[Architecture] introduce BackstackNode

libraries/architecture/src/main/kotlin/io/element/android/libraries/architecture/BackstackNode.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.element.android.libraries.architecture
+
+import androidx.compose.runtime.Stable
+import com.bumble.appyx.Appyx
+import com.bumble.appyx.core.children.ChildEntry
+import com.bumble.appyx.core.modality.BuildContext
+import com.bumble.appyx.core.node.ParentNode
+import com.bumble.appyx.core.plugin.Plugin
+import com.bumble.appyx.navmodel.backstack.BackStack
+
+@Stable
+abstract class BackstackNode<NavTarget : Any>(
+    val backstack: BackStack<NavTarget>,
+    buildContext: BuildContext,
+    childKeepMode: ChildEntry.KeepMode = Appyx.defaultChildKeepMode,
+    plugins: List<Plugin>
+) : ParentNode<NavTarget>(
+    navModel = backstack,
+    buildContext = buildContext,
+    plugins = plugins,
+    childKeepMode = childKeepMode,
+)