store [nfc]: The event-poll loop has-a store, not is-a store

This seems to make more sense conceptually.

For its most immediate practical effect, this means
UpdateMachine.fromInitialSnapshot doesn't care whether
PerAccountStore.fromInitialSnapshot is a generative or a
factory constructor, which will give us the flexibility to
make it the latter.

This change will also probably be helpful for making other
decouplings of the polling and registerNotificationToken logic
from the data structures of PerAccountStore.

Author: gnprice

lib/model/store.dart

@@ -418,8 +418,9 @@ class LiveGlobalStore extends GlobalStore {
   final AppDatabase _db;
 
   @override
-  Future<PerAccountStore> loadPerAccount(Account account) {
-    return LivePerAccountStore.load(account);
+  Future<PerAccountStore> loadPerAccount(Account account) async {
+    final updateMachine = await UpdateMachine.load(account);
+    return updateMachine.store;
   }
 
   @override
@@ -436,26 +437,24 @@ class LiveGlobalStore extends GlobalStore {
   }
 }
 
-/// A [PerAccountStore] which polls an event queue to stay up to date.
+/// A [PerAccountStore] plus an event-polling loop to stay up to date.
 // TODO decouple "live"ness from polling and registerNotificationToken;
 //   the latter are made up of testable internal logic, not external integration
-class LivePerAccountStore extends PerAccountStore {
-  LivePerAccountStore.fromInitialSnapshot({
-    required super.account,
-    required super.connection,
-    required super.initialSnapshot,
+class UpdateMachine {
+  UpdateMachine.fromInitialSnapshot({
+    required this.store,
+    required InitialSnapshot initialSnapshot,
   }) : queueId = initialSnapshot.queueId ?? (() {
          // The queueId is optional in the type, but should only be missing in the
          // case of unauthenticated access to a web-public realm.  We authenticated.
          throw Exception("bad initial snapshot: missing queueId");
        })(),
-       lastEventId = initialSnapshot.lastEventId,
-       super.fromInitialSnapshot();
+       lastEventId = initialSnapshot.lastEventId;
 
   /// Load the user's data from the server, and start an event queue going.
   ///
   /// In the future this might load an old snapshot from local storage first.
-  static Future<PerAccountStore> load(Account account) async {
+  static Future<UpdateMachine> load(Account account) async {
     final connection = ApiConnection.live(
       realmUrl: account.realmUrl, zulipFeatureLevel: account.zulipFeatureLevel,
       email: account.email, apiKey: account.apiKey);
@@ -466,30 +465,33 @@ class LivePerAccountStore extends PerAccountStore {
     // TODO log the time better
     if (kDebugMode) print("initial fetch time: ${t.inMilliseconds}ms");
 
-    final store = LivePerAccountStore.fromInitialSnapshot(
+    final store = PerAccountStore.fromInitialSnapshot(
       account: account,
       connection: connection,
       initialSnapshot: initialSnapshot,
     );
-    store.poll();
+    final updateMachine = UpdateMachine.fromInitialSnapshot(
+      store: store, initialSnapshot: initialSnapshot);
+    updateMachine.poll();
     // TODO do registerNotificationToken before registerQueue:
     //   https://github.com/zulip/zulip-flutter/pull/325#discussion_r1365982807
-    store.registerNotificationToken();
-    return store;
+    updateMachine.registerNotificationToken();
+    return updateMachine;
   }
 
+  final PerAccountStore store;
   final String queueId;
   int lastEventId;
 
   void poll() async {
     while (true) {
-      final result = await getEvents(connection,
+      final result = await getEvents(store.connection,
         queueId: queueId, lastEventId: lastEventId);
       // TODO handle errors on get-events; retry with backoff
       // TODO abort long-poll and close ApiConnection on [dispose]
       final events = result.events;
       for (final event in events) {
-        handleEvent(event);
+        store.handleEvent(event);
       }
       if (events.isNotEmpty) {
         lastEventId = events.last.id;
@@ -513,6 +515,6 @@ class LivePerAccountStore extends PerAccountStore {
   Future<void> _registerNotificationToken() async {
     final token = NotificationService.instance.token.value;
     if (token == null) return;
-    await NotificationService.registerToken(connection, token: token);
+    await NotificationService.registerToken(store.connection, token: token);
   }
 }

test/example_data.dart

@@ -473,11 +473,11 @@ PerAccountStore store({Account? account, InitialSnapshot? initialSnapshot}) {
     initialSnapshot: initialSnapshot ?? _initialSnapshot(),
   );
 }
+const _store = store;
 
-LivePerAccountStore liveStore({Account? account, InitialSnapshot? initialSnapshot}) {
-  return LivePerAccountStore.fromInitialSnapshot(
-    account: account ?? selfAccount,
-    connection: FakeApiConnection.fromAccount(account ?? selfAccount),
-    initialSnapshot: initialSnapshot ?? _initialSnapshot(),
-  );
+UpdateMachine updateMachine({Account? account, InitialSnapshot? initialSnapshot}) {
+  initialSnapshot ??= _initialSnapshot();
+  final store = _store(account: account, initialSnapshot: initialSnapshot);
+  return UpdateMachine.fromInitialSnapshot(
+    store: store, initialSnapshot: initialSnapshot);
 }

test/model/store_test.dart

@@ -108,13 +108,13 @@ void main() {
     check(completers(1)).length.equals(1);
   });
 
-  group('PerAccountStore.registerNotificationToken', () {
-    late LivePerAccountStore store;
+  group('UpdateMachine.registerNotificationToken', () {
+    late UpdateMachine updateMachine;
     late FakeApiConnection connection;
 
     void prepareStore() {
-      store = eg.liveStore();
-      connection = store.connection as FakeApiConnection;
+      updateMachine = eg.updateMachine();
+      connection = updateMachine.store.connection as FakeApiConnection;
     }
 
     void checkLastRequestApns({required String token, required String appid}) {
@@ -143,7 +143,7 @@ void main() {
       // On store startup, send the token.
       prepareStore();
       connection.prepare(json: {});
-      await store.registerNotificationToken();
+      await updateMachine.registerNotificationToken();
       if (defaultTargetPlatform == TargetPlatform.android) {
         checkLastRequestFcm(token: '012abc');
       } else {
@@ -177,7 +177,7 @@ void main() {
 
       // On store startup, send nothing (because we have nothing to send).
       prepareStore();
-      await store.registerNotificationToken();
+      await updateMachine.registerNotificationToken();
       check(connection.lastRequest).isNull();
 
       // When the token later appears, send it.