Implemented expense creation functionality.

A new `ExpenseCreationScreen` and `ExpenseCreationViewModel` have been added to allow users to create new expenses. This includes fields for the title, amount, and a participant selection using filter chips.

Key changes:
- Added `ExpenseCreationViewModel` to handle user loading and persistent storage of expenses and shares.
- Created `ExpenseCreationScreen` UI with validation for the "Save" button.
- Updated `DashboardScreen` to include a Floating Action Button (FAB) for navigating to the expense creation flow.
- Added `expenseCreate` API endpoint and related data types (`ExpenseCreationRequest`, `ExpenseCreationResponse`).
- Integrated `ExpenseCreationViewModel` into `MainActivity` and `AppContent`.

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

@@ -8,11 +8,14 @@ import androidx.compose.runtime.collectAsState
 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.TokenStorage
 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.ExpenseCreationViewModel
+import de.miaurizius.shap_planner.viewmodels.ExpenseDetailViewModel
 import de.miaurizius.shap_planner.viewmodels.LoginViewModel
 import de.miaurizius.shap_planner.viewmodels.MainViewModel
 
@@ -23,9 +26,26 @@ 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
+        )
+        val detailViewModel = ExpenseDetailViewModel(
+            database.expenseDao(),
+            database.expenseShareDao(),
+            database.userDao(),
+            tokenStorage
+        )
+        val creationViewModel = ExpenseCreationViewModel(
+            database.userDao(),
+            database.expenseDao(),
+            database.expenseShareDao(),
+            tokenStorage
+        )
 
 
         setContent {
@@ -33,7 +53,6 @@ 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
@@ -54,9 +73,10 @@ class MainActivity : ComponentActivity() {
                     sessionState = mainViewModel.sessionState,
                     onValidateSession = { mainViewModel.validateSession(selectedAccount!!) },
                     onSessionInvalid = { mainViewModel.logoutFromAccount() },
-                    expenses = expenses,
                     onExpenseClick = { expense -> println("Clicked: ${expense.title}") },
-                    viewModel = mainViewModel
+                    viewModel = mainViewModel,
+                    detailViewModel = detailViewModel,
+                    creationViewModel = creationViewModel,
                 )
             }
         }

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 +24,10 @@ 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?>
+
+    @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/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?
 )
@@ -21,6 +22,9 @@ interface UserDao {
     @Query("SELECT * FROM users")
     fun getAllUsers(): Flow<List<User>>
 
+    @Query("SELECT * FROM users WHERE id = :userId")
+    fun getUserById(userId: UUID): Flow<User?>
+
     @Insert(onConflict = OnConflictStrategy.REPLACE)
     suspend fun insertUser(user: User)
 

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
@@ -21,15 +23,32 @@ interface APIService {
 
     // Expenses
     @GET("api/expenses")
-    suspend fun expenseGet(@Header("Authorization") token: String): Response<ExpenseResponse>
+    suspend fun expensesGet(@Header("Authorization") token: String): Response<ExpensesResponse>
     @POST("api/expenses")
-    suspend fun expenseCreate(@Header("Authorization") token: String)
+    suspend fun expenseCreate(@Header("Authorization") token: String, @Body req: ExpenseCreationRequest): Response<ExpenseCreationResponse>
     @PUT("api/expenses")
     suspend fun expenseUpdate(@Header("Authorization") token: String)
     @DELETE("api/expenses")
     suspend fun expenseDelete(@Header("Authorization") token: String)
 
+    // Shares
+    @GET("api/shares")
+    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)
+    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

@@ -1,6 +1,7 @@
 package de.miaurizius.shap_planner.network
 
 import de.miaurizius.shap_planner.entities.Expense
+import de.miaurizius.shap_planner.entities.ExpenseShare
 
 // Login
 data class LoginRequest(val username: String, val password: String)
@@ -12,4 +13,10 @@ data class RefreshRequest(val refresh_token: String)
 data class RefreshResponse(val access_token: String, val refresh_token: String)
 
 // Expenses
-data class ExpenseResponse(val expenses: List<Expense>)
+data class ExpensesResponse(val expenses: List<Expense>)
+data class ExpenseCreationRequest(val expense: Expense, val shares: List<ExpenseShare>)
+data class ExpenseCreationResponse(val expense: Expense, val shares: List<ExpenseShare>)
+
+// ExpenseShares
+data class ExpenseSharesResponse(val shares: List<ExpenseShare>)
+data class ExpenseShareResponse(val share: ExpenseShare)

