From 416959a855dc09501e4c83b6f410d79836cbb0d5 Mon Sep 17 00:00:00 2001
From: forhad013 <forhad013@gmail.com>
Date: Thu, 26 Oct 2023 10:28:48 +0800
Subject: [PATCH] Added function to retrieve instance from backstack

---
 decompose-router/build.gradle.kts             |  1 +
 .../github/xxfast/decompose/router/Router.kt  | 40 +++++++++++++++++++
 gradle/libs.versions.toml                     |  1 +
 3 files changed, 42 insertions(+)

diff --git a/decompose-router/build.gradle.kts b/decompose-router/build.gradle.kts
index 0a32093..a4757e3 100644
--- a/decompose-router/build.gradle.kts
+++ b/decompose-router/build.gradle.kts
@@ -36,6 +36,7 @@ kotlin {
         implementation(libs.essenty.parcelable)
         implementation(libs.decompose)
         implementation(libs.decompose.compose.multiplatform)
+        implementation(libs.kotlin.reflect)
       }
     }
 
diff --git a/decompose-router/src/commonMain/kotlin/io/github/xxfast/decompose/router/Router.kt b/decompose-router/src/commonMain/kotlin/io/github/xxfast/decompose/router/Router.kt
index 48b9aa7..7cc0ea4 100644
--- a/decompose-router/src/commonMain/kotlin/io/github/xxfast/decompose/router/Router.kt
+++ b/decompose-router/src/commonMain/kotlin/io/github/xxfast/decompose/router/Router.kt
@@ -8,6 +8,7 @@ import androidx.compose.runtime.State
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.staticCompositionLocalOf
+import com.arkivanov.decompose.Child
 import com.arkivanov.decompose.router.stack.ChildStack
 import com.arkivanov.decompose.router.stack.StackNavigation
 import com.arkivanov.decompose.router.stack.childStack
@@ -119,3 +120,42 @@ fun <T : Instance> rememberOnRoute(
 
   return instance
 }
+
+/***
+ * Retrieve a instance of [V] that is scoped to the current route
+ *
+ * @param type of [V] instance
+ * @param childClass class of stack child[T]
+ * @param keyBlock lambda to configure the key [which was used to save the instance [T]] by default [type].key
+ */
+
+private inline fun <C : Parcelable, reified T : Any, reified V : Instance> Router<C>.getInstanceFromBackStack(
+  type: KClass<V>,
+  childClass: KClass<T>,
+  keyBlock: ((childConfiguration: T) -> Any?) = { null }
+): V {
+  val child: Child.Created<C, RouterContext>? = this.stack.value.backStack
+    .firstOrNull { it.configuration is T }
+
+  require(child != null) {
+    "Couldn't find the ${T::class} in the backstack"
+  }
+
+  val configuration: C = child.configuration
+  require(configuration is T) {
+    "Couldn't find the ${T::class} in the backstack"
+  }
+
+  val childConfiguration: T = configuration
+  val key: Any? = keyBlock(childConfiguration)
+  val keyInstance: String = if (key == null) "${type.key}.instance"
+  else "${key}.instance"
+
+  val viewModelInstance: Instance? = child.instance.instanceKeeper.get(keyInstance)
+
+  require(viewModelInstance is V) {
+    "Couldn't find the viewModel for  ${T::class} in the backstack"
+  }
+
+  return viewModelInstance
+}
\ No newline at end of file
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index ca35220..e4034ca 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -24,6 +24,7 @@ decompose-compose-multiplatform = { module = "com.arkivanov.decompose:extensions
 essenty-parcelable = { module = "com.arkivanov.essenty:parcelable", version.ref = "essenty" }
 horologist-compose-layouts = { module = "com.google.android.horologist:horologist-compose-layout", version.ref = "horologist" }
 kotlin-gradle-plugin = { module = "org.jetbrains.kotlin:kotlin-gradle-plugin", version.ref = "kotlin" }
+kotlin-reflect = { module = "org.jetbrains.kotlin:kotlin-reflect", version.ref = "kotlin" }
 kotlinx-coroutines-swing = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-swing", version.ref = "kotlinx-coroutines" }
 wear-compose-foundation = { module = "androidx.wear.compose:compose-foundation", version.ref = "wear-compose" }
 wear-compose-material = { module = "androidx.wear.compose:compose-material", version.ref = "wear-compose" }