wordpress-activitypub/includes/transformer/class-post.php

<?php
namespace Activitypub\Transformer;

use WP_Post;
use Activitypub\Shortcodes;
use Activitypub\Model\Blog;
use Activitypub\Collection\Users;
use Activitypub\Transformer\Base;

use function Activitypub\esc_hashtag;
use function Activitypub\is_single_user;
use function Activitypub\get_enclosures;
use function Activitypub\site_supports_blocks;
use function Activitypub\get_rest_url_by_path;
use function Activitypub\is_user_type_disabled;
use function Activitypub\generate_post_summary;

/**
 * WordPress Post Transformer
 *
 * The Post Transformer is responsible for transforming a WP_Post object into different other
 * Object-Types.
 *
 * Currently supported are:
 *
 * - Activitypub\Activity\Base_Object
 */
class Post extends Base {
	/**
	 * The User as Actor Object.
	 *
	 * @var Activitypub\Activity\Actor
	 */
	private $actor_object = null;

	/**
	 * Returns the ID of the WordPress Post.
	 *
	 * @return int The ID of the WordPress Post
	 */
	public function get_wp_user_id() {
		return $this->wp_object->post_author;
	}

	/**
	 * Change the User-ID of the WordPress Post.
	 *
	 * @return int The User-ID of the WordPress Post
	 */
	public function change_wp_user_id( $user_id ) {
		$this->wp_object->post_author = $user_id;

		return $this;
	}

	/**
	 * Transforms the WP_Post object to an ActivityPub Object
	 *
	 * @see \Activitypub\Activity\Base_Object
	 *
	 * @return \Activitypub\Activity\Base_Object The ActivityPub Object
	 */
	public function to_object() {
		$post = $this->wp_object;
		$object = parent::to_object();

		$published = \strtotime( $post->post_date_gmt );

		$object->set_published( \gmdate( 'Y-m-d\TH:i:s\Z', $published ) );

		$updated = \strtotime( $post->post_modified_gmt );

		if ( $updated > $published ) {
			$object->set_updated( \gmdate( 'Y-m-d\TH:i:s\Z', $updated ) );
		}

		$object->set_content_map(
			array(
				$this->get_locale() => $this->get_content(),
			)
		);

		$object->set_to(
			array(
				'https://www.w3.org/ns/activitystreams#Public',
				$this->get_actor_object()->get_followers(),
			)
		);

		return $object;
	}

	/**
	 * Returns the User-Object of the Author of the Post.
	 *
	 * If `single_user` mode is enabled, the Blog-User is returned.
	 *
	 * @return Activitypub\Activity\Actor The User-Object.
	 */
	protected function get_actor_object() {
		if ( $this->actor_object ) {
			return $this->actor_object;
		}

		$blog_user         = new Blog();
		$this->actor_object = $blog_user;

		if ( is_single_user() ) {
			return $blog_user;
		}

		$user = Users::get_by_id( $this->wp_object->post_author );

		if ( $user && ! is_wp_error( $user ) ) {
			$this->actor_object = $user;
			return $user;
		}

		return $blog_user;
	}

	/**
	 * Returns the ID of the Post.
	 *
	 * @return string The Posts ID.
	 */
	public function get_id() {
		return $this->get_url();
	}

	/**
	 * Returns the URL of the Post.
	 *
	 * @return string The Posts URL.
	 */
	public function get_url() {
		$post = $this->wp_object;

		switch ( \get_post_status( $post ) ) {
			case 'trash':
				$permalink = \get_post_meta( $post->ID, 'activitypub_canonical_url', true );
				break;
			case 'draft':
				// get_sample_permalink is in wp-admin, not always loaded
				if ( ! \function_exists( '\get_sample_permalink' ) ) {
					require_once ABSPATH . 'wp-admin/includes/post.php';
				}
				$sample    = \get_sample_permalink( $post->ID );
				$permalink = \str_replace( array( '%pagename%', '%postname%' ), $sample[1], $sample[0] );
				break;
			default:
				$permalink = \get_permalink( $post );
				break;
		}

		return \esc_url( $permalink );
	}

	/**
	 * Returns the User-URL of the Author of the Post.
	 *
	 * If `single_user` mode is enabled, the URL of the Blog-User is returned.
	 *
	 * @return string The User-URL.
	 */
	protected function get_attributed_to() {
		return $this->get_actor_object()->get_url();
	}

