DEV: Small refactor to header offset (#15421)

Centralizes calculations in a helper under the site header component.

This also reverts a small CSS change to the composer: since ac79c5ef,
the composer height was not including the grippie, which means that the
composer height was off by 11 pixels, and the topic progress widget was
sometimes being displayed cut off by 11 pixels.

app/assets/javascripts/discourse/app/components/composer-body.js

@@ -8,7 +8,7 @@ import Composer from "discourse/models/composer";
 import KeyEnterEscape from "discourse/mixins/key-enter-escape";
 import afterTransition from "discourse/lib/after-transition";
 import discourseDebounce from "discourse-common/lib/debounce";
-import { headerHeight } from "discourse/components/site-header";
+import { headerOffset } from "discourse/components/site-header";
 import positioningWorkaround from "discourse/lib/safari-hacks";
 
 const START_DRAG_EVENTS = ["touchstart", "mousedown"];
@@ -130,7 +130,7 @@ export default Component.extend(KeyEnterEscape, {
     const currentMousePos = mouseYPos(event);
     let size = this.origComposerSize + (this.lastMousePos - currentMousePos);
 
-    size = Math.min(size, window.innerHeight - headerHeight());
+    size = Math.min(size, window.innerHeight - headerOffset());
     this.movePanels(size);
     this.element.style.height = size ? `${size}px` : "";
   },

app/assets/javascripts/discourse/app/components/site-header.js

@@ -183,13 +183,13 @@ const SiteHeaderComponent = MountWidget.extend(
       }
 
       const headerRect = header.getBoundingClientRect();
-      let headerOffset = headerRect.top + headerRect.height;
+      let headerOffsetCalc = headerRect.top + headerRect.height;
 
       if (window.scrollY < 0) {
-        headerOffset += window.scrollY;
+        headerOffsetCalc += window.scrollY;
       }
 
-      const newValue = `${headerOffset}px`;
+      const newValue = `${headerOffsetCalc}px`;
       if (newValue !== this.currentHeaderOffsetValue) {
         this.currentHeaderOffsetValue = newValue;
         document.documentElement.style.setProperty("--header-offset", newValue);
@@ -389,7 +389,7 @@ const SiteHeaderComponent = MountWidget.extend(
             headerCloak.style.display = "block";
           }
 
-          const menuTop = this.site.mobileView ? headerTop() : headerHeight();
+          const menuTop = this.site.mobileView ? headerTop() : headerOffset();
 
           const winHeightOffset = 16;
           let initialWinHeight = window.innerHeight;
@@ -438,16 +438,13 @@ export default SiteHeaderComponent.extend({
   classNames: ["d-header-wrap"],
 });
 
-export function headerHeight() {
+export function headerOffset() {
-  const header = document.querySelector("header.d-header");
+  return (
-
+    parseInt(
-  // Header may not exist in tests (e.g. in the user menu component test).
+      document.documentElement.style.getPropertyValue("--header-offset"),
-  if (!header) {
+      10
-    return 0;
+    ) || 0
-  }
+  );
-
-  const headerOffsetTop = header.offsetTop ? header.offsetTop : 0;
-  return header.offsetHeight + headerOffsetTop - document.body.scrollTop;
 }
 
 export function headerTop() {

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

@@ -1,5 +1,6 @@
 import Docking from "discourse/mixins/docking";
 import MountWidget from "discourse/components/mount-widget";
+import { headerOffset } from "discourse/components/site-header";
 import { next } from "@ember/runloop";
 import { observes } from "discourse-common/utils/decorators";
 import optionalService from "discourse/lib/optional-service";
@@ -50,7 +51,7 @@ export default MountWidget.extend(Docking, {
     const timelineHeight = (timeline && timeline.offsetHeight) || 400;
 
     const prev = this.dockAt;
-    const posTop = this.headerOffset() + window.pageYOffset;
+    const posTop = headerOffset() + window.pageYOffset;
     const pos = posTop + timelineHeight;
 
     this.dockBottom = false;
@@ -72,12 +73,6 @@ export default MountWidget.extend(Docking, {
     }
   },
 
-  headerOffset() {
-    return (
-      parseInt(document.body.style.getPropertyValue("--header-offset"), 10) || 0
-    );
-  },
-
   didInsertElement() {
     this._super(...arguments);
 

app/assets/javascripts/discourse/app/lib/sticky-avatars.js

@@ -1,6 +1,7 @@
 import { addWidgetCleanCallback } from "discourse/components/mount-widget";
 import Site from "discourse/models/site";
 import { bind } from "discourse-common/utils/decorators";
+import { headerOffset } from "discourse/components/site-header";
 import { schedule } from "@ember/runloop";
 
 export default class StickyAvatars {
@@ -78,11 +79,6 @@ export default class StickyAvatars {
   @bind
   _initIntersectionObserver() {
     schedule("afterRender", () => {
-      const headerOffset =
-        parseInt(document.body.style.getPropertyValue("--header-offset"), 10) ||
-        0;
-      const headerHeight = Math.max(headerOffset, 0);
-
       this.intersectionObserver = new IntersectionObserver(
         (entries) => {
           entries.forEach((entry) => {
@@ -95,13 +91,16 @@ export default class StickyAvatars {
               ?.clientHeight;
             if (
               this.direction === "⬆️" ||
-              postContentHeight > window.innerHeight - headerHeight
+              postContentHeight > window.innerHeight - headerOffset()
             ) {
               entry.target.classList.add(this.stickyClass);
             }
           });
         },
-        { threshold: [0.0, 1.0], rootMargin: `-${headerHeight}px 0px 0px 0px` }
+        {
+          threshold: [0.0, 1.0],
+          rootMargin: `-${headerOffset()}px 0px 0px 0px`,
+        }
       );
     });
   }

app/assets/stylesheets/desktop/compose.scss

@@ -3,7 +3,7 @@
     margin: 0 auto;
     padding: 8px;
     box-sizing: border-box;
-    height: 100%;
+    height: calc(100% - 11px);
     width: 100%;
 
     .submit-panel {
@@ -60,7 +60,6 @@
     cursor: row-resize;
     padding: 4px 0;
     background: var(--tertiary);
-    margin-top: -11px;
 
     &:before {
       content: "";

plugins/discourse-narrative-bot/assets/javascripts/initializers/new-user-narrative.js

@@ -1,5 +1,6 @@
 import { ajax } from "discourse/lib/ajax";
 import discourseDebounce from "discourse-common/lib/debounce";
+import { headerOffset } from "discourse/components/site-header";
 import isElementInViewport from "discourse/lib/is-element-in-viewport";
 import { withPluginApi } from "discourse/lib/plugin-api";
 
@@ -85,17 +86,10 @@ function initialize(api) {
             return;
           }
 
-          const headerOffset =
-            parseInt(
-              getComputedStyle(document.body).getPropertyValue(
-                "--header-offset"
-              ),
-              10
-            ) || 0;
           const viewportOffset = post.getBoundingClientRect();
 
           window.scrollTo({
-            top: window.scrollY + viewportOffset.top - headerOffset,
+            top: window.scrollY + viewportOffset.top - headerOffset(),
             behavior: "smooth",
           });
         },