From 4cc57c507061d5f563c2a3571b9c3a5248a9a017 Mon Sep 17 00:00:00 2001
From: Rens Rikkerink <rens.rikkerink@eastbridgerfid.nl>
Date: Wed, 9 May 2018 14:18:30 +0200
Subject: [PATCH] Added copy of previous Message state to MessageUpdate

---
 events.go | 2 ++
 state.go  | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/events.go b/events.go
index e784cac..8c560db 100644
--- a/events.go
+++ b/events.go
@@ -162,6 +162,8 @@ type MessageCreate struct {
 // MessageUpdate is the data for a MessageUpdate event.
 type MessageUpdate struct {
 	*Message
+	// BeforeUpdate will be nil if the Message was not previously cached in the state cache.
+	BeforeUpdate *Message `json:"-"`
 }
 
 // MessageDelete is the data for a MessageDelete event.
diff --git a/state.go b/state.go
index 695f47c..df1b47a 100644
--- a/state.go
+++ b/state.go
@@ -863,6 +863,12 @@ func (s *State) OnInterface(se *Session, i interface{}) (err error) {
 		}
 	case *MessageUpdate:
 		if s.MaxMessageCount != 0 {
+			old, err := s.Message(t.ChannelID, t.ID)
+			if err == nil {
+				oldCopy := *old
+				t.BeforeUpdate = &oldCopy
+			}
+
 			err = s.MessageAdd(t.Message)
 		}
 	case *MessageDelete: