feat: add rules to recognize user and @here mentions

lib/ExpensiMark.js

@@ -49,6 +49,29 @@ export default class ExpensiMark {
                 replacement: '$1<code>$2</code>$3',
             },
 
+            /**
+             *Apply the hereMention first because the string @here is still a valid mention for the userMention regex.
+             *This ensures that the hereMention is always considered first, even if it is followed by a valid userMention.
+            */
+            {
+                name: 'hereMention',
+                regex: /(^|\s)@here\b/g,
+                replacement: match => `<mention-here>${match}</mention-here>`,
+            },
+
+            /**
+             * This regex matches a valid user mention in a string.
+             * A user mention is a string that starts with the '@' symbol and is followed by a valid username.
+             * The username can contain any combination of letters, numbers, periods, underscores, and hyphens
+             */
+            {
+                // (?<![^~#*-]+) excludes every mention with a character infront except ~, #, * and +
+                // this is to allow bold, italic, strikethrough, quote, heading1 on a mention
+                name: 'userMention',
+                regex: /(?!@here)(?<![^~#*-]+)@([\w.@+-]+(?:\.[\w@+-]+)*\b)/g,
+                replacement: match => `<mention-user>${match}</mention-user>`,
+            },
+
             /**
              * Converts markdown style links to anchor tags e.g. [Expensify]([email protected])
              * We need to convert before the auto email link rule and the manual link rule since it will not try to create a link