Improved UI and enhanced expense creation

Updated the UI across all screens (Login, Dashboard, Account Selection, Expense Details, and Creation) with a more modern, card-based design and improved layouts.

Expense creation now includes:
- Real-time split validation to ensure shares match the total amount.
- An "Equal Split" shortcut for quick allocation.
- Support for optional descriptions and multiple file attachments.
- Strict save validation.

The `MainActivity` now supports edge-to-edge display, and the `AccountDao` includes a new query to fetch accounts by ID. Added `material-icons-extended` dependency for enhanced iconography.

.gitignore

@@ -1,10 +1,36 @@
+# Build artifacts
+bin/
+gen/
+out/
+build/
+app/build/
+
+# Kotlin / Java
 *.iml
-.gradle
+*.ipr
-/local.properties
+*.iws
-/.idea
+.idea/
-.DS_Store
+.gradle/
-/build
-/captures
-.externalNativeBuild
-.cxx
 local.properties
+
+# Android Studio
+captures/
+.externalNativeBuild/
+.cxx/
+.navigation/
+
+# Keys & Secrets
+*.jks
+*.keystore
+*.p12
+google-services.json
+
+# OS generated files
+.DS_Store
+Thumbs.db
+
+# Log files
+*.log
+
+# Bundle/Release
+/app/release/

LICENSE

@@ -0,0 +1,121 @@
+Creative Commons Legal Code
+
+CC0 1.0 Universal
+
+    CREATIVE COMMONS CORPORATION IS NOT A LAW FIRM AND DOES NOT PROVIDE
+    LEGAL SERVICES. DISTRIBUTION OF THIS DOCUMENT DOES NOT CREATE AN
+    ATTORNEY-CLIENT RELATIONSHIP. CREATIVE COMMONS PROVIDES THIS
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+    REGARDING THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS
+    PROVIDED HEREUNDER, AND DISCLAIMS LIABILITY FOR DAMAGES RESULTING FROM
+    THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS PROVIDED
+    HEREUNDER.
+
+Statement of Purpose
+
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+exclusive Copyright and Related Rights (defined below) upon the creator
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+1. Copyright and Related Rights. A Work made available under CC0 may be
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+purposes (the "Waiver"). Affirmer makes the Waiver for the benefit of each
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+successors, fully intending that such Waiver shall not be subject to
+revocation, rescission, cancellation, termination, or any other legal or
+equitable action to disrupt the quiet enjoyment of the Work by the public
+as contemplated by Affirmer's express Statement of Purpose.
+
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+be judged legally invalid or ineffective under applicable law, then the
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+account Affirmer's express Statement of Purpose. In addition, to the
+extent the Waiver is so judged Affirmer hereby grants to each affected
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+time extensions), (iii) in any current or future medium and for any number
+of copies, and (iv) for any purpose whatsoever, including without
+limitation commercial, advertising or promotional purposes (the
+"License"). The License shall be deemed effective as of the date CC0 was
+applied by Affirmer to the Work. Should any part of the License for any
+reason be judged legally invalid or ineffective under applicable law, such
+partial invalidity or ineffectiveness shall not invalidate the remainder
+of the License, and in such case Affirmer hereby affirms that he or she
+will not (i) exercise any of his or her remaining Copyright and Related
+Rights in the Work or (ii) assert any associated claims and causes of
+action with respect to the Work, in either case contrary to Affirmer's
+express Statement of Purpose.
+
+4. Limitations and Disclaimers.
+
+ a. No trademark or patent rights held by Affirmer are waived, abandoned,
+    surrendered, licensed or otherwise affected by this document.
+ b. Affirmer offers the Work as-is and makes no representations or
+    warranties of any kind concerning the Work, express, implied,
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+    title, merchantability, fitness for a particular purpose, non
+    infringement, or the absence of latent or other defects, accuracy, or
+    the present or absence of errors, whether or not discoverable, all to
+    the greatest extent permissible under applicable law.
+ c. Affirmer disclaims responsibility for clearing rights of other persons
+    that may apply to the Work or any use thereof, including without
+    limitation any person's Copyright and Related Rights in the Work.
+    Further, Affirmer disclaims responsibility for obtaining any necessary
+    consents, permissions or other rights required for any use of the
+    Work.
+ d. Affirmer understands and acknowledges that Creative Commons is not a
+    party to this document and has no duty or obligation with respect to
+    this CC0 or use of the Work.

README.md

@@ -0,0 +1,20 @@
+# ShAp-Planner
+
+ShAp-Planner is a **self-hosted app** for managing finances, tasks, and data within shared households.  
+The app is fully open source, lightweight, and can run on small devices like Raspberry Pi or older computers.
+
+**[Backend](https://git.miaurizius.de/MiauRizius/shap-planner-backend):** Go  
+**[Frontend](https://git.miaurizius.de/MiauRizius/shap-planner-android):** Android (Kotlin)  
+**[License](https://git.miaurizius.de/MiauRizius/shap-planner-android/src/branch/main/LICENSE):** [CC0 1.0](https://creativecommons.org/publicdomain/zero/1.0/)
+
+---
+
+## Installation
+
+You can either build the app from source or download the apk _(will be available soon)_
+
+---
+
+## License
+
+This work is marked <a href="https://creativecommons.org/publicdomain/zero/1.0/">CC0 1.0</a>

app/.gitignore

@@ -1 +0,0 @@
-/build

app/build.gradle.kts

@@ -61,8 +61,17 @@ dependencies {
 
     //Manually added
     implementation("androidx.datastore:datastore-preferences:1.2.0")
+    implementation("androidx.compose.material:material-icons-extended:1.6.0")
 
     val room_version = "2.8.4"
     implementation("androidx.room:room-runtime:$room_version")
     ksp("androidx.room:room-compiler:$room_version")
+
+    // Retrofit + Gson
+    implementation("com.squareup.retrofit2:retrofit:2.9.0")
+    implementation("com.squareup.retrofit2:converter-gson:2.9.0")
+    // OkHttp logging (debug)
+    implementation("com.squareup.okhttp3:logging-interceptor:4.9.3")
+    // AndroidX Security (EncryptedSharedPreferences)
+    implementation("androidx.security:security-crypto:1.1.0-alpha03")
 }

app/src/main/AndroidManifest.xml

@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
-    xmlns:tools="http://schemas.android.com/tools">
+    <uses-permission android:name="android.permission.INTERNET" />
-
     <application
         android:allowBackup="true"
         android:dataExtractionRules="@xml/data_extraction_rules"
@@ -10,18 +9,16 @@
         android:label="@string/app_name"
         android:roundIcon="@mipmap/ic_launcher_round"
         android:supportsRtl="true"
+        android:networkSecurityConfig="@xml/network_security_config"
         android:theme="@style/Theme.ShapPlanner">
         <activity
             android:name=".activities.MainActivity"
             android:exported="true"
-            android:label="@string/app_name"
             android:theme="@style/Theme.ShapPlanner">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
-
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
     </application>
-
 </manifest>

app/src/main/java/de/miaurizius/shap_planner/TokenStorage.kt

@@ -0,0 +1,40 @@
+package de.miaurizius.shap_planner
+
+import android.content.Context
+import androidx.security.crypto.EncryptedSharedPreferences
+import androidx.security.crypto.MasterKey
+
+class TokenStorage(context: Context) {
+
+    private val masterKey = MasterKey.Builder(context)
+        .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
+        .build()
+
+    private val prefs = EncryptedSharedPreferences.create(
+        context,
+        "wg_token_prefs2",
+        masterKey,
+        EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
+        EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
+    )
+
+    fun saveTokens(accountId: String, accessToken: String, refreshToken: String) {
+//        println("Account ID: ${accountId}\nAToken: ${accessToken}\nRToken: ${refreshToken}")
+        prefs.edit()
+            .putString("access_$accountId", accessToken)
+            .putString("refresh_$accountId", refreshToken)
+            .apply()
+    }
+
+    fun getAccess(accountId: String): String? = prefs.getString("access_$accountId", null)
+    fun getRefresh(accountId: String): String? = prefs.getString("refresh_$accountId", null)
+
+    fun clearTokens(accountId: String) {
+        prefs.edit()
+            .remove("access_$accountId")
+            .remove("refresh_$accountId")
+            .apply()
+    }
+
+
+}

