#4755 Combining consecutive user join/leave system messages to single message and few other changes. (#5945)

fix 7 and 8

remove @ at "{username} joined the channel"

refactor and update test

app/notification.go

@@ -306,6 +306,91 @@ func SendNotifications(post *model.Post, team *model.Team, channel *model.Channe
 	return mentionedUsersList, nil
 }
 
+func SendNotificationsForSystemMessageAddRemove(user *model.User, otherUser *model.User, channel *model.Channel, post *model.Post) *model.AppError {
+	otherUserChannelMember, _ := GetChannelMember(channel.Id, otherUser.Id)
+	team, err := GetTeam(channel.TeamId)
+	if err != nil {
+		return err
+	}
+
+	err = (<-Srv.Store.Channel().IncrementMentionCount(channel.Id, otherUser.Id)).Err
+	if err != nil {
+		return err
+	}
+
+	if utils.Cfg.EmailSettings.SendEmailNotifications {
+		userAllowsEmails := otherUser.NotifyProps[model.EMAIL_NOTIFY_PROP] != "false"
+		if otherUserChannelMember != nil {
+			channelEmail, ok := otherUserChannelMember.NotifyProps[model.EMAIL_NOTIFY_PROP]
+			if ok && channelEmail != model.CHANNEL_NOTIFY_DEFAULT {
+				userAllowsEmails = channelEmail != "false"
+			}
+		}
+
+		var status *model.Status
+		var err *model.AppError
+		if status, err = GetStatus(otherUser.Id); err != nil {
+			status = &model.Status{
+				UserId:         otherUser.Id,
+				Status:         model.STATUS_OFFLINE,
+				Manual:         false,
+				LastActivityAt: 0,
+				ActiveChannel:  "",
+			}
+		}
+
+		senderName := utils.T("system.message.name")
+		if userAllowsEmails && status.Status != model.STATUS_ONLINE && otherUser.DeleteAt == 0 {
+			if err = sendNotificationEmail(post, otherUser, channel, team, senderName, user); err != nil {
+				return err
+			}
+		}
+	}
+
+	if otherUserChannelMember != nil {
+		sendPushNotifications := false
+		if *utils.Cfg.EmailSettings.SendPushNotifications {
+			pushServer := *utils.Cfg.EmailSettings.PushNotificationServer
+			if pushServer == model.MHPNS && (!utils.IsLicensed || !*utils.License.Features.MHPNS) {
+				l4g.Warn(utils.T("api.post.send_notifications_and_forget.push_notification.mhpnsWarn"))
+				sendPushNotifications = false
+			} else {
+				sendPushNotifications = true
+			}
+		}
+
+		channelName := channel.DisplayName
+		senderUsername := user.Username
+
+		if sendPushNotifications {
+			var status *model.Status
+			var err *model.AppError
+			if status, err = GetStatus(otherUser.Id); err != nil {
+				status = &model.Status{UserId: otherUser.Id, Status: model.STATUS_OFFLINE, Manual: false, LastActivityAt: 0, ActiveChannel: ""}
+			}
+
+			if ShouldSendPushNotification(otherUser, otherUserChannelMember.NotifyProps, true, status, post) {
+				if err = sendPushNotification(post, otherUser, channel, senderUsername, channelName, true); err != nil {
+					return err
+				}
+			}
+		}
+
+		message := model.NewWebSocketEvent(model.WEBSOCKET_EVENT_POSTED, "", post.ChannelId, "", nil)
+		message.Add("post", post.ToJson())
+		message.Add("channel_type", channel.Type)
+		message.Add("channel_display_name", channelName)
+		message.Add("channel_name", channel.Name)
+		message.Add("sender_name", senderUsername)
+		message.Add("team_id", channel.TeamId)
+		message.Add("mentions", otherUser.Username)
+
+		Publish(message)
+	}
+
+	return nil
+}
+
 func sendNotificationEmail(post *model.Post, user *model.User, channel *model.Channel, team *model.Team, senderName string, sender *model.User) *model.AppError {
 	if channel.IsGroupOrDirect() {
 		if result := <-Srv.Store.Team().GetTeamsByUserId(user.Id); result.Err != nil {