From f19ba2ea20f5dfb2acdcc3c3235c22da5ed3e747 Mon Sep 17 00:00:00 2001
From: Andrew Kingston <andrew@kingston.dev>
Date: Thu, 2 Mar 2023 11:08:48 +0000
Subject: [PATCH] Improve scroll logic and handle horizontal wheel events

---
 .../src/components/sheet/ScrollOverlay.svelte |  75 ++++-------
 .../src/components/sheet/Sheet.svelte         |   4 +-
 .../sheet/SheetScrollWrapper.svelte           | 123 ++++--------------
 .../src/components/sheet/stores/scroll.js     |  78 +++++++++++
 4 files changed, 126 insertions(+), 154 deletions(-)
 create mode 100644 packages/frontend-core/src/components/sheet/stores/scroll.js

diff --git a/packages/frontend-core/src/components/sheet/ScrollOverlay.svelte b/packages/frontend-core/src/components/sheet/ScrollOverlay.svelte
index 7506318072..2362e0b29b 100644
--- a/packages/frontend-core/src/components/sheet/ScrollOverlay.svelte
+++ b/packages/frontend-core/src/components/sheet/ScrollOverlay.svelte
@@ -1,13 +1,20 @@
 <script>
   import { getContext } from "svelte"
-  import { domDebounce, debounce, throttle } from "../../utils/utils"
+  import { domDebounce } from "../../utils/utils"
 
-  const { scroll, bounds, rows, cellHeight, columns, stickyColumn } =
-    getContext("spreadsheet")
+  const {
+    scroll,
+    bounds,
+    cellHeight,
+    stickyColumn,
+    contentHeight,
+    maxScrollTop,
+    contentWidth,
+    maxScrollLeft,
+  } = getContext("spreadsheet")
 
   // Bar config
   const barOffset = 4
-  const padding = 180
 
   // State for dragging bars
   let initialMouse
@@ -21,61 +28,23 @@
 
   // Calculate V scrollbar size and offset
   // Terminology is the same for both axes:
-  //   contentX - the size of the rendered content, including padding
   //   renderX - the space available to render the bar in, edge to edge
-  //   barX - the length of the bar
   //   availX - the space available to render the bar in, until the edge
-  //   barX - the offset of the bar
-  $: contentHeight = ($rows.length + 1) * cellHeight + padding
   $: renderHeight = height - 2 * barOffset
-  $: barHeight = Math.max(50, (height / contentHeight) * renderHeight)
+  $: barHeight = Math.max(50, (height / $contentHeight) * renderHeight)
   $: availHeight = renderHeight - barHeight
-  $: maxScrollTop = Math.max(contentHeight - height, 0)
-  $: barTop = barOffset + cellHeight + availHeight * (scrollTop / maxScrollTop)
+  $: barTop = barOffset + cellHeight + availHeight * (scrollTop / $maxScrollTop)
 
   // Calculate H scrollbar size and offset
-  $: contentWidth = calculateContentWidth($columns, $stickyColumn) + padding
-  $: totalWidth = width + 40 + $stickyColumn?.width || 0
+  $: totalWidth = width + 40 + ($stickyColumn?.width || 0)
   $: renderWidth = totalWidth - 2 * barOffset
-  $: barWidth = Math.max(50, (totalWidth / contentWidth) * renderWidth)
+  $: barWidth = Math.max(50, (totalWidth / $contentWidth) * renderWidth)
   $: availWidth = renderWidth - barWidth
-  $: maxScrollLeft = Math.max(contentWidth - totalWidth, 0)
-  $: barLeft = barOffset + availWidth * (scrollLeft / maxScrollLeft)
+  $: barLeft = barOffset + availWidth * (scrollLeft / $maxScrollLeft)
 
