mostly working

src/components/ClipClopTest/ClipClopList.tsx

@@ -1,17 +1,15 @@
 import React from 'react'
-import {
-  FlatList,
-  LayoutChangeEvent,
-  ListRenderItemInfo,
-  View,
-  ViewToken,
-} from 'react-native'
+import {Button, FlatList, View, ViewToken} from 'react-native'
 
-import {atoms as a, useTheme} from '#/alf'
-import {ClipClop as ClipClopInterface} from '#/components/ClipClopTest/RandomClipClops'
+import {useTheme} from '#/alf'
+import {atoms as a} from '#/alf'
+import {
+  ClipClop,
+  placeholderClops,
+} from '#/components/ClipClopTest/RandomClipClops'
 import {Text} from '#/components/Typography'
 
-function ClipClop({message}: {message: ClipClopInterface}) {
+function ClipClopItem({item}: {item: ClipClop}) {
   const t = useTheme()
   return (
     <View
@@ -25,57 +23,80 @@ function ClipClop({message}: {message: ClipClopInterface}) {
           borderRadius: 10,
         },
       ]}>
-      <Text style={{lineHeight: 1.2}}>{message.text}</Text>
+      <Text style={{lineHeight: 1.2}}>{item.text}</Text>
     </View>
   )
 }
 
-function renderItem({item}: ListRenderItemInfo<ClipClopInterface>) {
-  return <ClipClop message={item} />
+function renderItem({item}: {item: ClipClop}) {
+  return <ClipClopItem item={item} />
 }
 
-function keyExtractor(item: ClipClopInterface, index: number) {
-  return `${item.id}-${index}`
-}
+// Generate unique key list item.
+export const generateUniqueKey = () =>
+  `_${Math.random().toString(36).substr(2, 9)}`
 
-function HeaderPlaceholder({height}: {height: number}) {
-  return <View style={{height}} />
-}
+export const ClipClopList = () => {
+  const flatListRef = React.useRef<FlatList>(null)
 
-export function ClipClopList({clipClops}: {clipClops: ClipClopInterface[]}) {
-  const flatlistRef = React.useRef<FlatList>(null)
-  const contentHeight = React.useRef(0)
+  // Whenever we reach the end (visually the top), we don't want to keep calling it. We will set `isFetching` to true
+  // once the request for new posts starts. Then, we will change it back to false after the content size changes.
+  const isFetching = React.useRef(false)
 
-  const totalClipClops = React.useRef(0)
+  // We use this to know if we should scroll after a new clop is added to the list
+  const isAtBottom = React.useRef(false)
 
-  const isAtBottom = React.useRef(true)
-  const [placeholderHeight, setPlaceholderHeight] = React.useState(0)
+  // Because the viewableItemsChanged callback won't have access to the updated state, we use a ref to store the
+  // total number of clops
+  const totalClops = React.useRef(10)
 
-  // This creates a placeholder that adjusts with the whitespace above the last chat item
-  const onScreenLayout = React.useCallback((e: LayoutChangeEvent) => {
-    setPlaceholderHeight(e.nativeEvent.layout.height)
-  }, [])
-
-  const onContentSizeChange = React.useCallback(
-    (_: number, height: number) => {
-      if (isAtBottom.current) {
-        flatlistRef.current?.scrollToOffset({offset: height, animated: true})
-      }
-
-      contentHeight.current = height
-      totalClipClops.current = clipClops.length
-    },
-    [clipClops],
+  const [clops, setClops] = React.useState(
+    Array.from(Array(10).keys()).map(n => ({
+      id: generateUniqueKey(),
+      text: placeholderClops[n % placeholderClops.length],
+    })),
   )
 
+  const addOldClops = () => {
+    setClops(prev => {
+      const oldClops: ClipClop[] = Array.from(Array(5).keys()).map(n => ({
+        id: generateUniqueKey(),
+        text:
+          placeholderClops[n % placeholderClops.length] + generateUniqueKey(),
+      }))
+
+      totalClops.current += oldClops.length
+      return prev.concat(oldClops)
+    })
+  }
+
+  const addNewClip = () => {
+    setClops(prev => {
+      const newClops = Array.from(Array(1).keys())
+        .map(n => ({
+          id: generateUniqueKey(),
+          text:
+            placeholderClops[n % placeholderClops.length] + generateUniqueKey(),
+        }))
+        .reverse()
+
+      totalClops.current += newClops.length
+      return newClops.concat(prev)
+    })
+  }
+
   const [onViewableItemsChanged, viewabilityConfig] = React.useMemo(() => {
     return [
       (info: {viewableItems: Array<ViewToken>; changed: Array<ViewToken>}) => {
-        const lastVisibleItem =
-          info.viewableItems[info.viewableItems.length - 1]
-        const lastViewableIndex = lastVisibleItem?.index ?? -1
+        const firstVisibleIndex = info.viewableItems[0]?.index
 
