isions_controller->get_parent( $parent_id );
	}

	/**
	 * Checks if a given request has access to get autosaves.
	 *
	 * @since 5.0.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return true|WP_Error True if the request has read access, WP_Error object otherwise.
	 */
	public function get_items_permissions_check( $request ) {
		$parent = $this->get_parent( $request['id'] );
		if ( is_wp_error( $parent ) ) {
			return $parent;
		}

		if ( ! current_user_can( 'edit_post', $parent->ID ) ) {
			return new WP_Error(
				'rest_cannot_read',
				__( 'Sorry, you are not allowed to view autosaves of this post.' ),
				array( 'status' => rest_authorization_required_code() )
			);
		}

		return true;
	}

	/**
	 * Checks if a given request has access to create an autosave revision.
	 *
	 * Autosave revisions inherit permissions from the parent post,
	 * check if the current user has permission to edit the post.
	 *
	 * @since 5.0.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return true|WP_Error True if the request has access to create the item, WP_Error object otherwise.
	 */
	public function create_item_permissions_check( $request ) {
		$id = $request->get_param( 'id' );

		if ( empty( $id ) ) {
			return new WP_Error(
				'rest_post_invalid_id',
				__( 'Invalid item ID.' ),
				array( 'status' => 404 )
			);
		}

		return $this->parent_controller->update_item_permissions_check( $request );
	}

	/**
	 * Creates, updates or deletes an autosave revision.
	 *
	 * @since 5.0.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return WP_REST_Response|WP_Error Response object on success, or WP_Error object on failure.
	 */
	public function create_item( $request ) {

		if ( ! defined( 'WP_RUN_CORE_TESTS' ) && ! defined( 'DOING_AUTOSAVE' ) ) {
			define( 'DOING_AUTOSAVE', true );
		}

		$post = $this->get_parent( $request['id'] );

		if ( is_wp_error( $post ) ) {
			return $post;
		}

		$prepared_post     = $this->parent_controller->prepare_item_for_database( $request );
		$prepared_post->ID = $post->ID;
		$user_id           = get_current_user_id();

		// We need to check post lock to ensure the original author didn't leave their browser tab open.
		if ( ! function_exists( 'wp_check_post_lock' ) ) {
			require_once ABSPATH . 'wp-admin/includes/post.php';
		}

		$post_lock = wp_check_post_lock( $post->ID );
		$is_draft  = 'draft' === $post->post_status || 'auto-draft' === $post->post_status;

		if ( $is_draft && (int) $post->post_author === $user_id && ! $post_lock ) {
			/*
			 * Draft posts for the same author: autosaving updates the post and does not create a revision.
			 * Convert the post object to an array and add slashes, wp_update_post() expects escaped array.
			 */
			$autosave_id = wp_update_post( wp_slash( (array) $prepared_post ), true );
		} else {
			// Non-draft posts: create or update the post autosave. Pass the meta data.
			$autosave_id = $this->create_post_autosave( (array) $prepared_post, (array) $request->get_param( 'meta' ) );
		}

		if ( is_wp_error( $autosave_id ) ) {
			return $autosave_id;
		}

		$autosave = get_post( $autosave_id );
		$request->set_param( 'context', 'edit' );

		$response = $this->prepare_item_for_response( $autosave, $request );
		$response = rest_ensure_response( $response );

		return $response;
	}

	/**
	 * Get the autosave, if the ID is valid.
	 *
	 * @since 5.0.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return WP_Post|WP_Error Revision post object if ID is valid, WP_Error otherwise.
	 */
	public function get_item( $request ) {
		$parent_id = (int) $request->get_param( 'parent' );

		if ( $parent_id <= 0 ) {
			return new WP_Error(
				'rest_post_invalid_id',
				__( 'Invalid post parent ID.' ),
				array( 'status' => 404 )
			);
		}

		$autosave = wp_get_post_autosave( $parent_id );

		if ( ! $autosave ) {
			return new WP_Error(
				'rest_post_no_autosave',
				__( 'There is no autosave revision for this post.' ),
				array( 'status' => 404 )
			);
		}

		$response = $this->prepare_item_for_response( $autosave, $request );
		return $response;
	}

	/**
	 * Gets a collection of autosaves using wp_get_post_autosave.
	 *
	 * Contains the user's autosave, for empty if it doesn't exist.
	 *
	 * @since 5.0.0
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return WP_REST_Response|WP_Error Response object on success, or WP_Error object on failure.
	 */
	public function get_items( $request ) {
		$parent = $this->get_parent( $request['id'] );
		if ( is_wp_error( $parent ) ) {
			return $parent;
		}

		if ( $request->is_method( 'HEAD' ) ) {
			// Return early as this handler doesn't add any response headers.
			return new WP_REST_Response( array() );
		}
		$response  = array();
		$parent_id = $parent->ID;
		$revisions = wp_get_post_revisions( $parent_id, array( 'check_enabled' => false ) );

		foreach ( $revisions as $revision ) {
			if ( str_contains( $revision->post_name, "{$parent_id}-autosave" ) ) {
				$data       = $this->prepare_item_for_response( $revision, $request );
				$response[] = $this->prepare_response_for_collection( $data );
			}
		}

		return rest_ensure_response( $response );
	}


	/**
	 * Retrieves the autosave's schema, conforming to JSON Schema.
	 *
	 * @since 5.0.0
	 *
	 * @return array Item schema data.
	 */
	public function get_item_schema() {
		if ( $this->schema ) {
			return $this->add_additional_fields_schema( $this->schema );
		}

		$schema = $this->revisions_controller->get_item_schema();

