Implemented a repository-based data layer for expenses and updated Room entities.

The `ExpenseRepository` was introduced to handle data fetching with a caching strategy, utilizing a new `Resource` sealed class to represent Loading, Success, and Error states.

Key changes include:
- Added `ExpenseRepository` to manage data flow between the local database and remote API.
- Updated `MainViewModel` to use the repository and expose expenses via a `StateFlow<Resource<List<Expense>>>`.
- Enhanced Room entities (`Expense`, `ExpenseShare`, `User`) with `@PrimaryKey` annotations and added a `Converters` class to handle `List<String>` types.
- Expanded `AppDatabase` to include DAOs for `Expense`, `ExpenseShare`, and `User`.
- Updated `DashboardScreen` to reactively display loading indicators, error messages, and cached/remote expense data.

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

@@ -23,9 +23,14 @@ class MainActivity : ComponentActivity() {
         val prefs = UserPreferences(this)
         val loginViewModel = LoginViewModel(prefs, applicationContext)
         val database = AppDatabase.getDatabase(applicationContext)
-        val dao = database.accountDao()
+        val accountDao = database.accountDao()
+        val expenseDao = database.expenseDao()
         val tokenStorage = TokenStorage(applicationContext)
-        val mainViewModel = MainViewModel(dao, tokenStorage)
+        val mainViewModel = MainViewModel(
+            accountDao,
+            expenseDao,
+            tokenStorage
+        )
 
 
         setContent {
@@ -33,7 +38,6 @@ class MainActivity : ComponentActivity() {
                 val accountList by mainViewModel.accounts.collectAsState()
                 val selectedAccount = mainViewModel.selectedAccount
                 val showLoginForNewAccount = remember { mutableStateOf(false) }
-                val expenses by mainViewModel.expenses.collectAsState()
 
                 BackHandler(enabled = showLoginForNewAccount.value && accountList.isNotEmpty()) {
                     showLoginForNewAccount.value = false
@@ -54,7 +58,6 @@ class MainActivity : ComponentActivity() {
                     sessionState = mainViewModel.sessionState,
                     onValidateSession = { mainViewModel.validateSession(selectedAccount!!) },
                     onSessionInvalid = { mainViewModel.logoutFromAccount() },
-                    expenses = expenses,
                     onExpenseClick = { expense -> println("Clicked: ${expense.title}") },
                     viewModel = mainViewModel
                 )

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

@@ -5,21 +5,22 @@ import androidx.room.Delete
 import androidx.room.Entity
 import androidx.room.Insert
 import androidx.room.OnConflictStrategy
+import androidx.room.PrimaryKey
 import androidx.room.Query
 import kotlinx.coroutines.flow.Flow
 import java.util.UUID
 
 @Entity(tableName = "expenses")
 data class Expense (
-    val id: UUID,
+    @PrimaryKey val id: UUID,
     val payer_id: UUID,
     val amount: Int,
     val title: String,
     val description: String,
-    val attachments: List<String>,
+    val attachments: List<String>?,
     val created_at: Int,
     val last_updated_at: Int
-    )
+)
 
 @Dao
 interface ExpenseDao {

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

@@ -5,13 +5,14 @@ import androidx.room.Delete
 import androidx.room.Entity
 import androidx.room.Insert
 import androidx.room.OnConflictStrategy
+import androidx.room.PrimaryKey
 import androidx.room.Query
 import kotlinx.coroutines.flow.Flow
 import java.util.UUID
 
 @Entity(tableName = "expense_shares")
 data class ExpenseShare(
-    val id: UUID,
+    @PrimaryKey val id: UUID,
     val expense_id: UUID,
     val user_id: UUID,
     val share_cents: Int
@@ -23,7 +24,7 @@ interface ExpenseShareDao {
     fun getAllShares(): Flow<List<ExpenseShare>>
 
     @Query("SELECT * FROM expense_shares WHERE id = :shareId")
-    fun getShareById(shareId: UUID)
+    fun getShareById(shareId: UUID): Flow<ExpenseShare>
 
     @Insert(onConflict = OnConflictStrategy.REPLACE)
     suspend fun insertShare(share: ExpenseShare)

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

@@ -5,13 +5,14 @@ import androidx.room.Delete
 import androidx.room.Entity
 import androidx.room.Insert
 import androidx.room.OnConflictStrategy
+import androidx.room.PrimaryKey
 import androidx.room.Query
 import kotlinx.coroutines.flow.Flow
 import java.util.UUID
 
