<?php

/**
 * @file
 * Documentation related to JSON:API.
 */

use Drupal\Core\Entity\EntityTypeInterface;
use Drupal\Core\Session\AccountInterface;
use Drupal\Core\Field\FieldDefinitionInterface;
use Drupal\Core\Access\AccessResult;

/**
 * @defgroup jsonapi_architecture JSON:API Architecture
 * @{
 *
 * @section overview Overview
 * The JSON:API module is a Drupal-centric implementation of the JSON:API
 * specification. By its own definition, the JSON:API specification "is a
 * specification for how a client should request that resources be fetched or
 * modified, and how a server should respond to those requests. [It] is designed
 * to minimize both the number of requests and the amount of data transmitted
 * between clients and servers. This efficiency is achieved without compromising
 * readability, flexibility, or discoverability."
 *
 * While "Drupal-centric", the JSON:API module is committed to strict compliance
 * with the specification. Wherever possible, the module attempts to implement
 * the specification in a way which is compatible and familiar with the patterns
 * and concepts inherent to Drupal. However, when "Drupalisms" cannot be
 * reconciled with the specification, the module will always choose the
 * implementation most faithful to the specification.
 *
 * @see http://jsonapi.org/
 *
 * @section resources Resources
 * Every unit of data in the specification is a "resource". The specification
 * defines how a client should interact with a server to fetch and manipulate
 * these resources.
 *
 * The JSON:API module maps every entity type + bundle to a resource type.
 * Since the specification does not have a concept of resource type inheritance
 * or composition, the JSON:API module implements different bundles of the same
 * entity type as *distinct* resource types.
 *
 * While it is theoretically possible to expose arbitrary data as resources, the
 * JSON:API module only exposes resources from (config and content) entities.
 * This eliminates the need for another abstraction layer in order implement
 * certain features of the specification.
 *
 * @section relationships Relationships
 * The specification defines semantics for the "relationships" between
 * resources. Since the JSON:API module defines every entity type + bundle as a
 * resource type and does not allow non-entity resources, it is able to use
 * entity references to automatically define and represent the relationships
 * between all resources.
 *
 * @section revisions Resource versioning
 * The JSON:API module exposes entity revisions in a manner inspired by RFC5829:
 * Link Relation Types for Simple Version Navigation between Web Resources.
 *
 * Revision support is not an official part of the JSON:API specification.
 * However, a number of "profiles" are being developed (also not officially part
 * in the spec, but already committed to JSON:API v1.1) to standardize any
 * custom behaviors that the JSON:API module has developed (all of which are
 * still specification-compliant).
 *
 * @see https://github.com/json-api/json-api/pull/1268
 * @see https://github.com/json-api/json-api/pull/1311
 * @see https://www.drupal.org/project/drupal/issues/2955020
 *
 * By implementing revision support as a profile, the JSON:API module should be
 * maximally compatible with other systems.
 *
 * A "version" in the JSON:API module is any revision that was previously, or is
 * currently, a default revision. Not all revisions are considered to be a
 * "version". Revisions that are not marked as a "default" revision are
 * considered "working copies" since they are not usually publicly available
 * and are the revisions to which most new work is applied.
 *
 * When the Content Moderation module is installed, it is possible that the
 * most recent default revision is *not* the latest revision.
 *
 * Requesting a resource version is done via a URL query parameter. It has the
 * following form:
 *
 * @code
 *              version-identifier
 *                    __|__
 *                   /     \
 * ?resourceVersion=foo:bar
 *                   \_/ \_/
 *                    |   |
 *    version-negotiator  |
 *                version-argument
 * @endcode
 *
 * A version identifier is a string with enough information to load a
 * particular revision. The version negotiator component names the negotiation
 * mechanism for loading a revision. Currently, this can be either `id` or
 * `rel`. The `id` negotiator takes a version argument which is the desired
 * revision ID. The `rel` negotiator takes a version argument which is either
 * the string `latest-version` or the string `working-copy`.
 *
 * In the future, other negotiators may be developed, such as negotiators that
 * are UUID-, timestamp-, or workspace-based.
 *
 * To illustrate how a particular entity revision is requested, imagine a node
 * that has a "Published" revision and a subsequent "Draft" revision.
 *
 * Using JSON:API, one could request the "Published" node by requesting
