interface FieldItemInterface

interface FieldItemInterface extends ComplexDataInterface {

  /**
   * Defines field item properties.
   *
   * Properties that are required to constitute a valid, non-empty item should
   * be denoted with \Drupal\Core\TypedData\DataDefinition::setRequired().
   *
   * @return \Drupal\Core\TypedData\DataDefinitionInterface[]
   *   An array of property definitions of contained properties, keyed by
   *   property name.
   *
   * @see \Drupal\Core\Field\BaseFieldDefinition
   */
  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition);

  /**
   * Returns the name of the main property, if any.
   *
   * Some field items consist mainly of one main property, e.g. the value of a
   * text field or the target_id of an entity reference. If the field item has
   * no main property, the method returns NULL.
   *
   * @return string|null
   *   The name of the value property, or NULL if there is none.
   *
   * @see \Drupal\Core\Field\BaseFieldDefinition
   */
  public static function mainPropertyName();

  /**
   * Returns the schema for the field.
   *
   * This method is static because the field schema information is needed on
   * creation of the field. FieldItemInterface objects instantiated at that
   * time are not reliable as field settings might be missing.
   *
   * Computed fields having no schema should return an empty array.
   *
   * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $field_definition
   *   The field definition.
   *
   * @return array
   *   An empty array if there is no schema, or an associative array with the
   *   following key/value pairs:
   *   - columns: An array of Schema API column specifications, keyed by column
   *     name. The columns need to be a subset of the properties defined in
   *     propertyDefinitions(). The 'not null' property is ignored if present,
   *     as it is determined automatically by the storage controller depending
   *     on the table layout and the property definitions. It is recommended to
   *     avoid having the column definitions depend on field settings when
   *     possible. No assumptions should be made on how storage engines
   *     internally use the original column name to structure their storage.
   *   - unique keys: (optional) An array of Schema API unique key definitions.
   *     Only columns that appear in the 'columns' array are allowed.
   *   - indexes: (optional) An array of Schema API index definitions. Only
   *     columns that appear in the 'columns' array are allowed. Those indexes
   *     will be used as default indexes. Field definitions can specify
   *     additional indexes or, at their own risk, modify the default indexes
   *     specified by the field-type module. Some storage engines might not
   *     support indexes.
   *   - foreign keys: (optional) An array of Schema API foreign key
   *     definitions. Note, however, that the field data is not necessarily
   *     stored in SQL. Also, the possible usage is limited, as you cannot
   *     specify another field as related, only existing SQL tables,
   *     such as {taxonomy_term_data}.
   *
   * @throws \Drupal\Core\Field\FieldException
   *   Throws an exception if the schema is invalid.
   */
  public static function schema(FieldStorageDefinitionInterface $field_definition);

  /**
   * Gets the entity that field belongs to.
   *
   * @return \Drupal\Core\Entity\FieldableEntityInterface
   *   The entity object.
   */
  public function getEntity();

  /**
   * Gets the langcode of the field values held in the object.
   *
   * @return string
   *   The langcode.
   */
  public function getLangcode();

  /**
   * Gets the field definition.
   *
   * @return \Drupal\Core\Field\FieldDefinitionInterface
   *   The field definition.
   */
  public function getFieldDefinition();

  /**
   * Magic method: Gets a property value.
   *
   * @param string $property_name
   *   The name of the property to get; e.g., 'title' or 'name'.
   *
   * @return mixed
   *   The property value.
   *
   * @throws \InvalidArgumentException
   *   If a non-existent property is accessed.
   */
  public function __get($property_name);

  /**
   * Magic method: Sets a property value.
   *
   * @param string $property_name
   *   The name of the property to set; e.g., 'title' or 'name'.
   * @param mixed $value
   *   The value to set, or NULL to unset the property. Optionally, a typed
   *   data object implementing Drupal\Core\TypedData\TypedDataInterface may be
   *   passed instead of a plain value.
   *
   * @throws \InvalidArgumentException
   *   If a non-existent property is set.
   */
  public function __set($property_name, $value);

  /**
   * Magic method: Determines whether a property is set.
   *
   * @param string $property_name
   *   The name of the property to get; e.g., 'title' or 'name'.
   *
   * @return bool
   *   Returns TRUE if the property exists and is set, FALSE otherwise.
   */
  public function __isset($property_name);

  /**
   * Magic method: Unsets a property.
   *
   * @param string $property_name
   *   The name of the property to get; e.g., 'title' or 'name'.
   */
  public function __unset($property_name);

  /**
   * Returns a renderable array for a single field item.
   *
   * @param string|array $display_options
   *   Can be either the name of a view mode, or an array of display settings.
   *   See EntityViewBuilderInterface::viewField() for more information.
   *
   * @return array
   *   A renderable array for the field item.
   *
   * @see \Drupal\Core\Entity\EntityViewBuilderInterface::viewField()
   * @see \Drupal\Core\Entity\EntityViewBuilderInterface::viewFieldItem()
   * @see \Drupal\Core\Field\FieldItemListInterface::view()
   */
  public function view($display_options = []);