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

@@ -2,184 +2,85 @@ package de.miaurizius.shap_planner.activities
 
 import android.os.Bundle
 import androidx.activity.ComponentActivity
+import androidx.activity.compose.BackHandler
 import androidx.activity.compose.setContent
-import androidx.compose.foundation.background
+import androidx.activity.enableEdgeToEdge
-import androidx.compose.foundation.clickable
-import androidx.compose.foundation.layout.Arrangement
-import androidx.compose.foundation.layout.Box
-import androidx.compose.foundation.layout.Column
-import androidx.compose.foundation.layout.Row
-import androidx.compose.foundation.layout.Spacer
-import androidx.compose.foundation.layout.fillMaxSize
-import androidx.compose.foundation.layout.fillMaxWidth
-import androidx.compose.foundation.layout.height
-import androidx.compose.foundation.layout.padding
-import androidx.compose.foundation.layout.size
-import androidx.compose.foundation.layout.statusBarsPadding
-import androidx.compose.foundation.layout.width
-import androidx.compose.foundation.lazy.LazyColumn
-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.MaterialTheme
-import androidx.compose.material3.Text
-import androidx.compose.material3.TextField
-import androidx.compose.runtime.Composable
-import androidx.compose.runtime.LaunchedEffect
 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 androidx.compose.ui.Alignment
+import de.miaurizius.shap_planner.TokenStorage
-import androidx.compose.ui.Modifier
-import androidx.compose.ui.graphics.Color
-import androidx.compose.ui.text.font.FontWeight
-import androidx.compose.ui.unit.dp
 import de.miaurizius.shap_planner.UserPreferences
-import de.miaurizius.shap_planner.entities.Account
 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
-import java.util.UUID
 
 class MainActivity : ComponentActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
+        enableEdgeToEdge()
         super.onCreate(savedInstanceState)
-//        enableEdgeToEdge()
 
         val prefs = UserPreferences(this)
-        val loginViewModel = LoginViewModel(prefs)
+        val loginViewModel = LoginViewModel(prefs, applicationContext)
-
         val database = AppDatabase.getDatabase(applicationContext)
-        val dao = database.accountDao()
+        val accountDao = database.accountDao()
-        val mainViewModel = MainViewModel(dao)
+        val expenseDao = database.expenseDao()
+        val tokenStorage = TokenStorage(applicationContext)
+        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 {
             ShapPlannerTheme {
-                val isLoggedIn by loginViewModel.isLoggedIn.collectAsState()
                 val accountList by mainViewModel.accounts.collectAsState()
                 val selectedAccount = mainViewModel.selectedAccount
+                val showLoginForNewAccount = remember { mutableStateOf(false) }
 
-                when {
+                BackHandler(enabled = showLoginForNewAccount.value && accountList.isNotEmpty()) {
-                    !isLoggedIn || accountList.isEmpty() -> {
+                    showLoginForNewAccount.value = false
-                        LoginScreen { userId ->
-                            val acc = Account(userId, "MiauRizius", "Pfadi-WG") //TODO: get data from backend
-                            mainViewModel.addAccount(acc)
-                            loginViewModel.login(acc.id.toString())
-                        }
-                    }
-
-                    selectedAccount != null -> {
-                        DashboardScreen(
-                            account = selectedAccount,
-                            onBack = { mainViewModel.logoutFromAccount() }
-                        )
-                    }
-
-                    else -> {
-                        AccountSelectionScreen(
-                            accounts = accountList,
-                            onAccountClick = { account ->
-                                mainViewModel.selectAccount(account)
-                            },
-                            onAddAccountClick = {
-                                loginViewModel.logout()
-                            }
-                        )
-                    }
                 }
+
+                AppContent(
+                    accountList = accountList,
+                    selectedAccount = selectedAccount,
+                    showLoginForNewAccount = showLoginForNewAccount.value,
+                    onLogin = { server, user, pass ->
+                        loginViewModel.login(server, user, pass, mainViewModel)
+                        showLoginForNewAccount.value = false
+                    },
+                    onSelectAccount = { mainViewModel.selectAccount(it) },
+                    onLogoutAccount = { mainViewModel.logoutFromAccount() },
+                    onAddAccountClick = { showLoginForNewAccount.value = true },
+                    onDeleteAccount = { mainViewModel.deleteAccount(selectedAccount!!) },
+                    sessionState = mainViewModel.sessionState,
+                    onValidateSession = { mainViewModel.validateSession(selectedAccount!!) },
+                    onSessionInvalid = { mainViewModel.logoutFromAccount() },
+                    onExpenseClick = { expense -> println("Clicked: ${expense.title}") },
+                    viewModel = mainViewModel,
+                    detailViewModel = detailViewModel,
+                    creationViewModel = creationViewModel,
+                )
             }
         }
     }
-}
-
-@Composable
-fun AccountSelectionScreen(accounts: List<Account>, onAccountClick: (Account) -> Unit, onAddAccountClick: () -> Unit) {
-    LazyColumn(
-        modifier = Modifier.fillMaxSize().padding(16.dp).statusBarsPadding(),
-        verticalArrangement = Arrangement.spacedBy(12.dp)
-    ) {
-        item {
-            Text("Wähle einen Account", style = MaterialTheme.typography.headlineSmall)
-        }
-
-        items(accounts) { account ->
-            Card(modifier = Modifier.fillMaxWidth().clickable{ onAccountClick(account) }) {
-                Row(modifier = Modifier.padding(16.dp), verticalAlignment = Alignment.CenterVertically) {
-                    Box(modifier = Modifier.size(40.dp).background(Color.Gray, shape = CircleShape))
-                    Spacer(modifier = Modifier.width(16.dp))
-                    Column {
-                        Text(text = account.name, fontWeight = FontWeight.Bold)
-                        Text(text = account.wgName, style = MaterialTheme.typography.bodyMedium)
-                    }
-                }
-            }
-        }
-        item {
-            Spacer(modifier = Modifier.height(8.dp))
-            Button(
-                onClick = onAddAccountClick,
-                modifier = Modifier.fillMaxWidth()
-            ) {
-                Text("Anderen Account hinzufügen")
-            }
-        }
-    }
-}
-
-@Composable
-fun LoginScreen(onLogin: (UUID) -> Unit) {
-    var userId by remember { mutableStateOf("") }
-
-    Column(modifier = Modifier.padding(16.dp).statusBarsPadding()) {
-        Text("Bitte anmelden")
-        Spacer(modifier = Modifier.height(8.dp))
-        TextField(
-            value = userId,
-            onValueChange = { userId = it },
-            label = { Text("User ID") }
-        )
-        Spacer(modifier = Modifier.height(8.dp))
-        Button(onClick = { if(userId.isNotEmpty()) onLogin(UUID.fromString(userId)) }) {
-            Text("Login")
-        }
-    }
-}
-
-@Composable
-fun DashboardScreen(account: Account, onBack: () -> Unit) {
-    Column(
-        modifier = Modifier
-            .fillMaxSize()
-            .padding(16.dp)
-            .statusBarsPadding()
-    ) {
-        Row(
-            modifier = Modifier.fillMaxWidth(),
-            horizontalArrangement = Arrangement.SpaceBetween,
-            verticalAlignment = Alignment.CenterVertically
-        ) {
-            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")
-            }
-        }
-
-        Spacer(modifier = Modifier.height(32.dp))
-
-        Box(
-            modifier = Modifier
-                .fillMaxSize()
-                .background(MaterialTheme.colorScheme.surfaceVariant, shape = MaterialTheme.shapes.medium),
-            contentAlignment = Alignment.Center
-        ) {
-            Text("Hier kommen bald deine WG-Kosten hin 🚀")
-        }
-    }
 }

