feat(item-form): add unit dropdown with predefined list and custom option

Provides 8 predefined units (Stück, g, kg, ml, l, Packung, Dose, Flasche)
plus a custom input option. Normalizes legacy unit strings on app start.
Dynamic price label shows selected unit.

Closes #114

app/src/main/java/de/bollwerk/app/data/db/dao/ItemDao.kt

@@ -57,4 +57,7 @@ internal interface ItemDao {
 
     @Query("SELECT location_id FROM items ORDER BY last_updated DESC LIMIT 1")
     suspend fun getLastUsedLocationId(): Int?
+
+    @Query("UPDATE items SET unit = 'Stück' WHERE unit IN ('Stk', 'Stk.')")
+    suspend fun normalizeUnits()
 }

app/src/main/java/de/bollwerk/app/data/repository/ItemRepositoryImpl.kt

@@ -33,6 +33,9 @@ internal class ItemRepositoryImpl @Inject constructor(
 ) : ItemRepository {
 
     init {
+        scope.launch {
+            withContext(Dispatchers.IO) { dao.normalizeUnits() }
+        }
         scope.launch {
             webSocketClient.events.collect { event ->
                 if (event is WebSocketEvent.Connected) {

app/src/main/java/de/bollwerk/app/domain/model/UnitOption.kt

@@ -0,0 +1,25 @@
+package de.bollwerk.app.domain.model
+
+/// Vordefinierte Einheiten für das Item-Formular.
+internal object UnitOptions {
+
+    const val CUSTOM_OPTION = "Benutzerdefiniert"
+
+    val predefined: List<String> = listOf(
+        "Stück",
+        "g",
+        "kg",
+        "ml",
+        "l",
+        "Packung",
+        "Dose",
+        "Flasche"
+    )
+
+    /// Alle Dropdown-Einträge inkl. Custom-Option am Ende.
+    val dropdownEntries: List<String> = predefined + CUSTOM_OPTION
+
+    /// Prüft ob ein Wert in der Vordefiniert-Liste enthalten ist.
+    fun isPredefined(value: String): Boolean =
+        predefined.any { it.equals(value, ignoreCase = true) }
+}

app/src/main/java/de/bollwerk/app/ui/item/ItemFormScreen.kt

@@ -40,6 +40,7 @@ import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.unit.dp
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import de.bollwerk.app.domain.model.UnitOptions
 import java.time.LocalDate
 import java.time.YearMonth
 import java.time.format.DateTimeFormatter
@@ -135,15 +136,25 @@ internal fun ItemFormScreen(
 
             Spacer(modifier = Modifier.height(8.dp))
 
-            // Einheit
+            // Einheit Dropdown
-            OutlinedTextField(
+            UnitDropdown(
-                value = uiState.unit,
+                selectedUnit = uiState.unit,
-                onValueChange = viewModel::updateUnit,
+                onUnitSelected = viewModel::updateUnit
-                label = { Text("Einheit") },
-                singleLine = true,
-                modifier = Modifier.fillMaxWidth()
             )
 
+            // Benutzerdefiniertes Einheit-Feld
+            if (uiState.isCustomUnit) {
+                Spacer(modifier = Modifier.height(8.dp))
+                OutlinedTextField(
+                    value = uiState.customUnit,
+                    onValueChange = viewModel::updateCustomUnit,
+                    label = { Text("Eigene Einheit") },
+                    placeholder = { Text("z.B. Karton") },
+                    singleLine = true,
+                    modifier = Modifier.fillMaxWidth()
+                )
+            }
+
             Spacer(modifier = Modifier.height(8.dp))
 
             // Lagerort Dropdown
@@ -169,7 +180,14 @@ internal fun ItemFormScreen(
             OutlinedTextField(
                 value = uiState.unitPrice,
                 onValueChange = viewModel::updateUnitPrice,
-                label = { Text("Preis (€)") },
+                label = {
+                    val unitLabel = if (uiState.isCustomUnit) {
+                        uiState.customUnit.ifBlank { "Einheit" }
+                    } else {
+                        uiState.unit
+                    }
+                    Text("Preis pro $unitLabel (€)")
+                },
                 keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Decimal),
                 singleLine = true,
                 modifier = Modifier.fillMaxWidth()
@@ -458,3 +476,42 @@ private fun MonthYearPickerDialog(
         }
     )
 }
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+private fun UnitDropdown(
+    selectedUnit: String,
+    onUnitSelected: (String) -> Unit
+) {
+    var isExpanded by remember { mutableStateOf(false) }
+
+    ExposedDropdownMenuBox(
+        expanded = isExpanded,
+        onExpandedChange = { isExpanded = it }
+    ) {
+        OutlinedTextField(
+            value = selectedUnit,
+            onValueChange = {},
+            readOnly = true,
+            label = { Text("Einheit") },
+            trailingIcon = { ExposedDropdownMenuDefaults.TrailingIcon(expanded = isExpanded) },
+            modifier = Modifier
+                .fillMaxWidth()
+                .menuAnchor(MenuAnchorType.PrimaryNotEditable)
+        )
+        ExposedDropdownMenu(
+            expanded = isExpanded,
+            onDismissRequest = { isExpanded = false }
+        ) {
+            UnitOptions.dropdownEntries.forEach { unit ->
+                DropdownMenuItem(
+                    text = { Text(unit) },
+                    onClick = {
+                        onUnitSelected(unit)
+                        isExpanded = false
+                    }
+                )
+            }
+        }
+    }
+}

