From 79188818e2339019492a902b700248c9e3900dcf Mon Sep 17 00:00:00 2001
From: Colin Reeder <vpzomtrrfrt@gmail.com>
Date: Sat, 18 Dec 2021 12:23:54 -0700
Subject: [PATCH] Handle replies from matrix

---
 bridge/matrix/matrix.go | 34 ++++++++++++++++++++++++++++++++++
 gateway/gateway.go      |  4 ++--
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/bridge/matrix/matrix.go b/bridge/matrix/matrix.go
index 01a2379c..577c89f8 100644
--- a/bridge/matrix/matrix.go
+++ b/bridge/matrix/matrix.go
@@ -386,6 +386,35 @@ func (b *Bmatrix) handleEdit(ev *matrix.Event, rmsg config.Message) bool {
 	return true
 }
 
+func (b *Bmatrix) handleReply(ev *matrix.Event, rmsg config.Message) bool {
+	relationInterface, present := ev.Content["m.relates_to"]
+	if !present {
+		return false
+	}
+
+	var relation InReplyToRelation
+	if err := interface2Struct(relationInterface, &relation); err != nil {
+		// probably fine
+		return false
+	}
+
+	body := rmsg.Text
+	for strings.HasPrefix(body, "> ") {
+		lineIdx := strings.IndexRune(body, '\n')
+		if lineIdx == -1 {
+			body = ""
+		} else {
+			body = body[(lineIdx + 1):]
+		}
+	}
+
+	rmsg.Text = body
+	rmsg.ParentID = relation.InReplyTo.EventID
+	b.Remote <- rmsg
+
+	return true
+}
+
 func (b *Bmatrix) handleMemberChange(ev *matrix.Event) {
 	// Update the displayname on join messages, according to https://matrix.org/docs/spec/client_server/r0.6.1#events-on-change-of-profile-information
 	if ev.Content["membership"] == "join" {
@@ -448,6 +477,11 @@ func (b *Bmatrix) handleEvent(ev *matrix.Event) {
 			return
 		}
 
+		// Is it a reply?
+		if b.handleReply(ev, rmsg) {
+			return
+		}
+
 		// Do we have attachments
 		if b.containsAttachment(ev.Content) {
 			err := b.handleDownloadFile(&rmsg, ev.Content)
diff --git a/gateway/gateway.go b/gateway/gateway.go
index 1c6c21c3..7da4defa 100644
--- a/gateway/gateway.go
+++ b/gateway/gateway.go
@@ -454,9 +454,9 @@ func (gw *Gateway) SendMessage(
 		msg.Channel = rmsg.Channel
 	}
 
-	msg.ParentID = gw.getDestMsgID(rmsg.Protocol+" "+canonicalParentMsgID, dest, channel)
+	msg.ParentID = gw.getDestMsgID(canonicalParentMsgID, dest, channel)
 	if msg.ParentID == "" {
-		msg.ParentID = canonicalParentMsgID
+		msg.ParentID = strings.Replace(canonicalParentMsgID, dest.Protocol+" ", "", 1)
 	}
 
 	// if the parentID is still empty and we have a parentID set in the original message