Keep last seen indicator around for five seconds

Helps calm the user experience a little more, makes it easier to
understand what's happening when messages are coming in quickly.

FREEBIE

js/views/conversation_view.js

@@ -251,8 +251,11 @@
             }
         },
 
-        removeLastSeenIndicator: function() {
-            if (this.lastSeenIndicator) {
+        removeLastSeenIndicator: function(options) {
+            options = options || {};
+            _.defaults(options, {force: false});
+
+            if (this.lastSeenIndicator && (options.force || this.lastSeenIndicator.isOldEnough())) {
                 this.lastSeenIndicator.remove();
                 this.lastSeenIndicator = null;
             }
@@ -275,7 +278,7 @@
             options = options || {};
             _.defaults(options, {scroll: true});
 
-            this.removeLastSeenIndicator();
+            this.removeLastSeenIndicator({force: true});
 
             var oldestUnread = this.model.messageCollection.find(function(model) {
                 return model.get('unread');
@@ -341,6 +344,12 @@
             this.model.messageCollection.add(message, {merge: true});
             message.setToExpire();
 
+            // if the last seen indicator is old enough, it will go away.
+            // if it isn't, we want to make sure it's up to date
+            if (this.lastSeenIndicator) {
+                this.lastSeenIndicator.increment(1);
+            }
+
             if (!this.isHidden() && !window.isFocused()) {
                 this.updateLastSeenIndicator({scroll: false});
             }

js/views/last_seen_indicator_view.js

@@ -5,12 +5,27 @@
     'use strict';
     window.Whisper = window.Whisper || {};
 
+    var FIVE_SECONDS = 5 * 1000;
+
     Whisper.LastSeenIndicatorView = Whisper.View.extend({
         className: 'last-seen-indicator-view',
         templateName: 'last-seen-indicator-view',
         initialize: function(options) {
           options = options || {};
           this.count = options.count || 0;
+          this.start = Date.now();
+        },
+
+        isOldEnough: function() {
+          var now = Date.now();
+          if (now - this.start > FIVE_SECONDS) {
+            return true;
+          }
+        },
+
+        increment: function(count) {
+            this.count += count;
+            this.render();
         },
 
         render_attributes: function() {

test/views/last_seen_indicator_view_test.js

@@ -9,4 +9,11 @@ describe('LastSeenIndicatorView', function() {
         assert.equal(view.count, 10);
     });
 
+    it('increments count', function() {
+        var view = new Whisper.LastSeenIndicatorView({count: 4});
+        assert.equal(view.count, 4);
+        view.increment(3);
+        assert.equal(view.count, 7);
+    });
+
 });