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

@@ -15,7 +15,9 @@ data class Account (
     @PrimaryKey val id: UUID,
     val name: String,
     val wgName: String,
-    val avatarUrl: String? = null
+    val avatarUrl: String? = null,
+    val serverUrl: String,
+    val role: String,
 )
 
 @Dao
@@ -23,6 +25,9 @@ interface AccountDao {
     @Query("SELECT * FROM accounts")
     fun getAllAccounts(): Flow<List<Account>>
 
+    @Query("SELECT * FROM accounts WHERE id = :userId")
+    fun getAccountById(userId: UUID): Flow<Account?>
+
     @Insert(onConflict = OnConflictStrategy.REPLACE)
     suspend fun insertAccount(account: Account)
 

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

@@ -1,12 +1,35 @@
 package de.miaurizius.shap_planner.entities
 
+import androidx.room.Dao
+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 amt: Double,
+    val payer_id: UUID,
-    val desc: String,
+    val amount: Int,
+    val title: String,
+    val description: String,
+    val attachments: List<String>?,
+    val created_at: Int,
+    val last_updated_at: Int
+)
 
-    val payerId: UUID,
+@Dao
-    val debtors: List<User>
+interface ExpenseDao {
-)
+    @Query("SELECT * FROM expenses")
+    fun getAllExpenses(): Flow<List<Expense>>
+
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun insertExpense(expense: Expense)
+
+    @Delete
+    suspend fun deleteExpense(expense: Expense)
+}

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

@@ -0,0 +1,37 @@
+package de.miaurizius.shap_planner.entities
+
+import androidx.room.Dao
+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(
+    @PrimaryKey val id: UUID,
+    val expense_id: UUID,
+    val user_id: UUID,
+    val share_cents: Int
+)
+
+@Dao
+interface ExpenseShareDao {
+    @Query("SELECT * FROM expense_shares")
+    fun getAllShares(): Flow<List<ExpenseShare>>
+
+    @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)
+
+    @Delete
+    suspend fun deleteShare(share: ExpenseShare)
+}

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

@@ -1,8 +1,33 @@
 package de.miaurizius.shap_planner.entities
 
+import androidx.room.Dao
+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?
+)
+
+@Dao
+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)
+
+    @Delete
+    suspend fun deleteUser(user: User)
+}

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

@@ -0,0 +1,54 @@
+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
+import retrofit2.http.GET
+import retrofit2.http.Header
+import retrofit2.http.POST
+import retrofit2.http.PUT
+import retrofit2.http.Query
+import java.util.UUID
+
+interface APIService {
+    // Account
+    @POST("api/login")
+    suspend fun login(@Body req: LoginRequest): Response<LoginResponse>
+    @POST("api/refresh")
+    suspend fun refresh(@Body req: RefreshRequest): Response<RefreshResponse>
+    @GET("api/ping")
+    suspend fun ping(@Header("Authorization") token: String): Response<Map<String, String>>
+
+    // Expenses
+    @GET("api/expenses")
+    suspend fun expensesGet(@Header("Authorization") token: String): Response<ExpensesResponse>
+    @POST("api/expenses")
+    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): 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

@@ -0,0 +1,22 @@
+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)
+data class LoginUser(val id: String, val username: String, val role: String, val avatarUrl: String?)
+data class LoginResponse(val access_token: String, val refresh_token: String, val user: LoginUser, val wgName: String)
+
+// Refresh-Tokens
+data class RefreshRequest(val refresh_token: String)
+data class RefreshResponse(val access_token: String, val refresh_token: String)
+
+// Expenses
+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/network/RetrofitProvider.kt

@@ -0,0 +1,28 @@
+package de.miaurizius.shap_planner.network
+
+import okhttp3.OkHttpClient
+import okhttp3.logging.HttpLoggingInterceptor
+import retrofit2.Retrofit
+import retrofit2.converter.gson.GsonConverterFactory
+
+object RetrofitProvider {
+
+    fun create(serverUrl: String): APIService {
+        val base = if (serverUrl.endsWith("/")) "https://$serverUrl" else "https://$serverUrl/"
+
+        val logger = HttpLoggingInterceptor().apply { level = HttpLoggingInterceptor.Level.BASIC }
+
+        val client = OkHttpClient.Builder()
+            .addInterceptor(logger)
+            .build()
+
+        val retrofit = Retrofit.Builder()
+            .baseUrl(base)
+            .client(client)
+            .addConverterFactory(GsonConverterFactory.create())
+            .build()
+
+        return retrofit.create(APIService::class.java)
+    }
+
+}

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

@@ -0,0 +1,8 @@
+package de.miaurizius.shap_planner.network
+
+sealed class SessionState {
+    object Loading : SessionState()
+    object Valid : SessionState()
+    object Invalid : SessionState()
+    data class Error(val message: String) : SessionState()
+}

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 +1,72 @@
+package de.miaurizius.shap_planner.repository
+
+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 = 1)
+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
@@ -20,7 +39,7 @@ abstract class AppDatabase : RoomDatabase() {
                     context.applicationContext,
                     AppDatabase::class.java,
                     "shap_planner_database"
-                ).build()
+                ).fallbackToDestructiveMigration(true).build()
                 INSTANCE = instance
                 instance
             }

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

@@ -0,0 +1,89 @@
+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.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
+fun AppContent(
+    // Login
+    accountList: List<Account>,
+    selectedAccount: Account?,
+    showLoginForNewAccount: Boolean,
+    onLogin: (String, String, String) -> Unit,
+
+    // Expenses
+    onExpenseClick: (Expense) -> Unit,
+
+    // Account
+    onSelectAccount: (Account) -> Unit,
+    onLogoutAccount: () -> Unit,
+    onAddAccountClick: () -> Unit,
+    onDeleteAccount: () -> Unit,
+
+    // Session
+    sessionState: SessionState,
+    onValidateSession: () -> Unit,
+    onSessionInvalid: () -> Unit,
+
+    //Important
+    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,
+            onExpenseClick = { selectedExpense = it },
+
+            // Default Methods
+            mainViewModel = viewModel,
+            onBack = onLogoutAccount,
+            onDelete = onDeleteAccount,
+            sessionState = sessionState,
+            onValidate = onValidateSession,
+            onSessionInvalid = onSessionInvalid,
+            onAddExpenseClick = { showAddExpenseScreen = true },
+        )
+        else -> AccountSelectionScreen(
+            accounts = accountList,
+            onAccountClick = onSelectAccount,
+            onAddAccountClick = onAddAccountClick
+        )
+    }
+}

