From b0644c3a17dfd1a55f4ed5f4f91fcc84e74359ed Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Fri, 21 Feb 2020 19:28:00 +0100
Subject: Basic backlogging

---
 connector/connector.go             | 11 +++++++++++
 connector/mattermost/mattermost.go | 31 +++++++++++++++++++++++++++----
 2 files changed, 38 insertions(+), 4 deletions(-)

(limited to 'connector')

diff --git a/connector/connector.go b/connector/connector.go
index 2235318..30dfea4 100644
--- a/connector/connector.go
+++ b/connector/connector.go
@@ -98,6 +98,11 @@ const (
 type Event struct {
 	Type EventType
 
+	// If non-empty, the event Id is used to deduplicate events in a channel
+	// This is usefull for backends that provide a backlog of channel messages
+	// when (re-)joining a room
+	Id string
+
 	// UserID of the user that sent the event
 	// If this is a direct message event, this event can only have been authored
 	// by the user we are talking to (and not by ourself)
@@ -120,12 +125,18 @@ type Event struct {
 
 type UserInfo struct {
 	DisplayName string
+
+	// If non-empty, the Filename of the avatar object will be used by Easybridge
+	// to deduplicate the update events and prevent needless reuploads.
+	// Example strategy that works for the mattermost backend: use the update timestamp as fictious file name
 	Avatar      MediaObject
 }
 
 type RoomInfo struct {
 	Name    string
 	Topic   string
+
+	// Same deduplication comment as for UserInfo.Avatar
 	Picture MediaObject
 }
 
diff --git a/connector/mattermost/mattermost.go b/connector/mattermost/mattermost.go
index 6282831..117286b 100644
--- a/connector/mattermost/mattermost.go
+++ b/connector/mattermost/mattermost.go
@@ -354,6 +354,22 @@ func (mm *Mattermost) handleConnected() {
 		} else {
 			log.Warnf("Could not get channel members: %s", resp.Error)
 		}
+
+		// Read backlog
+		// TODO: remember what was the last seen post in this channel
+		backlog, resp := mm.conn.Client.GetPostsForChannel(ch.Id, 0, 1000, "")
+		if resp.Error == nil {
+			for i := 0; i < len(backlog.Order); i++ {
+				post_id := backlog.Order[len(backlog.Order)-i-1]
+				post := backlog.Posts[post_id]
+				post_time := time.Unix(post.CreateAt/1000, 0)
+				post.Message = fmt.Sprintf("[%s] %s",
+					post_time.Format("2006-01-02 15:04:05 MST"), post.Message)
+				mm.handlePost(ch.Name, post, true)
+			}
+		} else {
+			log.Warnf("Could not get channel backlog: %s", resp.Error)
+		}
 	}
 }
 
@@ -425,6 +441,10 @@ func (mm *Mattermost) handlePosted(msg *model.WebSocketEvent) error {
 		return err
 	}
 
+	return mm.handlePost(channel_name, &post, false)
+}
+
+func (mm *Mattermost) handlePost(channel_name string, post *model.Post, only_messages bool) error {
 	// Skip self messages
 	if post.UserId == mm.conn.User.Id {
 		return nil
@@ -440,6 +460,7 @@ func (mm *Mattermost) handlePosted(msg *model.WebSocketEvent) error {
 
 	// Build message event
 	msg_ev := &Event{
+		Id: post.Id,
 		Author: userId,
 		Text: post.Message,
 		Type: EVENT_MESSAGE,
@@ -489,10 +510,12 @@ func (mm *Mattermost) handlePosted(msg *model.WebSocketEvent) error {
 		mm.ensureJoined(user, roomId)
 
 		if post.Type == "system_header_change" {
-			new_header := post.Props["new_header"].(string)
-			mm.handler.RoomInfoUpdated(roomId, userId, &RoomInfo{
-				Topic: new_header,
-			})
+			if !only_messages {
+				new_header := post.Props["new_header"].(string)
+				mm.handler.RoomInfoUpdated(roomId, userId, &RoomInfo{
+					Topic: new_header,
+				})
+			}
 		} else if post.Type == "" || post.Type == "me" {
 			msg_ev.Room = roomId
 			mm.handler.Event(msg_ev)
-- 
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