From 37cf2ac60c12a1f81ae0a0f01344a872dce7557a Mon Sep 17 00:00:00 2001
From: Nolan Lawson <nolan@nolanlawson.com>
Date: Thu, 22 Mar 2018 09:35:22 -0700
Subject: [PATCH] try to calculate list offset

---
 .../pseudoVirtualList/PseudoVirtualList.html  | 27 +++++++++++++++---
 .../_components/virtualList/VirtualList.html  | 28 ++++++++++++++++++-
 .../virtualList/virtualListStore.js           | 14 ++++++----
 routes/_pages/accounts/[accountId].html       |  1 -
 routes/_utils/getRectFromEntry.js             | 25 +++++++++++++----
 5 files changed, 78 insertions(+), 17 deletions(-)

diff --git a/routes/_components/pseudoVirtualList/PseudoVirtualList.html b/routes/_components/pseudoVirtualList/PseudoVirtualList.html
index e783e42f..4f735c20 100644
--- a/routes/_components/pseudoVirtualList/PseudoVirtualList.html
+++ b/routes/_components/pseudoVirtualList/PseudoVirtualList.html
@@ -1,4 +1,6 @@
-<div class="pseudo-virtual-list {{shown ? '' : 'hidden'}}" on:initializedVisibleItems ref:node>
+<div class="pseudo-virtual-list {{shown ? '' : 'hidden'}}"
+     on:initializedVisibleItems
+     ref:node>
   {{#if wrappedItems}}
     {{#each wrappedItems as wrappedItem, i @item}}
       <PseudoVirtualListLazyItem
@@ -22,9 +24,8 @@
   }
 </style>
 <script>
-
   import PseudoVirtualListLazyItem from './PseudoVirtualListLazyItem.html'
-  import { getRectFromEntry } from '../../_utils/getRectFromEntry'
+  import { getRectFromEntry, getRootRectFromEntry } from '../../_utils/getRectFromEntry'
   import { mark, stop } from '../../_utils/marks'
   import { pseudoVirtualListStore } from './pseudoVirtualListStore'
 
@@ -42,8 +43,9 @@
       }
       this.store.setForRealm({intersectionStates: intersectionStates})
 
+      let container = document.querySelector(this.get('containerQuery'))
       let intersectionObserver = new IntersectionObserver(this.onIntersection.bind(this), {
-        root: document.querySelector(this.get('containerQuery')),
+        root: container,
         rootMargin: '300% 0px'
       })
       this.set({intersectionObserver})
@@ -55,6 +57,8 @@
           this.fire('initializedVisibleItems')
         }
       })
+
+      this.calculateListOffset()
       stop('PseudoVirtualList oncreate()')
     },
     ondestroy() {
@@ -114,6 +118,21 @@
         intersectionStates = Object.assign(intersectionStates, newIntersectionStates)
         this.store.setForRealm({intersectionStates: intersectionStates})
         stop('onIntersection')
+      },
+      calculateListOffset() {
+        let node = this.refs.node
+        let container = document.querySelector(this.get('containerQuery'))
+        let containerObserver = new IntersectionObserver(entries => {
+          entries.forEach(entry => {
+            let rect = getRectFromEntry(entry)
+            let rootRect = getRootRectFromEntry(entry, container)
+            let listOffset = rect.top - rootRect.top
+            console.log('listOffset', listOffset)
+            this.store.setForRealm({listOffset})
+          })
+          containerObserver.disconnect()
+        }, {root: container})
+        containerObserver.observe(node)
       }
     },
     computed: {
diff --git a/routes/_components/virtualList/VirtualList.html b/routes/_components/virtualList/VirtualList.html
index 1061b761..0da3fe54 100644
--- a/routes/_components/virtualList/VirtualList.html
+++ b/routes/_components/virtualList/VirtualList.html
@@ -1,5 +1,7 @@
 <VirtualListContainer :realm :containerQuery >
-  <div class="virtual-list {{shown ? '' : 'hidden'}}" style="height: {{$height}}px;">
+  <div class="virtual-list {{shown ? '' : 'hidden'}}"
+       style="height: {{$height}}px;"
+       ref:node >
     <VirtualListHeader component="{{headerComponent}}" virtualProps="{{headerProps}}" shown="{{$showHeader}}"/>
     {{#if $visibleItems}}
       {{#each $visibleItems as visibleItem @key}}
@@ -31,6 +33,7 @@
   import throttle from 'lodash/throttle'
   import { mark, stop } from '../../_utils/marks'
   import isEqual from 'lodash/isEqual'
+  import { getRectFromEntry, getRootRectFromEntry } from '../../_utils/getRectFromEntry'
 