	/**
	 * Generates all Media Attachments for a Post.
	 *
	 * @return array The Attachments.
	 */
	protected function get_attachment() {
		// Remove attachments from drafts.
		if ( 'draft' === \get_post_status( $this->wp_object ) ) {
			return array();
		}

		// Once upon a time we only supported images, but we now support audio/video as well.
		// We maintain the image-centric naming for backwards compatibility.
		$max_media = \intval(
			\apply_filters(
				'activitypub_max_image_attachments',
				\get_option( 'activitypub_max_image_attachments', ACTIVITYPUB_MAX_IMAGE_ATTACHMENTS )
			)
		);

		$media = array(
			'audio' => array(),
			'video' => array(),
			'image' => array(),
		);
		$id    = $this->wp_object->ID;

		// list post thumbnail first if this post has one
		if ( \function_exists( 'has_post_thumbnail' ) && \has_post_thumbnail( $id ) ) {
			$media['image'][] = array( 'id' => \get_post_thumbnail_id( $id ) );
		}

		$media = $this->get_enclosures( $media );

		if ( site_supports_blocks() && \has_blocks( $this->wp_object->post_content ) ) {
			$media = $this->get_block_attachments( $media, $max_media );
		} else {
			$media = $this->get_classic_editor_images( $media, $max_media );
		}

		$media      = self::filter_media_by_object_type( $media, \get_post_format( $this->wp_object ), $this->wp_object );
		$unique_ids = \array_unique( \array_column( $media, 'id' ) );
		$media      = \array_intersect_key( $media, $unique_ids );
		$media      = \array_slice( $media, 0, $max_media );

		/**
		 * Filter the attachment IDs for a post.
		 *
		 * @param array   $media           The media array grouped by type.
		 * @param WP_Post $this->wp_object The post object.
		 *
		 * @return array The filtered attachment IDs.
		 */
		$media = \apply_filters( 'activitypub_attachment_ids', $media, $this->wp_object );

		$attchments = \array_filter( \array_map( array( self::class, 'wp_attachment_to_activity_attachment' ), $media ) );

		/**
		 * Filter the attachments for a post.
		 *
		 * @param array   $attchments      The attachments.
		 * @param WP_Post $this->wp_object The post object.
		 *
		 * @return array The filtered attachments.
		 */
		return \apply_filters( 'activitypub_attachments', $attchments, $this->wp_object );
	}

	/**
	 * Get enclosures for a post.
	 *
	 * @param array $media The media array grouped by type.
	 *
	 * @return array The media array extended with enclosures.
	 */
	public function get_enclosures( $media ) {
		$enclosures = get_enclosures( $this->wp_object->ID );

		if ( ! $enclosures ) {
			return $media;
		}

		foreach ( $enclosures as $enclosure ) {
			// check if URL is an attachment
			$attachment_id = \attachment_url_to_postid( $enclosure['url'] );
			if ( $attachment_id ) {
				$enclosure['id']        = $attachment_id;
				$enclosure['url']       = \wp_get_attachment_url( $attachment_id );
				$enclosure['mediaType'] = \get_post_mime_type( $attachment_id );
			}

