INCOMPLETE: Untested refactor to reduce number of chain subscriptions and simply the management thereof

lib/electrumx_rpc/electrumx_chain_height_service.dart

@@ -1,14 +1,57 @@
 import 'dart:async';
 
+import 'package:electrum_adapter/electrum_adapter.dart';
 import 'package:stackwallet/utilities/enums/coin_enum.dart';
 
-/// Store chain height subscriptions for each coin.
-abstract class ElectrumxChainHeightService {
-  // Used to hold chain height subscriptions for each coin as in:
-  // ElectrumxChainHeightService.subscriptions[cryptoCurrency.coin] = sub;
-  static Map<Coin, StreamSubscription<dynamic>?> subscriptions = {};
+/// Manage chain height subscriptions for each coin.
+abstract class ChainHeightServiceManager {
+  static final Map<Coin, ChainHeightService> _services = {};
 
-  // Used to hold chain height completers for each coin as in:
-  // ElectrumxChainHeightService.completers[cryptoCurrency.coin] = completer;
-  static Map<Coin, Completer<int>?> completers = {};
+  static ChainHeightService? getService(Coin coin) {
+    return _services[coin];
+  }
+
+  static void add(ChainHeightService service, Coin coin) {
+    if (_services[coin] == null) {
+      _services[coin] = service;
+    } else {
+      throw Exception("Chain height service for $coin already managed");
+    }
+  }
+}
+
+// Basic untested impl. Needs error handling and branching to handle
+// various other scenarios
+class ChainHeightService {
+  ElectrumClient client;
+
+  StreamSubscription<dynamic>? _subscription;
+  bool get started => _subscription != null;
+
+  int? _height;
+  int? get height => _height;
+
+  ChainHeightService({required this.client});
+
+  Future<int> fetchHeightAndStartListenForUpdates() async {
+    if (_subscription != null) {
+      throw Exception(
+        "Attempted to start a chain height service where an existing"
+        " subscription already exists!",
+      );
+    }
+
+    final completer = Completer<int>();
+    _subscription = client.subscribeHeaders().listen((event) {
+      _height = event.height;
+      if (!completer.isCompleted) {
+        completer.complete(_height);
+      }
+    });
+
+    return completer.future;
+  }
+
+  /// Untested/Unknown implications. USE AT OWN RISK
+  Future<void> cancelListen() async => await _subscription?.cancel();
 }

lib/wallets/wallet/wallet.dart

@@ -4,7 +4,6 @@ import 'package:isar/isar.dart';
 import 'package:meta/meta.dart';
 import 'package:mutex/mutex.dart';
 import 'package:stackwallet/db/isar/main_db.dart';
-import 'package:stackwallet/electrumx_rpc/electrumx_chain_height_service.dart';
 import 'package:stackwallet/models/isar/models/blockchain_data/address.dart';
 import 'package:stackwallet/models/isar/models/ethereum/eth_contract.dart';
 import 'package:stackwallet/models/node_model.dart';
@@ -617,9 +616,10 @@ abstract class Wallet<T extends CryptoCurrency> {
 
     switch (prefs.syncType) {
       case SyncingType.currentWalletOnly:
-        // Close the subscription for this coin's chain height.
-        await ElectrumxChainHeightService.subscriptions[cryptoCurrency.coin]
-            ?.cancel();
+      // Close the subscription for this coin's chain height.
+      // NOTE: This does not work now that the subscription is shared
+      // await  (await ChainHeightServiceManager.getService(cryptoCurrency.coin))
+      //     ?.cancelListen();
       case SyncingType.selectedWalletsAtStartup:
         // Close the subscription if this wallet is not in the list to be synced.
         if (!prefs.walletIdsSyncOnStartup.contains(walletId)) {
@@ -639,8 +639,10 @@ abstract class Wallet<T extends CryptoCurrency> {
 
           // If there are no other wallets of this coin, then close the sub.
           if (walletIds.isEmpty) {
-            await ElectrumxChainHeightService.subscriptions[cryptoCurrency.coin]
-                ?.cancel();
+            // NOTE: This does not work now that the subscription is shared
+            // await (await ChainHeightServiceManager.getService(
+            //         cryptoCurrency.coin))
+            //     ?.cancelListen();
           }
         }
       case SyncingType.allWalletsOnStartup:

lib/wallets/wallet/wallet_mixin_interfaces/electrumx_interface.dart

@@ -44,8 +44,6 @@ mixin ElectrumXInterface<T extends Bip39HDCurrency> on Bip39HDWallet<T> {
 
   int? get maximumFeerate => null;
 
-  int? _latestHeight;
-
   StreamSubscription<TorPreferenceChangedEvent>? _torPreferenceListener;
   StreamSubscription<TorConnectionStatusChangedEvent>? _torStatusListener;
 
@@ -815,53 +813,20 @@ mixin ElectrumXInterface<T extends Bip39HDCurrency> on Bip39HDWallet<T> {
 
   Future<int> fetchChainHeight() async {
     try {
-      // _checkChainHeightSubscription();
-      // TODO above.  Make sure that the subscription/stream is alive.
+      ChainHeightService? service = ChainHeightServiceManager.getService(
+        cryptoCurrency.coin,
+      );
 
-      // Don't set a stream subscription if one already exists.
-      if (ElectrumxChainHeightService.subscriptions[cryptoCurrency.coin] ==
-          null) {
-        final Completer<int> completer = Completer<int>();
-
-        // Make sure we only complete once.
-        final isFirstResponse = _latestHeight == null;
-
-        await electrumXClient.checkElectrumAdapter();
-        // TODO [prio=extreme]: Does this update anything in this file?? Thinking no.
-
-        final stream = electrumAdapterClient.subscribeHeaders();
-
-        ElectrumxChainHeightService.subscriptions[cryptoCurrency.coin] =
-            stream.asBroadcastStream().listen((response) {
-          final int chainHeight = response.height;
-          // print("Current chain height: $chainHeight");
-
-          _latestHeight = chainHeight;
-
-          if (isFirstResponse && !completer.isCompleted) {
-            // Return the chain height.
-            completer.complete(chainHeight);
-          }
-        });
-      } else {
-        // Don't set a stream subscription if one already exists.
-
-        // Check if the stream subscription is paused.
-        if (ElectrumxChainHeightService
-            .subscriptions[cryptoCurrency.coin]!.isPaused) {
-          // If it's paused, resume it.
-          ElectrumxChainHeightService.subscriptions[cryptoCurrency.coin]!
-              .resume();
-        }
-
-        if (_latestHeight != null) {
-          return _latestHeight!;
-        }
+      if (service == null) {
+        service = ChainHeightService(client: electrumAdapterClient);
+        ChainHeightServiceManager.add(service, cryptoCurrency.coin);
       }
 
-      // Probably waiting on the subscription to receive the latest block height
-      // fallback to cached value
-      return info.cachedChainHeight;
+      if (!service.started) {
+        return await service.fetchHeightAndStartListenForUpdates();
+      }
+
+      return service.height ?? info.cachedChainHeight;
     } catch (e, s) {
       Logging.instance.log(
           "Exception rethrown in fetchChainHeight\nError: $e\nStack trace: $s",