-        isAtBottom.current = lastViewableIndex >= totalClipClops.current - 2
+        isAtBottom.current = Number(firstVisibleIndex) < 2
+
+        console.log({
+          firstVisibleIndex,
+          totalClops: totalClops.current,
+          isAtBottom: isAtBottom.current,
+        })
       },
       {
         itemVisiblePercentThreshold: 100,
@@ -84,21 +105,50 @@ export function ClipClopList({clipClops}: {clipClops: ClipClopInterface[]}) {
     ]
   }, [])
 
+  const onContentSizeChange = React.useCallback(
+    (_: number, height: number) => {
+      if (isAtBottom.current) {
+        flatListRef.current?.scrollToOffset({offset: 0, animated: true})
+      }
+
+      isFetching.current = false
+    },
+    [clops],
+  )
+
+  const onEndReached = () => {
+    if (isFetching.current) return
+    isFetching.current = true
+
+    // We wouldn't actually use a timeout, but there would be a delay while loading
+    setTimeout(() => {
+      addOldClops()
+    }, 1000)
+  }
+
   return (
-    <View style={{flex: 1}} onLayout={onScreenLayout}>
+    <View style={{flex: 1, marginBottom: 100}}>
+      <Button title="Add Old Clops" onPress={addOldClops} />
       <FlatList
-        data={clipClops}
+        data={clops}
+        keyExtractor={item => item.id}
+        maintainVisibleContentPosition={{
+          minIndexForVisible: 1,
+        }}
         renderItem={renderItem}
-        keyExtractor={keyExtractor}
-        // maintainVisibleContentPosition={{
-        //   minIndexForVisible: 0,
-        // }}
-        // ListHeaderComponent={<HeaderPlaceholder height={placeholderHeight} />}
+        onContentSizeChange={onContentSizeChange}
         onViewableItemsChanged={onViewableItemsChanged}
         viewabilityConfig={viewabilityConfig}
-        ref={flatlistRef}
-        onContentSizeChange={onContentSizeChange}
+        ref={flatListRef}
+        onScrollToIndexFailed={info => {
+          console.log('Failed to scroll to index', info)
+        }}
+        initialNumToRender={20}
+        maxToRenderPerBatch={20}
+        inverted
+        onEndReached={onEndReached}
       />
+      <Button title="Add New Clip" onPress={addNewClip} />
     </View>
   )
 }

src/view/screens/Home.tsx

@@ -51,52 +51,7 @@ type Props = NativeStackScreenProps<HomeTabNavigatorParams, 'Home'>
  */
 
 export function HomeScreen(props: Props) {
-  const lastMessageId = React.useRef(0)
-  const [clipClops, setClipClops] = React.useState<ClipClop[]>([])
-
-  const addMessage = () => {
-    lastMessageId.current += 1
-
-    setClipClops(prev => {
-      return [
-        ...prev,
-
-        {
-          id: lastMessageId.current.toString(),
-          text: `${
-            placeholderClops[lastMessageId.current % placeholderClops.length]
-          }`,
-        },
-      ]
-    })
-  }
-
-  const addMessages = (count: number) => {
-    for (let i = 0; i < count; i++) {
-      addMessage()
-    }
-  }
-
-  return (
-    <CenteredView style={{flex: 1, marginBottom: 100}}>
-      <View style={{flexDirection: 'row'}}>
-        <Button
-          title="Add One"
-          onPress={() => {
-            addMessages(1)
-          }}
-        />
-        <Button
-          title="Add Five"
-          onPress={() => {
-            addMessages(5)
-          }}
-        />
-        <Button title="Reset" onPress={() => setClipClops([])} />
-      </View>
-      <ClipClopList clipClops={clipClops} />
-    </CenteredView>
-  )
+  return <ClipClopList />
 }
 
 function HomeScreenReady({