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

@@ -0,0 +1,33 @@
+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()
+        emit(Resource.Loading(cachedExpense))
+
+        if(cachedExpense.isEmpty() || forceRefresh) {
+            try {
+                val response = api.expensesGet("Bearer $token")
+                if(response.isSuccessful) {
+                    val remoteExpense = response.body()?.expenses ?: emptyList()
+                    remoteExpense.forEach {
+                        dao.insertExpense(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/ExpenseShareRepository.kt

@@ -0,0 +1,73 @@
+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
+import java.util.UUID
+
+class ExpenseShareRepository(
+    private val dao: ExpenseShareDao,
+    private val api: APIService
+) {
+    fun getShares(token: String, forceRefresh: Boolean = false): Flow<Resource<List<ExpenseShare>>> = flow {
+        val cachedData = dao.getAllShares().first()
+        emit(Resource.Loading(cachedData))
+
+        if(cachedData.isEmpty() || forceRefresh) {
+            try {
+                val response = api.sharesGet("Bearer $token")
+                if(response.isSuccessful) {
+                    val remoteShare = response.body()?.shares ?: emptyList()
+                    remoteShare.forEach {
+                        dao.insertShare(it)
+                    }
+                }
+            } catch(e: Exception) {
+                emit(Resource.Error("Network Error: ${e.localizedMessage}", cachedData))
+            }
+        }
+        dao.getAllShares().collect { emit(Resource.Success(it)) }
+    }
+
+    fun getShareById(token: String, shareId: UUID, forceRefresh: Boolean = false): Flow<Resource<ExpenseShare>> = flow {
+        val cached = dao.getShareById(shareId).first()
+        emit(Resource.Loading(cached))
+        if(cached == null || forceRefresh) {
+            try {
+                val response = api.shareGet("Bearer $token", shareId)
+                if(response.isSuccessful) {
+                    response.body()?.share?.let { remoteShare -> dao.insertShare(remoteShare) }
+                }
+            } catch(e: Exception) {
+                emit(Resource.Error("Network-Error: ${e.localizedMessage}", cached))
+            }
+        }
+        dao.getShareById(shareId).collect { share ->
+            if(share != null) emit(Resource.Success(share))
+            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/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/repository/UserRepository.kt

@@ -0,0 +1,32 @@
+package de.miaurizius.shap_planner.repository
+
+import de.miaurizius.shap_planner.entities.User
+import de.miaurizius.shap_planner.entities.UserDao
+import de.miaurizius.shap_planner.network.APIService
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.flow
+import java.util.UUID
+
+class UserRepository(
+    private val dao: UserDao,
+    private val api: APIService
+) {
+    fun getUser(token: String, userId: UUID, forceRefresh: Boolean = false): Flow<Resource<User>> = flow {
+        val cached = dao.getUserById(userId).first()
+        emit(Resource.Loading(cached))
+        if(cached == null || forceRefresh) {
+            try {
+                val response = api.userinfo("Bearer $token", userId)
+                if(response.isSuccessful) {
+                    println("Body: ${response.body()}")
+                    response.body()?.let { remoteUser -> dao.insertUser(remoteUser) }
+                }
+            } catch(e: Exception) {
+                emit(Resource.Error("Network-Error: ${e.localizedMessage}", cached))
+            }
+        }
+        dao.getUserById(userId).collect { user -> if(user != null) emit(Resource.Success(user)) else emit(
+            Resource.Error("User nicht gefunden", null)) }
+    }
+}

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

@@ -1,12 +1,22 @@
 package de.miaurizius.shap_planner.ui
 
+import androidx.activity.compose.BackHandler
+import androidx.compose.material3.Text
 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.ExpenseCreationScreen
+import de.miaurizius.shap_planner.ui.screens.ExpenseDetailScreen
 import de.miaurizius.shap_planner.ui.screens.LoginScreen
+import de.miaurizius.shap_planner.viewmodels.ExpenseCreationViewModel
+import de.miaurizius.shap_planner.viewmodels.ExpenseDetailViewModel
 import de.miaurizius.shap_planner.viewmodels.MainViewModel
 
 @Composable
@@ -18,7 +28,6 @@ fun AppContent(
     onLogin: (String, String, String) -> Unit,
 