			$mime_type       = $enclosure['mediaType'];
			$mime_type_parts = \explode( '/', $mime_type );

			switch ( $mime_type_parts[0] ) {
				case 'image':
					$media['image'][] = $enclosure;
					break;
				case 'audio':
					$media['audio'][] = $enclosure;
					break;
				case 'video':
					$media['video'][] = $enclosure;
					break;
			}
		}

		return $media;
	}

	/**
	 * Get media attachments from blocks. They will be formatted as ActivityPub attachments, not as WP attachments.
	 *
	 * @param array $media     The media array grouped by type.
	 * @param int   $max_media The maximum number of attachments to return.
	 *
	 * @return array The attachments.
	 */
	protected function get_block_attachments( $media, $max_media ) {
		// max media can't be negative or zero
		if ( $max_media <= 0 ) {
			return array();
		}

		$blocks = \parse_blocks( $this->wp_object->post_content );
		$media = self::get_media_from_blocks( $blocks, $media );

		return $media;
	}

	/**
	 * Recursively get media IDs from blocks.
	 * @param array $blocks The blocks to search for media IDs
	 * @param array $media The media IDs to append new IDs to
	 * @param int $max_media The maximum number of media to return.
	 *
	 * @return array The image IDs.
	 */
	protected static function get_media_from_blocks( $blocks, $media ) {
		foreach ( $blocks as $block ) {
			// recurse into inner blocks
			if ( ! empty( $block['innerBlocks'] ) ) {
				$media = self::get_media_from_blocks( $block['innerBlocks'], $media );
			}

			switch ( $block['blockName'] ) {
				case 'core/image':
				case 'core/cover':
					if ( ! empty( $block['attrs']['id'] ) ) {
						$alt   = '';
						$check = preg_match( '/<img.*?alt\s*=\s*([\"\'])(.*?)\1.*>/i', $block['innerHTML'], $match );

						if ( $check ) {
							$alt = $match[2];
						}

						$media['image'][] = array(
							'id'  => $block['attrs']['id'],
							'alt' => $alt,
						);
					}
					break;
				case 'core/audio':
					if ( ! empty( $block['attrs']['id'] ) ) {
						$media['audio'][] = array( 'id' => $block['attrs']['id'] );
					}
					break;
				case 'core/video':
				case 'videopress/video':
					if ( ! empty( $block['attrs']['id'] ) ) {
						$media['video'][] = array( 'id' => $block['attrs']['id'] );
					}
					break;
				case 'jetpack/slideshow':
				case 'jetpack/tiled-gallery':
					if ( ! empty( $block['attrs']['ids'] ) ) {
						$media['image'] = array_merge(
							$media['image'],
							array_map(
								function ( $id ) {
									return array( 'id' => $id );
								},
								$block['attrs']['ids']
							)
						);
					}
					break;
				case 'jetpack/image-compare':
					if ( ! empty( $block['attrs']['beforeImageId'] ) ) {
						$media['image'][] = array( 'id' => $block['attrs']['beforeImageId'] );
					}
					if ( ! empty( $block['attrs']['afterImageId'] ) ) {
						$media['image'][] = array( 'id' => $block['attrs']['afterImageId'] );
					}
					break;
			}
		}

		return $media;
	}

	/**
	 * Get post images from the classic editor.
	 * Note that audio/video attachments are only supported in the block editor.
	 *
	 * @param array $media      The media array grouped by type.
	 * @param int   $max_images The maximum number of images to return.
	 *
	 * @return array The attachments.
	 */
	protected function get_classic_editor_images( $media, $max_images ) {
		// max images can't be negative or zero
		if ( $max_images <= 0 ) {
			return array();
		}

		if ( \count( $media['image'] ) <= $max_images ) {
			if ( \class_exists( '\WP_HTML_Tag_Processor' ) ) {
				$media['image'] = \array_merge( $media['image'], $this->get_classic_editor_image_embeds( $max_images ) );
			} else {
				$media['image'] = \array_merge( $media['image'], $this->get_classic_editor_image_attachments( $max_images ) );
			}
		}

		return $media;
	}

	/**
	 * Get image embeds from the classic editor by parsing HTML.
	 *
	 * @param int $max_images The maximum number of images to return.
	 *
	 * @return array The attachments.
	 */
	protected function get_classic_editor_image_embeds( $max_images ) {
		// if someone calls that function directly, bail
		if ( ! \class_exists( '\WP_HTML_Tag_Processor' ) ) {
			return array();
		}

