[Nicer Tabs] Fork TabBar, simplify Pager (#6762)

* Fork TabBar.web.tsx

* Trim dead code from both forks

* Remove onPageSelecting event

It's difficult to tell what exactly it's supposed to represent, and in practice it's not really used aside from logging. Let's rip it out for now to keep other changes simpler.

* Remove early onPageSelected call

It was added to try to do some work eagerly when we're sure which way the scroll is snapping. This is not necessarily a good idea though. It schedules a potentially expensive re-render right during the deceleration animation, which is not great. Whatever we're optimizing there, we should optimize smarter (e.g. prewarm just the network call). The other thing it used to help with is triggering the pager header autoscroll earlier. But we're going to rewrite that part differently anyway so that's not relevant either.

* Prune more dead code from the native version

We'll have to revisit this when adding tablet support but for now I'd prefer to remove a codepath that is not being tested or ever run.

* Use regular ScrollView on native

The Draggable thing was needed for web-only behavior so we can drop it in the native fork.

src/lib/statsig/events.ts

@@ -80,12 +80,6 @@ export type LogEvents = {
     feedUrl: string
     feedType: string
     index: number
-    reason:
-      | 'focus'
-      | 'tabbar-click'
-      | 'pager-swipe'
-      | 'desktop-sidebar-click'
-      | 'starter-pack-initial-feed'
   }
   'feed:endReached': {
     feedUrl: string

src/view/com/pager/Pager.tsx

@@ -1,21 +1,16 @@
 import React, {forwardRef} from 'react'
 import {View} from 'react-native'
 import PagerView, {
-  PagerViewOnPageScrollEvent,
   PagerViewOnPageSelectedEvent,
   PageScrollStateChangedNativeEvent,
 } from 'react-native-pager-view'
 
-import {LogEvents} from '#/lib/statsig/events'
 import {atoms as a, native} from '#/alf'
 
 export type PageSelectedEvent = PagerViewOnPageSelectedEvent
 
 export interface PagerRef {
-  setPage: (
-    index: number,
-    reason: LogEvents['home:feedDisplayed']['reason'],
-  ) => void
+  setPage: (index: number) => void
 }
 
 export interface RenderTabBarFnProps {
@@ -29,10 +24,6 @@ interface Props {
   initialPage?: number
   renderTabBar: RenderTabBarFn
   onPageSelected?: (index: number) => void
-  onPageSelecting?: (
-    index: number,
-    reason: LogEvents['home:feedDisplayed']['reason'],
-  ) => void
   onPageScrollStateChanged?: (
     scrollState: 'idle' | 'dragging' | 'settling',
   ) => void
@@ -46,24 +37,16 @@ export const Pager = forwardRef<PagerRef, React.PropsWithChildren<Props>>(
       renderTabBar,
       onPageScrollStateChanged,
       onPageSelected,
-      onPageSelecting,
       testID,
     }: React.PropsWithChildren<Props>,
     ref,
   ) {
     const [selectedPage, setSelectedPage] = React.useState(0)
-    const lastOffset = React.useRef(0)
-    const lastDirection = React.useRef(0)
-    const scrollState = React.useRef('')
     const pagerView = React.useRef<PagerView>(null)
 
     React.useImperativeHandle(ref, () => ({
-      setPage: (
-        index: number,
-        reason: LogEvents['home:feedDisplayed']['reason'],
-      ) => {
+      setPage: (index: number) => {
         pagerView.current?.setPage(index)
-        onPageSelecting?.(index, reason)
       },
     }))
 
@@ -75,60 +58,18 @@ export const Pager = forwardRef<PagerRef, React.PropsWithChildren<Props>>(
       [setSelectedPage, onPageSelected],
     )
 
-    const onPageScroll = React.useCallback(
-      (e: PagerViewOnPageScrollEvent) => {
-        const {position, offset} = e.nativeEvent
-        if (offset === 0) {
-          // offset hits 0 in some awkward spots so we ignore it
-          return
-        }
-        // NOTE
-        // we want to call `onPageSelecting` as soon as the scroll-gesture
-        // enters the "settling" phase, which means the user has released it
-        // we can't infer directionality from the scroll information, so we
-        // track the offset changes. if the offset delta is consistent with
-        // the existing direction during the settling phase, we can say for
-        // certain where it's going and can fire
-        // -prf
-        if (scrollState.current === 'settling') {
-          if (lastDirection.current === -1 && offset < lastOffset.current) {
-            onPageSelecting?.(position, 'pager-swipe')
-            setSelectedPage(position)
-            lastDirection.current = 0
-          } else if (
-            lastDirection.current === 1 &&
-            offset > lastOffset.current
-          ) {
-            onPageSelecting?.(position + 1, 'pager-swipe')
-            setSelectedPage(position + 1)
-            lastDirection.current = 0
-          }
-        } else {
-          if (offset < lastOffset.current) {
-            lastDirection.current = -1
-          } else if (offset > lastOffset.current) {
-            lastDirection.current = 1
-          }
-        }
-        lastOffset.current = offset
-      },
-      [lastOffset, lastDirection, onPageSelecting],
-    )
-
     const handlePageScrollStateChanged = React.useCallback(
       (e: PageScrollStateChangedNativeEvent) => {
-        scrollState.current = e.nativeEvent.pageScrollState
         onPageScrollStateChanged?.(e.nativeEvent.pageScrollState)
       },
-      [scrollState, onPageScrollStateChanged],
+      [onPageScrollStateChanged],
     )
 
