feat(settings): add JSON import with SAF file picker

SettingsScreen: Added import button that opens the system file picker
(ActivityResultContracts.OpenDocument) filtered to application/json.
After file selection, a confirmation dialog warns that existing data
will be overwritten. Import result is shown in a success/error dialog.

SettingsViewModel: Added onImportFileSelected(uri), onImportConfirmed(),
onImportDismissed(), onImportResultDismissed() methods. The import reads
the file via contentResolver.openInputStream() and delegates to the
existing ImportExportRepository.importFromJson(). Settings are reloaded
after successful import.

SettingsUiState: Extended with isImporting, importResult (sealed
interface ImportResult with Success/Error), and pendingImportUri for
the confirmation dialog flow.

SettingsViewModelTest: Added 6 unit tests covering import success,
invalid JSON error, empty file, null input stream, dialog state
management, and result dismissal.

Closes #38

app/src/main/java/de/krisenvorrat/app/ui/settings/SettingsScreen.kt

@@ -2,6 +2,8 @@ package de.krisenvorrat.app.ui.settings
 
 import android.content.Intent
 import android.widget.Toast
+import androidx.activity.compose.rememberLauncherForActivityResult
+import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
@@ -11,6 +13,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.text.KeyboardOptions
 import androidx.compose.foundation.verticalScroll
+import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.Button
 import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.ExperimentalMaterial3Api
@@ -19,6 +22,7 @@ import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
 import androidx.compose.material3.TopAppBar
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
@@ -38,6 +42,12 @@ internal fun SettingsScreen(
     val uiState by viewModel.uiState.collectAsStateWithLifecycle()
     val context = LocalContext.current
 
+    val filePickerLauncher = rememberLauncherForActivityResult(
+        contract = ActivityResultContracts.OpenDocument()
+    ) { uri ->
+        uri?.let { viewModel.onImportFileSelected(it) }
+    }
+
     LaunchedEffect(uiState.shareContent) {
         val content = uiState.shareContent ?: return@LaunchedEffect
         val shareIntent = when (content) {
@@ -158,7 +168,17 @@ internal fun SettingsScreen(
                     Text("Als Markdown teilen")
                 }
 
-                if (uiState.isExporting) {
+                Spacer(modifier = Modifier.height(8.dp))
+
+                OutlinedButton(
+                    onClick = { filePickerLauncher.launch(arrayOf("application/json")) },
+                    enabled = !uiState.isImporting,
+                    modifier = Modifier.fillMaxWidth()
+                ) {
+                    Text("Daten importieren")
+                }
+
+                if (uiState.isExporting || uiState.isImporting) {
                     Spacer(modifier = Modifier.height(8.dp))
                     CircularProgressIndicator(
                         modifier = Modifier.padding(8.dp)
@@ -167,5 +187,51 @@ internal fun SettingsScreen(
             }
         }
     }
+
+    if (uiState.pendingImportUri != null) {
+        AlertDialog(
+            onDismissRequest = viewModel::onImportDismissed,
+            title = { Text("Daten importieren?") },
+            text = { Text("Bestehende Daten werden durch den Import überschrieben. Möchten Sie fortfahren?") },
+            confirmButton = {
+                TextButton(onClick = viewModel::onImportConfirmed) {
+                    Text("Importieren")
+                }
+            },
+            dismissButton = {
+                TextButton(onClick = viewModel::onImportDismissed) {
+                    Text("Abbrechen")
+                }
+            }
+        )
+    }
+
+    val importResult = uiState.importResult
+    if (importResult != null) {
+        AlertDialog(
+            onDismissRequest = viewModel::onImportResultDismissed,
+            title = {
+                Text(
+                    when (importResult) {
+                        is ImportResult.Success -> "Import erfolgreich"
+                        is ImportResult.Error -> "Import fehlgeschlagen"
+                    }
+                )
+            },
+            text = {
+                Text(
+                    when (importResult) {
+                        is ImportResult.Success -> "Daten wurden erfolgreich importiert."
+                        is ImportResult.Error -> importResult.message
+                    }
+                )
+            },
+            confirmButton = {
+                TextButton(onClick = viewModel::onImportResultDismissed) {
+                    Text("OK")
+                }
+            }
+        )
+    }
 }
 

app/src/main/java/de/krisenvorrat/app/ui/settings/SettingsUiState.kt

@@ -1,5 +1,7 @@
 package de.krisenvorrat.app.ui.settings
 
+import android.net.Uri
+
 internal data class SettingsUiState(
     val householdSize: String = "",
     val dailyKcalPerPerson: String = "",
@@ -7,5 +9,13 @@ internal data class SettingsUiState(
     val isSaved: Boolean = false,
     val isExporting: Boolean = false,
     val shareContent: ShareContent? = null,
-    val exportError: String? = null
+    val exportError: String? = null,
+    val isImporting: Boolean = false,
+    val importResult: ImportResult? = null,
+    val pendingImportUri: Uri? = null
 )
+
+internal sealed interface ImportResult {
+    data object Success : ImportResult
+    data class Error(val message: String) : ImportResult
+}