		// max images can't be negative or zero
		if ( $max_images <= 0 ) {
			return array();
		}

		$images  = array();
		$base    = \wp_get_upload_dir()['baseurl'];
		$content = \get_post_field( 'post_content', $this->wp_object );
		$tags    = new \WP_HTML_Tag_Processor( $content );

		// This linter warning is a false positive - we have to
		// re-count each time here as we modify $images.
		// phpcs:ignore Squiz.PHP.DisallowSizeFunctionsInLoops.Found
		while ( $tags->next_tag( 'img' ) && ( \count( $images ) <= $max_images ) ) {
			$src = $tags->get_attribute( 'src' );

			// If the img source is in our uploads dir, get the
			// associated ID. Note: if there's a -500x500
			// type suffix, we remove it, but we try the original
			// first in case the original image is actually called
			// that. Likewise, we try adding the -scaled suffix for
			// the case that this is a small version of an image
			// that was big enough to get scaled down on upload:
			// https://make.wordpress.org/core/2019/10/09/introducing-handling-of-big-images-in-wordpress-5-3/
			if ( null !== $src && \str_starts_with( $src, $base ) ) {
				$img_id = \attachment_url_to_postid( $src );

				if ( 0 === $img_id ) {
					$count = 0;
					$src = preg_replace( '/-(?:\d+x\d+)(\.[a-zA-Z]+)$/', '$1', $src, 1, $count );
					if ( $count > 0 ) {
						$img_id = \attachment_url_to_postid( $src );
					}
				}

				if ( 0 === $img_id ) {
					$src = preg_replace( '/(\.[a-zA-Z]+)$/', '-scaled$1', $src );
					$img_id = \attachment_url_to_postid( $src );
				}

				if ( 0 !== $img_id ) {
					$images[] = array(
						'id'  => $img_id,
						'alt' => $tags->get_attribute( 'alt' ),
					);
				}
			}
		}

		return $images;
	}

	/**
	 * Get image attachments from the classic editor.
	 * This is imperfect as the contained images aren't necessarily the
	 * same as the attachments.
	 *
	 * @param int $max_images The maximum number of images to return.
	 *
	 * @return array The attachment IDs.
	 */
	protected function get_classic_editor_image_attachments( $max_images ) {
		// max images can't be negative or zero
		if ( $max_images <= 0 ) {
			return array();
		}

		$images = array();
		$query  = new \WP_Query(
			array(
				'post_parent' => $this->wp_object->ID,
				'post_status' => 'inherit',
				'post_type' => 'attachment',
				'post_mime_type' => 'image',
				'order' => 'ASC',
				'orderby' => 'menu_order ID',
				'posts_per_page' => $max_images,
			)
		);

		foreach ( $query->get_posts() as $attachment ) {
			if ( ! \in_array( $attachment->ID, $images, true ) ) {
				$images[] = array( 'id' => $attachment->ID );
			}
		}

		return $images;
	}

	/**
	 * Filter media IDs by object type.
	 *
	 * @param array  $media The media array grouped by type.
	 * @param string $type  The object type.
	 *
	 * @return array The filtered media IDs.
	 */
	protected static function filter_media_by_object_type( $media, $type, $wp_object ) {
		$type = \apply_filters( 'filter_media_by_object_type', \strtolower( $type ), $wp_object );

		if ( ! empty( $media[ $type ] ) ) {
			return $media[ $type ];
		}

		return array_filter( array_merge( ...array_values( $media ) ) );
	}

	/**
	 * Converts a WordPress Attachment to an ActivityPub Attachment.
	 *
	 * @param array $media The Attachment array.
	 *
	 * @return array The ActivityPub Attachment.
	 */
	public static function wp_attachment_to_activity_attachment( $media ) {
		if ( ! isset( $media['id'] ) ) {
			return $media;
		}

