Add threading support with token (discord) (#1342)

Webhooks don't support the threading yet, so this is token only.
In discord you can reply on each message of a thread, but this is not possible in mattermost (so some changes added there to make sure we always answer on the rootID of the thread).

Also needs some more testing with slack.

update : It now also uses the token when replying to a thread (even if webhooks are enabled), until webhooks have support for threads.

bridge/mattermost/handlers.go

@@ -108,7 +108,7 @@ func (b *Bmattermost) handleMatterClient(messages chan *config.Message) {
 			Channel:  message.Channel,
 			Text:     message.Text,
 			ID:       message.Post.Id,
-			ParentID: message.Post.ParentId,
+			ParentID: message.Post.RootId, // ParentID is obsolete with mattermost
 			Extra:    make(map[string][]interface{}),
 		}
 

bridge/mattermost/mattermost.go

@@ -127,6 +127,15 @@ func (b *Bmattermost) Send(msg config.Message) (string, error) {
 		msg.Text = fmt.Sprintf("[thread]: %s", msg.Text)
 	}
 
+	// we only can reply to the root of the thread, not to a specific ID (like discord for example does)
+	if msg.ParentID != "" {
+		post, res := b.mc.Client.GetPost(msg.ParentID, "")
+		if res.Error != nil {
+			b.Log.Errorf("getting post %s failed: %s", msg.ParentID, res.Error.DetailedError)
+		}
+		msg.ParentID = post.RootId
+	}
+
 	// Upload a file if it exists
 	if msg.Extra != nil {
 		for _, rmsg := range helper.HandleExtra(&msg, b.General) {