     // Expenses
-    expenses: List<Expense>,
     onExpenseClick: (Expense) -> Unit,
 
     // Account
@@ -33,16 +42,36 @@ fun AppContent(
     onSessionInvalid: () -> Unit,
 
     //Important
-    viewModel: MainViewModel
+    viewModel: MainViewModel,
+    detailViewModel: ExpenseDetailViewModel,
+    creationViewModel: ExpenseCreationViewModel
 ) {
+    var selectedExpense by remember { mutableStateOf<Expense?>(null) }
+    var showAddExpenseScreen by remember { mutableStateOf(false) }
+
     when {
+        showAddExpenseScreen -> {
+            ExpenseCreationScreen(
+                account = selectedAccount!!,
+                viewModel = creationViewModel,
+                onBack = { showAddExpenseScreen = false },
+                onSaved = { showAddExpenseScreen = false }
+            )
+        }
+        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,
-            expenses = expenses,
-            onExpenseClick = onExpenseClick,
+            onExpenseClick = { selectedExpense = it },
 
             // Default Methods
             mainViewModel = viewModel,
@@ -50,7 +79,8 @@ fun AppContent(
             onDelete = onDeleteAccount,
             sessionState = sessionState,
             onValidate = onValidateSession,
-            onSessionInvalid = onSessionInvalid
+            onSessionInvalid = onSessionInvalid,
+            onAddExpenseClick = { showAddExpenseScreen = true },
         )
         else -> AccountSelectionScreen(
             accounts = accountList,

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(
@@ -41,7 +43,7 @@ fun AccountSelectionScreen(accounts: List<Account>, onAccountClick: (Account) ->
         verticalArrangement = Arrangement.spacedBy(12.dp)
     ) {
         item {
-            Text("Wähle einen Account", style = MaterialTheme.typography.headlineSmall)
+            Text("Choose an account", style = MaterialTheme.typography.headlineSmall)
         }
 
         items(accounts) { account ->
@@ -62,7 +64,7 @@ fun AccountSelectionScreen(accounts: List<Account>, onAccountClick: (Account) ->
                 onClick = onAddAccountClick,
                 modifier = Modifier.fillMaxWidth()
             ) {
-                Text("Anderen Account hinzufügen")
+                Text("Add account")
             }
         }
     }

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

@@ -1,5 +1,6 @@
 package de.miaurizius.shap_planner.ui.screens
 
+import android.annotation.SuppressLint
 import androidx.activity.compose.BackHandler
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
@@ -19,11 +20,15 @@ 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.Scaffold
 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
@@ -32,14 +37,16 @@ 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
 
+@OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun DashboardScreen(
     // Data and regarding Methods
     account: Account,
-    expenses: List<Expense>,
     onExpenseClick: (Expense) -> Unit,
+    onAddExpenseClick: () -> Unit,
 