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

@@ -0,0 +1,188 @@
+package de.miaurizius.shap_planner.ui.screens
+
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.navigationBarsPadding
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.KeyboardArrowRight
+import androidx.compose.material.icons.filled.Add
+import androidx.compose.material.icons.filled.Home
+import androidx.compose.material3.Button
+import androidx.compose.material3.CardDefaults
+import androidx.compose.material3.CenterAlignedTopAppBar
+import androidx.compose.material3.ElevatedCard
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+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.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
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun AccountSelectionScreen(
+    accounts: List<Account>,
+    onAccountClick: (Account) -> Unit,
+    onAddAccountClick: () -> Unit
+) {
+    Scaffold(
+        topBar = {
+            CenterAlignedTopAppBar(
+                title = { Text("ShAp-Planner", fontWeight = FontWeight.Black) }
+            )
+        },
+        bottomBar = {
+            Surface(
+                modifier = Modifier.fillMaxWidth(),
+                tonalElevation = 2.dp
+            ) {
+                Button(
+                    onClick = onAddAccountClick,
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .padding(20.dp)
+                        .navigationBarsPadding()
+                        .height(56.dp),
+                    shape = MaterialTheme.shapes.medium
+                ) {
+                    Icon(Icons.Default.Add, contentDescription = null)
+                    Spacer(modifier = Modifier.width(8.dp))
+                    Text("Add New Account", style = MaterialTheme.typography.titleMedium)
+                }
+            }
+        }
+    ) { padding ->
+        Column(
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(padding)
+                .padding(horizontal = 20.dp)
+        ) {
+            Spacer(modifier = Modifier.height(16.dp))
+
+            Text(
+                text = "Welcome back!",
+                style = MaterialTheme.typography.headlineLarge,
+                fontWeight = FontWeight.Bold
+            )
+            Text(
+                text = "Select an account to continue",
+                style = MaterialTheme.typography.bodyLarge,
+                color = MaterialTheme.colorScheme.secondary,
+                modifier = Modifier.padding(bottom = 16.dp)
+            )
+
+            LazyColumn(
+                modifier = Modifier.fillMaxSize(),
+                verticalArrangement = Arrangement.spacedBy(12.dp),
+                contentPadding = PaddingValues(bottom = 16.dp)
+            ) {
+                if (accounts.isEmpty()) {
+                    item {
+                        Box(
+                            modifier = Modifier.fillParentMaxHeight(0.6f).fillMaxWidth(),
+                            contentAlignment = Alignment.Center
+                        ) {
+                            Text(
+                                "No accounts yet.\nTap 'Add New Account' to start.",
+                                textAlign = TextAlign.Center,
+                                color = Color.Gray
+                            )
+                        }
+                    }
+                }
+
+                items(accounts) { account ->
+                    AccountItem(account = account, onClick = { onAccountClick(account) })
+                }
+            }
+        }
+    }
+}
+
+@Composable
+fun AccountItem(account: Account, onClick: () -> Unit) {
+    ElevatedCard(
+        modifier = Modifier
+            .fillMaxWidth()
+            .clickable { onClick() },
+        shape = MaterialTheme.shapes.large,
+        colors = CardDefaults.elevatedCardColors(
+            containerColor = MaterialTheme.colorScheme.surface
+        )
+    ) {
+        Row(
+            modifier = Modifier.padding(16.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            // Stylized Avatar with Initial
+            Surface(
+                modifier = Modifier.size(52.dp),
+                shape = CircleShape,
+                color = MaterialTheme.colorScheme.primaryContainer
+            ) {
+                Box(contentAlignment = Alignment.Center) {
+                    Text(
+                        text = account.name.take(1).uppercase(),
+                        style = MaterialTheme.typography.titleLarge,
+                        fontWeight = FontWeight.Bold,
+                        color = MaterialTheme.colorScheme.onPrimaryContainer
+                    )
+                }
+            }
+
+            Spacer(modifier = Modifier.width(16.dp))
+
+            Column(modifier = Modifier.weight(1f)) {
+                Text(
+                    text = account.name,
+                    style = MaterialTheme.typography.titleMedium,
+                    fontWeight = FontWeight.Bold
+                )
+                Row(verticalAlignment = Alignment.CenterVertically) {
+                    Icon(
+                        Icons.Default.Home,
+                        contentDescription = null,
+                        modifier = Modifier.size(14.dp),
+                        tint = MaterialTheme.colorScheme.secondary
+                    )
+                    Spacer(modifier = Modifier.width(4.dp))
+                    Text(
+                        text = account.wgName,
+                        style = MaterialTheme.typography.bodyMedium,
+                        color = MaterialTheme.colorScheme.secondary
+                    )
+                }
+            }
+
+            // Trailing Chevron
+            Icon(
+                Icons.AutoMirrored.Filled.KeyboardArrowRight,
+                contentDescription = null,
+                tint = MaterialTheme.colorScheme.outline
+            )
+        }
+    }
+}