app/src/main/java/de/krisenvorrat/app/ui/settings/SettingsViewModel.kt

@@ -1,6 +1,7 @@
 package de.krisenvorrat.app.ui.settings
 
 import android.content.Context
+import android.net.Uri
 import androidx.core.content.FileProvider
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
@@ -127,6 +128,44 @@ internal class SettingsViewModel @Inject constructor(
         _uiState.update { it.copy(exportError = null) }
     }
 
+    fun onImportFileSelected(uri: Uri) {
+        _uiState.update { it.copy(pendingImportUri = uri) }
+    }
+
+    fun onImportConfirmed() {
+        val uri = _uiState.value.pendingImportUri ?: return
+        _uiState.update { it.copy(pendingImportUri = null, isImporting = true, importResult = null) }
+        viewModelScope.launch {
+            try {
+                val json = context.contentResolver.openInputStream(uri)?.bufferedReader()?.use { it.readText() }
+                if (json.isNullOrBlank()) {
+                    _uiState.update { it.copy(isImporting = false, importResult = ImportResult.Error("Datei ist leer oder konnte nicht gelesen werden")) }
+                    return@launch
+                }
+                val result = importExportRepository.importFromJson(json)
+                result.fold(
+                    onSuccess = {
+                        loadSettings()
+                        _uiState.update { it.copy(isImporting = false, importResult = ImportResult.Success) }
+                    },
+                    onFailure = { e ->
+                        _uiState.update { it.copy(isImporting = false, importResult = ImportResult.Error(e.message ?: "Import fehlgeschlagen")) }
+                    }
+                )
+            } catch (e: Exception) {
+                _uiState.update { it.copy(isImporting = false, importResult = ImportResult.Error("Datei konnte nicht gelesen werden")) }
+            }
+        }
+    }
+
+    fun onImportDismissed() {
+        _uiState.update { it.copy(pendingImportUri = null) }
+    }
+
+    fun onImportResultDismissed() {
+        _uiState.update { it.copy(importResult = null) }
+    }
+
     companion object {
         const val KEY_HOUSEHOLD_SIZE = "household_size"
         const val KEY_DAILY_KCAL_PER_PERSON = "daily_kcal_per_person"

app/src/test/java/de/krisenvorrat/app/ui/settings/SettingsViewModelTest.kt

@@ -2,6 +2,8 @@ package de.krisenvorrat.app.ui.settings
 
 import android.content.Context
 import androidx.core.content.FileProvider
+import android.content.ContentResolver
+import android.net.Uri
 import de.krisenvorrat.app.data.db.entity.SettingsEntity
 import de.krisenvorrat.app.domain.repository.ImportExportRepository
 import de.krisenvorrat.app.domain.repository.SettingsRepository
@@ -27,6 +29,7 @@ import org.junit.Assert.assertNull
 import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
+import java.io.ByteArrayInputStream
 import java.io.File
 
