refactor(assistant): inject TimeProvider and IdGenerator seams

app/src/main/java/com/plainstudio/stackcasino/di/AppModule.kt

@@ -5,6 +5,10 @@ import com.google.firebase.auth.FirebaseAuth
 import com.google.firebase.auth.auth
 import com.google.firebase.firestore.FirebaseFirestore
 import com.google.firebase.firestore.firestore
+import com.plainstudio.stackcasino.util.IdGenerator
+import com.plainstudio.stackcasino.util.SystemTimeProvider
+import com.plainstudio.stackcasino.util.TimeProvider
+import com.plainstudio.stackcasino.util.UuidIdGenerator
 import dagger.Module
 import dagger.Provides
 import dagger.hilt.InstallIn
@@ -14,9 +18,10 @@ import javax.inject.Singleton
 /**
  * Application-scoped Hilt bindings.
  *
- * Currently exposes only the Firebase singletons. They are not consumed
- * yet; the providers exist so downstream cards (Login, Wallet, History,
- * etc.) inject the SDK without touching DI plumbing.
+ * Exposes the Firebase singletons plus the app-wide testability seams
+ * ([TimeProvider], [IdGenerator]). The Firebase providers exist so
+ * downstream cards (Login, Wallet, History, etc.) inject the SDK
+ * without touching DI plumbing.
  *
  * FirebaseApp is initialized implicitly by FirebaseInitProvider (which
  * the google-services Gradle plugin registers in the merged manifest),
@@ -36,4 +41,12 @@ object AppModule {
     @Provides
     @Singleton
     fun provideFirebaseFirestore(): FirebaseFirestore = Firebase.firestore
+
+    @Provides
+    @Singleton
+    fun provideTimeProvider(): TimeProvider = SystemTimeProvider()
+
+    @Provides
+    @Singleton
+    fun provideIdGenerator(): IdGenerator = UuidIdGenerator()
 }

app/src/main/java/com/plainstudio/stackcasino/feature/assistant/AssistantViewModel.kt

@@ -5,16 +5,16 @@ import androidx.lifecycle.viewModelScope
 import com.plainstudio.stackcasino.domain.assistant.AssistantRepository
 import com.plainstudio.stackcasino.domain.assistant.ChatTurn
 import com.plainstudio.stackcasino.domain.assistant.Role
+import com.plainstudio.stackcasino.util.IdGenerator
+import com.plainstudio.stackcasino.util.TimeProvider
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import java.text.SimpleDateFormat
-import java.util.Date
 import java.util.Locale
-import java.util.UUID
 import javax.inject.Inject
 
 /**
@@ -37,6 +37,8 @@ class AssistantViewModel
     @Inject
     constructor(
         private val repository: AssistantRepository,
+        private val timeProvider: TimeProvider,
+        private val idGenerator: IdGenerator,
     ) : ViewModel() {
         private val _uiState = MutableStateFlow<AssistantUiState>(AssistantUiState.Welcome)
         val uiState: StateFlow<AssistantUiState> = _uiState.asStateFlow()
@@ -116,11 +118,11 @@ class AssistantViewModel
                     copy(messages = messages + message)
             }
 
-        private fun nowLabel(): String = TIMESTAMP_FORMAT.format(Date())
+        private fun nowLabel(): String = TIMESTAMP_FORMAT.format(timeProvider.now())
 
-        // Random per-message handle so the LazyColumn key never collides
-        // on repeated identical questions sent inside the same minute.
-        private fun newId(): String = UUID.randomUUID().toString()
+        // Per-message handle so the LazyColumn key never collides on
+        // repeated identical questions sent inside the same minute.
+        private fun newId(): String = idGenerator.newId()
 
         companion object {
             const val MAX_USER_MESSAGE_LENGTH = 300

app/src/main/java/com/plainstudio/stackcasino/util/IdGenerator.kt

@@ -0,0 +1,19 @@
+package com.plainstudio.stackcasino.util
+
+import java.util.UUID
+
+/**
+ * Seam over random id generation so classes that key list items by id
+ * stay deterministic under unit tests. Production code gets
+ * [UuidIdGenerator]; tests inject a fake that returns predictable ids.
+ */
+fun interface IdGenerator {
+    fun newId(): String
+}
+
+/**
+ * Default [IdGenerator] backed by random UUIDs.
+ */
+class UuidIdGenerator : IdGenerator {
+    override fun newId(): String = UUID.randomUUID().toString()
+}

app/src/main/java/com/plainstudio/stackcasino/util/TimeProvider.kt

@@ -0,0 +1,20 @@
+package com.plainstudio.stackcasino.util
+
+import java.util.Date
+
+/**
+ * Seam over the system clock so time-dependent classes (chat message
+ * timestamps, round labels, ...) stay deterministic under unit tests.
+ * Production code gets [SystemTimeProvider]; tests inject a fake that
+ * returns a fixed instant.
+ */
+fun interface TimeProvider {
+    fun now(): Date
+}
+
+/**
+ * Default [TimeProvider] backed by the real wall clock.
+ */
+class SystemTimeProvider : TimeProvider {
+    override fun now(): Date = Date()
+}

app/src/test/java/com/plainstudio/stackcasino/feature/assistant/AssistantViewModelTest.kt

@@ -5,6 +5,8 @@ import com.plainstudio.stackcasino.domain.assistant.AssistantRepository
 import com.plainstudio.stackcasino.domain.assistant.ChatTurn
 import com.plainstudio.stackcasino.domain.assistant.Role
 import com.plainstudio.stackcasino.testing.MainDispatcherRule
+import com.plainstudio.stackcasino.util.IdGenerator
+import com.plainstudio.stackcasino.util.TimeProvider
 import io.mockk.coEvery
 import io.mockk.coVerify
 import io.mockk.mockk
@@ -15,14 +17,21 @@ import org.junit.Assert.assertFalse
 import org.junit.Assert.assertTrue
 import org.junit.Rule
 import org.junit.Test
+import java.util.Date
 
 class AssistantViewModelTest {
     @get:Rule
     val mainDispatcherRule = MainDispatcherRule()
 
     private val repository = mockk<AssistantRepository>()
 
-    private fun viewModel(): AssistantViewModel = AssistantViewModel(repository)
+    // Deterministic seams so message ids and timestamps stay stable
+    // across runs instead of leaning on UUID / the wall clock.
+    private val fixedTime = TimeProvider { Date(0L) }
+    private var idCounter = 0
+    private val sequentialIds = IdGenerator { "msg-${idCounter++}" }
+
+    private fun viewModel(): AssistantViewModel = AssistantViewModel(repository, fixedTime, sequentialIds)
 
     // --- initial state ----------------------------------------------------