     // Default Methods
     mainViewModel: MainViewModel,
@@ -49,8 +56,10 @@ 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) {
@@ -62,55 +71,74 @@ fun DashboardScreen(
             BackHandler {
                 onBack()
             }
-            Column(
-                modifier = Modifier
-                    .fillMaxSize()
-                    .padding(16.dp)
-                    .statusBarsPadding()
-                    .navigationBarsPadding()
-            ) {
-                // Header
-                Row(
-                    modifier = Modifier.fillMaxWidth(),
-                    horizontalArrangement = Arrangement.SpaceBetween,
-                    verticalAlignment = Alignment.CenterVertically
+            Scaffold(floatingActionButton = {
+                androidx.compose.material3.FloatingActionButton(
+                    onClick = onAddExpenseClick,
+                    containerColor = MaterialTheme.colorScheme.primary,
+                    contentColor = MaterialTheme.colorScheme.onPrimary
                 ) {
-                    Column {
-                        Text(
-                            text = "Hallo, ${account.name}!",
-                            style = MaterialTheme.typography.headlineMedium
-                        )
-                        Text(
-                            text = "WG: ${account.wgName}",
-                            style = MaterialTheme.typography.bodyLarge,
-                            color = Color.Gray
-                        )
-                    }
-                    Button(onClick = onBack) {
-                        Text("Wechseln")
-                    }
+                    Text("+", style = MaterialTheme.typography.headlineSmall)
                 }
-
-                Spacer(modifier = Modifier.height(5.dp))
-
-                Button(onClick = onDelete) {
-                    Text("Löschen")
-                }
-
-                Spacer(modifier = Modifier.height(10.dp))
-
-                Text("WG-Kosten", style = MaterialTheme.typography.titleLarge)
-                Spacer(modifier = Modifier.height(8.dp))
-
-                LazyColumn(
+            }) { paddingValues ->
+                Column(
                     modifier = Modifier
                         .fillMaxSize()
-                        .background(MaterialTheme.colorScheme.surfaceVariant, shape = MaterialTheme.shapes.medium),
-                    contentPadding = PaddingValues(8.dp),
-                    verticalArrangement = Arrangement.spacedBy(8.dp)
+                        .padding(paddingValues)
+                        .padding(16.dp)
+                        .statusBarsPadding()
+                        .navigationBarsPadding()
                 ) {
-                    items(expenses) { expense ->
-                        ExpenseItem(expense = expense, onClick = { onExpenseClick(expense) })
+                    // Header
+                    Row(
+                        modifier = Modifier.fillMaxWidth(),
+                        horizontalArrangement = Arrangement.SpaceBetween,
+                        verticalAlignment = Alignment.CenterVertically
+                    ) {
+                        Column {
+                            Text(
+                                text = "Hello, ${account.name}!",
+                                style = MaterialTheme.typography.headlineMedium
+                            )
+                            Text(
+                                text = "Household: ${account.wgName}",
+                                style = MaterialTheme.typography.bodyLarge,
+                                color = Color.Gray
+                            )
+                        }
+                        Button(onClick = onBack) {
+                            Text("Switch")
+                        }
+                    }
+
+                    Spacer(modifier = Modifier.height(5.dp))
+
+                    Button(onClick = onDelete) {
+                        Text("Delete")
+                    }
+
+                    Spacer(modifier = Modifier.height(10.dp))
+
+                    Text("Costs", 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("Error: ${expenseResource.message}", color = Color.Red)
+                    }
+
+                    LazyColumn(
+                        modifier = Modifier
+                            .fillMaxSize()
+                            .background(MaterialTheme.colorScheme.surfaceVariant, shape = MaterialTheme.shapes.medium),
+                        contentPadding = PaddingValues(8.dp),
+                        verticalArrangement = Arrangement.spacedBy(8.dp)
+                    ) {
+                        items(expenseResource.data ?: emptyList()) { expense ->
+                            ExpenseItem(expense = expense, onClick = { onExpenseClick(expense) })
+                        }
                     }
                 }
             }
@@ -128,6 +156,7 @@ fun DashboardScreen(
     }
 }
 
+@SuppressLint("DefaultLocale")
 @Composable
 fun ExpenseItem(expense: Expense, onClick: () -> Unit) {
     Surface(modifier = Modifier
@@ -137,7 +166,7 @@ fun ExpenseItem(expense: Expense, onClick: () -> Unit) {
         color = MaterialTheme.colorScheme.surface) {
         Row(modifier = Modifier.padding(16.dp), horizontalArrangement = Arrangement.SpaceBetween) {
             Text(text = expense.title, style = MaterialTheme.typography.bodyLarge)
-            Text(text = expense.amount.toString()+"€", style = MaterialTheme.typography.bodyLarge, fontWeight = FontWeight.Bold)
+            Text(text = String.format("%.2f€", expense.amount / 100.0), style = MaterialTheme.typography.bodyLarge, fontWeight = FontWeight.Bold)
         }
     }
 }

