class MessageModel(
      val content: MessageContent,
      val timestampMillis: Long,
      val senderUserId: UserId,
      ...
  )

  sealed class MessageContent {
      data object Empty: MessageContent()

      data class Error(val errorType: ErrorType): MessageContent()

      data class Text(val text: String): MessageContent()

      data class Event(val eventType: EventType): MessageContent()
  }

  fun bindToViews(message: MessageModel) {
    val isVisible = isContentValid(message.messageContent)
    layoutContainer.isVisible = isVisible
    if (!isVisible) {
        return
    }

    timestampTextView.text = formatter.format(message.timestampMillis)
    ... // 기타 뷰 업데이트 로직
    contentTextView.text = getMessageText(message.content)
  }

  private fun isContentValid(content: MessageContent): Boolean = when (content) {
      MessageContent.Empty,
      is MessageContent.Error -> false
      is MessageContent.TextMessage,
      is MessageContent.EventMessage -> true
  }

  private fun getMessageText(content: MessageContent): String = when (content) {
      MessageContent.Empty,
      is MessageContent.Error -> error("Invalid message type as `messageText`")
      is MessageContent.TextMessage -> content.text
      is MessageContent.EventMessage -> content.eventType.toMessageString()
  }

  private fun isContentValid(content: MessageContent): Boolean = 
      getMessageText(content) != null

  /**
  * 메시지 콘텐츠[content]를 표시 가능한 텍스트 표현으로 변환하여 반환한다.
  * 단 표시할 수 없는 콘텐츠 유형(error/empty)인 경우 null을 반환한다.
  */
  private fun getMessageText(content: MessageContent): String? = when (content) {
      MessageContent.Empty,
      is MessageContent.Error -> null
      is MessageContent.TextMessage -> content.text
      is MessageContent.EventMessage -> content.eventType.toMessageString()
  }