Added Expense Detail screen and functionality

The new `ExpenseDetailScreen` displays expense information, including title, amount, and a breakdown of cost shares among users.

Key changes:
- Created `ExpenseDetailViewModel` to manage loading and combining expense shares with user information.
- Added `ExpenseDetailScreen` UI with a list of shares and a back navigation option.
- Updated `MainActivity` and `AppContent` to handle navigation to the expense detail view.
- Extended `ExpenseShareDao` and `ExpenseShareRepository` to support fetching shares by expense ID.
- Updated `APIService` and `UserRepository` to simplify user information retrieval and support querying shares by different ID types.
- Added `@OptIn(ExperimentalMaterial3Api::class)` to several UI components to support Material 3 features.

app/src/main/java/de/miaurizius/shap_planner/activities/MainActivity.kt

@@ -13,6 +13,7 @@ import de.miaurizius.shap_planner.UserPreferences
 import de.miaurizius.shap_planner.room.AppDatabase
 import de.miaurizius.shap_planner.ui.AppContent
 import de.miaurizius.shap_planner.ui.theme.ShapPlannerTheme
+import de.miaurizius.shap_planner.viewmodels.ExpenseDetailViewModel
 import de.miaurizius.shap_planner.viewmodels.LoginViewModel
 import de.miaurizius.shap_planner.viewmodels.MainViewModel
 
@@ -31,6 +32,12 @@ class MainActivity : ComponentActivity() {
             expenseDao,
             tokenStorage
         )
+        val detailViewModel = ExpenseDetailViewModel(
+            database.expenseDao(),
+            database.expenseShareDao(),
+            database.userDao(),
+            tokenStorage
+        )
 
 
         setContent {
@@ -59,7 +66,8 @@ class MainActivity : ComponentActivity() {
                     onValidateSession = { mainViewModel.validateSession(selectedAccount!!) },
                     onSessionInvalid = { mainViewModel.logoutFromAccount() },
                     onExpenseClick = { expense -> println("Clicked: ${expense.title}") },
-                    viewModel = mainViewModel
+                    viewModel = mainViewModel,
+                    detailViewModel = detailViewModel
                 )
             }
         }

app/src/main/java/de/miaurizius/shap_planner/entities/ExpenseShare.kt

@@ -26,6 +26,9 @@ interface ExpenseShareDao {
     @Query("SELECT * FROM expense_shares WHERE id = :shareId")
     fun getShareById(shareId: UUID): Flow<ExpenseShare?>
 
+    @Query("SELECT * FROM expense_shares WHERE expense_id = :expense_id")
+    fun getSharesByExpense(expense_id: UUID): Flow<List<ExpenseShare>>
+
     @Insert(onConflict = OnConflictStrategy.REPLACE)
     suspend fun insertShare(share: ExpenseShare)
 

app/src/main/java/de/miaurizius/shap_planner/network/APIService.kt

@@ -1,5 +1,7 @@
 package de.miaurizius.shap_planner.network
 
+import com.google.gson.annotations.SerializedName
+import de.miaurizius.shap_planner.entities.User
 import retrofit2.Response
 import retrofit2.http.Body
 import retrofit2.http.DELETE
@@ -34,8 +36,19 @@ interface APIService {
     suspend fun sharesGet(@Header("Authorization") token: String): Response<ExpenseSharesResponse>
     @GET("api/shares")
     suspend fun shareGet(@Header("Authorization") token: String, @Query("id") shareId: UUID): Response<ExpenseShareResponse>
+    @GET("api/shares")
+    suspend fun shareGet(@Header("Authorization") token: String, @Query("id") expenseId: UUID, @Query("idType") idType: IDType): Response<ExpenseSharesResponse>
 