  /**
   * Defines custom presave behavior for field values.
   *
   * This method is called during the process of saving an entity, just before
   * values are written into storage. When storing a new entity, its identifier
   * will not be available yet. This should be used to massage item property
   * values or perform any other operation that needs to happen before values
   * are stored. For instance this is the proper phase to auto-create a new
   * entity for an entity reference field item, because this way it will be
   * possible to store the referenced entity identifier.
   */
  public function preSave();

  /**
   * Defines custom post-save behavior for field values.
   *
   * This method is called during the process of saving an entity, just after
   * values are written into storage. This is useful mostly when the business
   * logic to be implemented always requires the entity identifier, even when
   * storing a new entity. For instance, when implementing circular entity
   * references, the referenced entity will be created on pre-save with a dummy
   * value for the referring entity identifier, which will be updated with the
   * actual one on post-save.
   *
   * In the rare cases where item properties depend on the entity identifier,
   * massaging logic will have to be implemented on post-save and returning TRUE
   * will allow them to be rewritten to the storage with the updated values.
   *
   * @param bool $update
   *   Specifies whether the entity is being updated or created.
   *
   * @return bool
   *   Whether field items should be rewritten to the storage as a consequence
   *   of the logic implemented by the custom behavior.
   */
  public function postSave($update);

  /**
   * Defines custom delete behavior for field values.
   *
   * This method is called during the process of deleting an entity, just before
   * values are deleted from storage.
   */
  public function delete();

  /**
   * Defines custom revision delete behavior for field values.
   *
   * This method is called from during the process of deleting an entity
   * revision, just before the field values are deleted from storage. It is only
   * called for entity types that support revisioning.
   */
  public function deleteRevision();

  /**
   * Generates placeholder field values.
   *
   * Useful when populating site with placeholder content during site building
   * or profiling.
   *
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The field definition.
   *
   * @return array
   *   An associative array of values.
   */
  public static function generateSampleValue(FieldDefinitionInterface $field_definition);

  /**
   * Defines the storage-level settings for this plugin.
   *
   * @return array
   *   A list of default settings, keyed by the setting name.
   */
  public static function defaultStorageSettings();

  /**
   * Defines the field-level settings for this plugin.
   *
   * @return array
   *   A list of default settings, keyed by the setting name.
   */
  public static function defaultFieldSettings();

  /**
   * Returns a short summary of the field's storage-level settings.
   *
   * All information returned by this function should communicate fundamental
   * information about the field storage settings for users. For example, in the
   * case of a reference field, the configured target entity type is a crucial
   * piece of information for understanding how the field can be used.
   *
   * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $storage_definition
   *   The field storage definition.
   *
   * @return array
   *   A renderable array summarizing storage-level settings.
   */
  public static function storageSettingsSummary(FieldStorageDefinitionInterface $storage_definition) : array;

  /**
   * Returns a short summary of the field's field-level settings.
   *
   * All information returned by this function should communicate fundamental
   * information about the field settings for users. For example, in the case of
   * a reference field, the selected target entity bundles are a crucial
   * piece of information for understanding how the field can be used.
   *
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The field entity.
   *
   * @return array
   *   A renderable array summarizing the field-level settings.
   */
  public static function fieldSettingsSummary(FieldDefinitionInterface $field_definition) : array;

  /**
   * Returns a settings array that can be stored as a configuration value.
   *
   * For all use cases where field settings are stored and managed as
   * configuration, this method is used to map from the field type's
   * representation of its settings to a representation compatible with
   * deployable configuration. This includes:
   * - Array keys at any depth must not contain a ".".
   * - Ideally, array keys at any depth are either numeric or can be enumerated
   *   as a "mapping" within the configuration schema. While not strictly
   *   required, this simplifies configuration translation UIs, configuration
   *   migrations between Drupal versions, and other use cases.
   * - To support configuration deployments, references to content entities
   *   must use UUIDs rather than local IDs.
   *
   * An example of a conversion between representations might be an
   * "allowed_values" setting that's structured by the field type as a
   * \Drupal\Core\TypedData\OptionsProviderInterface::getPossibleOptions()
   * result (i.e., values as keys and labels as values). For such a use case,
   * in order to comply with the above, this method could convert that
   * representation to a numerically indexed array whose values are sub-arrays
   * with the schema definable keys of "value" and "label".
   *
   * @param array $settings
   *   The field's settings in the field type's canonical representation.
   *
   * @return array
   *   An array (either the unmodified $settings or a modified representation)
   *   that is suitable for storing as a deployable configuration value.
   *
   * @see \Drupal\Core\Config\Config::set()
   */
  public static function storageSettingsToConfigData(array $settings);

  /**
   * Returns a settings array in the field type's canonical representation.
   *
   * This function does the inverse of static::storageSettingsToConfigData(). It's
   * called when loading a field's settings from a configuration object.
   *
   * @param array $settings
   *   The field's settings, as it is stored within a configuration object.
   *
   * @return array
   *   The settings, in the representation expected by the field type and code
   *   that interacts with it.
   *
   * @see \Drupal\Core\Field\FieldItemInterface::storageSettingsToConfigData()
   */
  public static function storageSettingsFromConfigData(array $settings);

