From 4f1c26961d8e127488174a0172be380b75f30dce Mon Sep 17 00:00:00 2001
From: Evan Henley <evan.henley@gmail.com>
Date: Mon, 4 Dec 2017 13:27:54 -0600
Subject: [PATCH] refactor scroll logic (#1428)

---
 .../src/utils/scroll-to-selection.js          | 88 +++++++++++++++----
 1 file changed, 71 insertions(+), 17 deletions(-)

diff --git a/packages/slate-react/src/utils/scroll-to-selection.js b/packages/slate-react/src/utils/scroll-to-selection.js
index 44c0f24f7..25c340fda 100644
--- a/packages/slate-react/src/utils/scroll-to-selection.js
+++ b/packages/slate-react/src/utils/scroll-to-selection.js
@@ -20,13 +20,13 @@ const OVERFLOWS = [
  * @param {el} Element
  */
 
-function findScrollContainer(el) {
-  const window = getWindow(el)
+function findScrollContainer(el, window) {
   let parent = el.parentNode
   let scroller
 
   while (!scroller) {
     if (!parent.parentNode) break
+
     const style = window.getComputedStyle(parent)
     const { overflowY } = style
 
@@ -38,7 +38,14 @@ function findScrollContainer(el) {
     parent = parent.parentNode
   }
 
-  if (!scroller) return window
+  // COMPAT: Because Chrome does not allow doucment.body.scrollTop, we're
+  // assuming that window.scrollTo() should be used if the scrollable element
+  // turns out to be document.body or document.documentElement. This will work
+  // unless body is intentionally set to scrollable by restricting its height
+  // (e.g. height: 100vh).
+  if (!scroller) {
+    return window.document.body
+  }
 
   return scroller
 }
@@ -53,41 +60,88 @@ function scrollToSelection(selection) {
   if (!selection.anchorNode) return
 
   const window = getWindow(selection.anchorNode)
-  const scroller = findScrollContainer(selection.anchorNode)
-  const isWindow = scroller == window
+  const scroller = findScrollContainer(selection.anchorNode, window)
+  const isWindow = scroller == window.document.body || scroller == window.document.documentElement
   const backward = isBackward(selection)
+
   const range = selection.getRangeAt(0)
-  const rect = range.getBoundingClientRect()
+  let selectionRect = range.getBoundingClientRect()
+
+  // COMPAT: range.getBoundingClientRect() returns 0s in Safari when range is
+  // collapsed. Expanding the range by 1 is a relatively effective workaround
+  // for vertical scroll, although horizontal may be off by 1 character.
+  // https://bugs.webkit.org/show_bug.cgi?id=138949
+  // https://bugs.chromium.org/p/chromium/issues/detail?id=435438
+  if (range.collapsed && selectionRect.top == 0 && selectionRect.height == 0) {
+    if (range.startOffset == 0) {
+      range.setEnd(range.endContainer, 1)
+    } else {
+      range.setStart(range.startContainer, range.startOffset - 1)
+    }
+
+    selectionRect = range.getBoundingClientRect()
+  }
+
   let width
   let height
   let yOffset
   let xOffset
+  let scrollerTop = 0
+  let scrollerLeft = 0
+  let scrollerBordersY = 0
+  let scrollerBordersX = 0
 
   if (isWindow) {
-    const { innerWidth, innerHeight, pageYOffset, pageXOffset } = scroller
+    const { innerWidth, innerHeight, pageYOffset, pageXOffset } = window
     width = innerWidth
     height = innerHeight
     yOffset = pageYOffset
     xOffset = pageXOffset
   } else {
     const { offsetWidth, offsetHeight, scrollTop, scrollLeft } = scroller
+    const {
+      borderTopWidth,
+      borderBottomWidth,
+      borderLeftWidth,
+      borderRightWidth,
+    } = window.getComputedStyle(scroller)
+
     const scrollerRect = scroller.getBoundingClientRect()
     width = offsetWidth
     height = offsetHeight
-    yOffset = scrollTop - scrollerRect.top
-    xOffset = scrollLeft - scrollerRect.left
+    scrollerTop = scrollerRect.top + parseInt(borderTopWidth, 10)
+    scrollerLeft = scrollerRect.left + parseInt(borderLeftWidth, 10)
+    scrollerBordersY = parseInt(borderTopWidth, 10) + parseInt(borderBottomWidth, 10)
+    scrollerBordersX = parseInt(borderLeftWidth, 10) + parseInt(borderRightWidth, 10)
+    yOffset = scrollTop
+    xOffset = scrollLeft
   }
 
-  const top = (backward ? rect.top : rect.bottom) + yOffset
-  const left = (backward ? rect.left : rect.right) + xOffset
+  const selectionFocusTop = backward ? selectionRect.top : selectionRect.bottom
+  const selectionTop = selectionFocusTop + yOffset - scrollerTop
 
-  const x = left < yOffset || (width + xOffset) < left
-    ? left - width / 2
-    : xOffset
+  const selectionFocusLeft = backward ? selectionRect.left : selectionRect.right
+  const selectionLeft = selectionFocusLeft + xOffset - scrollerLeft
+
+  let x = xOffset
+  let y = yOffset
+
+  if (selectionLeft < xOffset) {
+    // selection to the left of viewport
+    x = selectionLeft
+  } else if (selectionLeft + selectionRect.width + scrollerBordersX > xOffset + width) {
+    // selection to the right of viewport
+    x = selectionLeft + scrollerBordersX - width
+  }
+
+  if (selectionTop < yOffset) {
+    // selection above viewport
+    y = selectionTop
+  } else if (selectionTop + selectionRect.height + scrollerBordersY > yOffset + height) {
+    // selection below viewport
+    y = selectionTop + scrollerBordersY + selectionRect.height - height
+  }
 
-  const y = top < yOffset || (height + yOffset) < top
-    ? top - height / 2
-    : yOffset
 
   if (isWindow) {
     window.scrollTo(x, y)