BIT-144: Setup root level app navigation (#8)

app/src/main/java/com/x8bit/bitwarden/MainActivity.kt

@@ -3,13 +3,7 @@ package com.x8bit.bitwarden
 import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
-import androidx.compose.foundation.layout.fillMaxSize
-import androidx.compose.material3.MaterialTheme
-import androidx.compose.material3.Surface
-import androidx.compose.material3.Text
-import androidx.compose.ui.Modifier
-import androidx.compose.ui.res.stringResource
-import com.x8bit.bitwarden.ui.theme.BitwardenTheme
+import com.x8bit.bitwarden.ui.feature.rootnav.RootNavScreen
 import dagger.hilt.android.AndroidEntryPoint
 
 /**
@@ -19,17 +13,6 @@ import dagger.hilt.android.AndroidEntryPoint
 class MainActivity : ComponentActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
-        setContent {
-            BitwardenTheme {
-                Surface(
-                    modifier = Modifier.fillMaxSize(),
-                    color = MaterialTheme.colorScheme.background,
-                ) {
-                    Text(
-                        text = stringResource(id = R.string.app_name),
-                    )
-                }
-            }
-        }
+        setContent { RootNavScreen() }
     }
 }

app/src/main/java/com/x8bit/bitwarden/ui/components/PlaceholderComposable.kt

@@ -0,0 +1,27 @@
+package com.x8bit.bitwarden.ui.components
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+
+/**
+ * Temporary composable that can be used as a navigation placeholder.
+ */
+@Composable
+fun PlaceholderComposable(
+    text: String = "Placeholder Composable"
+) {
+    Box(
+        modifier = Modifier
+            .fillMaxSize()
+            .background(Color.White),
+        contentAlignment = Alignment.Center,
+    ) {
+        Text(text = text)
+    }
+}

app/src/main/java/com/x8bit/bitwarden/ui/feature/rootnav/RootNavScreen.kt

@@ -0,0 +1,110 @@
+package com.x8bit.bitwarden.ui.feature.rootnav
+
+import androidx.compose.animation.EnterTransition
+import androidx.compose.animation.ExitTransition
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import androidx.lifecycle.viewmodel.compose.viewModel
+import androidx.navigation.NavController
+import androidx.navigation.NavGraphBuilder
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.composable
+import androidx.navigation.compose.rememberNavController
+import com.x8bit.bitwarden.ui.components.PlaceholderComposable
+
+/**
+ * Controls root level [NavHost] for the app.
+ */
+@Composable
+fun RootNavScreen(
+    viewModel: RootNavViewModel = viewModel()
+) {
+    val navController = rememberNavController()
+    val state by viewModel.state.collectAsStateWithLifecycle()
+
+    NavHost(
+        navController = navController,
+        startDestination = SplashRoute,
+        enterTransition = { EnterTransition.None },
+        exitTransition = { ExitTransition.None },
+    ) {
+        splashDestinations()
+        loginDestinations()
+    }
+
+    // When state changes, navigate to different root navigation state
+    when (state) {
+        RootNavState.Login -> navController.navigateToLoginAsRoot()
+        RootNavState.Splash -> navController.navigateToSplashAsRoot()
+    }
+}
+
+/**
+ * The functions below should be moved to their respective feature packages once they exist.
+ *
+ * For an example of how to setup these nav extensions, see NIA project.
+ */
+
+/**
+ * TODO: move to splash package (BIT-147)
+ */
+private const val SplashRoute = "splash"
+
+/**
+ * Add splash destinations to the nav graph.
+ *
+ * TODO: move to splash package (BIT-147)
+ */
+private fun NavGraphBuilder.splashDestinations() {
+    composable(SplashRoute) {
+        PlaceholderComposable(text = "Splash")
+    }
+}
+
+/**
+ * Navigate to the splash screen. Note this will only work if splash destination was added
+ * via [splashDestinations].
+ *
+ * TODO: move to splash package (BIT-147)
+ *
+ */
+private fun NavController.navigateToSplashAsRoot() {
+    navigate(SplashRoute) {
+        // When changing root navigation state, pop everything else off the back stack:
+        popUpTo(graph.id) {
+            inclusive = true
+        }
+    }
+}
+
+/**
+ * TODO move to login package(BIT-146)
+ */
+private val LoginRoute = "login"
+
+/**
+ * Add login destinations to the nav graph.
+ *
+ * TODO: move to login package (BIT-146)
+ */
+private fun NavGraphBuilder.loginDestinations() {
+    composable(LoginRoute) {
+        PlaceholderComposable(text = "Login")
+    }
+}
+
+/**
+ * Navigate to the splash screen. Note this will only work if login destination was added
+ * via [loginDestinations].
+ *
+ * TODO: move to login package (BIT-146)
+ */
+private fun NavController.navigateToLoginAsRoot() {
+    navigate(LoginRoute) {
+        // When changing root navigation state, pop everything else off the back stack:
+        popUpTo(graph.id) {
+            inclusive = true
+        }
+    }
+}

app/src/main/java/com/x8bit/bitwarden/ui/feature/rootnav/RootNavViewModel.kt

@@ -0,0 +1,44 @@
+package com.x8bit.bitwarden.ui.feature.rootnav
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.launch
+import javax.inject.Inject
+
+/**
+ * Manages root level navigation state of the application.
+ */
+@HiltViewModel
+class RootNavViewModel @Inject constructor() : ViewModel() {
+
+    private val _state = MutableStateFlow<RootNavState>(RootNavState.Splash)
+    val state: StateFlow<RootNavState> = _state.asStateFlow()
+
+    init {
+        viewModelScope.launch {
+            delay(1000)
+            _state.value = RootNavState.Login
+        }
+    }
+
+}
+
+/**
+ * Models state of the root level navigation of the app.
+ */
+sealed class RootNavState {
+    /**
+     * Show the login screen.
+     */
+    data object Login : RootNavState()
+
+    /**
+     * Show the splash screen.
+     */
+    data object Splash : RootNavState()
+}