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

@@ -0,0 +1,217 @@
+package de.miaurizius.shap_planner.ui.screens
+
+import android.annotation.SuppressLint
+import androidx.compose.foundation.background
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Add
+import androidx.compose.material.icons.filled.Delete
+import androidx.compose.material.icons.filled.Refresh
+import androidx.compose.material3.CircularProgressIndicator
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Surface
+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.text.font.FontWeight
+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(
+    account: Account,
+    onExpenseClick: (Expense) -> Unit,
+    onAddExpenseClick: () -> Unit,
+    mainViewModel: MainViewModel,
+    onBack: () -> Unit,
+    onDelete: () -> Unit,
+    sessionState: SessionState,
+    onValidate: () -> Unit,
+    onSessionInvalid: () -> Unit
+) {
+    val expenseResource by mainViewModel.expenseResource.collectAsState()
+
+    LaunchedEffect(Unit) { onValidate() }
+    LaunchedEffect(account) { mainViewModel.loadExpenses(account, forceRefresh = false) }
+
+    if (sessionState == SessionState.Invalid) {
+        LaunchedEffect(Unit) { onSessionInvalid() }
+        return
+    }
+
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = {
+                    Column {
+                        Text(account.wgName, style = MaterialTheme.typography.titleLarge)
+                        Text("Household", style = MaterialTheme.typography.labelSmall)
+                    }
+                },
+                actions = {
+                    IconButton(onClick = onBack) {
+                        Icon(Icons.Default.Refresh, "Switch")
+                    }
+                    IconButton(onClick = onDelete) {
+                        Icon(Icons.Default.Delete, "Delete", tint = MaterialTheme.colorScheme.error)
+                    }
+                }
+            )
+        },
+        floatingActionButton = {
+            androidx.compose.material3.FloatingActionButton(
+                onClick = onAddExpenseClick,
+                containerColor = MaterialTheme.colorScheme.primary,
+                contentColor = MaterialTheme.colorScheme.onPrimary
+            ) {
+                Icon(Icons.Default.Add, "Neu")
+            }
+        }
+    ) { paddingValues ->
+        Column(
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(paddingValues)
+                .background(MaterialTheme.colorScheme.surface)
+        ) {
+            Column(modifier = Modifier.padding(16.dp)) {
+                Text(
+                    text = "Hello, ${account.name}!",
+                    style = MaterialTheme.typography.headlineMedium,
+                    fontWeight = FontWeight.Bold
+                )
+
+                Spacer(modifier = Modifier.height(16.dp))
+
+                SummaryCard(expenses = expenseResource.data ?: emptyList())
+            }
+
+            Text(
+                text = "Latest expenses",
+                style = MaterialTheme.typography.titleMedium,
+                modifier = Modifier.padding(horizontal = 16.dp, vertical = 8.dp),
+                color = MaterialTheme.colorScheme.secondary
+            )
+
+            Box(modifier = Modifier.fillMaxSize()) {
+                if (expenseResource is Resource.Loading && expenseResource.data?.isEmpty() == true) {
+                    CircularProgressIndicator(modifier = Modifier.align(Alignment.Center))
+                }
+
+                LazyColumn(
+                    modifier = Modifier.fillMaxSize(),
+                    contentPadding = PaddingValues(16.dp),
+                    verticalArrangement = Arrangement.spacedBy(12.dp)
+                ) {
+                    items(expenseResource.data ?: emptyList()) { expense ->
+                        ExpenseItem(expense = expense, onClick = { onExpenseClick(expense) })
+                    }
+                }
+            }
+        }
+    }
+}
+
+@SuppressLint("DefaultLocale")
+@Composable
+fun SummaryCard(expenses: List<Expense>) {
+    val total = expenses.sumOf { it.amount } / 100.0
+    androidx.compose.material3.Card(
+        modifier = Modifier.fillMaxWidth(),
+        colors = androidx.compose.material3.CardDefaults.cardColors(
+            containerColor = MaterialTheme.colorScheme.primaryContainer
+        )
+    ) {
+        Column(modifier = Modifier.padding(20.dp)) {
+            Text("Total expenditure", style = MaterialTheme.typography.labelMedium)
+            Text(
+                text = String.format("%.2f €", total),
+                style = MaterialTheme.typography.displaySmall,
+                fontWeight = FontWeight.Black
+            )
+        }
+    }
+}
+
+@SuppressLint("DefaultLocale")
+@Composable
+fun ExpenseItem(expense: Expense, onClick: () -> Unit) {
+    androidx.compose.material3.ElevatedCard(
+        modifier = Modifier
+            .fillMaxWidth()
+            .clickable { onClick() },
+        shape = MaterialTheme.shapes.medium,
+        colors = androidx.compose.material3.CardDefaults.elevatedCardColors(
+            containerColor = MaterialTheme.colorScheme.surface
+        )
+    ) {
+        Row(
+            modifier = Modifier
+                .padding(16.dp)
+                .fillMaxWidth(),
+            verticalAlignment = Alignment.CenterVertically,
+            horizontalArrangement = Arrangement.SpaceBetween
+        ) {
+            Row(verticalAlignment = Alignment.CenterVertically) {
+                Surface(
+                    shape = androidx.compose.foundation.shape.CircleShape,
+                    color = MaterialTheme.colorScheme.primaryContainer,
+                    modifier = Modifier.size(40.dp)
+                ) {
+                    Box(contentAlignment = Alignment.Center) {
+                        Text(
+                            text = expense.title.take(1).uppercase(),
+                            style = MaterialTheme.typography.titleMedium,
+                            color = MaterialTheme.colorScheme.onPrimaryContainer
+                        )
+                    }
+                }
+
+                Spacer(modifier = Modifier.width(16.dp))
+
+                Column {
+                    Text(
+                        text = expense.title,
+                        style = MaterialTheme.typography.titleMedium,
+                        fontWeight = FontWeight.Bold
+                    )
+                }
+            }
+
+            Text(
+                text = String.format("%.2f €", expense.amount / 100.0),
+                style = MaterialTheme.typography.titleLarge,
+                fontWeight = FontWeight.ExtraBold,
+                color = MaterialTheme.colorScheme.primary
+            )
+        }
+    }
+}