     const onTabBarSelect = React.useCallback(
       (index: number) => {
         pagerView.current?.setPage(index)
-        onPageSelecting?.(index, 'tabbar-click')
       },
-      [pagerView, onPageSelecting],
+      [pagerView],
     )
 
     return (
@@ -142,8 +83,7 @@ export const Pager = forwardRef<PagerRef, React.PropsWithChildren<Props>>(
           style={[a.flex_1]}
           initialPage={initialPage}
           onPageScrollStateChanged={handlePageScrollStateChanged}
-          onPageSelected={onPageSelectedInner}
-          onPageScroll={onPageScroll}>
+          onPageSelected={onPageSelectedInner}>
           {children}
         </PagerView>
       </View>

src/view/com/pager/Pager.web.tsx

@@ -2,7 +2,6 @@ import React from 'react'
 import {View} from 'react-native'
 import {flushSync} from 'react-dom'
 
-import {LogEvents} from '#/lib/statsig/events'
 import {s} from '#/lib/styles'
 
 export interface RenderTabBarFnProps {
@@ -16,18 +15,13 @@ interface Props {
   initialPage?: number
   renderTabBar: RenderTabBarFn
   onPageSelected?: (index: number) => void
-  onPageSelecting?: (
-    index: number,
-    reason: LogEvents['home:feedDisplayed']['reason'],
-  ) => void
 }
 export const Pager = React.forwardRef(function PagerImpl(
   {
     children,
     initialPage = 0,
     renderTabBar,
     onPageSelected,
-    onPageSelecting,
   }: React.PropsWithChildren<Props>,
   ref,
 ) {
@@ -36,16 +30,13 @@ export const Pager = React.forwardRef(function PagerImpl(
   const anchorRef = React.useRef(null)
 
   React.useImperativeHandle(ref, () => ({
-    setPage: (
-      index: number,
-      reason: LogEvents['home:feedDisplayed']['reason'],
-    ) => {
-      onTabBarSelect(index, reason)
+    setPage: (index: number) => {
+      onTabBarSelect(index)
     },
   }))
 
   const onTabBarSelect = React.useCallback(
-    (index: number, reason: LogEvents['home:feedDisplayed']['reason']) => {
+    (index: number) => {
       const scrollY = window.scrollY
       // We want to determine if the tabbar is already "sticking" at the top (in which
       // case we should preserve and restore scroll), or if it is somewhere below in the
@@ -64,7 +55,6 @@ export const Pager = React.forwardRef(function PagerImpl(
       flushSync(() => {
         setSelectedPage(index)
         onPageSelected?.(index)
-        onPageSelecting?.(index, reason)
       })
       if (isSticking) {
         const restoredScrollY = scrollYs.current[index]
@@ -75,15 +65,15 @@ export const Pager = React.forwardRef(function PagerImpl(
         }
       }
     },
-    [selectedPage, setSelectedPage, onPageSelected, onPageSelecting],
+    [selectedPage, setSelectedPage, onPageSelected],
   )
 
   return (
     <View style={s.hContentRegion}>
       {renderTabBar({
         selectedPage,
         tabBarAnchor: <View ref={anchorRef} />,
-        onSelect: e => onTabBarSelect(e, 'tabbar-click'),
+        onSelect: e => onTabBarSelect(e),
       })}
       {React.Children.map(children, (child, i) => (
         <View style={selectedPage === i ? s.flex1 : s.hidden} key={`page-${i}`}>

src/view/com/pager/PagerWithHeader.tsx

@@ -182,17 +182,12 @@ export const PagerWithHeader = React.forwardRef<PagerRef, PagerWithHeaderProps>(
       [onPageSelected, setCurrentPage],
     )
 
-    const onPageSelecting = React.useCallback((index: number) => {
-      setCurrentPage(index)
-    }, [])
-
     return (
       <Pager
         ref={ref}
         testID={testID}
         initialPage={initialPage}
         onPageSelected={onPageSelectedInner}
-        onPageSelecting={onPageSelecting}
         renderTabBar={renderTabBar}>
         {toArray(children)
           .filter(Boolean)

src/view/com/pager/PagerWithHeader.web.tsx

@@ -75,17 +75,12 @@ export const PagerWithHeader = React.forwardRef<PagerRef, PagerWithHeaderProps>(
       [onPageSelected, setCurrentPage],
     )
 
-    const onPageSelecting = React.useCallback((index: number) => {
-      setCurrentPage(index)
-    }, [])
-
     return (
       <Pager
         ref={ref}
         testID={testID}
         initialPage={initialPage}
         onPageSelected={onPageSelectedInner}
-        onPageSelecting={onPageSelecting}
         renderTabBar={renderTabBar}>
         {toArray(children)
           .filter(Boolean)