 * `/jsonapi/node/page/{{uuid}}?resourceVersion=rel:latest-version`.
 *
 * To preview an entity that is still a work-in-progress (i.e. the "Draft"
 * revision) one could request
 * `/jsonapi/node/page/{{uuid}}?resourceVersion=rel:working-copy`.
 *
 * To request a specific revision ID, one can request
 * `/jsonapi/node/page/{{uuid}}?resourceVersion=id:{{revision_id}}`.
 *
 * It is not yet possible to request a collection of revisions. This is still
 * under development in issue [#3009588].
 *
 * @see https://www.drupal.org/project/drupal/issues/3009588.
 * @see https://tools.ietf.org/html/rfc5829
 * @see https://www.drupal.org/docs/8/modules/jsonapi/revisions
 *
 * @section translations Resource translations
 *
 * Some multilingual features currently do not work well with JSON:API. See
 * JSON:API modules' multilingual support documentation online for more
 * information on the current status of multilingual support.
 *
 * @see https://www.drupal.org/docs/8/modules/jsonapi/translations
 *
 * @section api API
 * The JSON:API module provides an HTTP API that adheres to the JSON:API
 * specification.
 *
 * The JSON:API module provides *no PHP API to modify its behavior.* It is
 * designed to have zero configuration.
 *
 * - Adding new resources/resource types is unsupported: all entities/entity
 *   types are exposed automatically. If you want to expose more data via the
 *   JSON:API module, the data must be defined as entity. See the "Resources"
 *   section.
 * - Custom field type normalization is not supported because the JSON:API
 *   specification requires specific representations for resources (entities),
 *   attributes on resources (non-entity reference fields) and relationships
 *   between those resources (entity reference fields). A field contains
 *   properties, and properties are of a certain data type. All non-internal
 *   properties on a field are normalized.
 * - The same data type normalizers as those used by core's Serialization and
 *   REST modules are also used by the JSON:API module.
 * - All available authentication mechanisms are allowed.
 *
 * @section tests Test Coverage
 * The JSON:API module comes with extensive unit and kernel tests. But most
 * importantly for end users, it also has comprehensive integration tests. These
 * integration tests are designed to:
 *
 * - ensure a great DX (Developer Experience)
 * - detect regressions and normalization changes before shipping a release
 * - guarantee 100% of Drupal core's entity types work as expected
 *
 * The integration tests test the same common cases and edge cases using
 * \Drupal\Tests\jsonapi\Functional\ResourceTestBase, which is a base class
 * subclassed for every entity type that Drupal core ships with. It is ensured
 * that 100% of Drupal core's entity types are tested thanks to
 * \Drupal\Tests\jsonapi\Functional\TestCoverageTest.
 *
 * Custom entity type developers can get the same assurances by subclassing it
 * for their entity types.
 *
 * @section bc Backwards Compatibility
 * PHP API: there is no PHP API except for three security-related hooks. This
 * means that this module's implementation details are entirely free to
 * change at any time.
 *
 * Note that *normalizers are internal implementation details.* While
 * normalizers are services, they are *not* to be used directly. This is due to
 * the design of the Symfony Serialization component, not because the JSON:API
 * module wanted to publicly expose services.
 *
 * HTTP API: URLs and JSON response structures are considered part of this
 * module's public API. However, inconsistencies with the JSON:API specification
 * will be considered bugs. Fixes which bring the module into compliance with
 * the specification are *not* guaranteed to be backwards-compatible. When
 * compliance bugs are found, clients are expected to be made compatible with
 * both the pre-fix and post-fix representations.
 *
 * What this means for developing consumers of the HTTP API is that *clients
 * should be implemented from the specification first and foremost.* This should
 * mitigate implicit dependencies on implementation details or inconsistencies
 * with the specification that are specific to this module.
 *
 * To help develop compatible clients, every response indicates the version of
 * the JSON:API specification used under its "jsonapi" key. Future releases
 * *may* increment the minor version number if the module implements features of
 * a later specification. Remember that the specification stipulates that future
 * versions *will* remain backwards-compatible as only additions may be
 * released.
 *
 * @see http://jsonapi.org/faq/#what-is-the-meaning-of-json-apis-version
 *
 * Tests: subclasses of base test classes may contain BC breaks between minor
 * releases, to allow minor releases to A) comply better with the JSON:API spec,
 * B) guarantee that all resource types (and therefore entity types) function as
 * expected, C) update to future versions of the JSON:API spec.
 *
 * @}
 */

