From 6bf12562547c8f08f2c6efb4d95196c128b4e707 Mon Sep 17 00:00:00 2001
From: Roc Wong <roc@kiwiberry.nz>
Date: Sun, 13 Feb 2022 01:38:17 +1300
Subject: [PATCH] feat: support non-window scroll parent regarding the scrollTo
 prop

---
 src/Grid.vue    |  8 ++++----
 src/pipeline.ts | 38 +++++++++++++++++++++++---------------
 src/utilites.ts | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 19 deletions(-)

diff --git a/src/Grid.vue b/src/Grid.vue
index db59ca9..aa3b25f 100644
--- a/src/Grid.vue
+++ b/src/Grid.vue
@@ -47,7 +47,7 @@ import {
   fromWindowScroll,
   useObservable,
 } from "./utilites";
-import { PageProvider, pipeline } from "./pipeline";
+import { PageProvider, pipeline, ScrollAction } from "./pipeline";
 import { once } from "ramda";
 import { VueInstance } from "@vueuse/core";
 
@@ -95,7 +95,7 @@ export default defineComponent({
     const {
       buffer$, // the items in the current scanning window
       contentHeight$, // the height of the whole list
-      windowScrollTo$, // the value sent to window.scrollTo()
+      scrollAction$, // the value sent to window.scrollTo()
     } = pipeline({
       // streams of prop
       length$: fromProp(props, "length"),
@@ -113,8 +113,8 @@ export default defineComponent({
 
     onUpdated(
       once(() => {
-        windowScrollTo$.subscribe((next) => {
-          window.scrollTo({ top: next, behavior: "smooth" });
+        scrollAction$.subscribe(([el, top]: ScrollAction) => {
+          el.scrollTo({ top, behavior: "smooth" });
         });
       })
     );
diff --git a/src/pipeline.ts b/src/pipeline.ts
index ace1132..989e3f9 100644
--- a/src/pipeline.ts
+++ b/src/pipeline.ts
@@ -15,7 +15,6 @@ import {
   shareReplay,
   switchMap,
   take,
-  withLatestFrom,
 } from "rxjs";
 import {
   __,
@@ -35,6 +34,7 @@ import {
   without,
   zip,
 } from "ramda";
+import { getVerticalScrollParent } from "./utilites";
 
 export function computeHeightAboveWindowOf(el: Element): number {
   const top = el.getBoundingClientRect().top;
@@ -228,10 +228,12 @@ interface PipelineInput {
   scrollTo$: Observable<number | undefined>;
 }
 
+export type ScrollAction = [Element, number];
+
 interface PipelineOutput {
   buffer$: Observable<InternalItem[]>;
   contentHeight$: Observable<number>;
-  windowScrollTo$: Observable<number>;
+  scrollAction$: Observable<ScrollAction>;
 }
 
 export function pipeline({
@@ -262,20 +264,26 @@ export function pipeline({
   // endregion
 
   // region: scroll to a given item by index
-  const windowScrollTo$ = scrollTo$.pipe(
+  const scrollAction$: Observable<ScrollAction> = scrollTo$.pipe(
     filter(complement(isNil)),
-    switchMap((scrollTo) =>
-      combineLatest([of(scrollTo), resizeMeasurement$, rootResize$]).pipe(
-        take(1)
-      )
+    switchMap<number, Observable<[number, ResizeMeasurement, Element]>>(
+      (scrollTo) =>
+        combineLatest([of(scrollTo), resizeMeasurement$, rootResize$]).pipe(
+          take(1)
+        )
     ),
-    map(
-      ([scrollTo, { columns, itemHeightWithGap }, rootEl]) =>
-        // The offset within the grid
-        Math.floor(scrollTo / columns) * itemHeightWithGap +
-        // The offset of grid root to the document
-        (rootEl.getBoundingClientRect().top +
-          document.documentElement.scrollTop)
+    map<[number, ResizeMeasurement, Element], ScrollAction>(
+      ([scrollTo, { columns, itemHeightWithGap }, rootEl]) => {
+        const verticalScrollEl = getVerticalScrollParent(rootEl);
+
+        const scrollTop =
+          // The offset within the grid container
+          Math.floor((scrollTo - 1) / columns) * itemHeightWithGap +
+          // Offset to the offsetParent
+          (rootEl instanceof HTMLElement ? rootEl.offsetTop : 0);
+
+        return [verticalScrollEl, scrollTop];
+      }
     )
   );
   // endregion
@@ -319,5 +327,5 @@ export function pipeline({
   ).pipe(scan(accumulateBuffer, []));
   // endregion
 
-  return { buffer$, contentHeight$, windowScrollTo$ };
+  return { buffer$, contentHeight$, scrollAction$: scrollAction$ };
 }
diff --git a/src/utilites.ts b/src/utilites.ts
index 953d121..5323c7c 100644
--- a/src/utilites.ts
+++ b/src/utilites.ts
@@ -58,3 +58,35 @@ export function useObservable<H>(observable: Observable<H>): Readonly<Ref<H>> {
 
   return valueRef as Readonly<Ref<H>>;
 }
+
+export function getVerticalScrollParent(
+  element: Element,
+  includeHidden: boolean = false
+): Element {
+  const style = getComputedStyle(element);
+  const excludeStaticParent = style.position === "absolute";
+  const overflowRegex = includeHidden
+    ? /(auto|scroll|hidden)/
+    : /(auto|scroll)/;
+
+  if (style.position === "fixed") {
+    return document.body;
+  }
+
+  for (
+    let parent: Element | null = element;
+    (parent = parent.parentElement);
+
+  ) {
+    const parentStyle = getComputedStyle(parent);
+
+    if (excludeStaticParent && parentStyle.position === "static") {
+      continue;
+    }
+
+    if (overflowRegex.test(parentStyle.overflow + parentStyle.overflowY))
+      return parent;
+  }
+
+  return document.scrollingElement || document.documentElement;
+}