     // User
     @GET("api/userinfo")
-    suspend fun userinfo(@Header("Authorization") token: String, @Query("id") userId: UUID): Response<UserinfoResponse>
+    suspend fun userinfo(@Header("Authorization") token: String, @Query("id") userId: UUID): Response<User>
+}
+
+enum class IDType {
+    @SerializedName("share")
+    Share,
+    @SerializedName("expense")
+    Expense,
+    @SerializedName("user")
+    User,
 }

app/src/main/java/de/miaurizius/shap_planner/network/ComDataTypes.kt

@@ -18,7 +18,4 @@ data class ExpensesResponse(val expenses: List<Expense>)
 
 // ExpenseShares
 data class ExpenseSharesResponse(val shares: List<ExpenseShare>)
-data class ExpenseShareResponse(val share: ExpenseShare)
+data class ExpenseShareResponse(val share: ExpenseShare)
-
-// User
-data class UserinfoResponse(val user: User)

app/src/main/java/de/miaurizius/shap_planner/repository/ExpenseShareRepository.kt

@@ -1,8 +1,10 @@
 package de.miaurizius.shap_planner.repository
 
+import de.miaurizius.shap_planner.entities.Expense
 import de.miaurizius.shap_planner.entities.ExpenseShare
 import de.miaurizius.shap_planner.entities.ExpenseShareDao
 import de.miaurizius.shap_planner.network.APIService
+import de.miaurizius.shap_planner.network.IDType
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.flow
@@ -50,4 +52,22 @@ class ExpenseShareRepository(
             else emit(Resource.Error("Share nicht gefunden", null))
         }
     }
+
+    fun getSharesByExpenseId(token: String, expenseId: UUID, forceRefresh: Boolean = false): Flow<Resource<List<ExpenseShare>>> = flow {
+        val cached = dao.getSharesByExpense(expenseId).first()
+        emit(Resource.Loading(cached))
+        if(cached.isEmpty() || forceRefresh) {
+            try {
+                val response = api.shareGet("Bearer $token", expenseId, IDType.Expense)
+                if(response.isSuccessful) {
+                    println("Body: ${response.body()}")
+                    val remoteShare = response.body()?.shares ?: emptyList()
+                    remoteShare.forEach { dao.insertShare(it) }
+                }
+            } catch(e: Exception) {
+                emit(Resource.Error("Network Error: ${e.localizedMessage}", cached))
+            }
+        }
+        dao.getSharesByExpense(expenseId).collect { emit(Resource.Success(it)) }
+    }
 }

app/src/main/java/de/miaurizius/shap_planner/repository/UserRepository.kt

@@ -19,7 +19,8 @@ class UserRepository(
             try {
                 val response = api.userinfo("Bearer $token", userId)
                 if(response.isSuccessful) {
-                    response.body()?.user?.let { remoteUser -> dao.insertUser(remoteUser) }
+                    println("Body: ${response.body()}")
+                    response.body()?.let { remoteUser -> dao.insertUser(remoteUser) }
                 }
             } catch(e: Exception) {
                 emit(Resource.Error("Network-Error: ${e.localizedMessage}", cached))

app/src/main/java/de/miaurizius/shap_planner/ui/AppContent.kt

@@ -1,12 +1,18 @@
 package de.miaurizius.shap_planner.ui
 
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import de.miaurizius.shap_planner.entities.Account
 import de.miaurizius.shap_planner.entities.Expense
 import de.miaurizius.shap_planner.network.SessionState
 import de.miaurizius.shap_planner.ui.screens.AccountSelectionScreen
 import de.miaurizius.shap_planner.ui.screens.DashboardScreen
+import de.miaurizius.shap_planner.ui.screens.ExpenseDetailScreen
 import de.miaurizius.shap_planner.ui.screens.LoginScreen
+import de.miaurizius.shap_planner.viewmodels.ExpenseDetailViewModel
 import de.miaurizius.shap_planner.viewmodels.MainViewModel
 
 @Composable
@@ -32,15 +38,26 @@ fun AppContent(
     onSessionInvalid: () -> Unit,
 
