update

app/app/src/main/java/de/haushalt/app/MainScreen.kt

@@ -1,33 +1,34 @@
 package de.haushalt.app
 
-import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxWidth
-import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
-import androidx.compose.material3.CenterAlignedTopAppBar
-import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.foundation.layout.statusBarsPadding
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
+import androidx.navigation.NavController
 import androidx.navigation.compose.NavHost
 import androidx.navigation.compose.composable
+import androidx.navigation.compose.currentBackStackEntryAsState
 import androidx.navigation.compose.rememberNavController
 
-@OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun MainScreen() {
     val navController = rememberNavController()
+    val backStackEntry by navController.currentBackStackEntryAsState()
+    val currentRoute = backStackEntry?.destination?.route
+
     Scaffold(
-        topBar = {
-            Column {
-                Navigation()
-                Subnavigation()
-            }
-        }
+        topBar = { Breadcrumb(currentRoute = currentRoute, navController = navController) }
     ) { innerPadding ->
         NavHost(
             navController = navController,
@@ -39,20 +40,43 @@ fun MainScreen() {
     }
 }
 
-@OptIn(ExperimentalMaterial3Api::class)
 @Composable
-private fun Navigation() {
-    CenterAlignedTopAppBar(
-        title = { Text("Haushalt") }
+private fun Breadcrumb(currentRoute: String?, navController: NavController) {
+    // Trail: (route, label). Erweitert sich pro neuer Destination in späteren Modulen.
+    val trail = listOf(
+        "start" to "Haushalt",
     )
-}
-
-@Composable
-private fun Subnavigation() {
     Surface(
-        modifier = Modifier
-            .fillMaxWidth()
-            .height(32.dp),
-        color = MaterialTheme.colorScheme.surfaceVariant
-    ) {}
+        modifier = Modifier.fillMaxWidth(),
+        color = MaterialTheme.colorScheme.surfaceContainer
+    ) {
+        Row(
+            modifier = Modifier
+                .statusBarsPadding()
+                .padding(horizontal = 16.dp, vertical = 12.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            trail.forEachIndexed { index, (route, label) ->
+                if (index > 0) {
+                    Text(
+                        text = "›",
+                        modifier = Modifier.padding(horizontal = 6.dp),
+                        color = MaterialTheme.colorScheme.onSurfaceVariant
+                    )
+                }
+                val isCurrent = route == currentRoute
+                Text(
+                    text = label,
+                    fontWeight = if (isCurrent) FontWeight.SemiBold else FontWeight.Normal,
+                    modifier = if (isCurrent) {
+                        Modifier
+                    } else {
+                        Modifier.clickable {
+                            navController.popBackStack(route, inclusive = false)
+                        }
+                    }
+                )
+            }
+        }
+    }
 }