1 files changed, 341 insertions, 0 deletions
diff --git a/src/view/com/util/List.web.tsx b/src/view/com/util/List.web.tsx
new file mode 100644
index 000000000..3e81a8c37
--- /dev/null
+++ b/src/view/com/util/List.web.tsx
@@ -0,0 +1,341 @@
+import React, {isValidElement, memo, useRef, startTransition} from 'react'
+import {FlatListProps, StyleSheet, View, ViewProps} from 'react-native'
+import {addStyle} from 'lib/styles'
+import {usePalette} from 'lib/hooks/usePalette'
+import {useWebMediaQueries} from 'lib/hooks/useWebMediaQueries'
+import {useScrollHandlers} from '#/lib/ScrollContext'
+import {useNonReactiveCallback} from '#/lib/hooks/useNonReactiveCallback'
+import {batchedUpdates} from '#/lib/batchedUpdates'
+
+export type ListMethods = any // TODO: Better types.
+export type ListProps<ItemT> = Omit<
+  FlatListProps<ItemT>,
+  | 'onScroll' // Use ScrollContext instead.
+  | 'refreshControl' // Pass refreshing and/or onRefresh instead.
+  | 'contentOffset' // Pass headerOffset instead.
+> & {
+  onScrolledDownChange?: (isScrolledDown: boolean) => void
+  headerOffset?: number
+  refreshing?: boolean
+  onRefresh?: () => void
+  desktopFixedHeight: any // TODO: Better types.
+}
+export type ListRef = React.MutableRefObject<any | null> // TODO: Better types.
+
+function ListImpl<ItemT>(
+  {
+    ListHeaderComponent,
+    ListFooterComponent,
+    contentContainerStyle,
+    data,
+    desktopFixedHeight,
+    headerOffset,
+    keyExtractor,
+    refreshing: _unsupportedRefreshing,
+    onEndReached,
+    onEndReachedThreshold = 0,
+    onRefresh: _unsupportedOnRefresh,
+    onScrolledDownChange,
+    onContentSizeChange,
+    renderItem,
+    extraData,
+    style,
+    ...props
+  }: ListProps<ItemT>,
+  ref: React.Ref<ListMethods>,
+) {
+  const contextScrollHandlers = useScrollHandlers()
+  const pal = usePalette('default')
+  const {isMobile} = useWebMediaQueries()
+  if (!isMobile) {
+    contentContainerStyle = addStyle(
+      contentContainerStyle,
+      styles.containerScroll,
+    )
+  }
+
+  let header: JSX.Element | null = null
+  if (ListHeaderComponent != null) {
+    if (isValidElement(ListHeaderComponent)) {
+      header = ListHeaderComponent
+    } else {
+      // @ts-ignore Nah it's fine.
+      header = <ListHeaderComponent />
+    }
+  }
+
+  let footer: JSX.Element | null = null
+  if (ListFooterComponent != null) {
+    if (isValidElement(ListFooterComponent)) {
+      footer = ListFooterComponent
+    } else {
+      // @ts-ignore Nah it's fine.
+      footer = <ListFooterComponent />
+    }
+  }
+
+  if (headerOffset != null) {
+    style = addStyle(style, {
+      paddingTop: headerOffset,
+    })
+  }
+
+  const nativeRef = React.useRef(null)
+  React.useImperativeHandle(
+    ref,
+    () =>
+      ({
+        scrollToTop() {
+          window.scrollTo({top: 0})
+        },
+        scrollToOffset({
+          animated,
+          offset,
+        }: {
+          animated: boolean
+          offset: number
+        }) {
+          window.scrollTo({
+            left: 0,
+            top: offset,
+            behavior: animated ? 'smooth' : 'instant',
+          })
+        },
+      } as any), // TODO: Better types.
+    [],
+  )
+
+  // --- onContentSizeChange ---
+  const containerRef = useRef(null)
+  useResizeObserver(containerRef, onContentSizeChange)
+
+  // --- onScroll ---
+  const [isInsideVisibleTree, setIsInsideVisibleTree] = React.useState(false)
+  const handleWindowScroll = useNonReactiveCallback(() => {
+    if (isInsideVisibleTree) {
+      contextScrollHandlers.onScroll?.(
+        {
+          contentOffset: {
+            x: Math.max(0, window.scrollX),
+            y: Math.max(0, window.scrollY),
+          },
+        } as any, // TODO: Better types.
+        null as any,
+      )
+    }
+  })
+  React.useEffect(() => {
+    if (!isInsideVisibleTree) {
+      // Prevents hidden tabs from firing scroll events.
+      // Only one list is expected to be firing these at a time.
+      return
+    }
+    window.addEventListener('scroll', handleWindowScroll)
+    return () => {
+      window.removeEventListener('scroll', handleWindowScroll)
+    }
+  }, [isInsideVisibleTree, handleWindowScroll])
+
+  // --- onScrolledDownChange ---
+  const isScrolledDown = useRef(false)
+  function handleAboveTheFoldVisibleChange(isAboveTheFold: boolean) {
+    const didScrollDown = !isAboveTheFold
+    if (isScrolledDown.current !== didScrollDown) {
+      isScrolledDown.current = didScrollDown
+      startTransition(() => {
+        onScrolledDownChange?.(didScrollDown)
+      })
+    }
+  }
+
+  // --- onEndReached ---
+  const onTailVisibilityChange = useNonReactiveCallback(
+    (isTailVisible: boolean) => {
+      if (isTailVisible) {
+        onEndReached?.({
+          distanceFromEnd: onEndReachedThreshold || 0,
+        })
+      }
+    },
+  )
+
+  return (
+    <View {...props} style={style} ref={nativeRef}>
+      <Visibility
+        onVisibleChange={setIsInsideVisibleTree}
+        style={
+          // This has position: fixed, so it should always report as visible
+          // unless we're within a display: none tree (like a hidden tab).