   const DISTANCE_FROM_BOTTOM_TO_FIRE = 800
   const SCROLL_EVENT_THROTTLE = 1000
@@ -86,6 +89,8 @@
           this.fireScrollToTop()
         }
       })
+
+      this.calculateListOffset()
     },
     data: () => ({
       component: null
@@ -104,6 +109,27 @@
       scrollTop: ($scrollTop) => $scrollTop,
       // TODO: bug in svelte store, shouldn't need to do this
       allVisibleItemsHaveHeight: ($allVisibleItemsHaveHeight) => $allVisibleItemsHaveHeight,
+    },
+    methods: {
+      calculateListOffset() {
+        let node = this.refs.node
+        let container = document.querySelector(this.get('containerQuery'))
+
+        // TODO: this needs to dynamically update, e.g. after pinned
+        // toots are rendered and thus the distance between the .container
+        // and the .virtual-list has changed.
+        let containerObserver = new IntersectionObserver(entries => {
+          entries.forEach(entry => {
+            let rect = getRectFromEntry(entry)
+            let rootRect = getRootRectFromEntry(entry, container)
+            let listOffset = rect.top - rootRect.top
+            console.log('listOffset', listOffset)
+            this.store.setForRealm({listOffset})
+          })
+          containerObserver.disconnect()
+        }, {root: container})
+        containerObserver.observe(node)
+      }
     }
   }
 </script>
\ No newline at end of file
diff --git a/routes/_components/virtualList/virtualListStore.js b/routes/_components/virtualList/virtualListStore.js
index 6c1a91e9..598ab186 100644
--- a/routes/_components/virtualList/virtualListStore.js
+++ b/routes/_components/virtualList/virtualListStore.js
@@ -20,16 +20,20 @@ virtualListStore.computeForRealm('headerHeight', 0)
 virtualListStore.computeForRealm('scrollTop', 0)
 virtualListStore.computeForRealm('scrollHeight', 0)
 virtualListStore.computeForRealm('offsetHeight', 0)
+virtualListStore.computeForRealm('listOffset', 0)
 virtualListStore.computeForRealm('itemHeights', {})
 
 virtualListStore.compute('rawVisibleItems',
-    ['items', 'scrollTop', 'itemHeights', 'offsetHeight', 'showHeader', 'headerHeight'],
-    (items, scrollTop, itemHeights, offsetHeight, showHeader, headerHeight) => {
+    ['items', 'scrollTop', 'itemHeights', 'offsetHeight', 'showHeader', 'headerHeight', 'listOffset'],
+    (items, scrollTop, itemHeights, offsetHeight, showHeader, headerHeight, listOffset) => {
       window.rawVisibleItemsComputed = (window.rawVisibleItemsComputed || 0) + 1
       mark('compute visibleItems')
       if (!items) {
         return null
       }
+      // listOffset is the offset of the entire list within its scrollable container,
+      // so the effective scrollTop is what the "real" scrollTop is relative to the list.
+      let effectiveScrollTop = scrollTop - listOffset
       let renderBuffer = RENDER_BUFFER_FACTOR * offsetHeight
       let visibleItems = []
       let totalOffset = showHeader ? headerHeight : 0
@@ -40,13 +44,13 @@ virtualListStore.compute('rawVisibleItems',
         let height = itemHeights[key] || 0
         let currentOffset = totalOffset
         totalOffset += height
-        let isAboveViewport = (currentOffset < scrollTop)
+        let isAboveViewport = (currentOffset < effectiveScrollTop)
         if (isAboveViewport) {
-          if ((scrollTop - height - renderBuffer) > currentOffset) {
+          if ((effectiveScrollTop - height - renderBuffer) > currentOffset) {
             continue // above the area we want to render
           }
         } else {
-          if (currentOffset > (scrollTop + offsetHeight + renderBuffer)) {
+          if (currentOffset > (effectiveScrollTop + offsetHeight + renderBuffer)) {
             break // below the area we want to render
           }
         }
diff --git a/routes/_pages/accounts/[accountId].html b/routes/_pages/accounts/[accountId].html
index c11c481b..879a681b 100644
--- a/routes/_pages/accounts/[accountId].html
+++ b/routes/_pages/accounts/[accountId].html
@@ -30,7 +30,6 @@
   export default {
     oncreate() {
       let accountId = this.get('params').accountId
-      let instanceName = this.store.get('currentInstance')
       updateProfileAndRelationship(accountId)
     },
     store: () => store,
diff --git a/routes/_utils/getRectFromEntry.js b/routes/_utils/getRectFromEntry.js
index 8a0837a1..2d959e36 100644
--- a/routes/_utils/getRectFromEntry.js
+++ b/routes/_utils/getRectFromEntry.js
@@ -3,16 +3,29 @@
 
 let hasBoundingRectBug
 
+function rectsAreEqual(rectA, rectB) {
+  return rectA.height === rectB.height &&
+  rectA.top === rectB.top &&
+  rectA.width === rectB.width &&
+  rectA.bottom === rectB.bottom &&
+  rectA.left === rectB.left &&
+  rectA.right === rectB.right
+}
+
 export function getRectFromEntry (entry) {
   if (typeof hasBoundingRectBug !== 'boolean') {
     const boundingRect = entry.target.getBoundingClientRect()
     const observerRect = entry.boundingClientRect
-    hasBoundingRectBug = boundingRect.height !== observerRect.height ||
-      boundingRect.top !== observerRect.top ||
-      boundingRect.width !== observerRect.width ||
-      boundingRect.bottom !== observerRect.bottom ||
-      boundingRect.left !== observerRect.left ||
-      boundingRect.right !== observerRect.right
+    hasBoundingRectBug = !rectsAreEqual(boundingRect, observerRect)
   }
   return hasBoundingRectBug ? entry.target.getBoundingClientRect() : entry.boundingClientRect
 }
+
+export function getRootRectFromEntry (entry, root) {
+  if (typeof hasBoundingRectBug !== 'boolean') {
+    const boundingRect = root.getBoundingClientRect()
+    const rootRect = entry.rootBounds
+    hasBoundingRectBug = !rectsAreEqual(boundingRect, rootRect)
+  }
+  return hasBoundingRectBug ? root.getBoundingClientRect() : entry.rootBounds
+}
\ No newline at end of file