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

@@ -0,0 +1,249 @@
+package de.miaurizius.shap_planner.ui.screens
+
+import android.annotation.SuppressLint
+import androidx.compose.foundation.layout.*
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material.icons.filled.Delete
+import androidx.compose.material.icons.filled.Description
+import androidx.compose.material3.*
+import androidx.compose.runtime.*
+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.input.KeyboardType
+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.viewmodels.ExpenseCreationViewModel
+
+@SuppressLint("DefaultLocale")
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun ExpenseCreationScreen(
+    account: Account,
+    viewModel: ExpenseCreationViewModel,
+    onSaved: () -> Unit,
+    onBack: () -> Unit
+) {
+    var title by remember { mutableStateOf("") }
+    var description by remember { mutableStateOf("") }
+    var totalAmountStr by remember { mutableStateOf("") }
+    val attachmentUris = remember { mutableStateListOf<android.net.Uri>() }
+    val userShares = remember { mutableStateMapOf<java.util.UUID, String>() }
+    val users by viewModel.users.collectAsState()
+
+    // Real-time calculation logic
+    val totalCents = (totalAmountStr.replace(",", ".").toDoubleOrNull() ?: 0.0) * 100
+    val distributedCents = userShares.values.sumOf {
+        (it.replace(",", ".").toDoubleOrNull() ?: 0.0) * 100
+    }.toLong()
+
+    val diff = totalCents.toLong() - distributedCents
+    val isAmountMatched = totalCents > 0 && diff == 0L
+
+    // File Picker for multiple files (Images & PDFs)
+    val launcher = androidx.activity.compose.rememberLauncherForActivityResult(
+        contract = androidx.activity.result.contract.ActivityResultContracts.GetMultipleContents()
+    ) { uris ->
+        attachmentUris.addAll(uris)
+    }
+
+    LaunchedEffect(Unit) { viewModel.loadUsers() }
+
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = { Text("New Expense") },
+                navigationIcon = { IconButton(onClick = onBack) {
+                    Icon(Icons.AutoMirrored.Filled.ArrowBack, "Back")
+                } }
+            )
+        }
+    ) { padding ->
+        LazyColumn(
+            modifier = Modifier.fillMaxSize().padding(padding).padding(horizontal = 16.dp),
+            verticalArrangement = Arrangement.spacedBy(16.dp)
+        ) {
+            // Header Info
+            item {
+                Spacer(modifier = Modifier.height(8.dp))
+                ElevatedCard(modifier = Modifier.fillMaxWidth()) {
+                    Column(modifier = Modifier.padding(16.dp)) {
+                        OutlinedTextField(
+                            value = title,
+                            onValueChange = { title = it },
+                            label = { Text("Title *") },
+                            modifier = Modifier.fillMaxWidth()
+                        )
+                        Spacer(modifier = Modifier.height(12.dp))
+                        OutlinedTextField(
+                            value = totalAmountStr,
+                            onValueChange = { totalAmountStr = it },
+                            label = { Text("Total Amount (€) *") },
+                            keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Decimal),
+                            modifier = Modifier.fillMaxWidth()
+                        )
+                    }
+                }
+            }
+
+            // Optional Description & Multi-File Attachments
+            item {
+                Text("Additional Info", style = MaterialTheme.typography.titleMedium)
+                ElevatedCard(modifier = Modifier.fillMaxWidth()) {
+                    Column(modifier = Modifier.padding(16.dp)) {
+                        OutlinedTextField(
+                            value = description,
+                            onValueChange = { description = it },
+                            label = { Text("Description (Optional)") },
+                            modifier = Modifier.fillMaxWidth(),
+                            minLines = 2
+                        )
+                        Spacer(modifier = Modifier.height(16.dp))
+
+                        Text("Attachments (${attachmentUris.size})", style = MaterialTheme.typography.labelLarge)
+                        attachmentUris.forEach { uri ->
+                            Row(verticalAlignment = Alignment.CenterVertically) {
+                                Icon(Icons.Default.Description, "File", modifier = Modifier.size(20.dp))
+                                Text(" Document attached", modifier = Modifier.weight(1f), style = MaterialTheme.typography.bodySmall)
+                                IconButton(onClick = { attachmentUris.remove(uri) }) {
+                                    Icon(Icons.Default.Delete, "Remove", tint = Color.Red)
+                                }
+                            }
+                        }
+
+                        Button(onClick = { launcher.launch("*/*") }) {
+                            Text("Select Files (Images, PDF)")
+                        }
+                    }
+                }
+            }
+
+            // Split Details & Validation Message
+            item {
+                Column {
+                    Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.SpaceBetween, verticalAlignment = Alignment.CenterVertically) {
+                        Text("Split Details *", style = MaterialTheme.typography.titleMedium)
+                        TextButton(onClick = {
+                            if (totalCents > 0) {
+                                val share = String.format("%.2f", (totalCents / users.size) / 100.0)
+                                users.forEach { userShares[it.id] = share }
+                            }
+                        }) { Text("Split Equally") }
+                    }
+
+                    // VALIDATION MESSAGE
+                    if (totalCents > 0) {
+                        val statusText = when {
+                            diff > 0 -> "Remaining: ${String.format("%.2f", diff / 100.0)} €"
+                            diff < 0 -> "Over-allocated: ${String.format("%.2f", Math.abs(diff) / 100.0)} €"
+                            else -> "Amount matched! ✓"
+                        }
+                        val statusColor = if (diff == 0L) Color(0xFF2E7D32) else MaterialTheme.colorScheme.error
+
+                        Surface(
+                            color = statusColor.copy(alpha = 0.1f),
+                            shape = MaterialTheme.shapes.small,
+                            modifier = Modifier.fillMaxWidth().padding(vertical = 4.dp)
+                        ) {
+                            Text(
+                                text = statusText,
+                                color = statusColor,
+                                modifier = Modifier.padding(8.dp),
+                                style = MaterialTheme.typography.bodyMedium,
+                                fontWeight = FontWeight.Bold,
+                                textAlign = TextAlign.Center
+                            )
+                        }
+                    }
+                }
+            }
+
+            items(users) { user ->
+                UserShareInputItem(
+                    userName = user.name,
+                    amount = userShares[user.id] ?: "",
+                    onAmountChange = { userShares[user.id] = it }
+                )
+            }
+
+            // Save Actions
+            item {
+                Button(
+                    onClick = {
+                        viewModel.saveExpense(
+                            account = account,
+                            title = title,
+                            description = description,
+                            amountCents = totalCents.toInt(),
+                            shares = userShares.mapValues { (it.value.replace(",",".").toDoubleOrNull() ?: 0.0).toInt() * 100 }.filter { it.value > 0 },
+                            attachments = attachmentUris.map { it.toString() }
+                        )
+                        onSaved()
+                    },
+                    modifier = Modifier.fillMaxWidth().height(56.dp),
+                    enabled = title.isNotBlank() && isAmountMatched // STRICT VALIDATION
+                ) {
+                    Text("Save Expense")
+                }
+
+                if (totalAmountStr.isNotBlank() && !isAmountMatched) {
+                    Text(
+                        "Sum of shares must equal total amount to save.",
+                        style = MaterialTheme.typography.labelSmall,
+                        color = MaterialTheme.colorScheme.error,
+                        modifier = Modifier.fillMaxWidth().padding(top = 8.dp),
+                        textAlign = TextAlign.Center
+                    )
+                }
+
+                TextButton(onClick = onBack, modifier = Modifier.fillMaxWidth()) {
+                    Text("Cancel")
+                }
+                Spacer(modifier = Modifier.height(32.dp))
+            }
+        }
+    }
+}
+
+@Composable
+fun UserShareInputItem(userName: String, amount: String, onAmountChange: (String) -> Unit) {
+    Card(
+        modifier = Modifier.fillMaxWidth(),
+        colors = CardDefaults.cardColors(containerColor = MaterialTheme.colorScheme.surfaceVariant.copy(alpha = 0.3f))
+    ) {
+        Row(
+            modifier = Modifier.padding(12.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            Surface(
+                shape = androidx.compose.foundation.shape.CircleShape,
+                color = MaterialTheme.colorScheme.primaryContainer,
+                modifier = Modifier.size(32.dp)
+            ) {
+                Box(contentAlignment = Alignment.Center) {
+                    Text(userName.take(1).uppercase(), style = MaterialTheme.typography.bodySmall)
+                }
+            }
+            Spacer(modifier = Modifier.width(12.dp))
+            Text(userName, modifier = Modifier.weight(1f), style = MaterialTheme.typography.bodyLarge)
+
+            OutlinedTextField(
+                value = amount,
+                onValueChange = onAmountChange,
+                modifier = Modifier.width(100.dp),
+                placeholder = { Text("0.00") },
+                keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Decimal),
+                singleLine = true,
+                textStyle = MaterialTheme.typography.bodyMedium.copy(textAlign = TextAlign.End)
+            )
+            Spacer(modifier = Modifier.width(4.dp))
+            Text("€")
+        }
+    }
+}

