Some refactoring

app/src/main/java/chat/rocket/android/chatroom/viewmodel/MessageViewModel.kt

@@ -69,11 +69,11 @@ data class MessageViewModel(val context: Context,
             }
         }
 
-        message.attachments?.let {
-            if (it.isEmpty() || it[0] == null) return@let
-
-            if (it[0] is FileAttachment) {
-                val attachment = it[0] as FileAttachment
+        message.attachments?.let { attachments ->
+            val attachment = attachments.firstOrNull()
+            if (attachments.isEmpty() || attachment == null) return@let
+            when (attachment) {
+                is FileAttachment -> {
                     baseUrl?.let {
                         attachmentUrl = attachmentUrl("${baseUrl.value}${attachment.url}")
                         attachmentTitle = attachment.title
@@ -85,8 +85,8 @@ data class MessageViewModel(val context: Context,
                             else -> null
                         }
                     }
-            } else if (it[0] is MessageAttachment) {
-                val attachment = it[0] as MessageAttachment
+                }
+                is MessageAttachment -> {
                     attachmentType = AttachmentType.Message
                     attachmentMessageText = attachment.text ?: ""
                     attachmentMessageAuthor = attachment.author ?: ""
@@ -94,6 +94,7 @@ data class MessageViewModel(val context: Context,
                     attachmentTimestamp = attachment.timestamp
                 }
             }
+        }
 
         content = getContent(context)
     }
@@ -114,6 +115,9 @@ data class MessageViewModel(val context: Context,
         }
     }
 
+    /**
+     * Get the original message as a String.
+     */
     fun getOriginalMessage() = message.message
 
     private fun getTime(timestamp: Long) = DateTimeHelper.getTime(DateTimeHelper.getLocalDateTime(timestamp))