Add dark mode (#554)

src/redux/dark-mode/reducers.ts

@@ -0,0 +1,26 @@
+import { Reducer } from 'redux'
+import { determineDarkModeBrowserSetting, loadFromLocalStorage, saveToLocalStorage } from './methods'
+import { DarkModeConfig, DarkModeConfigActions, DarkModeConfigActionType, SetDarkModeConfigAction } from './types'
+
+export const getInitialState = (): DarkModeConfig => {
+  const initialMode = loadFromLocalStorage() ?? determineDarkModeBrowserSetting() ?? {
+    darkMode: false
+  }
+  saveToLocalStorage(initialMode)
+  return initialMode
+}
+
+export const DarkModeConfigReducer: Reducer<DarkModeConfig, DarkModeConfigActions> = (state: DarkModeConfig = getInitialState(), action: DarkModeConfigActions) => {
+  let darkModeConfigState: DarkModeConfig
+  switch (action.type) {
+    case DarkModeConfigActionType.SET_DARK_MODE:
+      darkModeConfigState = {
+        ...state,
+        darkMode: (action as SetDarkModeConfigAction).darkMode
+      }
+      saveToLocalStorage(darkModeConfigState)
+      return darkModeConfigState
+    default:
+      return state
+  }
+}