Introduce localStorage support to createState

Summary:
Per title.

Feature will be used in several plugins in next diffs.

Differential Revision: D29514456

fbshipit-source-id: c12427c2a7c53fa01cd1c7f429be8611be55496d

desktop/flipper-plugin/src/state/__tests__/atom-local-storage.node.tsx

@@ -0,0 +1,85 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {createState} from '../atom';
+import * as TestUtils from '../../test-utils/test-utils';
+
+beforeEach(() => {
+  window.localStorage.clear();
+});
+
+test('it can start a plugin and lifecycle events', () => {
+  window.localStorage.setItem('flipper:TestPlugin:atom:x', '{ "x": 2 }');
+
+  const testPlugin = {
+    plugin() {
+      const x = createState<{x: number}>(
+        {x: 1},
+        {
+          persist: 'x',
+          persistToLocalStorage: true,
+        },
+      );
+      const y = createState(true, {
+        persist: 'y',
+        persistToLocalStorage: true,
+      });
+
+      return {x, y};
+    },
+    Component() {
+      return null;
+    },
+  };
+
+  const {instance} = TestUtils.startPlugin(testPlugin);
+  expect(instance.x.get()).toEqual({x: 2});
+  expect(instance.y.get()).toEqual(true);
+  expect(getStorageSnapshot()).toMatchInlineSnapshot(`
+    Object {
+      "flipper:TestPlugin:atom:x": "{ \\"x\\": 2 }",
+    }
+  `);
+
+  instance.x.update((d) => {
+    d.x++;
+  });
+  instance.y.set(false);
+  expect(getStorageSnapshot()).toMatchInlineSnapshot(`
+    Object {
+      "flipper:TestPlugin:atom:x": "{\\"x\\":3}",
+      "flipper:TestPlugin:atom:y": "false",
+    }
+  `);
+});
+
+function getStorageSnapshot() {
+  const res: Record<string, string> = {};
+  for (let i = 0; i < window.localStorage.length; i++) {
+    const key = window.localStorage.key(i)!;
+    res[key] = window.localStorage.getItem(key)!;
+  }
+  return res;
+}
+
+test('localStorage requires persist key', () => {
+  expect(() =>
+    createState(3, {persistToLocalStorage: true}),
+  ).toThrowErrorMatchingInlineSnapshot(
+    `"The 'persist' option should be set when 'persistToLocalStorage' is set"`,
+  );
+});
+
+test('localStorage requires plugin context', () => {
+  expect(() =>
+    createState(3, {persistToLocalStorage: true, persist: 'x'}),
+  ).toThrowErrorMatchingInlineSnapshot(
+    `"The 'persistToLocalStorage' option cannot be used outside a plugin definition"`,
+  );
+});

desktop/flipper-plugin/src/state/atom.tsx

@@ -9,7 +9,11 @@
 
 import {produce, Draft, enableMapSet} from 'immer';
 import {useState, useEffect} from 'react';
-import {Persistable, registerStorageAtom} from '../plugin/PluginBase';
+import {
+  getCurrentPluginInstance,
+  Persistable,
+  registerStorageAtom,
+} from '../plugin/PluginBase';
 import {
   deserializeShallowObject,
   makeShallowSerializable,
@@ -85,6 +89,12 @@ type StateOptions = {
    * If set, the atom will be saved / loaded under the key provided
    */
   persist?: string;
+  /**
+   * Store this state in local storage, instead of as part of the plugin import / export.
+   * State stored in local storage is shared between the same plugin
+   * across multiple clients/ devices, but not actively synced.
+   */
+  persistToLocalStorage?: boolean;
 };
 
 export function createState<T>(
@@ -97,10 +107,36 @@ export function createState(
   options: StateOptions = {},
 ): Atom<any> {
   const atom = new AtomValue(initialValue);
-  registerStorageAtom(options.persist, atom);
+  if (options?.persistToLocalStorage) {
+    syncAtomWithLocalStorage(options, atom);
+  } else {
+    registerStorageAtom(options.persist, atom);
+  }
   return atom;
 }
 
+function syncAtomWithLocalStorage(options: StateOptions, atom: AtomValue<any>) {
+  if (!options?.persist) {
+    throw new Error(
+      "The 'persist' option should be set when 'persistToLocalStorage' is set",
+    );
+  }
+  const pluginInstance = getCurrentPluginInstance();
+  if (!pluginInstance) {
+    throw new Error(
+      "The 'persistToLocalStorage' option cannot be used outside a plugin definition",
+    );
+  }
+  const storageKey = `flipper:${pluginInstance.definition.id}:atom:${options.persist}`;
+  const storedValue = window.localStorage.getItem(storageKey);
+  if (storedValue != null) {
+    atom.deserialize(JSON.parse(storedValue));
+  }
+  atom.subscribe(() => {
+    window.localStorage.setItem(storageKey, JSON.stringify(atom.serialize()));
+  });
+}
+
 export function useValue<T>(atom: ReadOnlyAtom<T>): T;
 export function useValue<T>(
   atom: ReadOnlyAtom<T> | undefined,