		$id              = $media['id'];
		$attachment      = array();
		$mime_type       = \get_post_mime_type( $id );
		$mime_type_parts = \explode( '/', $mime_type );
		// switching on image/audio/video
		switch ( $mime_type_parts[0] ) {
			case 'image':
				$image_size = 'large';

				/**
				 * Filter the image URL returned for each post.
				 *
				 * @param array|false $thumbnail  The image URL, or false if no image is available.
				 * @param int         $id         The attachment ID.
				 * @param string      $image_size The image size to retrieve. Set to 'large' by default.
				 */
				$thumbnail = apply_filters(
					'activitypub_get_image',
					self::get_wordpress_attachment( $id, $image_size ),
					$id,
					$image_size
				);

				if ( $thumbnail ) {
					$image = array(
						'type'      => 'Image',
						'url'       => \esc_url( $thumbnail[0] ),
						'mediaType' => \esc_attr( $mime_type ),
					);

					if ( ! empty( $media['alt'] ) ) {
						$image['name'] = \wp_strip_all_tags( \html_entity_decode( $media['alt'] ) );
					} else {
						$alt = \get_post_meta( $id, '_wp_attachment_image_alt', true );
						if ( $alt ) {
							$image['name'] = \wp_strip_all_tags( \html_entity_decode( $alt ) );
						}
					}

					$attachment = $image;
				}
				break;

			case 'audio':
			case 'video':
				$attachment = array(
					'type'      => 'Document',
					'mediaType' => \esc_attr( $mime_type ),
					'url'       => \esc_url( \wp_get_attachment_url( $id ) ),
					'name'      => \esc_attr( \get_the_title( $id ) ),
				);
				$meta = wp_get_attachment_metadata( $id );
				// height and width for videos
				if ( isset( $meta['width'] ) && isset( $meta['height'] ) ) {
					$attachment['width'] = \esc_attr( $meta['width'] );
					$attachment['height'] = \esc_attr( $meta['height'] );
				}
				// @todo: add `icon` support for audio/video attachments. Maybe use post thumbnail?
				break;
		}

		return \apply_filters( 'activitypub_attachment', $attachment, $id );
	}

	/**
	 * Return details about an image attachment.
	 *
	 * @param int    $id         The attachment ID.
	 * @param string $image_size The image size to retrieve. Set to 'large' by default.
	 *
	 * @return array|false Array of image data, or boolean false if no image is available.
	 */
	protected static function get_wordpress_attachment( $id, $image_size = 'large' ) {
		/**
		 * Hook into the image retrieval process. Before image retrieval.
		 *
		 * @param int    $id         The attachment ID.
		 * @param string $image_size The image size to retrieve. Set to 'large' by default.
		 */
		do_action( 'activitypub_get_image_pre', $id, $image_size );

		$image = \wp_get_attachment_image_src( $id, $image_size );

		/**
		 * Hook into the image retrieval process. After image retrieval.
		 *
		 * @param int    $id         The attachment ID.
		 * @param string $image_size The image size to retrieve. Set to 'large' by default.
		 */
		do_action( 'activitypub_get_image_post', $id, $image_size );

		return $image;
	}

	/**
	 * Returns the ActivityStreams 2.0 Object-Type for a Post based on the
	 * settings and the Post-Type.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#activity-types
	 *
	 * @return string The Object-Type.
	 */
	protected function get_type() {
		$post_format_setting = \get_option( 'activitypub_object_type', ACTIVITYPUB_DEFAULT_OBJECT_TYPE );

		if ( 'wordpress-post-format' !== $post_format_setting ) {
			return \ucfirst( $post_format_setting );
		}

		$has_title = post_type_supports( $this->wp_object->post_type, 'title' );

		if ( ! $has_title ) {
			return 'Note';
		}

		// Default to Article.
		$object_type = 'Note';
		$post_format = 'standard';

		if ( \get_theme_support( 'post-formats' ) ) {
			$post_format = \get_post_format( $this->wp_object );
		}

