Initial setup for navigation display with nav3

Signed-off-by: Aayush Gupta <aayushgupta219@gmail.com>

shared/build.gradle.kts

@@ -9,6 +9,7 @@ plugins {
     alias(libs.plugins.jetbrains.kotlin.compose)
     alias(libs.plugins.jetbrains.compose.multiplatform)
     alias(libs.plugins.koin)
+    alias(libs.plugins.jetbrains.kotlinx.serialization)
 }
 
 kotlin {
@@ -80,6 +81,7 @@ kotlin {
 
                 implementation(libs.jetbrains.navigation3.ui)
                 implementation(libs.jetbrains.lifecycle.navigation3)
+                implementation(libs.kotlinx.serialization.json)
 
                 implementation(libs.koin.compose.viewmodel)
                 implementation(libs.koin.annotations)

shared/src/androidMain/kotlin/net/newpipe/Constants.kt

@@ -0,0 +1,11 @@
+/*
+ * SPDX-FileCopyrightText: 2026 NewPipe e.V. <https://newpipe-ev.de>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package net.newpipe
+
+object Constants {
+
+    const val INTENT_SCREEN_KEY = "SCREEN"
+}

shared/src/androidMain/kotlin/net/newpipe/app/ComposeActivity.kt

@@ -9,6 +9,9 @@ import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
+import kotlinx.serialization.json.Json
+import net.newpipe.Constants
+import net.newpipe.app.navigation.Screen
 
 /**
  * Entry point for compose-related UI components on Android
@@ -19,7 +22,12 @@ class ComposeActivity : ComponentActivity() {
         super.onCreate(savedInstanceState)
 
         setContent {
-            App()
+            App(
+                // TODO: Change when everything is in compose and this is the primary activity
+                startDestination = Json.decodeFromString<Screen>(
+                    intent.getStringExtra(Constants.INTENT_SCREEN_KEY)!!
+                )
+            )
         }
     }
 }

shared/src/androidMain/kotlin/net/newpipe/app/extensions/Context.kt

@@ -0,0 +1,22 @@
+/*
+ * SPDX-FileCopyrightText: 2026 NewPipe e.V. <https://newpipe-ev.de>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package net.newpipe.app.extensions
+
+import android.content.Context
+import android.content.Intent
+import kotlin.jvm.java
+import kotlinx.serialization.json.Json
+import net.newpipe.Constants
+import net.newpipe.app.ComposeActivity
+import net.newpipe.app.navigation.Screen
+
+/**
+ * Navigates to a given compose destination
+ */
+fun Context.navigateTo(screen: Screen) = Intent(this, ComposeActivity::class.java).also { intent ->
+    intent.putExtra(Constants.INTENT_SCREEN_KEY, Json.encodeToString(screen))
+    startActivity(intent)
+}

shared/src/commonMain/kotlin/net/newpipe/app/App.kt

@@ -6,15 +6,18 @@
 package net.newpipe.app
 
 import androidx.compose.runtime.Composable
-import androidx.compose.ui.tooling.preview.Preview
 import net.newpipe.app.di.KoinApp
+import net.newpipe.app.navigation.Screen
 import net.newpipe.app.theme.AppTheme
 import org.koin.compose.KoinApplication
 import org.koin.plugin.module.dsl.koinConfiguration
 
+/**
+ * Entry point for the multiplatform compose application
+ * @param startDestination Starting destination for the app
+ */
 @Composable
-@Preview
-fun App() {
+fun App(startDestination: Screen? = null) {
     KoinApplication(configuration = koinConfiguration<KoinApp>()) {
         AppTheme {
         }

shared/src/commonMain/kotlin/net/newpipe/app/navigation/NavDisplay.kt

@@ -0,0 +1,26 @@
+/*
+ * SPDX-FileCopyrightText: 2026 NewPipe e.V. <https://newpipe-ev.de>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package net.newpipe.app.navigation
+
+import androidx.compose.runtime.Composable
+import androidx.navigation3.runtime.entryProvider
+import androidx.navigation3.runtime.rememberNavBackStack
+import androidx.navigation3.ui.NavDisplay
+
+/**
+ * Navigation display for compose screens
+ * @param startDestination Starting destination for the app
+ */
+@Composable
+fun NavDisplay(startDestination: Screen) {
+    val backstack = rememberNavBackStack(screenConfig, startDestination)
+
+    NavDisplay(
+        backStack = backstack,
+        entryProvider = entryProvider {
+        }
+    )
+}

shared/src/commonMain/kotlin/net/newpipe/app/navigation/Screen.kt

@@ -0,0 +1,31 @@
+/*
+ * SPDX-FileCopyrightText: 2026 NewPipe e.V. <https://newpipe-ev.de>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package net.newpipe.app.navigation
+
+import androidx.navigation3.runtime.NavKey
+import androidx.savedstate.serialization.SavedStateConfiguration
+import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.modules.SerializersModule
+import kotlinx.serialization.modules.polymorphic
+
+/**
+ * Destinations for navigation in compose
+ */
+@Serializable
+sealed interface Screen : NavKey
+
+/**
+ * Saved state configuration for screens
+ */
+@OptIn(ExperimentalSerializationApi::class)
+internal val screenConfig = SavedStateConfiguration {
+    serializersModule = SerializersModule {
+        polymorphic(NavKey::class) {
+            subclassesOfSealed<Screen>()
+        }
+    }
+}