FIX: Better handling of position when near the top or bottom

app/assets/javascripts/discourse/components/scrolling-post-stream.js.es6

@@ -88,11 +88,6 @@ export default MountWidget.extend({
 
     const offset = offsetCalculator();
     const topCheck = Math.ceil(windowTop + offset);
-    if (windowTop < offset) {
-      currentPost = 0;
-      const $post = $($posts[0]);
-      percent = windowTop > 0 ? (topCheck - $post.offset().top) / $post.height() : 0;
-    }
 
     // uncomment to debug the eyeline
     // $('.debug-eyeline').css({ height: '1px', width: '100%', backgroundColor: 'blue', position: 'absolute', top: `${topCheck}px` });
@@ -106,15 +101,15 @@ export default MountWidget.extend({
 
       const viewTop = $post.offset().top;
       const postHeight = $post.height();
-      const viewBottom = viewTop + postHeight;
+      const viewBottom = Math.ceil(viewTop + postHeight);
 
       if (viewTop > viewportBottom) { break; }
 
-      if (viewBottom > windowTop && viewTop <= windowBottom) {
+      if (viewBottom >= windowTop && viewTop <= windowBottom) {
         onscreen.push(bottomView);
       }
 
-      if (currentPost === null && (viewTop <= topCheck) && (viewBottom > topCheck)) {
+      if (currentPost === null && (viewTop <= topCheck) && (viewBottom >= topCheck)) {
         percent = (topCheck - viewTop) / postHeight;
         currentPost = bottomView;
       }
@@ -163,10 +158,14 @@ export default MountWidget.extend({
         this.sendAction('currentPostChanged', { post });
       }
 
-      if (percent !== null && this._currentPercent !== percent) {
+      if (percent !== null) {
+        if (percent > 1.0) { percent = 1.0; }
+
+        if (this._currentPercent !== percent) {
           this._currentPercent = percent;
           this.sendAction('currentPostScrolled', { percent });
         }
+      }
 
     } else {
       this._topVisible = null;

app/assets/javascripts/discourse/controllers/topic.js.es6

@@ -211,7 +211,7 @@ export default Ember.Controller.extend(SelectedPostsCount, BufferedContent, {
 
     currentPostScrolled(event) {
       this.appEvents.trigger('topic:current-post-scrolled', {
-        postNumber: this._progressIndex,
+        postIndex: this._progressIndex,
         percent: event.percent
       });
     },

app/assets/javascripts/discourse/lib/offset-calculator.js.es6

@@ -1,8 +1,26 @@
 export default function offsetCalculator() {
   const $header = $('header');
   const $title = $('#topic-title');
-  const windowHeight = $(window).height() - $title.height();
+  const rawWinHeight = $(window).height();
+  const windowHeight = rawWinHeight - $title.height();
   const expectedOffset = $title.height() - $header.find('.contents').height() + (windowHeight / 5);
+  const ideal = $header.outerHeight(true) + ((expectedOffset < 0) ? 0 : expectedOffset);
 
-  return $header.outerHeight(true) + ((expectedOffset < 0) ? 0 : expectedOffset);
+  const $container = $('.posts-wrapper');
+  const topPos = $container.offset().top;
+
+  const scrollTop = $(window).scrollTop();
+  const docHeight = $(document).height();
+  const scrollPercent = (scrollTop / (docHeight-rawWinHeight));
+
+  const inter = topPos - scrollTop + ($container.height() * scrollPercent);
+
+  if (inter > ideal) {
+    const bottom = $('#topic-bottom').offset().top;
+    if (bottom > (scrollTop + rawWinHeight)) {
+      return ideal;
+    }
+  }
+
+  return inter;
 }

app/assets/javascripts/discourse/mixins/docking.js.es6

@@ -8,10 +8,15 @@ export default Ember.Mixin.create({
   init() {
     this._super();
     this.queueDockCheck = () => {
-      Ember.run.debounce(this, this.dockCheck, helper, 5);
+      Ember.run.debounce(this, this.safeDockCheck, 5);
     };
   },
 
+  safeDockCheck() {
+    if (this.isDestroyed || this.isDestroying) { return; }
+    this.dockCheck(helper);
+  },
+
   didInsertElement() {
     this._super();
 

app/assets/javascripts/discourse/widgets/topic-timeline.js.es6

@@ -96,7 +96,7 @@ createWidget('timeline-scrollarea', {
     const topic = attrs.topic;
     const postStream = topic.get('postStream');
     const total = postStream.get('filteredPostsCount');
-    let current = Math.floor(total * percentage);
+    let current = Math.floor(total * percentage) + 1;
 
     if (current < 1) { current = 1; }
     if (current > total) { current = total; }
@@ -168,15 +168,15 @@ createWidget('timeline-scrollarea', {
   },
 
   topicCurrentPostScrolled(event) {
-    const { postNumber, percent } = event;
+    const { postIndex, percent } = event;
 
     // If the post number didn't change keep our scroll position
-    this.state.percentage = this._percentFor(this.attrs.topic, parseFloat(postNumber) + percent);
+    this.state.percentage = this._percentFor(this.attrs.topic, parseFloat(postIndex) + percent);
   },
 
-  _percentFor(topic, postNumber) {
+  _percentFor(topic, postIndex) {
     const total = topic.get('postStream.filteredPostsCount');
-    let result = (postNumber === 1) ? 0.0 : parseFloat(postNumber) / total;
+    let result = parseFloat(postIndex - 1.0) / total;
 
     if (result < 0) { return 0.0; }
     if (result > 1.0) { return 1.0; }