DEV: Dock glimmer-topic-timeline with animation (#20166)

- Move docking logic (intersection / dockAt / etc) from `glimmer-topic-timeline` -> `topic-timeline/container` to live alongside the `postScrolled` hook.
- Toggle `timeline-docked` and `timeline-docked-bottom` when we are at the bottom of a topic. This returns the missing animation to the glimmer-topic-timeline (pictured below).

https://user-images.githubusercontent.com/50783505/216655735-906ccd2a-b77e-45af-9a7b-c22680eca2dc.mov

app/assets/javascripts/discourse/app/components/glimmer-topic-timeline.hbs

@@ -1,5 +1,5 @@
 <div
-  class={{concat "timeline-container " this.classes}}
+  class={{concat-class "timeline-container" this.classes}}
   {{did-insert this.addShowClass}}
 >
   <div class="topic-timeline" {{did-insert this.addUserTip}}>
@@ -13,7 +13,6 @@
       @jumpToPostPrompt={{@jumpToPostPrompt}}
       @fullscreen={{@fullscreen}}
       @mobileView={{@mobileView}}
-      @currentUser={{this.currentUser}}
       @toggleMultiSelect={{@toggleMultiSelect}}
       @showTopicSlowModeUpdate={{@showTopicSlowModeUpdate}}
       @deleteTopic={{@deleteTopic}}
@@ -28,6 +27,8 @@
       @convertToPublicTopic={{@convertToPublicTopic}}
       @convertToPrivateMessage={{@convertToPrivateMessage}}
       @replyToPost={{@replyToPost}}
+      @setDocked={{this.setDocked}}
+      @setDockedBottom={{this.setDockedBottom}}
     />
   </div>
 </div>

app/assets/javascripts/discourse/app/components/glimmer-topic-timeline.js

@@ -4,18 +4,17 @@ import optionalService from "discourse/lib/optional-service";
 import { inject as service } from "@ember/service";
 import { bind } from "discourse-common/utils/decorators";
 import I18n from "I18n";
+import { action } from "@ember/object";
 
 export default class GlimmerTopicTimeline extends Component {
-  @service site;
   @service siteSettings;
   @service currentUser;
 
-  @tracked dockAt = null;
-  @tracked dockBottom = null;
   @tracked enteredIndex = this.args.enteredIndex;
+  @tracked docked = false;
+  @tracked dockedBottom = false;
 
   adminTools = optionalService();
-  intersectionObserver = null;
 
   constructor() {
     super(...arguments);
@@ -23,29 +22,6 @@ export default class GlimmerTopicTimeline extends Component {
     if (this.args.prevEvent) {
       this.enteredIndex = this.args.prevEvent.postIndex - 1;
     }
-
-    if (!this.site.mobileView) {
-      this.intersectionObserver = new IntersectionObserver((entries) => {
-        for (const entry of entries) {
-          const bounds = entry.boundingClientRect;
-
-          if (entry.target.id === "topic-bottom") {
-            this.topicBottom = bounds.y + window.scrollY;
-          } else {
-            this.topicTop = bounds.y + window.scrollY;
-          }
-        }
-      });
-
-      const elements = [
-        document.querySelector(".container.posts"),
-        document.querySelector("#topic-bottom"),
-      ];
-
-      for (let i = 0; i < elements.length; i++) {
-        this.intersectionObserver.observe(elements[i]);
-      }
-    }
   }
 
   get displaySummary() {
@@ -57,15 +33,19 @@ export default class GlimmerTopicTimeline extends Component {
     );
   }
 
+  get createdAt() {
+    return new Date(this.args.model.created_at);
+  }
+
   get classes() {
     const classes = [];
     if (this.args.fullscreen) {
       classes.push("timeline-fullscreen");
     }
 
-    if (this.dockAt) {
+    if (this.docked) {
       classes.push("timeline-docked");
-      if (this.dockBottom) {
+      if (this.dockedBottom) {
         classes.push("timeline-docked-bottom");
       }
     }
@@ -73,10 +53,6 @@ export default class GlimmerTopicTimeline extends Component {
     return classes.join(" ");
   }
 
-  get createdAt() {
-    return new Date(this.args.model.created_at);
-  }
-
   @bind
   addShowClass(element) {
     if (this.args.fullscreen && !this.args.addShowClass) {
@@ -96,10 +72,17 @@ export default class GlimmerTopicTimeline extends Component {
     });
   }
 
-  willDestroy() {
+  @action
-    if (!this.site.mobileView) {
+  setDocked(value) {
-      this.intersectionObserver?.disconnect();
+    if (this.docked !== value) {
-      this.intersectionObserver = null;
+      this.docked = value;
+    }
+  }
+
+  @action
+  setDockedBottom(value) {
+    if (this.dockedBottom !== value) {
+      this.dockedBottom = value;
     }
   }
 }

app/assets/javascripts/discourse/app/components/topic-timeline/container.hbs

@@ -34,7 +34,7 @@
   </div>
 {{/if}}
 
-{{#if (and (not @fullscreen) @currentUser)}}
+{{#if (and (not @fullscreen) this.currentUser)}}
   <div class="timeline-controls">
     <PluginOutlet
       @name="timeline-controls-before"
@@ -130,7 +130,7 @@
       </button>
     {{/if}}
 
