fix emails in chat (#10912)

* additional regex checks to ignore the <tag attribute="content">

* extract highlightUsers method - add test

* refactor highlight regex

* refactor the regex without `lookbehind`

* remove unneeded regex

test/client/unit/specs/libs/highlightUsers.js

@@ -0,0 +1,32 @@
+import {highlightUsers} from '../../../../../website/client/libs/highlightUsers';
+import habiticaMarkdown from 'habitica-markdown';
+
+describe('highlightUserAndEmail', () => {
+  it('highlights displayname', () => {
+    const text = 'hello @displayedUser';
+
+    const result = highlightUsers(text, 'user', 'displayedUser');
+    expect(result).to.contain('<span class="at-highlight at-text">@displayedUser</span>');
+  });
+
+  it('highlights username', () => {
+    const text = 'hello @user';
+
+    const result = highlightUsers(text, 'user', 'displayedUser');
+    expect(result).to.contain('<span class="at-highlight at-text">@user</span>');
+  });
+
+  it('highlights email with username', () => {
+    const text = habiticaMarkdown.render('hello hello@user.com');
+
+    const result = highlightUsers(text, 'user', 'displayedUser');
+    expect(result).to.contain('>hello<span class="at-highlight at-text">@user</span>.com</a>');
+  });
+
+  it('highlights any mention', () => {
+    const text = habiticaMarkdown.render('hello y.@user.com other words');
+
+    const result = highlightUsers(text, 'test', 'displayedUser');
+    expect(result).to.contain('<span class="at-text">@user</span>');
+  });
+});