 @Entity(tableName = "users")
 data class User (
-    val id: UUID,
+    @PrimaryKey val id: UUID,
     val name: String,
     val avatar_url: String?
 )

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

@@ -0,0 +1,36 @@
+package de.miaurizius.shap_planner.repository
+
+import de.miaurizius.shap_planner.entities.Expense
+import de.miaurizius.shap_planner.entities.ExpenseDao
+import de.miaurizius.shap_planner.network.APIService
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.flow
+
+class ExpenseRepository(
+    private val dao: ExpenseDao,
+    private val api: APIService
+) {
+    fun getExpenses(token: String, forceRefresh: Boolean = false): Flow<Resource<List<Expense>>> = flow {
+        val cachedExpense = dao.getAllExpenses().first()
+        println("CachedExpense: $cachedExpense")
+        emit(Resource.Loading(cachedExpense))
+
+        if(cachedExpense.isEmpty() || forceRefresh) {
+            try {
+                val response = api.expenseGet("Bearer $token")
+                if(response.isSuccessful) {
+                    val remoteExpense = response.body()?.expenses ?: emptyList()
+                    println("Fetched expenses: $remoteExpense")
+                    remoteExpense.forEach {
+                        dao.insertExpense(it)
+                        println("Added $it")
+                    }
+                }
+            } catch(e: Exception) {
+                emit(Resource.Error("Network Error: ${e.localizedMessage}", cachedExpense))
+            }
+        }
+        dao.getAllExpenses().collect { emit(Resource.Success(it)) }
+    }
+}

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

@@ -0,0 +1,7 @@
+package de.miaurizius.shap_planner.repository
+
+sealed class Resource<T>(val data: T? = null, val message: String? = null) {
+    class Success<T>(data: T): Resource<T>(data)
+    class Loading<T>(data: T? = null): Resource<T>(data)
+    class Error<T>(message: String, data: T? = null): Resource<T>(data, message)
+}

app/src/main/java/de/miaurizius/shap_planner/room/AppDatabase.kt

@@ -4,12 +4,31 @@ import android.content.Context
 import androidx.room.Database
 import androidx.room.Room
 import androidx.room.RoomDatabase
+import androidx.room.TypeConverter
+import androidx.room.TypeConverters
 import de.miaurizius.shap_planner.entities.Account
 import de.miaurizius.shap_planner.entities.AccountDao
+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
 
-@Database(entities = [Account::class], version = 4)
+class Converters {
+    @TypeConverter
+    fun fromList(list: List<String>?): String? = list?.joinToString(",")
+    @TypeConverter
+    fun toList(data: String?): List<String>? = data?.split(",")?.map { it.trim() }
+}
+
+@Database(entities = [Account::class, Expense::class, ExpenseShare::class, User::class], version = 6)
+@TypeConverters(Converters::class)
 abstract class AppDatabase : RoomDatabase() {
     abstract fun accountDao(): AccountDao
+    abstract fun expenseDao(): ExpenseDao
+    abstract fun expenseShareDao(): ExpenseShareDao
+    abstract fun userDao(): UserDao
     companion object {
         @Volatile
         private var INSTANCE: AppDatabase? = null

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

@@ -18,7 +18,6 @@ fun AppContent(
     onLogin: (String, String, String) -> Unit,
 
     // Expenses
-    expenses: List<Expense>,
     onExpenseClick: (Expense) -> Unit,
 
     // Account
@@ -41,7 +40,6 @@ fun AppContent(
         selectedAccount != null -> DashboardScreen(
             // Data and regarding Methods
             account = selectedAccount,
-            expenses = expenses,
             onExpenseClick = onExpenseClick,
 
             // Default Methods

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

@@ -24,6 +24,8 @@ import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 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
@@ -32,13 +34,13 @@ 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.network.SessionState
+import de.miaurizius.shap_planner.repository.Resource
 import de.miaurizius.shap_planner.viewmodels.MainViewModel
 
 @Composable
 fun DashboardScreen(
     // Data and regarding Methods
     account: Account,
-    expenses: List<Expense>,
     onExpenseClick: (Expense) -> Unit,
 
     // Default Methods
@@ -49,8 +51,10 @@ fun DashboardScreen(
     onValidate: () -> Unit,
     onSessionInvalid: () -> Unit) {
 
