From 89131bd20c4b1aa83233384a91c67ed478338b20 Mon Sep 17 00:00:00 2001
From: Sumner Evans <sumner@beeper.com>
Date: Fri, 29 Apr 2022 16:59:27 -0600
Subject: [PATCH] backfill: add notification of disappearing messages at
 correct timestamp

This makes it so that the timestamp of the chat in Matrix looks correct,
even though the message is not there to be bridged since it has
disappeared.
---
 historysync.go | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/historysync.go b/historysync.go
index e7c8c83..61e6285 100644
--- a/historysync.go
+++ b/historysync.go
@@ -158,7 +158,19 @@ func (user *User) backfillInChunks(req *database.Backfill, conv *database.Histor
 		}
 	}
 	allMsgs := user.bridge.DB.HistorySyncQuery.GetMessagesBetween(user.MXID, conv.ConversationID, req.TimeStart, req.TimeEnd, req.MaxTotalEvents)
-	if len(allMsgs) == 0 {
+
+	sendDisappearedNotice := false
+	// If expired messages are on, and a notice has not been sent to this chat
+	// about it having disappeared messages at the conversation timestamp, send
+	// a notice indicating so.
+	if len(allMsgs) == 0 && conv.EphemeralExpiration != nil && *conv.EphemeralExpiration > 0 {
+		lastMessage := portal.bridge.DB.Message.GetLastInChat(portal.Key)
+		if lastMessage == nil || !conv.LastMessageTimestamp.Equal(lastMessage.Timestamp) {
+			sendDisappearedNotice = true
+		}
+	}
+
+	if !sendDisappearedNotice && len(allMsgs) == 0 {
 		user.log.Debugfln("Not backfilling %s: no bridgeable messages found", portal.Key.JID)
 		return
 	}
@@ -172,6 +184,28 @@ func (user *User) backfillInChunks(req *database.Backfill, conv *database.Histor
 		}
 	}
 
+	if sendDisappearedNotice {
+		user.log.Debugfln("Sending notice to %s that there are disappeared messages ending at %v", portal.Key.JID, conv.LastMessageTimestamp)
+		resp, err := portal.sendMessage(portal.MainIntent(), event.EventMessage, &event.MessageEventContent{
+			MsgType: event.MsgNotice,
+			Body:    portal.formatDisappearingMessageNotice(),
+		}, nil, conv.LastMessageTimestamp.UnixMilli())
+
+		if err != nil {
+			portal.log.Errorln("Error sending disappearing messages notice event")
+			return
+		}
+
+		msg := portal.bridge.DB.Message.New()
+		msg.Chat = portal.Key
+		msg.MXID = resp.EventID
+		msg.JID = types.MessageID(resp.EventID)
+		msg.Timestamp = conv.LastMessageTimestamp
+		msg.Sent = true
+		msg.Insert()
+		return
+	}
+
 	user.log.Infofln("Backfilling %d messages in %s, %d messages at a time (queue ID: %d)", len(allMsgs), portal.Key.JID, req.MaxBatchEvents, req.QueueID)
 	toBackfill := allMsgs[0:]
 	var insertionEventIds []id.EventID