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

@@ -0,0 +1,189 @@
+package de.miaurizius.shap_planner.ui.screens
+
+import android.annotation.SuppressLint
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+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.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Surface
+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 Details") },
+                navigationIcon = {
+                    IconButton(onClick = onBack) {
+                        Icon(Icons.AutoMirrored.Filled.ArrowBack, contentDescription = "Back")
+                    }
+                }
+            )
+        }
+    ) { padding ->
+        Column(
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(padding)
+                .padding(16.dp)
+        ) {
+            // Hero Section: Amount & Title
+            Column(
+                modifier = Modifier.fillMaxWidth().padding(bottom = 24.dp),
+                horizontalAlignment = Alignment.CenterHorizontally
+            ) {
+                Text(
+                    text = "Total Amount",
+                    style = MaterialTheme.typography.labelLarge,
+                    color = MaterialTheme.colorScheme.secondary
+                )
+                Text(
+                    text = String.format("%.2f €", expense.amount / 100.0),
+                    style = MaterialTheme.typography.displayMedium,
+                    fontWeight = FontWeight.Black,
+                    color = MaterialTheme.colorScheme.primary
+                )
+                Text(
+                    text = expense.title,
+                    style = MaterialTheme.typography.headlineSmall,
+                    fontWeight = FontWeight.Bold,
+                    textAlign = TextAlign.Center
+                )
+            }
+
+            // Description Card (only shown if not empty)
+            if (expense.description.isNotBlank()) {
+                androidx.compose.material3.ElevatedCard(
+                    modifier = Modifier.fillMaxWidth().padding(bottom = 24.dp),
+                    colors = androidx.compose.material3.CardDefaults.elevatedCardColors(
+                        containerColor = MaterialTheme.colorScheme.surfaceVariant.copy(alpha = 0.5f)
+                    )
+                ) {
+                    Column(modifier = Modifier.padding(16.dp)) {
+                        Text(
+                            text = "Description",
+                            style = MaterialTheme.typography.labelMedium,
+                            color = MaterialTheme.colorScheme.primary
+                        )
+                        Spacer(modifier = Modifier.height(4.dp))
+                        Text(text = expense.description, style = MaterialTheme.typography.bodyLarge)
+                    }
+                }
+            }
+
+            Text(
+                text = "Cost Distribution",
+                style = MaterialTheme.typography.titleMedium,
+                fontWeight = FontWeight.Bold,
+                modifier = Modifier.padding(bottom = 12.dp)
+            )
+
+            LazyColumn(
+                verticalArrangement = Arrangement.spacedBy(12.dp),
+                modifier = Modifier.fillMaxSize()
+            ) {
+                items(shares) { item ->
+                    ShareItem(
+                        name = item.user?.name ?: "Unknown User",
+                        amountCents = item.share.share_cents
+                    )
+                }
+            }
+        }
+    }
+}
+
+@SuppressLint("DefaultLocale")
+@Composable
+fun ShareItem(name: String, amountCents: Int) {
+    androidx.compose.material3.OutlinedCard(
+        modifier = Modifier.fillMaxWidth(),
+        shape = MaterialTheme.shapes.medium,
+        colors = androidx.compose.material3.CardDefaults.outlinedCardColors(
+            containerColor = MaterialTheme.colorScheme.surface
+        )
+    ) {
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(12.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            // User Avatar Circle
+            Surface(
+                shape = androidx.compose.foundation.shape.CircleShape,
+                color = MaterialTheme.colorScheme.secondaryContainer,
+                modifier = Modifier.size(36.dp)
+            ) {
+                Box(contentAlignment = Alignment.Center) {
+                    Text(
+                        text = name.take(1).uppercase(),
+                        style = MaterialTheme.typography.bodyMedium,
+                        fontWeight = FontWeight.Bold,
+                        color = MaterialTheme.colorScheme.onSecondaryContainer
+                    )
+                }
+            }
+
+            Spacer(modifier = Modifier.width(12.dp))
+
+            Text(
+                text = name,
+                style = MaterialTheme.typography.bodyLarge,
+                fontWeight = FontWeight.Medium,
+                modifier = Modifier.weight(1f)
+            )
+
+            Text(
+                text = String.format("%.2f €", amountCents / 100.0),
+                style = MaterialTheme.typography.bodyLarge,
+                fontWeight = FontWeight.Bold,
+                color = if (amountCents > 0) Color(0xFF2E7D32) else Color.Gray
+            )
+        }
+    }
+}

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

@@ -0,0 +1,176 @@
+package de.miaurizius.shap_planner.ui.screens
+
+import androidx.activity.compose.BackHandler
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.foundation.verticalScroll
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material.icons.filled.Cloud
+import androidx.compose.material.icons.filled.Lock
+import androidx.compose.material.icons.filled.Person
+import androidx.compose.material.icons.filled.Visibility
+import androidx.compose.material.icons.filled.VisibilityOff
+import androidx.compose.material.icons.filled.VpnKey
+import androidx.compose.material3.Button
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.material3.TopAppBar
+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 androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.input.ImeAction
+import androidx.compose.ui.text.input.KeyboardType
+import androidx.compose.ui.text.input.PasswordVisualTransformation
+import androidx.compose.ui.text.input.VisualTransformation
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.dp
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun LoginScreen(
+    onLogin: (String, String, String) -> Unit,
+    onBack: (() -> Unit)? = null
+) {
+    if (onBack != null) {
+        BackHandler { onBack() }
+    }
+
+    var serverUrl by remember { mutableStateOf("") }
+    var username by remember { mutableStateOf("") }
+    var password by remember { mutableStateOf("") }
+    var passwordVisible by remember { mutableStateOf(false) }
+
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = { Text("Add Account", fontWeight = FontWeight.Bold) },
+                navigationIcon = {
+                    if (onBack != null) {
+                        IconButton(onClick = onBack) {
+                            Icon(Icons.AutoMirrored.Filled.ArrowBack, contentDescription = "Back")
+                        }
+                    }
+                }
+            )
+        }
+    ) { padding ->
+        Column(
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(padding)
+                .padding(24.dp)
+                .verticalScroll(rememberScrollState()), // Scrollbar, falls die Tastatur den Platz wegnimmt
+            horizontalAlignment = Alignment.CenterHorizontally
+        ) {
+            // App Icon or Welcome Text
+            Icon(
+                imageVector = Icons.Default.Lock,
+                contentDescription = null,
+                modifier = Modifier.size(64.dp),
+                tint = MaterialTheme.colorScheme.primary
+            )
+
+            Text(
+                text = "Connect to Server",
+                style = MaterialTheme.typography.headlineMedium,
+                fontWeight = FontWeight.Bold,
+                modifier = Modifier.padding(top = 16.dp)
+            )
+
+            Text(
+                text = "Enter your credentials to link your account",
+                style = MaterialTheme.typography.bodyMedium,
+                color = MaterialTheme.colorScheme.secondary,
+                textAlign = TextAlign.Center,
+                modifier = Modifier.padding(bottom = 32.dp)
+            )
+
+            // Server URL Field
+            OutlinedTextField(
+                value = serverUrl,
+                onValueChange = { serverUrl = it },
+                label = { Text("Server URL") },
+                placeholder = { Text("your-server.com") },
+                modifier = Modifier.fillMaxWidth(),
+                singleLine = true,
+                leadingIcon = { Icon(Icons.Default.Cloud, contentDescription = null) },
+                keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Uri, imeAction = ImeAction.Next)
+            )
+
+            Spacer(modifier = Modifier.height(16.dp))
+
+            // Username Field
+            OutlinedTextField(
+                value = username,
+                onValueChange = { username = it },
+                label = { Text("Username") },
+                modifier = Modifier.fillMaxWidth(),
+                singleLine = true,
+                leadingIcon = { Icon(Icons.Default.Person, contentDescription = null) },
+                keyboardOptions = KeyboardOptions(imeAction = ImeAction.Next)
+            )
+
+            Spacer(modifier = Modifier.height(16.dp))
+
+            // Password Field
+            OutlinedTextField(
+                value = password,
+                onValueChange = { password = it },
+                label = { Text("Password") },
+                modifier = Modifier.fillMaxWidth(),
+                singleLine = true,
+                leadingIcon = { Icon(Icons.Default.VpnKey, contentDescription = null) },
+                visualTransformation = if (passwordVisible) VisualTransformation.None else PasswordVisualTransformation(),
+                keyboardOptions = KeyboardOptions(
+                    keyboardType = KeyboardType.Password,
+                    imeAction = ImeAction.Done
+                ),
+                trailingIcon = {
+                    val image = if (passwordVisible) Icons.Default.Visibility else Icons.Default.VisibilityOff
+                    IconButton(onClick = { passwordVisible = !passwordVisible }) {
+                        Icon(imageVector = image, contentDescription = "Toggle password visibility")
+                    }
+                }
+            )
+
+            Spacer(modifier = Modifier.height(32.dp))
+
+            // Login Button
+            Button(
+                onClick = { onLogin(serverUrl, username, password) },
+                modifier = Modifier
+                    .fillMaxWidth()
+                    .height(56.dp),
+                enabled = serverUrl.isNotBlank() && username.isNotBlank() && password.isNotBlank(),
+                shape = MaterialTheme.shapes.medium
+            ) {
+                Text("Connect Account", style = MaterialTheme.typography.titleMedium)
+            }
+
+            if (onBack != null) {
+                TextButton(onClick = onBack, modifier = Modifier.padding(top = 8.dp)) {
+                    Text("Cancel", color = MaterialTheme.colorScheme.secondary)
+                }
+            }
+        }
+    }
+}