   // Calculate whether to show scrollbars or not
-  $: showVScrollbar = contentHeight > height
-  $: showHScrollbar = contentWidth > totalWidth
-
-  // Ensure scroll state never goes invalid, which can happen when changing
-  // rows or tables
-  $: {
-    if (scrollTop > maxScrollTop) {
-      setTimeout(() => {
-        scroll.update(state => ({
-          ...state,
-          top: maxScrollTop,
-        }))
-      })
-    }
-  }
-  $: {
-    if (scrollLeft > maxScrollLeft) {
-      setTimeout(() => {
-        scroll.update(state => ({
-          ...state,
-          left: maxScrollLeft,
-        }))
-      })
-    }
-  }
-
-  const calculateContentWidth = (columns, stickyColumn) => {
-    let width = 40 + stickyColumn?.width
-    columns.forEach(col => {
-      width += col.width
-    })
-    return width
-  }
+  $: showVScrollbar = $contentHeight > height
+  $: showHScrollbar = $contentWidth > totalWidth
 
   // V scrollbar drag handlers
   const startVDragging = e => {
@@ -88,10 +57,10 @@
   const moveVDragging = domDebounce(e => {
     const delta = e.clientY - initialMouse
     const weight = delta / availHeight
-    const newScrollTop = initialScroll + weight * maxScrollTop
+    const newScrollTop = initialScroll + weight * $maxScrollTop
     scroll.update(state => ({
       ...state,
-      top: Math.max(0, Math.min(newScrollTop, maxScrollTop)),
+      top: Math.max(0, Math.min(newScrollTop, $maxScrollTop)),
     }))
   })
   const stopVDragging = () => {
@@ -110,10 +79,10 @@
   const moveHDragging = domDebounce(e => {
     const delta = e.clientX - initialMouse
     const weight = delta / availWidth
-    const newScrollLeft = initialScroll + weight * maxScrollLeft
+    const newScrollLeft = initialScroll + weight * $maxScrollLeft
     scroll.update(state => ({
       ...state,
-      left: Math.max(0, Math.min(newScrollLeft, maxScrollLeft)),
+      left: Math.max(0, Math.min(newScrollLeft, $maxScrollLeft)),
     }))
   })
   const stopHDragging = () => {
diff --git a/packages/frontend-core/src/components/sheet/Sheet.svelte b/packages/frontend-core/src/components/sheet/Sheet.svelte
index f5bdfbf18c..fa01a155a4 100644
--- a/packages/frontend-core/src/components/sheet/Sheet.svelte
+++ b/packages/frontend-core/src/components/sheet/Sheet.svelte
@@ -1,5 +1,3 @@
-<svelte:options immutable={true} />
-
 <script>
   import { setContext } from "svelte"
   import { writable } from "svelte/store"
@@ -7,6 +5,7 @@
   import { createViewportStores } from "./stores/viewport"
   import { createRowsStore } from "./stores/rows"
   import { createColumnsStores } from "./stores/columns"
+  import { createScrollStores } from "./stores/scroll"
   import SheetControls from "./SheetControls.svelte"
   import SheetBody from "./SheetBody.svelte"
   import SheetRow from "./SheetRow.svelte"
@@ -59,6 +58,7 @@
   context = { ...context, rows, schema }
   const { columns, stickyColumn } = createColumnsStores(context)
   context = { ...context, columns, stickyColumn }
+  context = { ...context, ...createScrollStores(context) }
   const { visibleRows, visibleColumns } = createViewportStores(context)
   context = { ...context, visibleRows, visibleColumns }
   const { reorder } = createReorderStores(context)
diff --git a/packages/frontend-core/src/components/sheet/SheetScrollWrapper.svelte b/packages/frontend-core/src/components/sheet/SheetScrollWrapper.svelte
index c3093d1b0f..42b1e4b324 100644
--- a/packages/frontend-core/src/components/sheet/SheetScrollWrapper.svelte
+++ b/packages/frontend-core/src/components/sheet/SheetScrollWrapper.svelte
@@ -5,84 +5,25 @@
     cellHeight,
     scroll,
     bounds,
-    rows,
     columns,
     visibleRows,
     visibleColumns,
     hoveredRowId,
+    maxScrollTop,
+    maxScrollLeft,
   } = getContext("spreadsheet")
 
   export let scrollVertically = true
   export let scrollHorizontally = true
   export let wheelInteractive = true
 
