Configure global storage

src/utils/localStorage.ts

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+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {
+  Schema,
+} from 'zod';
+import React from 'react';
+
+/*
+ * Initialises local storage to initial value if
+ * a value matching the schema is not in storage.
+ */
+export function persistReducer<T, A>(
+  stateKey: string,
+  initialState: T,
+  schema: Schema<T>,
+  reducer: React.Reducer<T, A>,
+): [T, React.Reducer<T, A>] {
+  let currentState = initialState;
+  // Try to load state from local storage
+  const stateInStorage = localStorage.getItem(stateKey);
+  if (stateInStorage) {
+    try {
+       // Validate state type
+       const parsedState = JSON.parse(stateInStorage);
+       if (parsedState as T) {
+          currentState = schema.parse(parsedState);
+       }
+    } catch (e) {
+      // if invalid delete state
+      localStorage.setItem(stateKey, JSON.stringify(initialState));
+    }
+  } else {
+    localStorage.setItem(stateKey, JSON.stringify(initialState));
+  }
+
+  return [
+    currentState, 
+    (state: T, action: A) => {
+      // state passed to this reducer is the source of truth
+      const newState = reducer(state, action);
+      localStorage.setItem(stateKey, JSON.stringify(newState));
+      return newState;
+    },
+  ];
+}