5 files changed, 403 insertions, 0 deletions
diff --git a/src/view/com/pager/FeedsTabBar.tsx b/src/view/com/pager/FeedsTabBar.tsx
new file mode 100644
index 000000000..9831218ec
--- /dev/null
+++ b/src/view/com/pager/FeedsTabBar.tsx
@@ -0,0 +1,64 @@
+import React from 'react'
+import {Animated, StyleSheet, TouchableOpacity} from 'react-native'
+import {observer} from 'mobx-react-lite'
+import {TabBar} from 'view/com/pager/TabBar'
+import {RenderTabBarFnProps} from 'view/com/pager/Pager'
+import {UserAvatar} from '../util/UserAvatar'
+import {useStores} from 'state/index'
+import {usePalette} from 'lib/hooks/usePalette'
+import {useAnimatedValue} from 'lib/hooks/useAnimatedValue'
+
+export const FeedsTabBar = observer(
+  (props: RenderTabBarFnProps & {onPressSelected: () => void}) => {
+    const store = useStores()
+    const pal = usePalette('default')
+    const interp = useAnimatedValue(0)
+
+    React.useEffect(() => {
+      Animated.timing(interp, {
+        toValue: store.shell.minimalShellMode ? 1 : 0,
+        duration: 100,
+        useNativeDriver: true,
+        isInteraction: false,
+      }).start()
+    }, [interp, store.shell.minimalShellMode])
+    const transform = {
+      transform: [{translateY: Animated.multiply(interp, -100)}],
+    }
+
+    const onPressAvi = React.useCallback(() => {
+      store.shell.openDrawer()
+    }, [store])
+
+    return (
+      <Animated.View style={[pal.view, styles.tabBar, transform]}>
+        <TouchableOpacity style={styles.tabBarAvi} onPress={onPressAvi}>
+          <UserAvatar avatar={store.me.avatar} size={30} />
+        </TouchableOpacity>
+        <TabBar
+          {...props}
+          items={['Following', "What's hot"]}
+          indicatorPosition="bottom"
+          indicatorColor={pal.colors.link}
+        />
+      </Animated.View>
+    )
+  },
+)
+
+const styles = StyleSheet.create({
+  tabBar: {
+    position: 'absolute',
+    zIndex: 1,
+    left: 0,
+    right: 0,
+    top: 0,
+    flexDirection: 'row',
+    alignItems: 'center',
+    paddingHorizontal: 18,
+  },
+  tabBarAvi: {
+    marginTop: 1,
+    marginRight: 18,
+  },
+})
diff --git a/src/view/com/pager/FeedsTabBar.web.tsx b/src/view/com/pager/FeedsTabBar.web.tsx
new file mode 100644
index 000000000..fc5932883
--- /dev/null
+++ b/src/view/com/pager/FeedsTabBar.web.tsx
@@ -0,0 +1,22 @@
+import React from 'react'
+import {observer} from 'mobx-react-lite'
+import {TabBar} from 'view/com/pager/TabBar'
+import {CenteredView} from 'view/com/util/Views'
+import {RenderTabBarFnProps} from 'view/com/pager/Pager'
+import {usePalette} from 'lib/hooks/usePalette'
+
+export const FeedsTabBar = observer(
+  (props: RenderTabBarFnProps & {onPressSelected: () => void}) => {
+    const pal = usePalette('default')
+    return (
+      <CenteredView>
+        <TabBar
+          {...props}
+          items={['Following', "What's hot"]}
+          indicatorPosition="bottom"
+          indicatorColor={pal.colors.link}
+        />
+      </CenteredView>
+    )
+  },
+)
diff --git a/src/view/com/pager/Pager.tsx b/src/view/com/pager/Pager.tsx
new file mode 100644
index 000000000..416828a27
--- /dev/null
+++ b/src/view/com/pager/Pager.tsx
@@ -0,0 +1,87 @@
+import React from 'react'
+import {Animated, View} from 'react-native'
+import PagerView, {PagerViewOnPageSelectedEvent} from 'react-native-pager-view'
+import {useAnimatedValue} from 'lib/hooks/useAnimatedValue'
+import {s} from 'lib/styles'
+
+export type PageSelectedEvent = PagerViewOnPageSelectedEvent
+const AnimatedPagerView = Animated.createAnimatedComponent(PagerView)
+
+export interface RenderTabBarFnProps {
+  selectedPage: number
+  position: Animated.Value
+  offset: Animated.Value
+  onSelect?: (index: number) => void
+}
+export type RenderTabBarFn = (props: RenderTabBarFnProps) => JSX.Element
+
+interface Props {
+  tabBarPosition?: 'top' | 'bottom'
+  initialPage?: number
+  renderTabBar: RenderTabBarFn