		$post_type = \get_post_type( $this->wp_object );
		switch ( $post_type ) {
			case 'post':
				switch ( $post_format ) {
					case 'standard':
					case '':
						$object_type = 'Article';
						break;
					default:
						$object_type = 'Note';
						break;
				}
				break;
			case 'page':
				$object_type = 'Page';
				break;
			default:
				$object_type = 'Note';
				break;
		}

		return $object_type;
	}

	/**
	 * Returns a list of Mentions, used in the Post.
	 *
	 * @see https://docs.joinmastodon.org/spec/activitypub/#Mention
	 *
	 * @return array The list of Mentions.
	 */
	protected function get_cc() {
		$cc = array();

		$mentions = $this->get_mentions();
		if ( $mentions ) {
			foreach ( $mentions as $url ) {
				$cc[] = $url;
			}
		}

		return $cc;
	}


	public function get_audience() {
		if ( is_single_user() ) {
			return null;
		} else {
			$blog = new Blog();
			return $blog->get_id();
		}
	}

	/**
	 * Returns a list of Tags, used in the Post.
	 *
	 * This includes Hash-Tags and Mentions.
	 *
	 * @return array The list of Tags.
	 */
	protected function get_tag() {
		$tags = array();

		$post_tags = \get_the_tags( $this->wp_object->ID );
		if ( $post_tags ) {
			foreach ( $post_tags as $post_tag ) {
				$tag = array(
					'type' => 'Hashtag',
					'href' => \esc_url( \get_tag_link( $post_tag->term_id ) ),
					'name' => esc_hashtag( $post_tag->name ),
				);
				$tags[] = $tag;
			}
		}

		$mentions = $this->get_mentions();
		if ( $mentions ) {
			foreach ( $mentions as $mention => $url ) {
				$tag = array(
					'type' => 'Mention',
					'href' => \esc_url( $url ),
					'name' => \esc_html( $mention ),
				);
				$tags[] = $tag;
			}
		}

		return $tags;
	}

	/**
	 * Returns the summary for the ActivityPub Item.
	 *
	 * The summary will be generated based on the user settings and only if the
	 * object type is not set to `note`.
	 *
	 * @return string|null The summary or null if the object type is `note`.
	 */
	protected function get_summary() {
		if ( 'Note' === $this->get_type() ) {
			return null;
		}

		// Remove Teaser from drafts.
		if ( 'draft' === \get_post_status( $this->wp_object ) ) {
			return \__( '(This post is being modified)', 'activitypub' );
		}

		return generate_post_summary( $this->wp_object );
	}

	/**
	 * Returns the title for the ActivityPub Item.
	 *
	 * The title will be generated based on the user settings and only if the
	 * object type is not set to `note`.
	 *
	 * @return string|null The title or null if the object type is `note`.
	 */
	protected function get_name() {
		if ( 'Note' === $this->get_type() ) {
			return null;
		}

		$title = \get_the_title( $this->wp_object->ID );

		if ( $title ) {
			return \wp_strip_all_tags(
				\html_entity_decode(
					$title
				)
			);
		}

		return null;
	}

	/**
	 * Returns the content for the ActivityPub Item.
	 *
	 * The content will be generated based on the user settings.
	 *
	 * @return string The content.
	 */
	protected function get_content() {
		add_filter( 'activitypub_reply_block', '__return_empty_string' );

		// Remove Content from drafts.
		if ( 'draft' === \get_post_status( $this->wp_object ) ) {
			return \__( '(This post is being modified)', 'activitypub' );
		}

		global $post;

		/**
		 * Provides an action hook so plugins can add their own hooks/filters before AP content is generated.
		 *
		 * Example: if a plugin adds a filter to `the_content` to add a button to the end of posts, it can also remove that filter here.
		 *
		 * @param WP_Post $post The post object.
		 */
		do_action( 'activitypub_before_get_content', $post );

		add_filter( 'render_block_core/embed', array( self::class, 'revert_embed_links' ), 10, 2 );

