeManager
            ->getStorage('field_storage_config');
        // Iterate at least once, until no field with the generated ID is found.
        do {
            $id = $base_id;
            // If we've tried before, increment and append the suffix.
            if ($tries) {
                $id .= '_' . $tries;
            }
            $field = $storage->load('media.' . $id);
            $tries++;
        } while ($field);
        return $id;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getSourceFieldValue(MediaInterface $media) {
        $source_field = $this->configuration['source_field'];
        if (empty($source_field)) {
            throw new \RuntimeException('Source field for media source is not defined.');
        }
        $items = $media->get($source_field);
        if ($items->isEmpty()) {
            return NULL;
        }
        $field_item = $items->first();
        return $field_item->{$field_item->mainPropertyName()};
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareViewDisplay(MediaTypeInterface $type, EntityViewDisplayInterface $display) {
        $display->setComponent($this->getSourceFieldDefinition($type)
            ->getName(), [
            'label' => 'visually_hidden',
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareFormDisplay(MediaTypeInterface $type, EntityFormDisplayInterface $display) {
        // Make sure the source field is placed just after the "name" basefield.
        $name_component = $display->getComponent('name');
        $source_field_weight = $name_component && isset($name_component['weight']) ? $name_component['weight'] + 5 : -50;
        $display->setComponent($this->getSourceFieldDefinition($type)
            ->getName(), [
            'weight' => $source_field_weight,
        ]);
    }

}