     //Important
-    viewModel: MainViewModel
+    viewModel: MainViewModel,
+    detailViewModel: ExpenseDetailViewModel
 ) {
+    var selectedExpense by remember { mutableStateOf<Expense?>(null) }
+
     when {
+        selectedExpense != null -> {
+            ExpenseDetailScreen(
+                expense = selectedExpense!!,
+                account = selectedAccount!!,
+                viewModel = detailViewModel,
+                onBack = { selectedExpense = null }
+            )
+        }
         showLoginForNewAccount -> LoginScreen(onLogin)
         accountList.isEmpty() -> LoginScreen(onLogin)
         selectedAccount != null -> DashboardScreen(
             // Data and regarding Methods
             account = selectedAccount,
-            onExpenseClick = onExpenseClick,
+            onExpenseClick = { selectedExpense = it },
 
             // Default Methods
             mainViewModel = viewModel,

app/src/main/java/de/miaurizius/shap_planner/ui/screens/AccountSelectionScreen.kt

@@ -20,6 +20,7 @@ import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.material3.Button
 import androidx.compose.material3.Card
+import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
@@ -30,6 +31,7 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import de.miaurizius.shap_planner.entities.Account
 
+@OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun AccountSelectionScreen(accounts: List<Account>, onAccountClick: (Account) -> Unit, onAddAccountClick: () -> Unit) {
     LazyColumn(

app/src/main/java/de/miaurizius/shap_planner/ui/screens/DashboardScreen.kt

@@ -19,6 +19,7 @@ import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
 import androidx.compose.material3.Button
 import androidx.compose.material3.CircularProgressIndicator
+import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
@@ -37,6 +38,7 @@ import de.miaurizius.shap_planner.network.SessionState
 import de.miaurizius.shap_planner.repository.Resource
 import de.miaurizius.shap_planner.viewmodels.MainViewModel
 
+@OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun DashboardScreen(
     // Data and regarding Methods

app/src/main/java/de/miaurizius/shap_planner/ui/screens/ExpenseDetailScreen.kt

@@ -0,0 +1,108 @@
+package de.miaurizius.shap_planner.ui.screens
+
+import android.annotation.SuppressLint
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material3.Card
+import androidx.compose.material3.DividerDefaults
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.HorizontalDivider
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.material3.TopAppBar
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.dp
+import de.miaurizius.shap_planner.entities.Account
+import de.miaurizius.shap_planner.entities.Expense
+import de.miaurizius.shap_planner.viewmodels.ExpenseDetailViewModel
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun ExpenseDetailScreen(
+    expense: Expense,
+    account: Account,
+    viewModel: ExpenseDetailViewModel,
+    onBack: () -> Unit
+) {
+    val shares by viewModel.sharesWithUser.collectAsState()
+
+    LaunchedEffect(expense) {
+        viewModel.loadExpenseDetail(account, expense)
+    }
+
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = { Text(expense.title) },
+                navigationIcon = { IconButton(onClick = onBack) {
+                    Icon(Icons.AutoMirrored.Filled.ArrowBack, "Zurück")
+                } }
+            )
+        }
+    ) { padding ->
+        Column(modifier = Modifier.padding(padding).padding(16.dp)) {
+            Text(
+                text = "${expense.amount / 100.0}€",
+                style = MaterialTheme.typography.displayMedium,
+                fontWeight = FontWeight.Bold,
+                color = MaterialTheme.colorScheme.primary
+            )
+            Text(expense.description, style = MaterialTheme.typography.bodyLarge)
+
+            Spacer(modifier = Modifier.height(24.dp))
+            HorizontalDivider(Modifier, DividerDefaults.Thickness, DividerDefaults.color)
+            Spacer(modifier = Modifier.height(16.dp))
+
+            Text("Kostenaufteilung", style = MaterialTheme.typography.titleLarge)
+            Spacer(modifier = Modifier.height(8.dp))
+
+            LazyColumn(verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                items(shares) { item ->
+                    ShareItem(item.user?.name ?: "Unbekannter Nutzer", item.share.share_cents)
+                }
+            }
+        }
+    }
+}
+
+@SuppressLint("DefaultLocale")
+@Composable
+fun ShareItem(name: String, amountCents: Int) {
+    Card(modifier = Modifier
+        .fillMaxWidth()
+        .padding(vertical = 4.dp)
+    ) {
+        Row(
+            modifier = Modifier.fillMaxWidth().padding(16.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            Text(name, fontWeight = FontWeight.Medium, modifier = Modifier.weight(1f))
+            Text(
+                text = String.format("%.2f€", amountCents / 100.0),
+                color = if (amountCents > 0) Color(0xFF4CAF50) else Color.Gray,
+                fontWeight = FontWeight.Bold,
+                style = MaterialTheme.typography.bodyLarge
+            )
+        }
+    }
+}