		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
		$post    = $this->wp_object;
		$content = $this->get_post_content_template();

		// Register our shortcodes just in time.
		Shortcodes::register();
		// Fill in the shortcodes.
		setup_postdata( $post );
		$content = do_shortcode( $content );
		wp_reset_postdata();

		$content = \wpautop( $content );
		$content = \preg_replace( '/[\n\r\t]/', '', $content );
		$content = \trim( $content );

		$content = \apply_filters( 'activitypub_the_content', $content, $post );

		// Don't need these any more, should never appear in a post.
		Shortcodes::unregister();

		return $content;
	}

	/**
	 * Gets the template to use to generate the content of the activitypub item.
	 *
	 * @return string The Template.
	 */
	protected function get_post_content_template() {
		$type = \get_option( 'activitypub_post_content_type', 'content' );

		switch ( $type ) {
			case 'excerpt':
				$template = "[ap_excerpt]\n\n[ap_permalink type=\"html\"]";
				break;
			case 'title':
				$template = "<h2>[ap_title]</h2>\n\n[ap_permalink type=\"html\"]";
				break;
			case 'content':
				$template = "[ap_content]\n\n[ap_permalink type=\"html\"]\n\n[ap_hashtags]";
				break;
			default:
				// phpcs:ignore Universal.Operators.DisallowShortTernary.Found
				$template = \get_option( 'activitypub_custom_post_content', ACTIVITYPUB_CUSTOM_POST_CONTENT ) ?: ACTIVITYPUB_CUSTOM_POST_CONTENT;
				break;
		}

		$post_format_setting = \get_option( 'activitypub_object_type', ACTIVITYPUB_DEFAULT_OBJECT_TYPE );

		if ( 'wordpress-post-format' === $post_format_setting ) {
			$template = '[ap_content]';
		}

		return apply_filters( 'activitypub_object_content_template', $template, $this->wp_object );
	}

	/**
	 * Helper function to get the @-Mentions from the post content.
	 *
	 * @return array The list of @-Mentions.
	 */
	protected function get_mentions() {
		return apply_filters(
			'activitypub_extract_mentions',
			array(),
			$this->wp_object->post_content . ' ' . $this->wp_object->post_excerpt,
			$this->wp_object
		);
	}

	/**
	 * Returns the locale of the post.
	 *
	 * @return string The locale of the post.
	 */
	public function get_locale() {
		$post_id = $this->wp_object->ID;
		$lang    = \strtolower( \strtok( \get_locale(), '_-' ) );

		/**
		 * Filter the locale of the post.
		 *
		 * @param string  $lang    The locale of the post.
		 * @param int     $post_id The post ID.
		 * @param WP_Post $post    The post object.
		 *
		 * @return string The filtered locale of the post.
		 */
		return apply_filters( 'activitypub_post_locale', $lang, $post_id, $this->wp_object );
	}

	/**
	 * Returns the in-reply-to URL of the post.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-inreplyto
	 *
	 * @return string|null The in-reply-to URL of the post.
	 */
	public function get_in_reply_to() {
		$blocks = \parse_blocks( $this->wp_object->post_content );

		foreach ( $blocks as $block ) {
			if ( 'activitypub/reply' === $block['blockName'] ) {
				// We only support one reply block per post for now.
				return $block['attrs']['url'];
			}
		}

		return null;
	}

	/**
	 * Transform Embed blocks to block level link.
	 *
	 * Remote servers will simply drop iframe elements, rendering incomplete content.
	 *
	 * @see https://www.w3.org/TR/activitypub/#security-sanitizing-content
	 * @see https://www.w3.org/wiki/ActivityPub/Primer/HTML
	 *
	 * @param string $block_content The block content (html)
	 * @param object $block The block object
	 *
	 * @return string A block level link
	 */
	public static function revert_embed_links( $block_content, $block ) {
		return '<p><a href="' . esc_url( $block['attrs']['url'] ) . '">' . $block['attrs']['url'] . '</a></p>';
	}
}