Implemented session validation and token refreshing

Added a `SessionState` sealed class to track the connection status and integrated it into the `DashboardScreen`. The dashboard now triggers a session validation on launch, showing a loading indicator during the check.

The `MainViewModel` has been updated with a `validateSession` function that:
- Pings the server using the stored access token.
- Attempts to refresh the token if a 401 Unauthorized response is received.
- Updates the `TokenStorage` with new tokens upon successful refresh.
- Redirects to logout if both tokens are invalid.

Additionally, the `APIService` was expanded with `ping` and `refresh` endpoints, and the `AppDatabase` version was incremented.

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

@@ -2,6 +2,7 @@ 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.compose.foundation.clickable
@@ -23,6 +24,7 @@ import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.material3.Button
 import androidx.compose.material3.Card
+import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextField
@@ -39,8 +41,10 @@ import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
+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.SessionState
 import de.miaurizius.shap_planner.room.AppDatabase
 import de.miaurizius.shap_planner.ui.theme.ShapPlannerTheme
 import de.miaurizius.shap_planner.viewmodels.LoginViewModel
@@ -57,23 +61,48 @@ class MainActivity : ComponentActivity() {
 
         val database = AppDatabase.getDatabase(applicationContext)
         val dao = database.accountDao()
-        val mainViewModel = MainViewModel(dao)
+
+        val tokenStorage = TokenStorage(applicationContext)
+
+        val mainViewModel = MainViewModel(dao, tokenStorage)
 
         setContent {
             ShapPlannerTheme {
                 val isLoggedIn by loginViewModel.isLoggedIn.collectAsState()
                 val accountList by mainViewModel.accounts.collectAsState()
                 val selectedAccount = mainViewModel.selectedAccount
+                var showLoginForNewAccount by remember { mutableStateOf(false) }
 
                 when {
-                    !isLoggedIn || accountList.isEmpty() -> {
-                        LoginScreen { serverUrl, username, password -> loginViewModel.login(serverUrl, username, password, mainViewModel) }
+
+                    showLoginForNewAccount -> {
+                        LoginScreen(
+                            onLogin = { serverUrl, username, password ->
+                                loginViewModel.login(serverUrl, username, password, mainViewModel)
+                                showLoginForNewAccount = false
+                            },
+                            onBack = {
+                                showLoginForNewAccount = false
+                            }
+                        )
+                    }
+
+                    accountList.isEmpty() -> {
+                        LoginScreen(
+                            onLogin = { serverUrl, username, password ->
+                                loginViewModel.login(serverUrl, username, password, mainViewModel)
+                            }
+                        )
                     }
 
                     selectedAccount != null -> {
                         DashboardScreen(
                             account = selectedAccount,
-                            onBack = { mainViewModel.logoutFromAccount() }
+                            onBack = { mainViewModel.logoutFromAccount() },
+                            onDelete = { mainViewModel.deleteAccount(selectedAccount) },
+                            sessionState = mainViewModel.sessionState,
+                            onValidate = { mainViewModel.validateSession(selectedAccount) },
+                            onSessionInvalid = { mainViewModel.logoutFromAccount() }
                         )
                     }
 
@@ -84,7 +113,7 @@ class MainActivity : ComponentActivity() {
                                 mainViewModel.selectAccount(account)
                             },
                             onAddAccountClick = {
-                                loginViewModel.logout()
+                                showLoginForNewAccount = true
                             }
                         )
                     }
@@ -133,7 +162,14 @@ fun AccountSelectionScreen(accounts: List<Account>, onAccountClick: (Account) ->
 }
 
 @Composable
-fun LoginScreen(onLogin: (String, String, String) -> Unit) {
+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("") }
@@ -177,37 +213,73 @@ fun LoginScreen(onLogin: (String, String, String) -> Unit) {
 }
 
 @Composable
-fun DashboardScreen(account: Account, onBack: () -> Unit) {
-    Column(
-        modifier = Modifier
-            .fillMaxSize()
-            .padding(16.dp)
-            .statusBarsPadding()
-            .navigationBarsPadding()
-    ) {
-        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")
+fun DashboardScreen(
+    account: Account,
+    onBack: () -> Unit,
+    onDelete: () -> Unit,
+    sessionState: SessionState,
+    onValidate: () -> Unit,
+    onSessionInvalid: () -> Unit) {
+
+    LaunchedEffect(Unit) { onValidate() }
+
+    when (sessionState) {
+        SessionState.Loading -> {
+            Box(Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
+                CircularProgressIndicator()
             }
         }
+        SessionState.Valid -> {
+            BackHandler {
+                onBack()
+            }
+            Column(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .padding(16.dp)
+                    .statusBarsPadding()
+                    .navigationBarsPadding()
+            ) {
+                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))
+                Spacer(modifier = Modifier.height(5.dp))
 