/**
 * @addtogroup hooks
 * @{
 */

/**
 * Controls access when filtering by entity data via JSON:API.
 *
 * This module supports filtering by resource object attributes referenced by
 * relationship fields. For example, a site may add a "Favorite Animal" field
 * to user entities, which would permit the following filtered query:
 * @code
 * /jsonapi/node/article?filter[uid.field_favorite_animal]=llama
 * @endcode
 * This query would return articles authored by users whose favorite animal is a
 * llama. However, the information about a user's favorite animal should not be
 * available to users without the "access user profiles" permission. The same
 * must hold true even if that user is referenced as an article's author.
 * Therefore, access to filter by this data must be restricted so that access
 * cannot be bypassed via a JSON:API filtered query.
 *
 * As a rule, clients should only be able to filter by data that they can
 * view.
 *
 * Conventionally, `$entity->access('view')` is how entity access is checked.
 * This call invokes the corresponding hooks. However, these access checks
 * require an `$entity` object. This means that they cannot be called prior to
 * executing a database query.
 *
 * In order to safely enable filtering across a relationship, modules
 * responsible for entity access must do two things:
 * - Implement this hook (or hook_jsonapi_ENTITY_TYPE_filter_access()) and
 *   return an array of AccessResults keyed by the named entity subsets below.
 * - If the AccessResult::allowed() returned by the above hook does not provide
 *   enough granularity (for example, if access depends on a bundle field value
 *   of the entity being queried), then hook_query_TAG_alter() must be
 *   implemented using the 'entity_access' or 'ENTITY_TYPE_access' query tag.
 *   See node_query_node_access_alter() for an example.
 *
 * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
 *   The entity type of the entity to be filtered upon.
 * @param \Drupal\Core\Session\AccountInterface $account
 *   The account for which to check access.
 *
 * @return \Drupal\Core\Access\AccessResultInterface[]
 *   An array keyed by a constant which identifies a subset of entities. For
 *   each subset, the value is one of the following access results:
 *   - AccessResult::allowed() if all entities within the subset (potentially
 *     narrowed by hook_query_TAG_alter() implementations) are viewable.
 *   - AccessResult::forbidden() if any entity within the subset is not
 *     viewable.
 *   - AccessResult::neutral() if the implementation has no opinion.
 *   The supported subsets for which an access result may be returned are:
 *   - JSONAPI_FILTER_AMONG_ALL: all entities of the given type.
 *   - JSONAPI_FILTER_AMONG_PUBLISHED: all published entities of the given type.
 *   - JSONAPI_FILTER_AMONG_ENABLED: all enabled entities of the given type.
 *   - JSONAPI_FILTER_AMONG_OWN: all entities of the given type owned by the
 *     user for whom access is being checked.
 *   See the documentation of the above constants for more information about
 *   each subset.
 *
 * @see hook_jsonapi_ENTITY_TYPE_filter_access()
 */
function hook_jsonapi_entity_filter_access(EntityTypeInterface $entity_type, AccountInterface $account) {
  // For every entity type that has an admin permission, allow access to filter
  // by all entities of that type to users with that permission.
  if ($admin_permission = $entity_type->getAdminPermission()) {
    return ([
      JSONAPI_FILTER_AMONG_ALL => AccessResult::allowedIfHasPermission($account, $admin_permission),
    ]);
  }
}

/**
 * Controls access to filtering by entity data via JSON:API.
 *
 * This is the entity-type-specific variant of
 * hook_jsonapi_entity_filter_access(). For implementations with logic that is
 * specific to a single entity type, it is recommended to implement this hook
 * rather than the generic hook_jsonapi_entity_filter_access() hook, which is
 * called for every entity type.
 *
 * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
 *   The entity type of the entities to be filtered upon.
 * @param \Drupal\Core\Session\AccountInterface $account
 *   The account for which to check access.
 *
 * @return \Drupal\Core\Access\AccessResultInterface[]
 *   The array of access results, keyed by subset. See
 *   hook_jsonapi_entity_filter_access() for details.
 *
 * @see hook_jsonapi_entity_filter_access()
 */
function hook_jsonapi_ENTITY_TYPE_filter_access(EntityTypeInterface $entity_type, AccountInterface $account) {
  return ([
    JSONAPI_FILTER_AMONG_ALL => AccessResult::allowedIfHasPermission($account, 'administer llamas'),
    JSONAPI_FILTER_AMONG_PUBLISHED => AccessResult::allowedIfHasPermission($account, 'view all published llamas'),
    JSONAPI_FILTER_AMONG_OWN => AccessResult::allowedIfHasPermissions($account, ['view own published llamas', 'view own unpublished llamas'], 'AND'),
  ]);
}

/**
 * Restricts filtering access to the given field.
 *
 * Some fields may contain sensitive information. In these cases, modules are
 * supposed to implement hook_entity_field_access(). However, this hook receives
 * an optional `$items` argument and often must return AccessResult::neutral()
 * when `$items === NULL`. This is because access may or may not be allowed
 * based on the field items or based on the entity on which the field is
 * attached (if the user is the entity owner, for example).
 *
 * Since JSON:API must check field access prior to having a field item list
 * instance available (access must be checked before a database query is made),
 * it is not sufficiently secure to check field 'view' access alone.
 *
 * This hook exists so that modules which cannot return
 * AccessResult::forbidden() from hook_entity_field_access() can still secure
 * JSON:API requests where necessary.
 *
 * If a corresponding implementation of hook_entity_field_access() *can* be
 * forbidden for one or more values of the `$items` argument, this hook *MUST*
 * return AccessResult::forbidden().
 *
 * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
 *   The field definition of the field to be filtered upon.
 * @param \Drupal\Core\Session\AccountInterface $account
 *   The account for which to check access.
 *
 * @return \Drupal\Core\Access\AccessResultInterface
 *   The access result.
 */
function hook_jsonapi_entity_field_filter_access(FieldDefinitionInterface $field_definition, AccountInterface $account) {
  if ($field_definition->getTargetEntityTypeId() === 'node' && $field_definition->getName() === 'field_sensitive_data') {
    $has_sufficient_access = FALSE;
    foreach (['administer nodes', 'view all sensitive field data'] as $permission) {
      $has_sufficient_access = $has_sufficient_access ?: $account->hasPermission($permission);
    }
    return AccessResult::forbiddenIf(!$has_sufficient_access)->cachePerPermissions();
  }
  return AccessResult::neutral();
}

/**
 * @} End of "addtogroup hooks".
 */
