redux [nfc]: Add an activeAccountDispatch for global thunk actions

And convert to using this in one spot where we were already
doing the equivalent ad hoc.

Co-authored-by: Chris Bobbe <[email protected]>

Author: gnprice

src/account/accountActions.js

@@ -1,12 +1,6 @@
 /* @flow strict-local */
 import * as NavigationService from '../nav/NavigationService';
-import type {
-  Dispatch,
-  PerAccountAction,
-  AllAccountsAction,
-  ThunkAction,
-  GlobalThunkAction,
-} from '../types';
+import type { PerAccountAction, AllAccountsAction, ThunkAction, GlobalThunkAction } from '../types';
 import {
   ACCOUNT_SWITCH,
   ACCOUNT_REMOVE,
@@ -34,30 +28,13 @@ const accountSwitchPlain = (index: number): AllAccountsAction => ({
 
 export const accountSwitch =
   (index: number): GlobalThunkAction<Promise<void>> =>
-  async (dispatch, getState) => {
+  async (dispatch, getState, { activeAccountDispatch }) => {
     NavigationService.dispatch(resetToMainTabs());
     dispatch(accountSwitchPlain(index));
 
-    /* $FlowFixMe[incompatible-type]
-
-     This is really a GlobalDispatch, because we're in a GlobalThunkAction.
-     (It's global because it needs to know about all the accounts to set the
-     pointer to the active one). But here, we pretend it's a Dispatch.
-     That's OK, for now, because:
-
-     - Our Dispatch function is secretly the same value as our
-       GlobalDispatch.
-     - The PerAccountState that Dispatch currently acts on is the one
-       belonging to the active account.
-     - We want this dispatch to act on the active account -- the new,
-       post-switch active account.
-     - It will act on that account, because at this point we've already
-       dispatched `accountSwitchPlain`.
-
-     TODO(#5006): perhaps have an `activeAccountDispatch: Dispatch` in
-       a new GlobalThunkExtras, modeled on ThunkExtras?
-  */
-    const activeAccountDispatch: Dispatch = dispatch;
+    // Now dispatch some actions on the new, post-switch active account.
+    // Because we just dispatched `accountSwitchPlain`, that new account
+    // is now the active account, so `activeAccountDispatch` will act on it.
 
     await activeAccountDispatch(registerAndStartPolling());
 

src/boot/store.js

@@ -20,7 +20,7 @@ import CompressedAsyncStorage from '../storage/CompressedAsyncStorage';
 import createMigration from '../redux-persist-migrate/index';
 import { getGlobalSession, getGlobalSettings } from '../directSelectors';
 import { migrations } from '../storage/migrations';
-import type { GlobalThunkExtras } from '../reduxTypes';
+import type { Dispatch, GlobalThunkExtras } from '../reduxTypes';
 
 if (process.env.NODE_ENV === 'development') {
   // Chrome dev tools for Immutable.
@@ -73,17 +73,29 @@ export const cacheKeys: $ReadOnlyArray<$Keys<GlobalState>> = [
   'realm', 'streams', 'subscriptions', 'unread', 'userGroups', 'users',
 ];
 
+/* eslint-disable no-use-before-define */
+
 const thunkExtras: $Exact<ThunkExtras> = {
-  // eslint-disable-next-line no-use-before-define
   getGlobalSession: () => getGlobalSession(store.getState()),
-
-  // eslint-disable-next-line no-use-before-define
   getGlobalSettings: () => getGlobalSettings(store.getState()),
 };
 
-const globalThunkExtras: $Exact<GlobalThunkExtras> = Object.freeze({
-  // TODO add things
-});
+const globalThunkExtras: $Exact<GlobalThunkExtras> = {
+  // $FlowFixMe[escaped-generic]
+  // $FlowFixMe[incompatible-type]
+  /* $FlowFixMe[incompatible-cast]
+     The `store` type isn't complete: in particular it ignores thunk actions.
+
+     We're also using here the fact that the one function `store.dispatch`
+     secretly plays both the role of our `GlobalDispatch` type and our
+     `Dispatch` type... and that in the latter role, the PerAccountState
+     that it acts on is the one belonging to the active account.
+
+     TODO(#5006): We'll have to add more logic here when per-account and
+       global state become distinct.
+   */
+  activeAccountDispatch: action => (store.dispatch: Dispatch)(action),
+};
 
 const combinedThunkExtras: ThunkExtras & GlobalThunkExtras = {
   ...thunkExtras,

src/reduxTypes.js

@@ -638,7 +638,8 @@ export type ThunkAction<T> = (Dispatch, () => PerAccountState, ThunkExtras) => T
 
 /** The extras object passed to a global thunk action. */
 export type GlobalThunkExtras = $ReadOnly<{
-  // TODO add things
+  /** A per-account `dispatch` that acts on the active account. */
+  activeAccountDispatch: Dispatch,
   ...
 }>;