Use Immutable Record for accounts in Redux state (#26559)

app/javascript/mastodon/reducers/accounts.ts

@@ -0,0 +1,82 @@
+import { Map as ImmutableMap } from 'immutable';
+
+import type { Reducer } from 'redux';
+
+import {
+  followAccountSuccess,
+  unfollowAccountSuccess,
+  importAccounts,
+  revealAccount,
+} from 'mastodon/actions/accounts_typed';
+import type { ApiAccountJSON } from 'mastodon/api_types/accounts';
+import { me } from 'mastodon/initial_state';
+import type { Account } from 'mastodon/models/account';
+import { createAccountFromServerJSON } from 'mastodon/models/account';
+
+const initialState = ImmutableMap<string, Account>();
+
+const normalizeAccount = (
+  state: typeof initialState,
+  account: ApiAccountJSON,
+) => {
+  return state.set(
+    account.id,
+    createAccountFromServerJSON(account).set(
+      'hidden',
+      state.get(account.id)?.hidden === false
+        ? false
+        : account.limited || false,
+    ),
+  );
+};
+
+const normalizeAccounts = (
+  state: typeof initialState,
+  accounts: ApiAccountJSON[],
+) => {
+  accounts.forEach((account) => {
+    state = normalizeAccount(state, account);
+  });
+
+  return state;
+};
+
+export const accountsReducer: Reducer<typeof initialState> = (
+  state = initialState,
+  action,
+) => {
+  const currentUserId = me;
+
+  if (!currentUserId)
+    throw new Error(
+      'No current user (me) defined when calling `accountsReducer`',
+    );
+
+  if (revealAccount.match(action))
+    return state.setIn([action.payload.id, 'hidden'], false);
+  else if (importAccounts.match(action))
+    return normalizeAccounts(state, action.payload.accounts);
+  else if (followAccountSuccess.match(action))
+    return state
+      .update(
+        action.payload.relationship.id,
+        (account) => account?.update('followers_count', (n) => n + 1),
+      )
+      .update(
+        currentUserId,
+        (account) => account?.update('following_count', (n) => n + 1),
+      );
+  else if (unfollowAccountSuccess.match(action))
+    return state
+      .update(
+        action.payload.relationship.id,
+        (account) =>
+          account?.update('followers_count', (n) => Math.max(0, n - 1)),
+      )
+      .update(
+        currentUserId,
+        (account) =>
+          account?.update('following_count', (n) => Math.max(0, n - 1)),
+      );
+  else return state;
+};