 @OptIn(ExperimentalCoroutinesApi::class)
@@ -305,6 +308,144 @@ class SettingsViewModelTest {
         // Then
         assertNull(viewModel.uiState.value.exportError)
     }
+
+    @Test
+    fun test_onImportFileSelected_setsPendingUri() = runTest(testDispatcher) {
+        // Given
+        viewModel = createViewModel()
+        advanceUntilIdle()
+        val mockUri = mockk<Uri>()
+
+        // When
+        viewModel.onImportFileSelected(mockUri)
+
+        // Then
+        assertEquals(mockUri, viewModel.uiState.value.pendingImportUri)
+    }
+
+    @Test
+    fun test_onImportDismissed_clearsPendingUri() = runTest(testDispatcher) {
+        // Given
+        viewModel = createViewModel()
+        advanceUntilIdle()
+        val mockUri = mockk<Uri>()
+        viewModel.onImportFileSelected(mockUri)
+
+        // When
+        viewModel.onImportDismissed()
+
+        // Then
+        assertNull(viewModel.uiState.value.pendingImportUri)
+    }
+
+    @Test
+    fun test_onImportConfirmed_success_setsSuccessResult() = runTest(testDispatcher) {
+        // Given
+        val mockUri = mockk<Uri>()
+        val mockContentResolver = mockk<ContentResolver>()
+        val jsonContent = """{"version":1,"categories":[],"locations":[],"items":[],"settings":[]}"""
+        every { mockContext.contentResolver } returns mockContentResolver
+        every { mockContentResolver.openInputStream(mockUri) } returns ByteArrayInputStream(jsonContent.toByteArray())
+        viewModel = createViewModel()
+        advanceUntilIdle()
+        viewModel.onImportFileSelected(mockUri)
+
+        // When
+        viewModel.onImportConfirmed()
+        advanceUntilIdle()
+
+        // Then
+        val state = viewModel.uiState.value
+        assertFalse(state.isImporting)
+        assertNull(state.pendingImportUri)
+        assertTrue(state.importResult is ImportResult.Success)
+    }
+
+    @Test
+    fun test_onImportConfirmed_invalidJson_setsErrorResult() = runTest(testDispatcher) {
+        // Given
+        val mockUri = mockk<Uri>()
+        val mockContentResolver = mockk<ContentResolver>()
+        every { mockContext.contentResolver } returns mockContentResolver
+        every { mockContentResolver.openInputStream(mockUri) } returns ByteArrayInputStream("{ not valid }".toByteArray())
+        fakeImportExportRepository.importShouldFail = true
+        viewModel = createViewModel()
+        advanceUntilIdle()
+        viewModel.onImportFileSelected(mockUri)
+
+        // When
+        viewModel.onImportConfirmed()
+        advanceUntilIdle()
+
+        // Then
+        val state = viewModel.uiState.value
+        assertFalse(state.isImporting)
+        assertTrue(state.importResult is ImportResult.Error)
+    }
+
+    @Test
+    fun test_onImportConfirmed_emptyFile_setsErrorResult() = runTest(testDispatcher) {
+        // Given
+        val mockUri = mockk<Uri>()
+        val mockContentResolver = mockk<ContentResolver>()
+        every { mockContext.contentResolver } returns mockContentResolver
+        every { mockContentResolver.openInputStream(mockUri) } returns ByteArrayInputStream(ByteArray(0))
+        viewModel = createViewModel()
+        advanceUntilIdle()
+        viewModel.onImportFileSelected(mockUri)
+
+        // When
+        viewModel.onImportConfirmed()
+        advanceUntilIdle()
+
+        // Then
+        val state = viewModel.uiState.value
+        assertFalse(state.isImporting)
+        assertTrue(state.importResult is ImportResult.Error)
+        assertEquals("Datei ist leer oder konnte nicht gelesen werden", (state.importResult as ImportResult.Error).message)
+    }
+
+    @Test
+    fun test_onImportConfirmed_nullInputStream_setsErrorResult() = runTest(testDispatcher) {
+        // Given
+        val mockUri = mockk<Uri>()
+        val mockContentResolver = mockk<ContentResolver>()
+        every { mockContext.contentResolver } returns mockContentResolver
+        every { mockContentResolver.openInputStream(mockUri) } returns null
+        viewModel = createViewModel()
+        advanceUntilIdle()
+        viewModel.onImportFileSelected(mockUri)
+
+        // When
+        viewModel.onImportConfirmed()
+        advanceUntilIdle()
+
+        // Then
+        val state = viewModel.uiState.value
+        assertFalse(state.isImporting)
+        assertTrue(state.importResult is ImportResult.Error)
+    }
+
+    @Test
+    fun test_onImportResultDismissed_clearsImportResult() = runTest(testDispatcher) {
+        // Given
+        val mockUri = mockk<Uri>()
+        val mockContentResolver = mockk<ContentResolver>()
+        val jsonContent = """{"version":1,"categories":[],"locations":[],"items":[],"settings":[]}"""
+        every { mockContext.contentResolver } returns mockContentResolver
+        every { mockContentResolver.openInputStream(mockUri) } returns ByteArrayInputStream(jsonContent.toByteArray())
+        viewModel = createViewModel()
+        advanceUntilIdle()
+        viewModel.onImportFileSelected(mockUri)
+        viewModel.onImportConfirmed()
+        advanceUntilIdle()
+
+        // When
+        viewModel.onImportResultDismissed()
+
+        // Then
+        assertNull(viewModel.uiState.value.importResult)
+    }
 }
 
 // region Test Helpers
@@ -330,6 +471,7 @@ private class FakeImportExportRepository : ImportExportRepository {
     var jsonResult = """{"version":1,"categories":[],"locations":[],"items":[],"settings":[]}"""
     var markdownResult = "# Krisenvorrat Inventar\n"
     var shouldThrow = false
+    var importShouldFail = false
 
     override suspend fun exportToJson(): String {
         if (shouldThrow) throw RuntimeException("Test error")
@@ -337,7 +479,7 @@ private class FakeImportExportRepository : ImportExportRepository {
     }
 
     override suspend fun importFromJson(json: String): Result<Unit> {
-        if (shouldThrow) return Result.failure(RuntimeException("Test error"))
+        if (shouldThrow || importShouldFail) return Result.failure(RuntimeException("Test error"))
         return Result.success(Unit)
     }