android: add message action state machine core

android/CHANGELOG.md

@@ -169,3 +169,10 @@
 - Implemented bulk-forward flow in `NetworkMessageRepository` with Room/chat last-message updates.
 - Added `ForwardMessageBulkUseCase` for future multi-select message actions.
 - Updated message repository unit test fakes to cover new API surface.
+
+### Step 27 - Core base / message action state machine
+- Added reusable `MessageActionState` reducer with explicit selection modes (`NONE`, `SINGLE`, `MULTI`).
+- Added action-intent contract for message operations (reply/edit/forward/delete/reaction/clear).
+- Integrated `ChatViewModel` with reducer-backed selection logic while preserving current UI behavior.
+- Added base ViewModel handlers for entering/toggling multi-select mode (`onEnterMultiSelect`, `onToggleMessageMultiSelection`, `onClearSelection`).
+- Added unit tests for reducer transitions and available intents (`MessageActionStateTest`).

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

@@ -71,16 +71,74 @@ class ChatViewModel @Inject constructor(
     }
 
     fun onSelectMessage(message: MessageItem?) {
+        if (message == null) {
+            onClearSelection()
+            return
+        }
+        val canEdit = canEdit(message)
+        val canDeleteForAll = canDeleteForAll(message)
         _uiState.update {
             it.copy(
                 selectedMessage = message,
-                selectedCanEdit = message?.let(::canEdit) == true,
-                selectedCanDeleteForAll = message?.let(::canDeleteForAll) == true,
+                selectedCanEdit = canEdit,
+                selectedCanDeleteForAll = canDeleteForAll,
+                actionState = it.actionState.selectSingle(
+                    message = message,
+                    canEdit = canEdit,
+                    canDeleteForAll = canDeleteForAll,
+                ),
             )
         }
-        if (message != null) {
         loadReactions(messageId = message.id)
     }
+
+    fun onEnterMultiSelect(message: MessageItem) {
+        _uiState.update {
+            it.copy(
+                selectedMessage = message,
+                selectedCanEdit = false,
+                selectedCanDeleteForAll = false,
+                actionState = it.actionState.selectMulti(
+                    selectedIds = setOf(message.id),
+                    focusedMessageId = message.id,
+                ),
+            )
+        }
+    }
+
+    fun onToggleMessageMultiSelection(message: MessageItem) {
+        val current = uiState.value.actionState
+        val nextState = if (current.mode != MessageSelectionMode.MULTI) {
+            current.selectMulti(selectedIds = setOf(message.id), focusedMessageId = message.id)
+        } else {
+            val toggledIds = current.selectedMessageIds.toMutableSet().apply {
+                if (contains(message.id)) remove(message.id) else add(message.id)
+            }.toSet()
+            current.selectMulti(
+                selectedIds = toggledIds,
+                focusedMessageId = message.id,
+            )
+        }
+        val focused = nextState.focusedMessageId?.let(::findMessageById)
+        _uiState.update {
+            it.copy(
+                selectedMessage = focused,
+                selectedCanEdit = focused?.let(::canEdit) == true,
+                selectedCanDeleteForAll = focused?.let(::canDeleteForAll) == true,
+                actionState = nextState,
+            )
+        }
+    }
+
+    fun onClearSelection() {
+        _uiState.update {
+            it.copy(
+                selectedMessage = null,
+                selectedCanEdit = false,
+                selectedCanDeleteForAll = false,
+                actionState = it.actionState.clearSelection(),
+            )
+        }
     }
 
     fun onReplySelected(message: MessageItem) {
@@ -91,6 +149,7 @@ class ChatViewModel @Inject constructor(
                 selectedMessage = null,
                 selectedCanEdit = false,
                 selectedCanDeleteForAll = false,
+                actionState = it.actionState.clearSelection(),
             )
         }
     }
@@ -103,6 +162,7 @@ class ChatViewModel @Inject constructor(
                 selectedMessage = null,
                 selectedCanEdit = false,
                 selectedCanDeleteForAll = false,
+                actionState = it.actionState.clearSelection(),
                 inputText = message.text.orEmpty(),
             )
         }
@@ -116,12 +176,13 @@ class ChatViewModel @Inject constructor(
                 selectedMessage = null,
                 selectedCanEdit = false,
                 selectedCanDeleteForAll = false,
+                actionState = it.actionState.clearSelection(),
             )
         }
     }
 