+          styles.parentTreeVisibilityDetector
+        }
+      />
+      <View
+        ref={containerRef}
+        style={[
+          styles.contentContainer,
+          contentContainerStyle,
+          desktopFixedHeight ? styles.minHeightViewport : null,
+          pal.border,
+        ]}>
+        <Visibility
+          onVisibleChange={handleAboveTheFoldVisibleChange}
+          style={[styles.aboveTheFoldDetector, {height: headerOffset}]}
+        />
+        {header}
+        {(data as Array<ItemT>).map((item, index) => (
+          <Row<ItemT>
+            key={keyExtractor!(item, index)}
+            item={item}
+            index={index}
+            renderItem={renderItem}
+            extraData={extraData}
+          />
+        ))}
+        {onEndReached && (
+          <Visibility
+            topMargin={(onEndReachedThreshold ?? 0) * 100 + '%'}
+            onVisibleChange={onTailVisibilityChange}
+          />
+        )}
+        {footer}
+      </View>
+    </View>
+  )
+}
+
+function useResizeObserver(
+  ref: React.RefObject<Element>,
+  onResize: undefined | ((w: number, h: number) => void),
+) {
+  const handleResize = useNonReactiveCallback(onResize ?? (() => {}))
+  const isActive = !!onResize
+  React.useEffect(() => {
+    if (!isActive) {
+      return
+    }
+    const resizeObserver = new ResizeObserver(entries => {
+      batchedUpdates(() => {
+        for (let entry of entries) {
+          const rect = entry.contentRect
+          handleResize(rect.width, rect.height)
+        }
+      })
+    })
+    const node = ref.current!
+    resizeObserver.observe(node)
+    return () => {
+      resizeObserver.unobserve(node)
+    }
+  }, [handleResize, isActive, ref])
+}
+
+let Row = function RowImpl<ItemT>({
+  item,
+  index,
+  renderItem,
+  extraData: _unused,
+}: {
+  item: ItemT
+  index: number
+  renderItem:
+    | null
+    | undefined
+    | ((data: {index: number; item: any; separators: any}) => React.ReactNode)
+  extraData: any
+}): React.ReactNode {
+  if (!renderItem) {
+    return null
+  }
+  return (
+    <View style={styles.row}>
+      {renderItem({item, index, separators: null as any})}
+    </View>
+  )
+}
+Row = React.memo(Row)
+
+let Visibility = ({
+  topMargin = '0px',
+  onVisibleChange,
+  style,
+}: {
+  topMargin?: string
+  onVisibleChange: (isVisible: boolean) => void
+  style?: ViewProps['style']
+}): React.ReactNode => {
+  const tailRef = React.useRef(null)
+  const isIntersecting = React.useRef(false)
+
+  const handleIntersection = useNonReactiveCallback(
+    (entries: IntersectionObserverEntry[]) => {
+      batchedUpdates(() => {
+        entries.forEach(entry => {
+          if (entry.isIntersecting !== isIntersecting.current) {
+            isIntersecting.current = entry.isIntersecting
+            onVisibleChange(entry.isIntersecting)
+          }
+        })
+      })
+    },
+  )
+
+  React.useEffect(() => {
+    const observer = new IntersectionObserver(handleIntersection, {
+      rootMargin: `${topMargin} 0px 0px 0px`,
+    })
+    const tail: Element | null = tailRef.current!
+    observer.observe(tail)
+    return () => {
+      observer.unobserve(tail)
+    }
+  }, [handleIntersection, topMargin])
+
+  return (
+    <View ref={tailRef} style={addStyle(styles.visibilityDetector, style)} />
+  )
+}
+Visibility = React.memo(Visibility)
+
+export const List = memo(React.forwardRef(ListImpl)) as <ItemT>(
+  props: ListProps<ItemT> & {ref?: React.Ref<ListMethods>},
+) => React.ReactElement
+
+const styles = StyleSheet.create({
+  contentContainer: {
+    borderLeftWidth: 1,
+    borderRightWidth: 1,
+  },
+  containerScroll: {
+    width: '100%',
+    maxWidth: 600,
+    marginLeft: 'auto',
+    marginRight: 'auto',
+  },
+  row: {
+    // @ts-ignore web only
+    contentVisibility: 'auto',
+  },
+  minHeightViewport: {
+    // @ts-ignore web only
+    minHeight: '100vh',
+  },
+  parentTreeVisibilityDetector: {
+    // @ts-ignore web only
+    position: 'fixed',
+    top: 0,
+    left: 0,
+    right: 0,
+    bottom: 0,
+  },
+  aboveTheFoldDetector: {
+    position: 'absolute',
+    top: 0,
+    left: 0,
+    right: 0,
+    // Bottom is dynamic.
+  },
+  visibilityDetector: {
+    pointerEvents: 'none',
+    zIndex: -1,
+  },
+})