feat: Add User and Expense entities with DAOs

This commit introduces the `User` and `Expense` data classes as Room entities. Each entity is accompanied by its corresponding Data Access Object (DAO) with methods for `getAll`, `insert`, and `delete` operations.

Additionally, unused comments were removed from `MainViewModel` and an unnecessary preview was removed from `MainActivity`.

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

@@ -37,6 +37,7 @@ 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.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
 import de.miaurizius.shap_planner.UserPreferences
 import de.miaurizius.shap_planner.entities.Account

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

@@ -1,7 +1,15 @@
 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.Query
+import kotlinx.coroutines.flow.Flow
 import java.util.UUID
 
+@Entity(tableName = "expenses")
 data class Expense (
     val id: UUID,
     val amt: Double,
@@ -10,3 +18,15 @@ data class Expense (
     val payerId: UUID,
     val debtors: List<User>
 )
+
+@Dao
+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/User.kt

@@ -1,8 +1,28 @@
 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.Query
+import kotlinx.coroutines.flow.Flow
 import java.util.UUID
 
+@Entity(tableName = "users")
 data class User (
     val id: UUID,
     val name: String,
 )
+
+@Dao
+interface UserDao {
+    @Query("SELECT * FROM users")
+    fun getAllUsers(): Flow<List<User>>
+
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun insertUser(user: User)
+
+    @Delete
+    suspend fun deleteUser(user: User)
+}

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

@@ -15,11 +15,9 @@ import kotlin.collections.emptyList
 
 class MainViewModel(private val accountDao: AccountDao) : ViewModel() {
 
-    // Das ist der State, den dein SetContent beobachtet
     val accounts: StateFlow<List<Account>> = accountDao.getAllAccounts()
         .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), emptyList())
 
-    // Funktion zum Hinzufügen (z.B. nach Login)
     fun addAccount(account: Account) {
         viewModelScope.launch {
             accountDao.insertAccount(account)