     fun onDeleteSelected(forAll: Boolean = false) {
-        val selected = uiState.value.selectedMessage ?: return
+        val selected = getFocusedSelectedMessage() ?: return
         if (forAll && !canDeleteForAll(selected)) {
             _uiState.update { it.copy(errorMessage = "Delete for all is available only for your own messages.") }
             return
@@ -133,6 +194,7 @@ class ChatViewModel @Inject constructor(
                         selectedMessage = null,
                         selectedCanEdit = false,
                         selectedCanDeleteForAll = false,
+                        actionState = it.actionState.clearSelection(),
                     )
                 }
                 is AppResult.Error -> _uiState.update { it.copy(errorMessage = result.reason.toUiMessage()) }
@@ -141,7 +203,7 @@ class ChatViewModel @Inject constructor(
     }
 
     fun onForwardSelected() {
-        val message = uiState.value.selectedMessage ?: return
+        val message = getFocusedSelectedMessage() ?: return
         viewModelScope.launch {
             val targets = observeChatsUseCase(archived = false)
                 .first()
@@ -157,6 +219,7 @@ class ChatViewModel @Inject constructor(
                     selectedMessage = null,
                     selectedCanEdit = false,
                     selectedCanDeleteForAll = false,
+                    actionState = it.actionState.clearSelection(),
                     errorMessage = null,
                 )
             }
@@ -200,7 +263,7 @@ class ChatViewModel @Inject constructor(
     }
 
     fun onToggleReaction(emoji: String) {
-        val selected = uiState.value.selectedMessage ?: return
+        val selected = getFocusedSelectedMessage() ?: return
         viewModelScope.launch {
             when (val result = toggleMessageReactionUseCase(messageId = selected.id, emoji = emoji)) {
                 is AppResult.Success -> {
@@ -424,6 +487,19 @@ class ChatViewModel @Inject constructor(
         return message.isOutgoing
     }
 
+    private fun getFocusedSelectedMessage(): MessageItem? {
+        val focusId = uiState.value.actionState.focusedMessageId
+        return if (focusId != null) {
+            findMessageById(focusId)
+        } else {
+            uiState.value.selectedMessage
+        }
+    }
+
+    private fun findMessageById(messageId: Long): MessageItem? {
+        return uiState.value.messages.firstOrNull { it.id == messageId }
+    }
+
     private fun AppError.toUiMessage(): String {
         return when (this) {
             AppError.Network -> "Network error."

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

@@ -0,0 +1,81 @@
+package ru.daemonlord.messenger.ui.chat
+
+import ru.daemonlord.messenger.domain.message.model.MessageItem
+
+enum class MessageSelectionMode {
+    NONE,
+    SINGLE,
+    MULTI,
+}
+
+enum class MessageActionIntent {
+    REPLY,
+    EDIT,
+    FORWARD,
+    FORWARD_BULK,
+    DELETE_FOR_ME,
+    DELETE_FOR_ALL,
+    TOGGLE_REACTION,
+    CLEAR_SELECTION,
+}
+
+data class MessageActionState(
+    val mode: MessageSelectionMode = MessageSelectionMode.NONE,
+    val selectedMessageIds: Set<Long> = emptySet(),
+    val focusedMessageId: Long? = null,
+    val availableIntents: Set<MessageActionIntent> = emptySet(),
+) {
+    val hasSelection: Boolean
+        get() = selectedMessageIds.isNotEmpty()
+
+    val selectedCount: Int
+        get() = selectedMessageIds.size
+}
+
+fun MessageActionState.selectSingle(
+    message: MessageItem,
+    canEdit: Boolean,
+    canDeleteForAll: Boolean,
+): MessageActionState {
+    val intents = buildSet {
+        add(MessageActionIntent.REPLY)
+        add(MessageActionIntent.FORWARD)
+        add(MessageActionIntent.DELETE_FOR_ME)
+        add(MessageActionIntent.TOGGLE_REACTION)
+        add(MessageActionIntent.CLEAR_SELECTION)
+        if (canEdit) add(MessageActionIntent.EDIT)
+        if (canDeleteForAll) add(MessageActionIntent.DELETE_FOR_ALL)
+    }
+    return copy(
+        mode = MessageSelectionMode.SINGLE,
+        selectedMessageIds = setOf(message.id),
+        focusedMessageId = message.id,
+        availableIntents = intents,
+    )
+}
+
+fun MessageActionState.selectMulti(
+    selectedIds: Set<Long>,
+    focusedMessageId: Long? = null,
+): MessageActionState {
+    if (selectedIds.isEmpty()) return clearSelection()
+    return copy(
+        mode = MessageSelectionMode.MULTI,
+        selectedMessageIds = selectedIds,
+        focusedMessageId = focusedMessageId ?: this.focusedMessageId ?: selectedIds.first(),
+        availableIntents = setOf(
+            MessageActionIntent.FORWARD_BULK,
+            MessageActionIntent.DELETE_FOR_ME,
+            MessageActionIntent.CLEAR_SELECTION,
+        ),
+    )
+}
+
+fun MessageActionState.clearSelection(): MessageActionState {
+    return copy(
+        mode = MessageSelectionMode.NONE,
+        selectedMessageIds = emptySet(),
+        focusedMessageId = null,
+        availableIntents = emptySet(),
+    )
+}

