Rewrite tag links to local friend links

feed-parsers/class-feed-parser-activitypub.php

@@ -1577,6 +1577,25 @@ function ( $m ) use ( &$protected_tags ) {
 
 		$the_content = str_replace( array_keys( $protected_tags ), array_values( $protected_tags ), $the_content );
 
+		// replace all links in <a href="mention hashtag"> with /friends/tag/tagname using the WP_HTML_Tag_Processor.
+		$processor = new \WP_HTML_Tag_Processor( $the_content );
+		while ( $processor->next_tag( array( 'tag_name' => 'a' ) ) ) {
+			if ( ! $processor->get_attribute( 'href' ) ) {
+				continue;
+			}
+			if ( ! $processor->get_attribute( 'class' ) || false === strpos( $processor->get_attribute( 'class' ), 'hashtag' ) ) {
+				// Also consider URLs that contain the word hashtag like https://twitter.com/hashtag/WordPress.
+				if ( false === strpos( $processor->get_attribute( 'href' ), '/hashtag/' ) ) {
+					continue;
+				}
+			}
+			$path_parts = explode( '/', wp_parse_url( $processor->get_attribute( 'href' ), PHP_URL_PATH ) );
+			$tag = array_pop( $path_parts );
+			$processor->set_attribute( 'href', '/friends/tag/' . sanitize_title_with_dashes( $tag ) . '/' );
+		}
+
+		$the_content = $processor->get_updated_html();
+
 		return $the_content;
 	}