Improve network state observer

app/src/main/java/org/koitharu/kotatsu/utils/MediatorStateFlow.kt

@@ -0,0 +1,42 @@
+package org.koitharu.kotatsu.utils
+
+import kotlinx.coroutines.flow.FlowCollector
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import java.util.concurrent.atomic.AtomicInteger
+
+abstract class MediatorStateFlow<T> : StateFlow<T> {
+
+	@Suppress("LeakingThis")
+	private val delegate = MutableStateFlow(initialValue)
+	private val collectors = AtomicInteger(0)
+
+	protected abstract val initialValue: T
+
+	final override val replayCache: List<T>
+		get() = delegate.replayCache
+
+	final override val value: T
+		get() = delegate.value
+
+	final override suspend fun collect(collector: FlowCollector<T>): Nothing {
+		try {
+			if (collectors.getAndIncrement() == 0) {
+				onActive()
+			}
+			delegate.collect(collector)
+		} finally {
+			if (collectors.decrementAndGet() == 0) {
+				onInactive()
+			}
+		}
+	}
+
+	protected fun publishValue(v: T) {
+		delegate.value = v
+	}
+
+	abstract fun onActive()
+
+	abstract fun onInactive()
+}