-  $: scrollTop = $scroll.top
-  $: scrollLeft = $scroll.left
-  $: offsetY = -1 * (scrollTop % cellHeight)
   $: hiddenWidths = calculateHiddenWidths($visibleColumns)
-  $: offsetX = -1 * scrollLeft + hiddenWidths
-  $: rowCount = $visibleRows.length
-  $: contentWidth = calculateContentWidth($visibleColumns, scrollHorizontally)
-  $: contentHeight = calculateContentHeight(rowCount, scrollVertically)
-  $: innerStyle = getInnerStyle(
-    offsetX,
-    offsetY,
-    contentWidth,
-    contentHeight,
-    scrollHorizontally,
-    scrollVertically
-  )
-  $: outerStyle = getOuterStyle(
-    offsetX,
-    offsetY,
-    contentWidth,
-    contentHeight,
-    scrollHorizontally,
-    scrollVertically
-  )
-
-  const getInnerStyle = (
-    offsetX,
-    offsetY,
-    contentWidth,
-    contentHeight,
-    scrollH,
-    scrollV
-  ) => {
-    if (!scrollH) {
-      offsetX = 0
-    }
-    if (!scrollV) {
-      offsetY = 0
-    }
-    let style = `--offset-x:${offsetX}px;--offset-y:${offsetY}px;`
-    // if (scrollH && contentWidth) {
-    //   style += `width:${contentWidth}px;`
-    // }
-    // if (scrollV && contentHeight) {
-    //   style += `height:${contentHeight}px;`
-    // }
-    return style
-  }
-
-  const getOuterStyle = (
-    offsetX,
-    offsetY,
-    contentWidth,
-    contentHeight,
-    scrollH,
-    scrollV
-  ) => {
-    let style = ""
-    // if (scrollV) {
-    //   style += `height:${contentHeight + offsetY}px;`
-    // }
-    // if (scrollH) {
-    //   style += `width:${contentWidth + offsetX}px;`
-    // }
-    return style
-  }
+  $: scrollLeft = $scroll.left
+  $: scrollTop = $scroll.top
+  $: offsetX = scrollHorizontally ? -1 * scrollLeft + hiddenWidths : 0
+  $: offsetY = scrollVertically ? -1 * (scrollTop % cellHeight) : 0
 
+  // Calculates with total width of all columns currently not rendered
   const calculateHiddenWidths = visibleColumns => {
     const idx = visibleColumns[0]?.idx
     let width = 0
@@ -94,37 +35,23 @@
     return width
   }
 
-  const calculateContentWidth = (columns, scroll) => {
-    if (!scroll) {
-      return null
-    }
-    let width = 0
-    columns.forEach(col => (width += col.width))
-    return width
-  }
-
-  const calculateContentHeight = (rowCount, scroll) => {
-    if (!scroll) {
-      return null
-    }
-    return (rowCount + 1) * cellHeight
-  }
-
+  // Handles a wheel even and updates the scroll offsets
   const handleWheel = e => {
-    const step = cellHeight * 3
-    const deltaY = e.deltaY < 0 ? -1 : 1
-    const offset = deltaY * step
-    let newScrollTop = scrollTop
-    newScrollTop += offset
-    newScrollTop = Math.min(
-      newScrollTop,
-      ($rows.length + 1) * cellHeight - $bounds.height + 180
-    )
-    newScrollTop = Math.max(0, newScrollTop)
-    scroll.update(state => ({
-      ...state,
+    e.preventDefault()
+
+    // Calculate new scroll top
+    let newScrollTop = scrollTop + e.deltaY
+    newScrollTop = Math.max(0, Math.min(newScrollTop, $maxScrollTop))
+
+    // Calculate new scroll left
+    let newScrollLeft = scrollLeft + e.deltaX
+    newScrollLeft = Math.max(0, Math.min(newScrollLeft, $maxScrollLeft))
+
+    // Update state
+    scroll.set({
+      left: newScrollLeft,
       top: newScrollTop,
-    }))
+    })
 
