fix(android): add tests for backstack and fix deeplink navigation

android/build.gradle.kts

@@ -6,6 +6,8 @@
  */
 @file:Suppress("UnstableApiUsage")
 
+import dev.msfjarvis.claw.gradle.addTestDependencies
+
 plugins {
   id("dev.msfjarvis.claw.android-application")
   id("dev.msfjarvis.claw.rename-artifacts")
@@ -118,4 +120,6 @@ dependencies {
   compileOnly(libs.androidx.compose.glance.preview)
 
   runtimeOnly(libs.androidx.profileinstaller)
+
+  addTestDependencies(project)
 }

android/src/main/kotlin/dev/msfjarvis/claw/android/MainActivity.kt

@@ -79,6 +79,7 @@ class MainActivity(
           windowSizeClass = windowSizeClass,
           setWebUri = { url -> webUri = url },
           deepLinkDestination = deepLinkDestination,
+          clearDeepLink = { deepLinkDestination = null },
         )
       }
     }

android/src/main/kotlin/dev/msfjarvis/claw/android/ui/screens/LobstersPostsScreen.kt

@@ -8,6 +8,7 @@ package dev.msfjarvis.claw.android.ui.screens
 
 import androidx.activity.compose.BackHandler
 import androidx.activity.compose.LocalActivity
+import androidx.annotation.VisibleForTesting
 import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.animation.EnterTransition
 import androidx.compose.animation.ExitTransition
@@ -87,6 +88,7 @@ fun LobstersPostsScreen(
   setWebUri: (String?) -> Unit,
   modifier: Modifier = Modifier,
   deepLinkDestination: NavKey? = null,
+  clearDeepLink: () -> Unit = {},
   viewModel: ClawViewModel = metroViewModel(),
   tagFilterViewModel: TagFilterViewModel = metroViewModel(key = "tag_filter"),
 ) {
@@ -113,7 +115,8 @@ fun LobstersPostsScreen(
 
   LaunchedEffect(deepLinkDestination) {
     if (deepLinkDestination != null) {
-      navigateTo(backStack, deepLinkDestination)
+      navigateTo(backStack, deepLinkDestination, allowStacking = true)
+      clearDeepLink()
     }
   }
 
@@ -296,7 +299,8 @@ fun LobstersPostsScreen(
   }
 }
 
-private fun navigateTo(
+@VisibleForTesting(otherwise = VisibleForTesting.PRIVATE)
+fun navigateTo(
   backStack: MutableList<NavKey>,
   destination: NavKey,
   allowStacking: Boolean = false,
@@ -306,24 +310,27 @@ private fun navigateTo(
     if (destination != Hottest) {
       backStack.add(Hottest)
     }
+    backStack.add(destination)
+    return
   }
 
   if (destination is NonStackable) {
+    if (allowStacking && destination is Comments) {
+      val lastItem = backStack.lastOrNull()
+      if (lastItem is Comments && lastItem.postId == destination.postId) {
+        return
+      }
+      backStack.add(destination)
+      return
+    }
+
     val existingEntry =
       backStack.firstOrNull {
         it is NonStackable && it::class.java.isAssignableFrom(destination::class.java)
       }
 
     if (existingEntry != null) {
-      val existingIndex = backStack.indexOf(existingEntry)
       backStack.remove(existingEntry)
-
-      if (allowStacking && destination is Comments && existingEntry is Comments) {
-        if (destination.postId != existingEntry.postId) {
-          backStack.add(existingIndex, destination)
-          return
-        }
-      }
     }
   }
 

android/src/test/kotlin/dev/msfjarvis/claw/android/ui/screens/BackStackBehaviorTest.kt

@@ -0,0 +1,71 @@
+/*
+ * Copyright © Harsh Shandilya.
+ * Use of this source code is governed by an MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT.
+ */
+package dev.msfjarvis.claw.android.ui.screens
+
+import androidx.navigation3.runtime.NavKey
+import com.google.common.truth.Truth.assertThat
+import dev.msfjarvis.claw.android.ui.navigation.Comments
+import dev.msfjarvis.claw.android.ui.navigation.Hottest
+import dev.msfjarvis.claw.android.ui.navigation.Newest
+import dev.msfjarvis.claw.android.ui.navigation.Saved
+import org.junit.jupiter.api.Test
+
+class BackStackBehaviorTest {
+
+  private fun makeBackStack(vararg keys: NavKey) = mutableListOf(*keys)
+
+  @Test
+  fun `navigating from between top level destinations prevents stacking`() {
+    val backStack = makeBackStack(Hottest)
+
+    navigateTo(backStack, Newest)
+
+    assertThat(backStack).containsExactly(Hottest, Newest).inOrder()
+
+    navigateTo(backStack, Saved)
+
+    assertThat(backStack).containsExactly(Hottest, Saved).inOrder()
+  }
+
+  @Test
+  fun `NonStackable destinations do not stack by default`() {
+    val backStack = makeBackStack(Hottest, Comments("abc123"))
+
+    navigateTo(backStack, Comments("def456"))
+
+    assertThat(backStack).containsExactly(Hottest, Comments("def456")).inOrder()
+  }
+
+  @Test
+  fun `NonStackable destinations stack when allowStacking = true`() {
+    val backStack = makeBackStack(Hottest, Comments("abc123"))
+
+    navigateTo(backStack, Comments("def456"), allowStacking = true)
+
+    assertThat(backStack).containsExactly(Hottest, Comments("abc123"), Comments("def456")).inOrder()
+  }
+
+  @Test
+  fun `Same destination cannot be stacked on itself`() {
+    val backStack = makeBackStack(Hottest, Comments("abc123"))
+
+    navigateTo(backStack, Comments("abc123"), allowStacking = true)
+
+    assertThat(backStack).containsExactly(Hottest, Comments("abc123")).inOrder()
+  }
+
+  @Test
+  fun `Same destination can be stacked with a gap in between`() {
+    val backStack = makeBackStack(Hottest, Comments("abc123"), Comments("def456"))
+
+    navigateTo(backStack, Comments("abc123"), allowStacking = true)
+
+    assertThat(backStack)
+      .containsExactly(Hottest, Comments("abc123"), Comments("def456"), Comments("abc123"))
+      .inOrder()
+  }
+}