* Basically a copy of {@link _oembed_rest_pre_serve_request()}. Unfortunate
	 * that we have to duplicate this just for a URL check.
	 *
	 * @since 2.6.0
	 *
	 * @param bool                      $served  Whether the request has already been served.
	 * @param WP_HTTP_ResponseInterface $result  Result to send to the client. Usually a WP_REST_Response.
	 * @param WP_REST_Request           $request Request used to generate the response.
	 * @param WP_REST_Server            $server  Server instance.
	 * @return bool
	 */
	public function oembed_xml_request( $served, $result, $request, $server ) {
		$params = $request->get_params();

		if ( ! isset( $params['format'] ) || 'xml' !== $params['format'] ) {
			return $served;
		}

		// Validate URL against our oEmbed endpoint. If not valid, bail.
		// This is our mod to _oembed_rest_pre_serve_request().
		$query_params = $request->get_query_params();
		if ( ! isset( $query_params['url'] ) || false === $this->validate_url_to_item_id( $query_params['url'] ) ) {
			return $served;
		}

		// Embed links inside the request.
		$data = $server->response_to_data( $result, false );

		if ( ! class_exists( 'SimpleXMLElement' ) ) {
			status_header( 501 );
			die( esc_html( get_status_header_desc( 501 ) ) );
		}

		$result = _oembed_create_xml( $data );

		// Bail if there's no XML.
		if ( ! $result ) {
			status_header( 501 );
			return get_status_header_desc( 501 );
		}

		if ( ! headers_sent() ) {
			$server->send_header( 'Content-Type', 'text/xml; charset=' . get_option( 'blog_charset' ) );
		}

		// phpcs:ignore WordPress.Security.EscapeOutput
		echo $result;

		return true;
	}

	/**
	 * Pass our BuddyPress activity permalink for embedding.
	 *
	 * @since 2.6.0
	 *
	 * @see bp_activity_embed_rest_route_callback()
	 *
	 * @param string $retval Current embed URL.
	 * @return string
	 */
	public function filter_embed_url( $retval ) {
		if ( false === isset( buddypress()->{$this->slug_endpoint}->embedurl_in_progress ) && ! $this->is_page() ) {
			return $retval;
		}

		$url = $this->is_page() ? $this->set_permalink() : buddypress()->{$this->slug_endpoint}->embedurl_in_progress;
		$url = trailingslashit( $url );

		// This is for the 'WordPress Embed' block
		// @see bp_activity_embed_comments_button().
		if ( 'the_permalink' !== current_filter() ) {
			$url = add_query_arg( 'embed', 'true', trailingslashit( $url ) );

			// Add custom route args to iframe.
			if ( isset( buddypress()->{$this->slug_endpoint}->embedargs_in_progress ) && buddypress()->{$this->slug_endpoint}->embedargs_in_progress ) {
				foreach( buddypress()->{$this->slug_endpoint}->embedargs_in_progress as $key => $value ) {
					$url = add_query_arg( $key, $value, $url );
				}
			}
		}

		return $url;
	}

	/**
	 * Filters the embed HTML for our BP oEmbed endpoint.
	 *
	 * @since 2.6.0
	 *
	 * @param string $retval Current embed HTML.
	 * @return string
	 */
	public function filter_embed_html( $retval ) {
		if ( false === isset( buddypress()->{$this->slug_endpoint}->embedurl_in_progress ) && ! $this->is_page() ) {
			return $retval;
		}

		$url = $this->set_permalink();

		$item_id = $this->is_page() ? $this->validate_url_to_item_id( $url ) : buddypress()->{$this->slug_endpoint}->embedid_in_progress;

		// Change 'Embedded WordPress Post' to custom title.
		$custom_title = $this->set_iframe_title( $item_id );
		if ( ! empty( $custom_title ) ) {
			$title_pos = strpos( $retval, 'title=' ) + 7;
			$title_end_pos = strpos( $retval, '"', $title_pos );

			$retval = substr_replace( $retval, esc_attr( $custom_title ), $title_pos, $title_end_pos - $title_pos );
		}

		// Add 'max-width' CSS attribute to IFRAME.
		// This will make our oEmbeds responsive.
		if ( false === strpos( $retval, 'style="max-width' ) ) {
			$retval = str_replace( '<iframe', '<iframe style="max-width:100%"', $retval );
		}

		// Remove default <blockquote>.
		$retval = substr( $retval, strpos( $retval, '</blockquote>' ) + 13 );

		// Set up new fallback HTML
		// @todo Maybe use KSES?
		$fallback_html = $this->set_fallback_html( $item_id );

		/**
		 * Dynamic filter to return BP oEmbed HTML.
		 *
		 * @since 2.6.0
		 *
		 * @var string $retval
		 */
		return apply_filters( "bp_{$this->slug_endpoint}_embed_html", $fallback_html . $retval );
	}

	/**
	 * Append our custom slug endpoint to oEmbed endpoint URL.
	 *
	 * Meant to be used as a filter on 'rest_url' before any call to
	 * {@link get_oembed_endpoint_url()} is used.
	 *
	 * @since 2.6.0
	 *
	 * @see add_oembed_discovery_links()
	 *
	 * @param string $retval Current oEmbed endpoint URL.
	 * @return string
	 */
	public function filter_rest_url( $retval = '' ) {
		return $retval . "/{$this->slug_endpoint}";
	}

	/**
	 * Inject content into the embed template.
	 *
	 * @since 2.6.0
	 */
	public function inject_content() {
		if ( ! $this->is_page() ) {
			return;
		}

		$this->content();
	}
}