FEATURE: highlight last visited topic in topic list

app/assets/javascripts/discourse/components/topic-list-item.js.es6

@@ -47,6 +47,10 @@ export default Ember.Component.extend(StringBuffer, {
       }
     });
 
+    if (topic === this.get('lastVisitedTopic')) {
+      classes.push('last-visit');
+    }
+
     return classes.join(' ');
   }.property(),
 

app/assets/javascripts/discourse/components/topic-list.js.es6

@@ -1,10 +1,11 @@
+import computed from 'ember-addons/ember-computed-decorators';
 
 export default Ember.Component.extend({
   tagName: 'table',
   classNames: ['topic-list'],
   showTopicPostBadges: true,
 
-  _observeHideCategory: function(){
+  _init: function(){
     this.addObserver('hideCategory', this.rerender);
     this.addObserver('order', this.rerender);
     this.addObserver('ascending', this.rerender);
@@ -30,6 +31,36 @@ export default Ember.Component.extend({
     return this.get('order') === "op_likes";
   }.property('order'),
 
+  @computed('topics.@each')
+  lastVisitedTopic() {
+    let user = Discourse.User.current();
+    if (!user || !user.previous_visit_at) {
+      return;
+    }
+
+    let prevVisit = user.get('previousVisitAt');
+    let prevTopic, topic;
+    let skipPinned = true;
+
+    this.get('topics').any(t => {
+      if (skipPinned && t.get('pinned')) {
+        return false;
+      }
+      skipPinned = false;
+
+      prevTopic = topic;
+      topic = t;
+      return t.get('bumpedAt') < prevVisit;
+    });
+
+
+    if (!prevTopic || !topic) {
+      return;
+    }
+
+    return prevTopic;
+  },
+
   click(e) {
     var self = this;
     var on = function(sel, callback){

app/assets/javascripts/discourse/models/user.js.es6

@@ -156,6 +156,11 @@ const User = RestModel.extend({
 
   isSuspended: Em.computed.equal('suspended', true),
 
+  @computed("previous_visit_at")
+  previousVisitAt(previous_visit_at) {
+    return new Date(previous_visit_at);
+  },
+
   @computed("suspended_till")
   suspended(suspendedTill) {
     return suspendedTill && moment(suspendedTill).isAfter();

app/assets/javascripts/discourse/templates/components/topic-list.hbs

@@ -26,6 +26,7 @@
                       showOpLikes=showOpLikes
                       expandGloballyPinned=expandGloballyPinned
                       expandAllPinned=expandAllPinned
+                      lastVisitedTopic=lastVisitedTopic
                       selected=selected}}
   {{/each}}
 </tbody>

app/assets/stylesheets/common/base/_topic-list.scss

@@ -31,6 +31,10 @@ html.anon .topic-list a.title:visited:not(.badge-notification) {color: dark-ligh
       margin-top: 2px;
     }
     border-bottom: 1px solid dark-light-diff($primary, $secondary, 90%, -75%);
+
+    &.last-visit {
+      border-bottom: 1px solid scale-color($danger, $lightness: 60%);
+    }
   }
 
   > tbody > tr:first-of-type {

app/serializers/current_user_serializer.rb

@@ -33,7 +33,8 @@ class CurrentUserSerializer < BasicUserSerializer
              :show_queued_posts,
              :read_faq,
              :automatically_unpin_topics,
-             :mailing_list_mode
+             :mailing_list_mode,
+             :previous_visit_at
 
   def include_site_flagged_posts_count?
     object.staff?