fix: only use username part of mention (#1843)

components/publish/PublishWidget.vue

@@ -71,6 +71,9 @@ const characterCount = $computed(() => {
   // taken from https://github.com/mastodon/mastodon/blob/07f8b4d1b19f734d04e69daeb4c3421ef9767aac/app/lib/text_formatter.rb
   const linkRegex = /(https?:\/\/(www\.)?|xmpp:)\S+/g
 
+  // taken from https://github.com/mastodon/mastodon/blob/af578e/app/javascript/mastodon/features/compose/util/counter.js
+  const countableMentionRegex = /(^|[^/\w])@(([a-z0-9_]+)@[a-z0-9.-]+[a-z0-9]+)/ig
+
   // maximum of 23 chars per link
   // https://github.com/elk-zone/elk/issues/1651
   const maxLength = 23
@@ -78,6 +81,9 @@ const characterCount = $computed(() => {
   for (const [fullMatch] of text.matchAll(linkRegex))
     length -= fullMatch.length - Math.min(maxLength, fullMatch.length)
 
+  for (const [fullMatch, before, handle, username] of text.matchAll(countableMentionRegex))
+    length -= fullMatch.length - (before + username).length - 1 // - 1 for the @
+
   if (draft.mentions) {
     // + 1 is needed as mentions always need a space seperator at the end
     length += draft.mentions.map((mention) => {