Design a chat app

@Serializable
data class OutgoingMessage(
    val clientId: String = UUID.randomUUID().toString(),   // created once, reused on every retry
    val conversationId: String,
    val text: String,
)

class ChatSync(private val api: ChatApi, private val dao: MessageDao, private val outbox: OutboxDao) {
    suspend fun send(message: OutgoingMessage) {
        outbox.insert(message)                              // survives process death
        socket.send(Frame.Message(message))                 // retried until acked
    }

    suspend fun onReconnect(conversationIds: List<String>) {
        for (id in conversationIds) {
            val after = dao.lastSeq(id) ?: 0
            dao.insertAll(api.messages(conversationId = id, after = after))
        }
    }
}

public record OutgoingMessage(String clientId, String conversationId, String text) {
    public static OutgoingMessage create(String conversationId, String text) {
        return new OutgoingMessage(UUID.randomUUID().toString(), conversationId, text); // reused on retries
    }
}

public final class ChatSync {
    public void send(OutgoingMessage message) {
        outbox.save(message);                               // survives restarts
        socket.send(Frame.message(message));                // retried until acked
    }

    public void onReconnect(List<String> conversationIds) {
        for (String id : conversationIds) {
            long after = store.lastSeq(id).orElse(0L);
            store.insertAll(api.messages(id, after));
        }
    }
}

interface OutgoingMessage { clientId: string; conversationId: string; text: string }

class ChatSync {
  async send(message: OutgoingMessage): Promise<void> {
    await this.outbox.save(message);                        // survives reloads (IndexedDB)
    this.socket.send({ type: "message", message });         // retried until acked
  }

  async onReconnect(conversationIds: string[]): Promise<void> {
    for (const id of conversationIds) {
      const after = (await this.store.lastSeq(id)) ?? 0;
      await this.store.insertAll(await this.api.messages(id, after));
    }
  }
}