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

@@ -0,0 +1,87 @@
+package de.miaurizius.shap_planner.ui.screens
+
+import androidx.compose.foundation.layout.*
+import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.material3.*
+import androidx.compose.runtime.*
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.input.KeyboardType
+import androidx.compose.ui.unit.dp
+import de.miaurizius.shap_planner.entities.Account
+import de.miaurizius.shap_planner.viewmodels.ExpenseCreationViewModel
+import java.util.UUID
+
+@OptIn(ExperimentalMaterial3Api::class, ExperimentalLayoutApi::class)
+@Composable
+fun ExpenseCreationScreen(
+    account: Account,
+    viewModel: ExpenseCreationViewModel,
+    onSaved: () -> Unit,
+    onBack: () -> Unit
+) {
+    var title by remember { mutableStateOf("") }
+    var amountStr by remember { mutableStateOf("") }
+    val users by viewModel.users.collectAsState()
+    val selectedUsers = remember { mutableStateListOf<UUID>() }
+
+    LaunchedEffect(Unit) { viewModel.loadUsers() }
+
+    Scaffold(
+        topBar = {
+            TopAppBar(title = { Text("New Expense") })
+        }
+    ) { padding ->
+        Column(modifier = Modifier.padding(padding).padding(16.dp)) {
+            OutlinedTextField(
+                value = title,
+                onValueChange = { title = it },
+                label = { Text("What was bought?") },
+                modifier = Modifier.fillMaxWidth()
+            )
+
+            Spacer(modifier = Modifier.height(8.dp))
+
+            OutlinedTextField(
+                value = amountStr,
+                onValueChange = { amountStr = it },
+                label = { Text("Amount in €") },
+                keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Decimal),
+                modifier = Modifier.fillMaxWidth()
+            )
+
+            Spacer(modifier = Modifier.height(16.dp))
+            Text("Who participated?", style = MaterialTheme.typography.titleMedium)
+
+            FlowRow(modifier = Modifier.padding(vertical = 8.dp), horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                users.forEach { user ->
+                    FilterChip(
+                        selected = selectedUsers.contains(user.id),
+                        onClick = {
+                            if (selectedUsers.contains(user.id)) selectedUsers.remove(user.id)
+                            else selectedUsers.add(user.id)
+                        },
+                        label = { Text(user.name) }
+                    )
+                }
+            }
+
+            Spacer(modifier = Modifier.weight(1f))
+
+            Button(
+                onClick = {
+                    val cents = (amountStr.replace(",", ".").toDoubleOrNull() ?: 0.0) * 100
+                    viewModel.saveExpense(account, title, cents.toInt(), selectedUsers.toList())
+                    onSaved()
+                },
+                modifier = Modifier.fillMaxWidth(),
+                enabled = title.isNotBlank() && amountStr.isNotBlank() && selectedUsers.isNotEmpty()
+            ) {
+                Text("Save")
+            }
+
+            TextButton(onClick = onBack, modifier = Modifier.fillMaxWidth()) {
+                Text("Cancel")
+            }
+        }
+    }
+}

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

@@ -0,0 +1,109 @@
+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
+
+@SuppressLint("DefaultLocale")
+@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, "Back")
+                } }
+            )
+        }
+    ) { padding ->
+        Column(modifier = Modifier.padding(padding).padding(16.dp)) {
+            Text(
+                text = String.format("%.2f€", 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("Cost Allocation", style = MaterialTheme.typography.titleLarge)
+            Spacer(modifier = Modifier.height(8.dp))
+
+            LazyColumn(verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                items(shares) { item ->
+                    ShareItem(item.user?.name ?: "Unknown User", 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/ExpenseCreationViewModel.kt

@@ -0,0 +1,64 @@
+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 kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.launch
+import java.util.UUID
+
+class ExpenseCreationViewModel(
+    private val userDao: UserDao,
+    private val expenseDao: ExpenseDao,
+    private val shareDao: ExpenseShareDao,
+    private val tokenStorage: TokenStorage
+) : ViewModel() {
+    private val _users = MutableStateFlow<List<User>>(emptyList())
+    val users: StateFlow<List<User>> = _users
+
+    fun loadUsers() {
+        viewModelScope.launch {
+            userDao.getAllUsers().collect { _users.value = it }
+        }
+    }
+
+    fun saveExpense(account: Account, title: String, amountCents: Int, selectedUserIds: List<UUID>) {
+        viewModelScope.launch {
+            val expenseId = UUID.randomUUID() //TODO: Backend  has to generate UUID
+            val newExpense = Expense(
+                id = expenseId,
+                payer_id = account.id,
+                amount = amountCents,
+                title = title,
+                description = "",
+                attachments = null,
+                created_at = (System.currentTimeMillis() / 1000).toInt(),
+                last_updated_at = 0
+            )
+
+            expenseDao.insertExpense(newExpense)
+
+            val shareAmount = amountCents / selectedUserIds.size
+            selectedUserIds.forEach { userId ->
+                shareDao.insertShare(
+                    ExpenseShare(
+                        UUID.randomUUID(), //TODO: Backend has to generate UUID
+                        expenseId,
+                        userId,
+                        shareAmount
+                    )
+                )
+            }
+
+            // API Calls
+        }
+    }
+}

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
+            }
+        }
+    }
+}

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 api = RetrofitProvider.create(account.serverUrl)
+            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