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

@@ -0,0 +1,66 @@
+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,
+        description: String,
+        amountCents: Int,
+        shares: Map<UUID, Int>,
+        attachments: List<String>
+    ) {
+//        viewModelScope.launch {
+//            val expenseId = UUID.randomUUID()
+//            val newExpense = Expense(
+//                id = expenseId,
+//                payer_id = account.id,
+//                amount = amountCents,
+//                title = title,
+//                description = description,
+//                attachments = if (attachments.isEmpty()) null else attachments,
+//                created_at = (System.currentTimeMillis() / 1000).toInt(),
+//                last_updated_at = 0
+//            )
+//
+//            expenseDao.insertExpense(newExpense)
+//
+//            shares.forEach { (userId, shareCents) ->
+//                shareDao.insertShare(
+//                    ExpenseShare(UUID.randomUUID(), expenseId, userId, shareCents)
+//                )
+//            }
+//
+//            // API POST Request
+//
+//        }
+    }
+}

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/LoginViewModel.kt

@@ -1,19 +1,66 @@
 package de.miaurizius.shap_planner.viewmodels
 
+import android.content.Context
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
+import de.miaurizius.shap_planner.TokenStorage
 import de.miaurizius.shap_planner.UserPreferences
+import de.miaurizius.shap_planner.entities.Account
+import de.miaurizius.shap_planner.network.LoginRequest
+import de.miaurizius.shap_planner.network.RetrofitProvider
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+import java.util.Locale.getDefault
+import java.util.UUID
 
-class LoginViewModel(private val prefs: UserPreferences) : ViewModel() {
+class LoginViewModel(private val prefs: UserPreferences, private val appContext: Context) : ViewModel() {
+
+    private val tokenStorage = TokenStorage(appContext)
 
     val isLoggedIn = prefs.isLoggedInFlow.stateIn(viewModelScope, SharingStarted.Lazily, false)
     val lastUserId = prefs.lastUserLoginFlow.stateIn(viewModelScope, SharingStarted.Lazily, null)
 
-    fun login(userId: String) {
+    fun login(serverUrl: String, username: String, password: String, viewModel: MainViewModel) {
-        viewModelScope.launch { prefs.saveLogin(userId) }
+        viewModelScope.launch {
+            val api = RetrofitProvider.create(serverUrl)
+
+            try {
+                val response = withContext(Dispatchers.IO) {
+                    api.login(LoginRequest(username.lowercase(getDefault()).trim(), password))
+                }
+
+                if(response.isSuccessful) {
+                    val body = response.body() ?: run {
+                        return@launch
+                    }
+
+                    val access = body.access_token
+                    val refresh = body.refresh_token
+
+                    tokenStorage.saveTokens(body.user.id, access, refresh)
+
+                    val account = Account(
+                        id = UUID.fromString(body.user.id),
+                        name = username.trim(),
+                        wgName = body.wgName,
+                        avatarUrl = null,
+                        serverUrl = serverUrl,
+                        role = body.user.role
+                    )
+
+                    viewModel.addAccount(account)
+
+                    prefs.saveLogin(body.user.id)
+                } else {
+                    println("Login failed: ${response.code()} ${response.errorBody()?.toString()}")
+                }
+            } catch(e: Exception) {
+                e.printStackTrace()
+            }
+        }
     }
 
     fun logout() {

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

@@ -5,34 +5,108 @@ import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.setValue
 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.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
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import kotlin.collections.emptyList
 
-class MainViewModel(private val accountDao: AccountDao) : ViewModel() {
+class MainViewModel(
+    private val accountDao: AccountDao,
+    private val expenseDao: ExpenseDao,
+    private val tokenStorage: TokenStorage
+) : ViewModel() {
 
-    // Das ist der State, den dein SetContent beobachtet
+    var selectedAccount by mutableStateOf<Account?>(null)
+        private set
     val accounts: StateFlow<List<Account>> = accountDao.getAllAccounts()
         .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), emptyList())
+    var sessionState by mutableStateOf<SessionState>(SessionState.Loading)
+        private set
+
+    private val _expenseResource = MutableStateFlow<Resource<List<Expense>>>(Resource.Loading(emptyList()))
+    val expenseResource: StateFlow<Resource<List<Expense>>> = _expenseResource
+
+    fun loadExpenses(account: Account, forceRefresh: Boolean = false) {
+        viewModelScope.launch {
+            val api = RetrofitProvider.create(account.serverUrl)
+            val repo = ExpenseRepository(expenseDao, api)
+            val accessToken = tokenStorage.getAccess(account.id.toString()) ?: ""
+
+            repo.getExpenses(accessToken, forceRefresh).collect { result -> _expenseResource.value = result }
+        }
+    }
+
+    fun validateSession(account: Account) {
+        viewModelScope.launch {
+            sessionState = SessionState.Loading
+            val api = RetrofitProvider.create(account.serverUrl)
+
+            val accessToken = tokenStorage.getAccess(account.id.toString())
+            val refreshToken = tokenStorage.getRefresh(account.id.toString())
+
+            if(accessToken == null || refreshToken == null) {
+                sessionState = SessionState.Invalid
+                return@launch
+            }
+
+            val pingResponse = api.ping("Bearer $accessToken")
+
+            if(pingResponse.isSuccessful) {
+                sessionState = SessionState.Valid
+                return@launch
+            }
+
+            if(pingResponse.code() == 401) {
+                val refreshResponse = api.refresh(RefreshRequest(refreshToken))
+
+                if(refreshResponse.isSuccessful) {
+                    val newTokens = refreshResponse.body()!!
+
+                    tokenStorage.saveTokens(
+                        account.id.toString(),
+                        newTokens.access_token,
+                        newTokens.refresh_token
+                    )
+
+                    sessionState = SessionState.Valid
+
+                    return@launch
+                } else {
+                    sessionState = SessionState.Invalid
+                    return@launch
+                }
+            }
+            sessionState = SessionState.Error("Server error")
+        }
+    }
 
-    // Funktion zum Hinzufügen (z.B. nach Login)
     fun addAccount(account: Account) {
         viewModelScope.launch {
             accountDao.insertAccount(account)
         }
     }
-
+    fun deleteAccount(account: Account) {
-    var selectedAccount by mutableStateOf<Account?>(null)
+        viewModelScope.launch {
-        private set
+            accountDao.deleteAccount(account)
-
+            tokenStorage.clearTokens(account.id.toString())
+            selectedAccount = null
+        }
+    }
     fun selectAccount(account: Account) {
         selectedAccount = account
     }
-
     fun logoutFromAccount() {
         selectedAccount = null
     }

app/src/main/res/xml/network_security_config.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<network-security-config>
+    <debug-overrides>
+        <trust-anchors>
+            <certificates src="user" />
+        </trust-anchors>
+    </debug-overrides>
+</network-security-config>