PLT-2408 Adds here mention for online users (#3619)

* Added @here mention that notifies online users

* Fixed existing race condition that would sometime cause clients to miss mention count changes

* Added missing localization strings

* Prevent @here from mentioning the user who posted it

webapp/components/suggestion/at_mention_provider.jsx

@@ -43,6 +43,15 @@ class AtMentionSuggestion extends Suggestion {
                 />
             );
             icon = <i className='mention__image fa fa-users fa-2x'/>;
+        } else if (user.username === 'here') {
+            username = 'here';
+            description = (
+                <FormattedMessage
+                    id='suggestion.mention.here'
+                    defaultMessage='Notifies everyone in the channel and online'
+                />
+            );
+            icon = <i className='mention__image fa fa-users fa-2x'/>;
         } else {
             username = user.username;
 
@@ -126,6 +135,9 @@ export default class AtMentionProvider {
                 if ('all'.startsWith(prefix)) {
                     filtered.push({username: 'all'});
                 }
+                if ('here'.startsWith(prefix)) {
+                    filtered.push({username: 'here'});
+                }
             }
 
             filtered.sort((a, b) => {

webapp/i18n/en.json

@@ -1410,6 +1410,7 @@
   "sso_signup.team_error": "Please enter a team name",
   "suggestion.mention.all": "Notifies everyone in the channel, use in {townsquare} to notify the whole team",
   "suggestion.mention.channel": "Notifies everyone in the channel",
+  "suggestion.mention.here": "Notifies everyone in the channel and online",
   "suggestion.search.private": "Private Groups",
   "suggestion.search.public": "Public Channels",
   "team_export_tab.download": "download",

webapp/utils/constants.jsx

@@ -217,7 +217,7 @@ export const Constants = {
         ONLINE: 'online'
     },
 
-    SPECIAL_MENTIONS: ['all', 'channel'],
+    SPECIAL_MENTIONS: ['all', 'channel', 'here'],
     CHARACTER_LIMIT: 4000,
     IMAGE_TYPES: ['jpg', 'gif', 'bmp', 'png', 'jpeg'],
     AUDIO_TYPES: ['mp3', 'wav', 'wma', 'm4a', 'flac', 'aac', 'ogg'],

webapp/utils/text_formatting.jsx

@@ -207,6 +207,7 @@ function highlightCurrentMentions(text, tokens) {
     let output = text;
 
     const mentionKeys = UserStore.getCurrentMentionKeys();
+    mentionKeys.push('@here');
 
     // look for any existing tokens which are self mentions and should be highlighted
     var newTokens = new Map();