app/src/main/java/de/miaurizius/shap_planner/ui/screens/LoginScreen.kt

@@ -8,6 +8,7 @@ import androidx.compose.foundation.layout.navigationBarsPadding
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.statusBarsPadding
 import androidx.compose.material3.Button
+import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextField
 import androidx.compose.runtime.Composable
@@ -18,6 +19,7 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
 
+@OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun LoginScreen(onLogin: (String, String, String) -> Unit, onBack: (() -> Unit)? = null) {
 

app/src/main/java/de/miaurizius/shap_planner/viewmodels/ExpenseDetailViewModel.kt

@@ -0,0 +1,59 @@
+package de.miaurizius.shap_planner.viewmodels
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import de.miaurizius.shap_planner.TokenStorage
+import de.miaurizius.shap_planner.entities.Account
+import de.miaurizius.shap_planner.entities.Expense
+import de.miaurizius.shap_planner.entities.ExpenseDao
+import de.miaurizius.shap_planner.entities.ExpenseShare
+import de.miaurizius.shap_planner.entities.ExpenseShareDao
+import de.miaurizius.shap_planner.entities.User
+import de.miaurizius.shap_planner.entities.UserDao
+import de.miaurizius.shap_planner.network.RetrofitProvider
+import de.miaurizius.shap_planner.repository.ExpenseShareRepository
+import de.miaurizius.shap_planner.repository.Resource
+import de.miaurizius.shap_planner.repository.UserRepository
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.launch
+
+data class ShareWithUser(
+    val share: ExpenseShare,
+    val user: User?
+)
+
+class ExpenseDetailViewModel(
+    private val expenseDao: ExpenseDao,
+    private val shareDao: ExpenseShareDao,
+    private val userDao: UserDao,
+    private val tokenStorage: TokenStorage
+) : ViewModel() {
+    private val _sharesWithUser = MutableStateFlow<List<ShareWithUser>>(emptyList())
+    val sharesWithUser: StateFlow<List<ShareWithUser>> = _sharesWithUser
+
+    fun loadExpenseDetail(account: Account, expense: Expense) {
+        viewModelScope.launch {
+            val api = RetrofitProvider.create(account.serverUrl)
+            val token = tokenStorage.getAccess(account.id.toString()) ?: ""
+
+            val shareRepo = ExpenseShareRepository(shareDao, api)
+            val userRepo = UserRepository(userDao, api)
+
+            shareRepo.getSharesByExpenseId(token, expense.id).collect { resource ->
+                val shares = resource.data ?: emptyList()
+                val combinedList = shares.map { share ->
+                    val cachedUser = userDao.getUserById(share.user_id).first()
+                    if (cachedUser == null) {
+                        val userResource = userRepo.getUser(token, share.user_id).first { it is Resource.Success || it is Resource.Error }
+                        ShareWithUser(share, userResource.data)
+                    } else {
+                        ShareWithUser(share, cachedUser)
+                    }
+                }
+                _sharesWithUser.value = combinedList
+            }
+        }
+    }
+}