fix theme cross-tab write loop (#2774)

* don't write on onUpdate, memoize

* refac useColorModeTheme

src/alf/util/useColorModeTheme.ts

@@ -1,5 +1,5 @@
 import React from 'react'
-import {useColorScheme} from 'react-native'
+import {ColorSchemeName, useColorScheme} from 'react-native'
 
 import {useThemePrefs} from 'state/shell'
 import {isWeb} from 'platform/detection'
@@ -10,21 +10,31 @@ export function useColorModeTheme(): ThemeName {
   const colorScheme = useColorScheme()
   const {colorMode, darkTheme} = useThemePrefs()
 
-  return React.useMemo(() => {
+  React.useLayoutEffect(() => {
+    const theme = getThemeName(colorScheme, colorMode, darkTheme)
+    updateDocument(theme)
+    updateSystemBackground(theme)
+  }, [colorMode, colorScheme, darkTheme])
+
+  return React.useMemo(
+    () => getThemeName(colorScheme, colorMode, darkTheme),
+    [colorScheme, colorMode, darkTheme],
+  )
+}
+
+function getThemeName(
+  colorScheme: ColorSchemeName,
+  colorMode: 'system' | 'light' | 'dark',
+  darkTheme?: ThemeName,
+) {
   if (
     (colorMode === 'system' && colorScheme === 'light') ||
     colorMode === 'light'
   ) {
-      updateDocument('light')
-      updateSystemBackground('light')
     return 'light'
   } else {
-      const themeName = darkTheme ?? 'dim'
-      updateDocument(themeName)
-      updateSystemBackground(themeName)
-      return themeName
+    return darkTheme ?? 'dim'
   }
-  }, [colorMode, darkTheme, colorScheme])
 }
 
 function updateDocument(theme: ThemeName) {

src/state/shell/color-mode.tsx

@@ -20,36 +20,38 @@ export function Provider({children}: React.PropsWithChildren<{}>) {
   const [colorMode, setColorMode] = React.useState(persisted.get('colorMode'))
   const [darkTheme, setDarkTheme] = React.useState(persisted.get('darkTheme'))
 
-  const setColorModeWrapped = React.useCallback(
-    (_colorMode: persisted.Schema['colorMode']) => {
+  const stateContextValue = React.useMemo(
+    () => ({
+      colorMode,
+      darkTheme,
+    }),
+    [colorMode, darkTheme],
+  )
+
+  const setContextValue = React.useMemo(
+    () => ({
+      setColorMode: (_colorMode: persisted.Schema['colorMode']) => {
         setColorMode(_colorMode)
         persisted.write('colorMode', _colorMode)
       },
-    [setColorMode],
-  )
-
-  const setDarkThemeWrapped = React.useCallback(
-    (_darkTheme: persisted.Schema['darkTheme']) => {
+      setDarkTheme: (_darkTheme: persisted.Schema['darkTheme']) => {
         setDarkTheme(_darkTheme)
         persisted.write('darkTheme', _darkTheme)
       },
-    [setDarkTheme],
+    }),
+    [],
   )
 
   React.useEffect(() => {
     return persisted.onUpdate(() => {
-      setColorModeWrapped(persisted.get('colorMode'))
-      setDarkThemeWrapped(persisted.get('darkTheme'))
+      setColorMode(persisted.get('colorMode'))
+      setDarkTheme(persisted.get('darkTheme'))
     })
-  }, [setColorModeWrapped, setDarkThemeWrapped])
+  }, [])
 
   return (
-    <stateContext.Provider value={{colorMode, darkTheme}}>
-      <setContext.Provider
-        value={{
-          setDarkTheme: setDarkThemeWrapped,
-          setColorMode: setColorModeWrapped,
-        }}>
+    <stateContext.Provider value={stateContextValue}>
+      <setContext.Provider value={setContextValue}>
         {children}
       </setContext.Provider>
     </stateContext.Provider>