android: add offline-first chat history reading and cache fallback

android/CHANGELOG.md

@@ -338,3 +338,8 @@
 - Added shared API error mapper (`ApiErrorMapper`) with mode-aware mapping (`DEFAULT`, `LOGIN`).
 - Switched auth/chat/message/media repositories to a single `Throwable -> AppError` mapping source.
 - Kept login-specific invalid-credentials mapping while standardizing unauthorized/server/network handling for other API calls.
+
+### Step 57 - Offline-first message history reading
+- Added paged local history reading path by introducing configurable message observe limit (`observeMessages(chatId, limit)`).
+- Updated chat screen loading strategy to expand local Room-backed history first when loading older messages.
+- Added network-failure fallback in message sync/load-more: if network is unavailable but local cache exists, chat remains readable without blocking error.

android/app/src/main/java/ru/daemonlord/messenger/data/message/local/dao/MessageDao.kt

@@ -27,6 +27,9 @@ interface MessageDao {
         limit: Int = 50,
     ): Flow<List<MessageLocalModel>>
 
+    @Query("SELECT COUNT(*) FROM messages WHERE chat_id = :chatId")
+    suspend fun countMessages(chatId: Long): Int
+
     @Query(
         """
         SELECT * FROM messages

android/app/src/main/java/ru/daemonlord/messenger/data/message/repository/NetworkMessageRepository.kt

@@ -18,6 +18,7 @@ import ru.daemonlord.messenger.data.message.mapper.toDomain
 import ru.daemonlord.messenger.data.message.mapper.toEntity
 import ru.daemonlord.messenger.data.media.api.MediaApiService
 import ru.daemonlord.messenger.di.IoDispatcher
+import ru.daemonlord.messenger.domain.common.AppError
 import ru.daemonlord.messenger.domain.common.AppResult
 import ru.daemonlord.messenger.domain.media.repository.MediaRepository
 import ru.daemonlord.messenger.domain.message.model.MessageItem
@@ -61,8 +62,8 @@ class NetworkMessageRepository @Inject constructor(
         }
     }
 
-    override fun observeMessages(chatId: Long): Flow<List<MessageItem>> {
-        return messageDao.observeRecentMessages(chatId = chatId).map { entities ->
+    override fun observeMessages(chatId: Long, limit: Int): Flow<List<MessageItem>> {
+        return messageDao.observeRecentMessages(chatId = chatId, limit = limit).map { entities ->
             entities.map { it.toDomain(currentUserId = currentUserId) }
         }
     }
@@ -80,7 +81,13 @@ class NetworkMessageRepository @Inject constructor(
             )
             AppResult.Success(Unit)
         } catch (error: Throwable) {
-            AppResult.Error(error.toAppError())
+            val mapped = error.toAppError()
+            val hasCached = messageDao.countMessages(chatId = chatId) > 0
+            if (mapped is AppError.Network && hasCached) {
+                AppResult.Success(Unit)
+            } else {
+                AppResult.Error(mapped)
+            }
         }
     }
 
@@ -102,7 +109,17 @@ class NetworkMessageRepository @Inject constructor(
             }
             AppResult.Success(Unit)
         } catch (error: Throwable) {
-            AppResult.Error(error.toAppError())
+            val mapped = error.toAppError()
+            val hasOlderLocal = messageDao.getMessagesPage(
+                chatId = chatId,
+                beforeMessageId = beforeMessageId,
+                limit = 1,
+            ).isNotEmpty()
+            if (mapped is AppError.Network && hasOlderLocal) {
+                AppResult.Success(Unit)
+            } else {
+                AppResult.Error(mapped)
+            }
         }
     }
 

android/app/src/main/java/ru/daemonlord/messenger/domain/message/repository/MessageRepository.kt