+  onPageSelected?: (index: number) => void
+}
+export const Pager = ({
+  children,
+  tabBarPosition = 'top',
+  initialPage = 0,
+  renderTabBar,
+  onPageSelected,
+}: React.PropsWithChildren<Props>) => {
+  const [selectedPage, setSelectedPage] = React.useState(0)
+  const position = useAnimatedValue(0)
+  const offset = useAnimatedValue(0)
+  const pagerView = React.useRef<PagerView>()
+
+  const onPageSelectedInner = React.useCallback(
+    (e: PageSelectedEvent) => {
+      setSelectedPage(e.nativeEvent.position)
+      onPageSelected?.(e.nativeEvent.position)
+    },
+    [setSelectedPage, onPageSelected],
+  )
+
+  const onTabBarSelect = React.useCallback(
+    (index: number) => {
+      pagerView.current?.setPage(index)
+    },
+    [pagerView],
+  )
+
+  return (
+    <View>
+      {tabBarPosition === 'top' &&
+        renderTabBar({
+          selectedPage,
+          position,
+          offset,
+          onSelect: onTabBarSelect,
+        })}
+      <AnimatedPagerView
+        ref={pagerView}
+        style={s.h100pct}
+        initialPage={initialPage}
+        onPageSelected={onPageSelectedInner}
+        onPageScroll={Animated.event(
+          [
+            {
+              nativeEvent: {
+                position: position,
+                offset: offset,
+              },
+            },
+          ],
+          {useNativeDriver: true},
+        )}>
+        {children}
+      </AnimatedPagerView>
+      {tabBarPosition === 'bottom' &&
+        renderTabBar({
+          selectedPage,
+          position,
+          offset,
+          onSelect: onTabBarSelect,
+        })}
+    </View>
+  )
+}
diff --git a/src/view/com/pager/Pager.web.tsx b/src/view/com/pager/Pager.web.tsx
new file mode 100644
index 000000000..3c2805833
--- /dev/null
+++ b/src/view/com/pager/Pager.web.tsx
@@ -0,0 +1,69 @@
+import React from 'react'
+import {Animated, View} from 'react-native'
+import {useAnimatedValue} from 'lib/hooks/useAnimatedValue'
+import {s} from 'lib/styles'
+
+export interface RenderTabBarFnProps {
+  selectedPage: number
+  position: Animated.Value
+  offset: Animated.Value
+  onSelect?: (index: number) => void
+}
+export type RenderTabBarFn = (props: RenderTabBarFnProps) => JSX.Element
+
+interface Props {
+  tabBarPosition?: 'top' | 'bottom'
+  initialPage?: number
+  renderTabBar: RenderTabBarFn
+  onPageSelected?: (index: number) => void
+}
+export const Pager = ({
+  children,
+  tabBarPosition = 'top',
+  initialPage = 0,
+  renderTabBar,
+  onPageSelected,
+}: React.PropsWithChildren<Props>) => {
+  const [selectedPage, setSelectedPage] = React.useState(initialPage)
+  const position = useAnimatedValue(0)
+  const offset = useAnimatedValue(0)
+
+  const onTabBarSelect = React.useCallback(
+    (index: number) => {
+      setSelectedPage(index)
+      onPageSelected?.(index)
+      Animated.timing(position, {
+        toValue: index,
+        duration: 200,
+        useNativeDriver: true,
+      }).start()
+    },
+    [setSelectedPage, onPageSelected, position],
+  )
+
+  return (
+    <View>
+      {tabBarPosition === 'top' &&
+        renderTabBar({
+          selectedPage,
+          position,
+          offset,
+          onSelect: onTabBarSelect,
+        })}
+      {children.map((child, i) => (
+        <View
+          style={selectedPage === i ? undefined : s.hidden}
+          key={`page-${i}`}>
+          {child}
+        </View>
+      ))}
+      {tabBarPosition === 'bottom' &&
+        renderTabBar({
+          selectedPage,
+          position,
+          offset,
+          onSelect: onTabBarSelect,
+        })}
+    </View>
+  )
+}
diff --git a/src/view/com/pager/TabBar.tsx b/src/view/com/pager/TabBar.tsx
new file mode 100644
index 000000000..0b45d95f5
--- /dev/null
+++ b/src/view/com/pager/TabBar.tsx
@@ -0,0 +1,161 @@
+import React, {createRef, useState, useMemo} from 'react'
+import {
+  Animated,
+  StyleSheet,
