refactor: move batch logic out of system

pub/alien_signals/lib/alien_signals.dart

@@ -1,3 +1,4 @@
+export 'src/batch.dart';
 export 'src/computed.dart';
 export 'src/effect.dart';
 export 'src/effect_scope.dart';

pub/alien_signals/lib/src/batch.dart

@@ -0,0 +1,39 @@
+import 'system.dart';
+
+int batchDepth = 0;
+
+/// Start a new batch of updates.
+///
+/// This function increments the batch depth counter, indicating the start of a new batch of updates.
+/// Batching updates can help optimize performance by reducing the number of times the system processes changes.
+///
+/// {@template alien_signals.batch.example}
+/// ```Example
+/// final a = signal(0);
+/// final b = signal(0);
+///
+/// effect(() {
+///   print('effect run');
+/// });
+///
+/// startBatch();
+/// a.set(1);
+/// b.set(1);
+/// endBatch();
+/// ```
+/// {@endtemplate}
+void startBatch() {
+  ++batchDepth;
+}
+
+/// End the current batch of updates.
+///
+/// This function decrements the batch depth counter. If the batch depth reaches zero, it triggers the processing
+/// of any queued effects that were accumulated during the batch.
+///
+/// {@macro alien_signals.batch.example}
+void endBatch() {
+  if ((--batchDepth) == 0) {
+    drainQueuedEffects();
+  }
+}

pub/alien_signals/lib/src/signal.dart

@@ -1,3 +1,4 @@
+import 'batch.dart';
 import 'effect.dart';
 import 'system.dart';
 import 'types.dart';
@@ -52,6 +53,9 @@ class Signal<T> implements Dependency, IWritableSignal<T> {
       currentValue = value;
       if (subs != null) {
         propagate(subs);
+        if (batchDepth == 0) {
+          drainQueuedEffects();
+        }
       }
     }
   }

pub/alien_signals/lib/src/system.dart

@@ -112,48 +112,11 @@ class Link {
   Link? nextDep;
 }
 
-int _batchDepth = 0;
 IEffect? _queuedEffects;
 IEffect? _queuedEffectsTail;
 Link? _linkPool;
 
-/// Start a new batch of updates.
-///
-/// This function increments the batch depth counter, indicating the start of a new batch of updates.
-/// Batching updates can help optimize performance by reducing the number of times the system processes changes.
-///
-/// {@template alien_signals.batch.example}
-/// ```Example
-/// final a = signal(0);
-/// final b = signal(0);
-///
-/// effect(() {
-///   print('effect run');
-/// });
-///
-/// startBatch();
-/// a.set(1);
-/// b.set(1);
-/// endBatch();
-/// ```
-/// {@endtemplate}
-void startBatch() {
-  ++_batchDepth;
-}
-
-/// End the current batch of updates.
-///
-/// This function decrements the batch depth counter. If the batch depth reaches zero, it triggers the processing
-/// of any queued effects that were accumulated during the batch.
-///
-/// {@macro alien_signals.batch.example}
-void endBatch() {
-  if ((--_batchDepth) == 0) {
-    _drainQueuedEffects();
-  }
-}
-
-void _drainQueuedEffects() {
+void drainQueuedEffects() {
   while (_queuedEffects != null) {
     final effect = _queuedEffects!;
     final queuedNext = effect.nextNotify;
@@ -329,10 +292,6 @@ void propagate(Link? link) {
 
     break;
   } while (true);
-
-  if (_batchDepth == 0) {
-    _drainQueuedEffects();
-  }
 }
 
 /// Propagate changes through the dependency graph shallowly