+    val expenseResource by mainViewModel.expenseResource.collectAsState()
+
     LaunchedEffect(Unit) { onValidate() }
-    mainViewModel.loadExpenses(account)
+    LaunchedEffect(account) { mainViewModel.loadExpenses(account, forceRefresh = false) }
     when (sessionState) {
         SessionState.Loading -> {
             Box(Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
@@ -102,6 +106,14 @@ fun DashboardScreen(
                 Text("WG-Kosten", style = MaterialTheme.typography.titleLarge)
                 Spacer(modifier = Modifier.height(8.dp))
 
+                if(expenseResource is Resource.Loading && expenseResource.data?.isEmpty() == true) {
+                    CircularProgressIndicator(modifier = Modifier.align(Alignment.CenterHorizontally))
+                }
+
+                if(expenseResource is Resource.Error) {
+                    Text("Fehler: ${expenseResource.message}", color = Color.Red)
+                }
+
                 LazyColumn(
                     modifier = Modifier
                         .fillMaxSize()
@@ -109,7 +121,7 @@ fun DashboardScreen(
                     contentPadding = PaddingValues(8.dp),
                     verticalArrangement = Arrangement.spacedBy(8.dp)
                 ) {
-                    items(expenses) { expense ->
+                    items(expenseResource.data ?: emptyList()) { expense ->
                         ExpenseItem(expense = expense, onClick = { onExpenseClick(expense) })
                     }
                 }

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

@@ -9,9 +9,12 @@ import de.miaurizius.shap_planner.TokenStorage
 import de.miaurizius.shap_planner.entities.Account
 import de.miaurizius.shap_planner.entities.AccountDao
 import de.miaurizius.shap_planner.entities.Expense
+import de.miaurizius.shap_planner.entities.ExpenseDao
 import de.miaurizius.shap_planner.network.RefreshRequest
 import de.miaurizius.shap_planner.network.RetrofitProvider
 import de.miaurizius.shap_planner.network.SessionState
+import de.miaurizius.shap_planner.repository.ExpenseRepository
+import de.miaurizius.shap_planner.repository.Resource
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
@@ -19,7 +22,11 @@ import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import kotlin.collections.emptyList
 
-class MainViewModel(private val accountDao: AccountDao, private val tokenStorage: TokenStorage) : ViewModel() {
+class MainViewModel(
+    private val accountDao: AccountDao,
+    private val expenseDao: ExpenseDao,
+    private val tokenStorage: TokenStorage
+) : ViewModel() {
 
     var selectedAccount by mutableStateOf<Account?>(null)
         private set
@@ -28,22 +35,16 @@ class MainViewModel(private val accountDao: AccountDao, private val tokenStorage
     var sessionState by mutableStateOf<SessionState>(SessionState.Loading)
         private set
 
-    private val _expenses = MutableStateFlow<List<Expense>>(emptyList())
-    val expenses: StateFlow<List<Expense>> = _expenses
+    private val _expenseResource = MutableStateFlow<Resource<List<Expense>>>(Resource.Loading(emptyList()))
+    val expenseResource: StateFlow<Resource<List<Expense>>> = _expenseResource
 
-    fun loadExpenses(account: Account) {
+    fun loadExpenses(account: Account, forceRefresh: Boolean = false) {
         viewModelScope.launch {
-            try {
             val api = RetrofitProvider.create(account.serverUrl)
-                val accessToken = tokenStorage.getAccess(account.id.toString())
+            val repo = ExpenseRepository(expenseDao, api)
+            val accessToken = tokenStorage.getAccess(account.id.toString()) ?: ""
 
-                val response = api.expenseGet("Bearer $accessToken")
-                if (response.isSuccessful) {
-                    _expenses.value = response.body()?.expenses ?: emptyList()
-                }
-            } catch (e: Exception) {
-                _expenses.value = emptyList()
-            }
+            repo.getExpenses(accessToken, forceRefresh).collect { result -> _expenseResource.value = result }
         }
     }
 
@@ -82,7 +83,7 @@ class MainViewModel(private val accountDao: AccountDao, private val tokenStorage
                     sessionState = SessionState.Valid
 
                     // Fetch data
-                    loadExpenses(account)
+//                    loadExpenses(account)
                     println("All data fetched")
 
                     return@launch