-    {{#if (and @currentUser (not @fullscreen))}}
+    {{#if (and this.currentUser (not @fullscreen))}}
       {{#if this.canCreatePost}}
         <button
           type="button"
@@ -156,7 +156,7 @@
       </button>
     {{/if}}
 
-    {{#if @currentUser}}
+    {{#if this.currentUser}}
       <TopicNotificationsButton
         @notificationLevel={{@model.details.notification_level}}
         @topic={{@model}}

app/assets/javascripts/discourse/app/components/topic-timeline/container.js

@@ -8,6 +8,7 @@ import { inject as service } from "@ember/service";
 import { bind, debounce } from "discourse-common/utils/decorators";
 import { actionDescriptionHtml } from "discourse/widgets/post-small-action";
 import domUtils from "discourse-common/utils/dom-utils";
+import { headerOffset } from "discourse/lib/offset-calculator";
 
 export const SCROLLER_HEIGHT = 50;
 const MIN_SCROLLAREA_HEIGHT = 170;
@@ -17,6 +18,7 @@ const LAST_READ_HEIGHT = 20;
 export default class TopicTimelineScrollArea extends Component {
   @service appEvents;
   @service siteSettings;
+  @service currentUser;
 
   @tracked showButton = false;
   @tracked current;
@@ -35,6 +37,8 @@ export default class TopicTimelineScrollArea extends Component {
   @tracked dragging = false;
   @tracked excerpt = "";
 
+  intersectionObserver = null;
+
   constructor() {
     super(...arguments);
 
@@ -48,7 +52,29 @@ export default class TopicTimelineScrollArea extends Component {
       this.appEvents.on("post-stream:posted", this.calculatePosition);
     }
 
+    this.intersectionObserver = new IntersectionObserver((entries) => {
+      for (const entry of entries) {
+        const bounds = entry.boundingClientRect;
+
+        if (entry.target.id === "topic-bottom") {
+          this.topicBottom = bounds.y + window.scrollY;
+        } else {
+          this.topicTop = bounds.y + window.scrollY;
+        }
+      }
+    });
+
+    const elements = [
+      document.querySelector(".container.posts"),
+      document.querySelector("#topic-bottom"),
+    ];
+
+    for (let i = 0; i < elements.length; i++) {
+      this.intersectionObserver.observe(elements[i]);
+    }
+
     this.calculatePosition();
+    this.dockCheck();
   }
 
   get displayTimeLineScrollArea() {
@@ -269,6 +295,7 @@ export default class TopicTimelineScrollArea extends Component {
     this.current = e.postIndex;
     this.percentage = e.percent;
     this.calculatePosition();
+    this.dockCheck();
   }
 
   @action
@@ -276,6 +303,40 @@ export default class TopicTimelineScrollArea extends Component {
     this.args.jumpToIndex(this.lastRead);
   }
 
+  dockCheck() {
+    const timeline = document.querySelector(".timeline-container");
+    const timelineHeight = (timeline && timeline.offsetHeight) || 400;
+
+    const prevDockAt = this.dockAt;
+    const positionTop = headerOffset() + window.pageYOffset;
+    const currentPosition = positionTop + timelineHeight;
+
+    this.dockBottom = false;
+    if (positionTop < this.topicTop) {
+      this.dockAt = parseInt(this.topicTop, 10);
+    } else if (currentPosition > this.topicBottom) {
+      this.dockAt = parseInt(this.topicBottom - timelineHeight, 10);
+      this.dockBottom = true;
+      if (this.dockAt < 0) {
+        this.dockAt = 0;
+      }
+    } else {
+      this.dockAt = null;
+    }
+
+    if (this.dockAt !== prevDockAt) {
+      if (this.dockAt) {
+        this.args.setDocked(true);
+        if (this.dockBottom) {
+          this.args.setDockedBottom(true);
+        }
+      } else {
+        this.args.setDocked(false);
+        this.args.setDockedBottom(false);
+      }
+    }
+  }
+
   commit() {
     this.calculatePosition();
 
@@ -298,6 +359,9 @@ export default class TopicTimelineScrollArea extends Component {
 
   willDestroy() {
     if (!this.args.mobileView) {
+      this.intersectionObserver?.disconnect();
+      this.intersectionObserver = null;
+
       this.appEvents.off("composer:opened", this.calculatePosition);
       this.appEvents.off("composer:resized", this.calculatePosition);
       this.appEvents.off("composer:closed", this.calculatePosition);