-        Box(
-            modifier = Modifier
-                .fillMaxSize()
-                .background(MaterialTheme.colorScheme.surfaceVariant, shape = MaterialTheme.shapes.medium),
-            contentAlignment = Alignment.Center
-        ) {
-            Text("Hier kommen bald deine WG-Kosten hin 🚀")
+                Button(onClick = onDelete) {
+                    Text("Löschen")
+                }
+
+                Spacer(modifier = Modifier.height(10.dp))
+
+                Box(
+                    modifier = Modifier
+                        .fillMaxSize()
+                        .background(MaterialTheme.colorScheme.surfaceVariant, shape = MaterialTheme.shapes.medium),
+                    contentAlignment = Alignment.Center
+                ) {
+                    Text("Hier kommen bald deine WG-Kosten hin 🚀")
+                }
+            }
+        }
+        SessionState.Invalid -> {
+            LaunchedEffect(Unit) {
+                onSessionInvalid()
+            }
+        }
+        is SessionState.Error -> {
+            Text("Server error")
         }
     }
+
 }

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

@@ -2,16 +2,25 @@ package de.miaurizius.shap_planner.network
 
 import retrofit2.Response
 import retrofit2.http.Body
+import retrofit2.http.GET
+import retrofit2.http.Header
+import retrofit2.http.Headers
 import retrofit2.http.POST
 
 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)
 
+data class RefreshRequest(val refreshToken: String)
+data class RefreshResponse(val accessToken: String, val refreshToken: String)
+
 interface APIService {
     @POST("api/login")
     suspend fun login(@Body req: LoginRequest): Response<LoginResponse>
 
     @POST("api/refresh")
-    suspend fun refresh(@Body req: Map<String, String>): Response<Map<String, String>>
+    suspend fun refresh(@Body req: RefreshRequest): Response<RefreshResponse>
+
+    @GET("api/ping")
+    suspend fun ping(@Header("Authorization") token: String): Response<Map<String, String>>
 }

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/room/AppDatabase.kt

@@ -7,7 +7,7 @@ import androidx.room.RoomDatabase
 import de.miaurizius.shap_planner.entities.Account
 import de.miaurizius.shap_planner.entities.AccountDao
 
-@Database(entities = [Account::class], version = 2)
+@Database(entities = [Account::class], version = 3)
 abstract class AppDatabase : RoomDatabase() {
     abstract fun accountDao(): AccountDao
     companion object {

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

@@ -13,6 +13,8 @@ import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import java.util.Locale
+import java.util.Locale.getDefault
 import java.util.UUID
 
 class LoginViewModel(private val prefs: UserPreferences, private val appContext: Context) : ViewModel() {
@@ -28,7 +30,7 @@ class LoginViewModel(private val prefs: UserPreferences, private val appContext:
 
             try {
                 val response = withContext(Dispatchers.IO) {
-                    api.login(LoginRequest(username, password))
+                    api.login(LoginRequest(username.lowercase(getDefault()), password))
                 }
 
                 if(response.isSuccessful) {

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

@@ -5,25 +5,85 @@ 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.network.RefreshRequest
+import de.miaurizius.shap_planner.network.RetrofitProvider
+import de.miaurizius.shap_planner.network.SessionState
 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 tokenStorage: TokenStorage) : ViewModel() {
 
     val accounts: StateFlow<List<Account>> = accountDao.getAllAccounts()
         .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), emptyList())
 
+    var sessionState by mutableStateOf<SessionState>(SessionState.Loading)
+        private set
+
+    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
+            }
+
+            println("Testing with AT $accessToken")
+            val pingResponse = api.ping("Bearer $accessToken")
+
+            if(pingResponse.isSuccessful) {
+                sessionState = SessionState.Valid
+                return@launch
+            }
+
+            if(pingResponse.code() == 401) {
+                println("Testing with RT $refreshToken")
+                val refreshResponse = api.refresh(RefreshRequest(refreshToken))
+
+                if(refreshResponse.isSuccessful) {
+                    val newTokens = refreshResponse.body()!!
+
+                    tokenStorage.saveTokens(
+                        account.id.toString(),
+                        newTokens.accessToken,
+                        newTokens.accessToken
+                    )
+
+                    sessionState = SessionState.Valid
+                    return@launch
+                } else {
+                    sessionState = SessionState.Invalid
+                    return@launch
+                }
+            }
+            sessionState = SessionState.Error("Server error")
+        }
+    }
+
     fun addAccount(account: Account) {
         viewModelScope.launch {
             accountDao.insertAccount(account)
         }
     }
 
+    fun deleteAccount(account: Account) {
+        viewModelScope.launch {
+            accountDao.deleteAccount(account)
+            tokenStorage.clearTokens(account.id.toString())
+            selectedAccount = null
+        }
+    }
+
     var selectedAccount by mutableStateOf<Account?>(null)
         private set