Persist color scheme prefence in localStorage

src/store/index.ts

@@ -6,7 +6,7 @@ import {actions} from './actions'
  */
 
 import * as redux from 'redux'
-import {setter, Reducer} from '../lib/typed-redux'
+import {setter, Reducer, Action} from '../lib/typed-redux'
 import {HashParams, getHashParams} from '../lib/hash-params'
 import {ProfileGroupState, profileGroup} from './profiles-state'
 import {SortMethod, SortField, SortDirection} from '../views/profile-table-view'
@@ -83,6 +83,47 @@ const protocol = window.location.protocol
 // however, XHR will be unavailable to fetching files in adjacent directories.
 export const canUseXHR = protocol === 'http:' || protocol === 'https:'
 
+function colorScheme(state: ColorScheme | undefined, action: Action<any>): ColorScheme {
+  const localStorageKey = 'speedscope-color-scheme'
+
+  if (state === undefined) {
+    const storedPreference = window.localStorage && window.localStorage[localStorageKey]
+    if (storedPreference === 'DARK') {
+      return ColorScheme.DARK
+    } else if (storedPreference === 'LIGHT') {
+      return ColorScheme.LIGHT
+    } else {
+      return ColorScheme.SYSTEM
+    }
+  }
+
+  if (actions.setColorScheme.matches(action)) {
+    const value = action.payload
+
+    switch (value) {
+      case ColorScheme.DARK: {
+        window.localStorage[localStorageKey] = 'DARK'
+        break
+      }
+      case ColorScheme.LIGHT: {
+        window.localStorage[localStorageKey] = 'LIGHT'
+        break
+      }
+      case ColorScheme.SYSTEM: {
+        delete window.localStorage[localStorageKey]
+        break
+      }
+      default: {
+        const _exhaustiveCheck: never = value
+        return _exhaustiveCheck
+      }
+    }
+    return value
+  }
+
+  return state
+}
+
 export function createAppStore(initialState?: ApplicationState): redux.Store<ApplicationState> {
   const hashParams = getHashParams()
 
@@ -111,7 +152,7 @@ export function createAppStore(initialState?: ApplicationState): redux.Store<App
       direction: SortDirection.DESCENDING,
     }),
 
-    colorScheme: setter<ColorScheme>(actions.setColorScheme, ColorScheme.SYSTEM),
+    colorScheme,
   })
 
   return redux.createStore(reducer, initialState)