Add SaveableMutableStateSource (#210)

vice-sources/build.gradle.kts

@@ -22,6 +22,7 @@ kotlin {
 
         implementation(libs.compose.lifecycle)
         api(compose.runtime)
+        api(compose.runtimeSaveable)
 
         api(libs.kotlinx.coroutines.core)
       }

vice-sources/src/commonMain/kotlin/com/eygraber/vice/sources/SaveableMutableStateSource.kt

@@ -0,0 +1,28 @@
+package com.eygraber.vice.sources
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.State
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.compose.runtime.snapshotFlow
+import com.eygraber.vice.ViceSource
+import kotlinx.coroutines.flow.Flow
+
+public abstract class SaveableMutableStateSource<T> : ViceSource<T>, State<T> {
+  private val state by lazy {
+    mutableStateOf(initial)
+  }
+
+  public val updates: Flow<T> get() = snapshotFlow { state.value }
+
+  override val value: T get() = state.value
+
+  protected abstract val initial: T
+
+  protected fun update(value: T) {
+    state.value = value
+  }
+
+  @Composable
+  override fun currentState(): T = rememberSaveable { state }.value
+}