		$schema['properties']['preview_link'] = array(
			'description' => __( 'Preview link for the post.' ),
			'type'        => 'string',
			'format'      => 'uri',
			'context'     => array( 'edit' ),
			'readonly'    => true,
		);

		$this->schema = $schema;

		return $this->add_additional_fields_schema( $this->schema );
	}

	/**
	 * Creates autosave for the specified post.
	 *
	 * From wp-admin/post.php.
	 *
	 * @since 5.0.0
	 * @since 6.4.0 The `$meta` parameter was added.
	 *
	 * @param array $post_data Associative array containing the post data.
	 * @param array $meta      Associative array containing the post meta data.
	 * @return mixed The autosave revision ID or WP_Error.
	 */
	public function create_post_autosave( $post_data, array $meta = array() ) {

		$post_id = (int) $post_data['ID'];
		$post    = get_post( $post_id );

		if ( is_wp_error( $post ) ) {
			return $post;
		}

		// Only create an autosave when it is different from the saved post.
		$autosave_is_different = false;
		$new_autosave          = _wp_post_revision_data( $post_data, true );

		foreach ( array_intersect( array_keys( $new_autosave ), array_keys( _wp_post_revision_fields( $post ) ) ) as $field ) {
			if ( normalize_whitespace( $new_autosave[ $field ] ) !== normalize_whitespace( $post->$field ) ) {
				$autosave_is_different = true;
				break;
			}
		}

		// Check if meta values have changed.
		if ( ! empty( $meta ) ) {
			$revisioned_meta_keys = wp_post_revision_meta_keys( $post->post_type );
			foreach ( $revisioned_meta_keys as $meta_key ) {
				// get_metadata_raw is used to avoid retrieving the default value.
				$old_meta = get_metadata_raw( 'post', $post_id, $meta_key, true );
				$new_meta = isset( $meta[ $meta_key ] ) ? $meta[ $meta_key ] : '';

				if ( $new_meta !== $old_meta ) {
					$autosave_is_different = true;
					break;
				}
			}
		}

		$user_id = get_current_user_id();

		// Store one autosave per author. If there is already an autosave, overwrite it.
		$old_autosave = wp_get_post_autosave( $post_id, $user_id );

		if ( ! $autosave_is_different && $old_autosave ) {
			// Nothing to save, return the existing autosave.
			return $old_autosave->ID;
		}

		if ( $old_autosave ) {
			$new_autosave['ID']          = $old_autosave->ID;
			$new_autosave['post_author'] = $user_id;

			/** This filter is documented in wp-admin/post.php */
			do_action( 'wp_creating_autosave', $new_autosave );

			// wp_update_post() expects escaped array.
			$revision_id = wp_update_post( wp_slash( $new_autosave ) );
		} else {
			// Create the new autosave as a special post revision.
			$revision_id = _wp_put_post_revision( $post_data, true );
		}

		if ( is_wp_error( $revision_id ) || 0 === $revision_id ) {
			return $revision_id;
		}

		// Attached any passed meta values that have revisions enabled.
		if ( ! empty( $meta ) ) {
			foreach ( $revisioned_meta_keys as $meta_key ) {
				if ( isset( $meta[ $meta_key ] ) ) {
					update_metadata( 'post', $revision_id, $meta_key, wp_slash( $meta[ $meta_key ] ) );
				}
			}
		}

		return $revision_id;
	}

	/**
	 * Prepares the revision for the REST response.
	 *
	 * @since 5.0.0
	 * @since 5.9.0 Renamed `$post` to `$item` to match parent class for PHP 8 named parameter support.
	 *
	 * @param WP_Post         $item    Post revision object.
	 * @param WP_REST_Request $request Request object.
	 * @return WP_REST_Response Response object.
	 */
	public function prepare_item_for_response( $item, $request ) {
		// Restores the more descriptive, specific name for use within this method.
		$post = $item;

		// Don't prepare the response body for HEAD requests.
		if ( $request->is_method( 'HEAD' ) ) {
			/** This filter is documented in wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php */
			return apply_filters( 'rest_prepare_autosave', new WP_REST_Response( array() ), $post, $request );
		}
		$response = $this->revisions_controller->prepare_item_for_response( $post, $request );
		$fields   = $this->get_fields_for_response( $request );

		if ( in_array( 'preview_link', $fields, true ) ) {
			$parent_id          = wp_is_post_autosave( $post );
			$preview_post_id    = false === $parent_id ? $post->ID : $parent_id;
			$preview_query_args = array();

			if ( false !== $parent_id ) {
				$preview_query_args['preview_id']    = $parent_id;
				$preview_query_args['preview_nonce'] = wp_create_nonce( 'post_preview_' . $parent_id );
			}

			$response->data['preview_link'] = get_preview_post_link( $preview_post_id, $preview_query_args );
		}

		$context        = ! empty( $request['context'] ) ? $request['context'] : 'view';
		$response->data = $this->add_additional_fields_to_object( $response->data, $request );
		$response->data = $this->filter_response_by_context( $response->data, $context );

		/**
		 * Filters a revision returned from the REST API.
		 *
		 * Allows modification of the revision right before it is returned.
		 *
		 * @since 5.0.0
		 *
		 * @param WP_REST_Response $response The response object.
		 * @param WP_Post          $post     The original revision object.
		 * @param WP_REST_Request  $request  Request used to generate the response.
		 */
		return apply_filters( 'rest_prepare_autosave', $response, $post, $request );
	}

	/**
	 * Retrieves the query params for the autosaves collection.
	 *
	 * @since 5.0.0
	 *
	 * @return array Collection parameters.
	 */
	public function get_collection_params() {
		return array(
			'context' => $this->get_context_param( array( 'default' => 'view' ) ),
		);
	}
}