feat(chat): DM 채팅 메시지 매퍼를 추가한다

app/src/main/java/kr/co/vividnext/sodalive/v2/main/chat/dm/model/DmChatMappers.kt

@@ -0,0 +1,38 @@
+package kr.co.vividnext.sodalive.v2.main.chat.dm.model
+
+import kr.co.vividnext.sodalive.v2.main.chat.dm.data.DmChatMessageResponse
+
+private const val MESSAGE_TYPE_TEXT = "TEXT"
+
+fun DmChatMessageResponse.toUiItem(): DmChatMessageUiItem? {
+    if (!messageType.equals(MESSAGE_TYPE_TEXT, ignoreCase = true) || textMessage == null) return null
+
+    return DmChatMessageUiItem(
+        messageId = messageId,
+        localId = null,
+        mine = mine,
+        textMessage = textMessage,
+        senderNickname = senderNickname,
+        senderProfileImageUrl = senderProfileImageUrl,
+        createdAt = createdAt,
+        status = DmChatMessageStatus.SENT
+    )
+}
+
+fun List<DmChatMessageResponse>.toUiItems(): List<DmChatMessageUiItem> = mapNotNull { it.toUiItem() }
+
+/** Sorts messages by server creation time, then by messageId for same-time messages. */
+fun List<DmChatMessageUiItem>.sortByCreatedAtAndMessageId(): List<DmChatMessageUiItem> =
+    sortedWith(compareBy<DmChatMessageUiItem> { it.createdAt }.thenBy { it.messageId ?: Long.MAX_VALUE })
+
+/** Merges new messages while keeping the first-arrived item when server messageId duplicates. */
+fun List<DmChatMessageUiItem>.mergeByMessageId(
+    incoming: List<DmChatMessageUiItem>
+): List<DmChatMessageUiItem> {
+    val seenMessageIds = mapNotNull { it.messageId }.toMutableSet()
+    val newItems = incoming.filter { item ->
+        val messageId = item.messageId
+        messageId == null || seenMessageIds.add(messageId)
+    }
+    return (this + newItems).sortByCreatedAtAndMessageId()
+}

app/src/main/java/kr/co/vividnext/sodalive/v2/main/chat/dm/model/DmChatUiModels.kt

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+package kr.co.vividnext.sodalive.v2.main.chat.dm.model
+
+enum class DmChatMessageStatus {
+    SENDING,
+    SENT,
+    FAILED
+}
+
+data class DmChatMessageUiItem(
+    val messageId: Long?,
+    val localId: String?,
+    val mine: Boolean,
+    val textMessage: String,
+    val senderNickname: String,
+    val senderProfileImageUrl: String,
+    val createdAt: Long,
+    val status: DmChatMessageStatus
+)

app/src/test/java/kr/co/vividnext/sodalive/v2/main/chat/dm/DmChatMapperTest.kt

@@ -0,0 +1,97 @@
+package kr.co.vividnext.sodalive.v2.main.chat.dm
+
+import kr.co.vividnext.sodalive.v2.main.chat.dm.data.DmChatMessageResponse
+import kr.co.vividnext.sodalive.v2.main.chat.dm.model.DmChatMessageStatus
+import kr.co.vividnext.sodalive.v2.main.chat.dm.model.mergeByMessageId
+import kr.co.vividnext.sodalive.v2.main.chat.dm.model.sortByCreatedAtAndMessageId
+import kr.co.vividnext.sodalive.v2.main.chat.dm.model.toUiItem
+import kr.co.vividnext.sodalive.v2.main.chat.dm.model.toUiItems
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class DmChatMapperTest {
+
+    @Test
+    fun `TEXT 메시지는 전송 완료 UI item으로 매핑된다`() {
+        val item = response(messageType = "TEXT", textMessage = "안녕하세요").toUiItem()
+
+        requireNotNull(item)
+        assertEquals(10L, item.messageId)
+        assertNull(item.localId)
+        assertEquals(true, item.mine)
+        assertEquals("안녕하세요", item.textMessage)
+        assertEquals("크리에이터", item.senderNickname)
+        assertEquals("https://example.com/profile.png", item.senderProfileImageUrl)
+        assertEquals(1000L, item.createdAt)
+        assertEquals(DmChatMessageStatus.SENT, item.status)
+    }
+
+    @Test
+    fun `messageType은 대소문자를 무시하고 TEXT로 매핑된다`() {
+        val item = response(messageType = "text", textMessage = "소문자 타입").toUiItem()
+
+        requireNotNull(item)
+        assertEquals("소문자 타입", item.textMessage)
+    }
+
+    @Test
+    fun `TEXT가 아니거나 textMessage가 null이면 UI item에서 제외된다`() {
+        val voice = response(messageType = "VOICE", textMessage = null, voiceMessageUrl = "https://example.com/voice.m4a")
+        val nullText = response(messageType = "TEXT", textMessage = null)
+
+        assertNull(voice.toUiItem())
+        assertNull(nullText.toUiItem())
+        assertEquals(emptyList<Any>(), listOf(voice, nullText).toUiItems())
+    }
+
+    @Test
+    fun `메시지는 createdAt 이후 messageId 오름차순으로 정렬된다`() {
+        val items = listOf(
+            response(messageId = 3L, createdAt = 2000L),
+            response(messageId = 2L, createdAt = 1000L),
+            response(messageId = 1L, createdAt = 1000L)
+        ).toUiItems().sortByCreatedAtAndMessageId()
+
+        assertEquals(listOf(1L, 2L, 3L), items.map { it.messageId })
+    }
+
+    @Test
+    fun `messageId가 중복된 서버 메시지는 병합 시 기존 item을 유지한다`() {
+        val existing = listOf(
+            response(messageId = 1L, textMessage = "기존").toUiItem(),
+            response(messageId = 2L, textMessage = "둘째").toUiItem()
+        ).filterNotNull()
+        val incoming = listOf(
+            response(messageId = 1L, textMessage = "중복 신규").toUiItem(),
+            response(messageId = 3L, textMessage = "셋째").toUiItem()
+        ).filterNotNull()
+
+        val merged = existing.mergeByMessageId(incoming)
+
+        assertEquals(listOf(1L, 2L, 3L), merged.map { it.messageId })
+        assertEquals("기존", merged.first { it.messageId == 1L }.textMessage)
+    }
+
+    private fun response(
+        messageId: Long = 10L,
+        messageType: String = "TEXT",
+        mine: Boolean = true,
+        createdAt: Long = 1000L,
+        textMessage: String? = "메시지",
+        voiceMessageUrl: String? = null,
+        senderId: Long = 20L,
+        senderNickname: String = "크리에이터",
+        senderProfileImageUrl: String = "https://example.com/profile.png"
+    ) = DmChatMessageResponse(
+        messageId = messageId,
+        messageType = messageType,
+        mine = mine,
+        createdAt = createdAt,
+        textMessage = textMessage,
+        voiceMessageUrl = voiceMessageUrl,
+        senderId = senderId,
+        senderNickname = senderNickname,
+        senderProfileImageUrl = senderProfileImageUrl
+    )
+}