  /**
   * Returns a settings array that can be stored as a configuration value.
   *
   * Same as static::storageSettingsToConfigData(), but for the field's settings.
   *
   * @param array $settings
   *   The field's settings in the field type's canonical representation.
   *
   * @return array
   *   An array (either the unmodified $settings or a modified representation)
   *   that is suitable for storing as a deployable configuration value.
   *
   * @see \Drupal\Core\Field\FieldItemInterface::storageSettingsToConfigData()
   */
  public static function fieldSettingsToConfigData(array $settings);

  /**
   * Returns a settings array in the field type's canonical representation.
   *
   * This function does the inverse of static::fieldSettingsToConfigData().
   * It's called when loading a field's settings from a configuration
   * object.
   *
   * @param array $settings
   *   The field's settings, as it is stored within a configuration
   *   object.
   *
   * @return array
   *   The field settings, in the representation expected by the field type
   *   and code that interacts with it.
   *
   * @see \Drupal\Core\Field\FieldItemInterface::fieldSettingsToConfigData()
   */
  public static function fieldSettingsFromConfigData(array $settings);

  /**
   * Returns a form for the storage-level settings.
   *
   * Invoked from \Drupal\field_ui\Form\FieldStorageConfigEditForm to allow
   * administrators to configure storage-level settings.
   *
   * Field storage might reject settings changes that affect the field
   * storage schema if the storage already has data. When the $has_data
   * parameter is TRUE, the form should not allow changing the settings that
   * take part in the schema() method. It is recommended to set #access to
   * FALSE on the corresponding elements.
   *
   * @param array $form
   *   The form where the settings form is being included in.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The form state of the (entire) configuration form.
   * @param bool $has_data
   *   TRUE if the field already has data, FALSE if not.
   *
   * @return array
   *   The form definition for the field settings.
   */
  public function storageSettingsForm(array &$form, FormStateInterface $form_state, $has_data);

  /**
   * Returns a form for the field-level settings.
   *
   * Invoked from \Drupal\field_ui\Form\FieldConfigEditForm to allow
   * administrators to configure field-level settings.
   *
   * @param array $form
   *   The form where the settings form is being included in.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The form state of the (entire) configuration form.
   *
   * @return array
   *   The form definition for the field settings.
   */
  public function fieldSettingsForm(array $form, FormStateInterface $form_state);

  /**
   * Calculates dependencies for field items.
   *
   * Dependencies are saved in the field configuration entity and are used to
   * determine configuration synchronization order. For example, if the field
   * type's default value is a content entity, this method should return an
   * array of dependencies listing the content entities.
   *
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The field definition.
   *
   * @return array
   *   An array of dependencies grouped by type (config, content, module,
   *   theme). For example:
   *   @code
   *   array(
   *     'config' => array('user.role.anonymous', 'user.role.authenticated'),
   *     'content' => array('node:article:f0a189e6-55fb-47fb-8005-5bef81c44d6d'),
   *     'module' => array('node', 'user'),
   *     'theme' => array('claro'),
   *   );
   *   @endcode
   *
   * @see \Drupal\Core\Config\Entity\ConfigDependencyManager
   * @see \Drupal\Core\Config\Entity\ConfigEntityInterface::getConfigDependencyName()
   */
  public static function calculateDependencies(FieldDefinitionInterface $field_definition);

  /**
   * Calculates dependencies for field items on the storage level.
   *
   * Dependencies are saved in the field storage configuration entity and are
   * used to determine configuration synchronization order. For example, if the
   * field type storage depends on a particular entity type, this method should
   * return an array of dependencies listing the module that provides the entity
   * type.
   *
   * Dependencies returned from this method are stored in field storage
   * configuration and are always considered hard dependencies. If the
   * dependency is removed the field storage configuration must be deleted.
   *
   * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $field_storage_definition
   *   The field storage definition.
   *
   * @return array
   *   An array of dependencies grouped by type (config, content, module,
   *   theme). For example:
   *   @code
   *   [
   *     'config' => ['user.role.anonymous', 'user.role.authenticated'],
   *     'content' => ['node:article:f0a189e6-55fb-47fb-8005-5bef81c44d6d'],
   *     'module' => ['node', 'user'],
   *     'theme' => ['claro'],
   *   ];
   *   @endcode
   *
   * @see \Drupal\Core\Config\Entity\ConfigDependencyManager
   * @see \Drupal\Core\Config\Entity\ConfigEntityInterface::getConfigDependencyName()
   */
  public static function calculateStorageDependencies(FieldStorageDefinitionInterface $field_storage_definition);

  /**
   * Informs the plugin that a dependency of the field will be deleted.
   *
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The field definition.
   * @param array $dependencies
   *   An array of dependencies that will be deleted keyed by dependency type.
   *   Dependency types are, for example, entity, module and theme.
   *
   * @return bool
   *   TRUE if the field definition has been changed as a result, FALSE if not.
   *
   * @see \Drupal\Core\Config\ConfigEntityInterface::onDependencyRemoval()
   */
  public static function onDependencyRemoval(FieldDefinitionInterface $field_definition, array $dependencies);

}