@@ -6,7 +6,7 @@ import ru.daemonlord.messenger.domain.message.model.MessageItem
 import ru.daemonlord.messenger.domain.message.model.MessageReaction
 
 interface MessageRepository {
-    fun observeMessages(chatId: Long): Flow<List<MessageItem>>
+    fun observeMessages(chatId: Long, limit: Int = 50): Flow<List<MessageItem>>
     suspend fun syncRecentMessages(chatId: Long): AppResult<Unit>
     suspend fun loadMoreMessages(chatId: Long, beforeMessageId: Long): AppResult<Unit>
     suspend fun sendTextMessage(chatId: Long, text: String, replyToMessageId: Long? = null): AppResult<Unit>

android/app/src/main/java/ru/daemonlord/messenger/domain/message/usecase/ObserveMessagesUseCase.kt

@@ -8,7 +8,7 @@ import javax.inject.Inject
 class ObserveMessagesUseCase @Inject constructor(
     private val messageRepository: MessageRepository,
 ) {
-    operator fun invoke(chatId: Long): Flow<List<MessageItem>> {
-        return messageRepository.observeMessages(chatId = chatId)
+    operator fun invoke(chatId: Long, limit: Int = 50): Flow<List<MessageItem>> {
+        return messageRepository.observeMessages(chatId = chatId, limit = limit)
     }
 }

android/app/src/main/java/ru/daemonlord/messenger/ui/chat/ChatViewModel.kt

@@ -4,11 +4,13 @@ import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.collectLatest
 import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import ru.daemonlord.messenger.core.notifications.ActiveChatTracker
@@ -36,6 +38,7 @@ import java.time.temporal.ChronoUnit
 import javax.inject.Inject
 
 @HiltViewModel
+@OptIn(ExperimentalCoroutinesApi::class)
 class ChatViewModel @Inject constructor(
     savedStateHandle: SavedStateHandle,
     private val observeMessagesUseCase: ObserveMessagesUseCase,
@@ -60,6 +63,7 @@ class ChatViewModel @Inject constructor(
     private val chatId: Long = checkNotNull(savedStateHandle["chatId"])
     private val _uiState = MutableStateFlow(MessageUiState(chatId = chatId))
     val uiState: StateFlow<MessageUiState> = _uiState.asStateFlow()
+    private val visibleMessagesLimit = MutableStateFlow(MESSAGES_PAGE_SIZE)
     private var lastDeliveredMessageId: Long? = null
     private var lastReadMessageId: Long? = null
 
@@ -415,6 +419,7 @@ class ChatViewModel @Inject constructor(
     fun loadMore() {
         val oldest = uiState.value.messages.firstOrNull() ?: return
         viewModelScope.launch {
+            visibleMessagesLimit.value += MESSAGES_PAGE_SIZE
             _uiState.update { it.copy(isLoadingMore = true) }
             when (val result = loadMoreMessagesUseCase(chatId, beforeMessageId = oldest.id)) {
                 is AppResult.Success -> _uiState.update { it.copy(isLoadingMore = false) }
@@ -430,7 +435,9 @@ class ChatViewModel @Inject constructor(
 
     private fun observeMessages() {
         viewModelScope.launch {
-            observeMessagesUseCase(chatId).collectLatest { messages ->
+            visibleMessagesLimit
+                .flatMapLatest { limit -> observeMessagesUseCase(chatId = chatId, limit = limit) }
+                .collectLatest { messages ->
                 _uiState.update {
                     val pinnedId = it.pinnedMessageId
                     it.copy(
@@ -596,4 +603,8 @@ class ChatViewModel @Inject constructor(
         handleRealtimeEventsUseCase.stop()
         super.onCleared()
     }
+
+    private companion object {
+        const val MESSAGES_PAGE_SIZE = 50
+    }
 }

docs/android-checklist.md

@@ -21,7 +21,7 @@
 - [x] Room для чатов/сообщений/пользователей
 - [x] DataStore для настроек
 - [ ] Кэш медиа (Coil/Exo cache)
-- [ ] Offline-first чтение истории
+- [x] Offline-first чтение истории
 - [ ] Очередь отложенных действий (send/edit/delete)
 - [x] Конфликт-резолв и reconcile после reconnect