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

@@ -23,6 +23,7 @@ data class MessageUiState(
     val isForwarding: Boolean = false,
     val canSendMessages: Boolean = true,
     val sendRestrictionText: String? = null,
+    val actionState: MessageActionState = MessageActionState(),
 )
 
 data class ForwardTargetUiModel(

android/app/src/test/java/ru/daemonlord/messenger/ui/chat/MessageActionStateTest.kt

@@ -0,0 +1,74 @@
+package ru.daemonlord.messenger.ui.chat
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import ru.daemonlord.messenger.domain.message.model.MessageItem
+
+class MessageActionStateTest {
+
+    @Test
+    fun selectSingle_setsSingleModeAndIntents() {
+        val message = message(id = 1L)
+        val state = MessageActionState().selectSingle(
+            message = message,
+            canEdit = true,
+            canDeleteForAll = true,
+        )
+
+        assertEquals(MessageSelectionMode.SINGLE, state.mode)
+        assertEquals(setOf(1L), state.selectedMessageIds)
+        assertEquals(1L, state.focusedMessageId)
+        assertTrue(state.availableIntents.contains(MessageActionIntent.REPLY))
+        assertTrue(state.availableIntents.contains(MessageActionIntent.EDIT))
+        assertTrue(state.availableIntents.contains(MessageActionIntent.DELETE_FOR_ALL))
+    }
+
+    @Test
+    fun selectMulti_setsMultiModeAndBulkIntent() {
+        val state = MessageActionState().selectMulti(
+            selectedIds = setOf(10L, 11L),
+            focusedMessageId = 11L,
+        )
+
+        assertEquals(MessageSelectionMode.MULTI, state.mode)
+        assertEquals(2, state.selectedCount)
+        assertEquals(11L, state.focusedMessageId)
+        assertTrue(state.availableIntents.contains(MessageActionIntent.FORWARD_BULK))
+        assertTrue(state.availableIntents.contains(MessageActionIntent.DELETE_FOR_ME))
+    }
+
+    @Test
+    fun clearSelection_resetsState() {
+        val state = MessageActionState(
+            mode = MessageSelectionMode.MULTI,
+            selectedMessageIds = setOf(1L, 2L),
+            focusedMessageId = 2L,
+            availableIntents = setOf(MessageActionIntent.FORWARD_BULK),
+        ).clearSelection()
+
+        assertEquals(MessageSelectionMode.NONE, state.mode)
+        assertTrue(state.selectedMessageIds.isEmpty())
+        assertEquals(null, state.focusedMessageId)
+        assertTrue(state.availableIntents.isEmpty())
+    }
+
+    private fun message(id: Long): MessageItem {
+        return MessageItem(
+            id = id,
+            chatId = 1L,
+            senderId = 1L,
+            senderDisplayName = null,
+            type = "text",
+            text = "hi",
+            createdAt = "2026-03-09T10:00:00Z",
+            updatedAt = null,
+            isOutgoing = true,
+            status = "sent",
+            replyToMessageId = null,
+            forwardedFromMessageId = null,
+            attachmentWaveform = null,
+            attachments = emptyList(),
+        )
+    }
+}