app/src/main/java/de/bollwerk/app/ui/item/ItemFormViewModel.kt

@@ -7,6 +7,7 @@ import dagger.hilt.android.lifecycle.HiltViewModel
 import de.bollwerk.app.data.db.entity.CategoryEntity
 import de.bollwerk.app.data.db.entity.ItemEntity
 import de.bollwerk.app.data.db.entity.LocationEntity
+import de.bollwerk.app.domain.model.UnitOptions
 import de.bollwerk.app.domain.repository.CategoryRepository
 import de.bollwerk.app.domain.repository.ItemRepository
 import de.bollwerk.app.domain.repository.LocationRepository
@@ -27,7 +28,9 @@ internal data class ItemFormUiState(
     val name: String = "",
     val categoryId: Int? = null,
     val quantity: String = "",
-    val unit: String = "",
+    val unit: String = "Stück",
+    val isCustomUnit: Boolean = false,
+    val customUnit: String = "",
     val unitPrice: String = "",
     val kcalPerUnit: String = "",
     val expiryDate: LocalDate? = null,
@@ -111,10 +114,13 @@ internal class ItemFormViewModel @Inject constructor(
     private fun applyPrefill(json: String) {
         try {
             val prefill = jsonParser.decodeFromString<ItemFormPrefill>(json)
+            val isCustom = prefill.unit.isNotBlank() && !UnitOptions.isPredefined(prefill.unit)
             _uiState.update { state ->
                 state.copy(
                     name = prefill.name,
-                    unit = prefill.unit,
+                    unit = if (isCustom) UnitOptions.CUSTOM_OPTION else prefill.unit.ifBlank { "Stück" },
+                    isCustomUnit = isCustom,
+                    customUnit = if (isCustom) prefill.unit else "",
                     kcalPerUnit = prefill.kcalPerUnit?.toString() ?: "",
                     notes = prefill.notes
                 )
@@ -133,6 +139,7 @@ internal class ItemFormViewModel @Inject constructor(
             try {
                 val item = itemRepository.getById(itemId)
                 if (item != null) {
+                    val isCustom = !UnitOptions.isPredefined(item.unit)
                     _uiState.update {
                         it.copy(
                             isEditMode = true,
@@ -140,7 +147,9 @@ internal class ItemFormViewModel @Inject constructor(
                             name = item.name,
                             categoryId = item.categoryId,
                             quantity = item.quantity.toBigDecimal().stripTrailingZeros().toPlainString(),
-                            unit = item.unit,
+                            unit = if (isCustom) UnitOptions.CUSTOM_OPTION else item.unit,
+                            isCustomUnit = isCustom,
+                            customUnit = if (isCustom) item.unit else "",
                             unitPrice = item.unitPrice.toBigDecimal().stripTrailingZeros().toPlainString(),
                             kcalPerUnit = item.kcalPerUnit?.toString() ?: "",
                             expiryDate = item.expiryDate,
@@ -171,7 +180,17 @@ internal class ItemFormViewModel @Inject constructor(
     }
 
     fun updateUnit(value: String) {
-        _uiState.update { it.copy(unit = value) }
+        if (value == UnitOptions.CUSTOM_OPTION) {
+            _uiState.update { it.copy(unit = value, isCustomUnit = true) }
+        } else {
+            _uiState.update { it.copy(unit = value, isCustomUnit = false, customUnit = "") }
+        }
+    }
+
+    fun updateCustomUnit(value: String) {
+        if (value.length <= 16) {
+            _uiState.update { it.copy(customUnit = value) }
+        }
     }
 
     fun updateUnitPrice(value: String) {
@@ -204,12 +223,14 @@ internal class ItemFormViewModel @Inject constructor(
 
         _uiState.update { it.copy(isSaving = true) }
 
+        val effectiveUnit = if (state.isCustomUnit) state.customUnit.trim() else state.unit.trim()
+
         val item = ItemEntity(
             id = if (state.isEditMode) state.itemId else UUID.randomUUID().toString(),
             name = state.name.trim(),
             categoryId = state.categoryId!!,
             quantity = state.quantity.toDouble(),
-            unit = state.unit.trim(),
+            unit = effectiveUnit,
             unitPrice = state.unitPrice.toDoubleOrNull() ?: 0.0,
             kcalPerUnit = state.kcalPerUnit.toIntOrNull(),
             expiryDate = state.expiryDate,

app/src/test/java/de/bollwerk/app/data/export/TestFakes.kt

@@ -92,6 +92,8 @@ internal class FakeItemDao : ItemDao {
         emit()
     }
 
+    override suspend fun normalizeUnits() {}
+
     fun getItems(): List<ItemEntity> = items.toList()
 }
 

app/src/test/java/de/bollwerk/app/data/repository/ItemRepositoryImplTest.kt

@@ -106,6 +106,11 @@ private class FakeItemDao : ItemDao {
         items.removeAll { it.id in ids }
         emit()
     }
+
+    override suspend fun normalizeUnits() {
+        items.replaceAll { if (it.unit in listOf("Stk", "Stk.")) it.copy(unit = "Stück") else it }
+        emit()
+    }
 }
 
 private class FakePendingSyncOpDao : PendingSyncOpDao {

app/src/test/java/de/bollwerk/app/ui/item/ItemFormViewModelTest.kt

@@ -227,7 +227,9 @@ class ItemFormViewModelTest {
         assertEquals("Konserve", state.name)
         assertEquals(1, state.categoryId)
         assertEquals("5", state.quantity)
-        assertEquals("Stk", state.unit)
+        assertEquals("Benutzerdefiniert", state.unit)
+        assertTrue(state.isCustomUnit)
+        assertEquals("Stk", state.customUnit)
         assertEquals("2.5", state.unitPrice)
         assertEquals("120", state.kcalPerUnit)
         assertEquals(LocalDate.of(2026, 12, 31), state.expiryDate)