     // Hover row under cursor
     const y = e.clientY - $bounds.top + (newScrollTop % cellHeight)
@@ -133,15 +60,13 @@
   }
 </script>
 
-<div class="outer" on:wheel|passive={wheelInteractive ? handleWheel : null}>
-  <div class="inner" style={innerStyle}>
+<div class="outer" on:wheel={wheelInteractive ? handleWheel : null}>
+  <div class="inner" style="--offset-x:{offsetX}px;--offset-y:{offsetY}px;">
     <slot />
   </div>
 </div>
 
 <style>
-  div {
-  }
   .outer {
     min-width: 100%;
     min-height: 100%;
diff --git a/packages/frontend-core/src/components/sheet/stores/scroll.js b/packages/frontend-core/src/components/sheet/stores/scroll.js
new file mode 100644
index 0000000000..ee08f415dd
--- /dev/null
+++ b/packages/frontend-core/src/components/sheet/stores/scroll.js
@@ -0,0 +1,78 @@
+import { derived } from "svelte/store"
+
+export const createScrollStores = context => {
+  const { scroll, rows, columns, stickyColumn, bounds, cellHeight } = context
+  const padding = 180
+
+  // Memoize store primitives
+  const scrollTop = derived(scroll, $scroll => $scroll.top)
+  const scrollLeft = derived(scroll, $scroll => $scroll.left)
+
+  // Derive vertical limits
+  const height = derived(bounds, $bounds => $bounds.height, 0)
+  const width = derived(bounds, $bounds => $bounds.width, 0)
+  const contentHeight = derived(
+    rows,
+    $rows => ($rows.length + 1) * cellHeight + padding,
+    0
+  )
+  const maxScrollTop = derived(
+    [height, contentHeight],
+    ([$height, $contentHeight]) => Math.max($contentHeight - $height, 0),
+    0
+  )
+
+  // Derive horizontal limits
+  const contentWidth = derived(
+    [columns, stickyColumn],
+    ([$columns, $stickyColumn]) => {
+      let width = 40 + padding + ($stickyColumn?.width || 0)
+      $columns.forEach(col => {
+        width += col.width
+      })
+      return width
+    },
+    0
+  )
+  const screenWidth = derived(
+    [width, stickyColumn],
+    ([$width, $stickyColumn]) => $width + 40 + ($stickyColumn?.width || 0),
+    0
+  )
+  const maxScrollLeft = derived(
+    [contentWidth, screenWidth],
+    ([$contentWidth, $screenWidth]) => {
+      return Math.max($contentWidth - $screenWidth, 0)
+    },
+    0
+  )
+
+  // Ensure scroll state never goes invalid, which can happen when changing
+  // rows or tables
+  derived([scrollTop, maxScrollTop], ([$scrollTop, $maxScrollTop]) => {
+    console.log($scrollTop, $maxScrollTop, "check")
+    if ($scrollTop > $maxScrollTop) {
+      scroll.update(state => ({
+        ...state,
+        top: $maxScrollTop,
+      }))
+    }
+  })
+  // $: {
+  //   if (scrollLeft > maxScrollLeft) {
+  //     setTimeout(() => {
+  //       scroll.update(state => ({
+  //         ...state,
+  //         left: maxScrollLeft,
+  //       }))
+  //     })
+  //   }
+  // }
+
+  return {
+    contentHeight,
+    contentWidth,
+    maxScrollTop,
+    maxScrollLeft,
+  }
+}