+  TouchableWithoutFeedback,
+  View,
+} from 'react-native'
+import {Text} from '../util/text/Text'
+import {usePalette} from 'lib/hooks/usePalette'
+import {isDesktopWeb} from 'platform/detection'
+
+interface Layout {
+  x: number
+  width: number
+}
+
+export interface TabBarProps {
+  selectedPage: number
+  items: string[]
+  position: Animated.Value
+  offset: Animated.Value
+  indicatorPosition?: 'top' | 'bottom'
+  indicatorColor?: string
+  onSelect?: (index: number) => void
+  onPressSelected?: () => void
+}
+
+export function TabBar({
+  selectedPage,
+  items,
+  position,
+  offset,
+  indicatorPosition = 'bottom',
+  indicatorColor,
+  onSelect,
+  onPressSelected,
+}: TabBarProps) {
+  const pal = usePalette('default')
+  const [itemLayouts, setItemLayouts] = useState<Layout[]>(
+    items.map(() => ({x: 0, width: 0})),
+  )
+  const itemRefs = useMemo(
+    () => Array.from({length: items.length}).map(() => createRef<View>()),
+    [items.length],
+  )
+  const panX = Animated.add(position, offset)
+
+  const indicatorStyle = {
+    backgroundColor: indicatorColor || pal.colors.link,
+    bottom:
+      indicatorPosition === 'bottom' ? (isDesktopWeb ? 0 : -1) : undefined,
+    top: indicatorPosition === 'top' ? (isDesktopWeb ? 0 : -1) : undefined,
+    transform: [
+      {
+        translateX: panX.interpolate({
+          inputRange: items.map((_item, i) => i),
+          outputRange: itemLayouts.map(l => l.x + l.width / 2),
+        }),
+      },
+      {
+        scaleX: panX.interpolate({
+          inputRange: items.map((_item, i) => i),
+          outputRange: itemLayouts.map(l => l.width),
+        }),
+      },
+    ],
+  }
+
+  const onLayout = () => {
+    const promises = []
+    for (let i = 0; i < items.length; i++) {
+      promises.push(
+        new Promise<Layout>(resolve => {
+          itemRefs[i].current?.measure(
+            (x: number, _y: number, width: number) => {
+              resolve({x, width})
+            },
+          )
+        }),
+      )
+    }
+    Promise.all(promises).then((layouts: Layout[]) => {
+      setItemLayouts(layouts)
+    })
+  }
+
+  const onPressItem = (index: number) => {
+    onSelect?.(index)
+    if (index === selectedPage) {
+      onPressSelected?.()
+    }
+  }
+
+  return (
+    <View style={[pal.view, styles.outer]} onLayout={onLayout}>
+      <Animated.View style={[styles.indicator, indicatorStyle]} />
+      {items.map((item, i) => {
+        const selected = i === selectedPage
+        return (
+          <TouchableWithoutFeedback key={i} onPress={() => onPressItem(i)}>
+            <View
+              style={
+                indicatorPosition === 'top' ? styles.itemTop : styles.itemBottom
+              }
+              ref={itemRefs[i]}>
+              <Text type="xl-bold" style={selected ? pal.text : pal.textLight}>
+                {item}
+              </Text>
+            </View>
+          </TouchableWithoutFeedback>
+        )
+      })}
+    </View>
+  )
+}
+
+const styles = isDesktopWeb
+  ? StyleSheet.create({
+      outer: {
+        flexDirection: 'row',
+        paddingHorizontal: 18,
+      },
+      itemTop: {
+        paddingTop: 16,
+        paddingBottom: 14,
+        marginRight: 24,
+      },
+      itemBottom: {
+        paddingTop: 14,
+        paddingBottom: 16,
+        marginRight: 24,
+      },
+      indicator: {
+        position: 'absolute',
+        left: 0,
+        width: 1,
+        height: 3,
+      },
+    })
+  : StyleSheet.create({
+      outer: {
+        flexDirection: 'row',
+        paddingHorizontal: 14,
+      },
+      itemTop: {
+        paddingTop: 10,
+        paddingBottom: 10,
+        marginRight: 24,
+      },
+      itemBottom: {
+        paddingTop: 8,
+        paddingBottom: 12,
+        marginRight: 24,
+      },
+      indicator: {
+        position: 'absolute',
+        left: 0,
+        width: 1,
+        height: 3,
+      },
+    })