Revert " #4755 Combining consecutive user join/leave system messages to single message and few other changes." (#7072)

* Revert "PLT-6603: Don't return all posts on invalid query. (#7061)"

This reverts commit 25a2013890c7e07b4621fa9b18342e7f35363049.

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

This reverts commit 8a91235fb3cdc8d094dbc2eaa0d7baa447132b3c.

14 files changed, 66 insertions, 574 deletions

diff --git a/api/post_test.go b/api/post_test.go
index 5b4e3c1a7..c7bd7a04c 100644
--- a/api/post_test.go
+++ b/api/post_test.go
@@ -394,7 +394,7 @@ func TestUpdatePost(t *testing.T) {
 		}
 	}
 
-	post3 := &model.Post{ChannelId: channel1.Id, Message: "zz" + model.NewId() + "a", Type: model.POST_HEADER_CHANGE}
+	post3 := &model.Post{ChannelId: channel1.Id, Message: "zz" + model.NewId() + "a", Type: model.POST_JOIN_LEAVE}
 	rpost3, err := Client.CreatePost(post3)
 	if err != nil {
 		t.Fatal(err)
diff --git a/api4/post_test.go b/api4/post_test.go
index 7d45d7cac..53babc6e6 100644
--- a/api4/post_test.go
+++ b/api4/post_test.go
@@ -359,7 +359,7 @@ func TestUpdatePost(t *testing.T) {
 		t.Fatal("failed to updates")
 	}
 
-	post2 := &model.Post{ChannelId: channel.Id, Message: "zz" + model.NewId() + "a", Type: model.POST_HEADER_CHANGE}
+	post2 := &model.Post{ChannelId: channel.Id, Message: "zz" + model.NewId() + "a", Type: model.POST_JOIN_LEAVE}
 	rpost2, resp := Client.CreatePost(post2)
 	CheckNoError(t, resp)
 
diff --git a/app/channel.go b/app/channel.go
index 083700795..03df0e800 100644
--- a/app/channel.go
+++ b/app/channel.go
@@ -897,75 +897,19 @@ func JoinChannel(channel *model.Channel, userId string) *model.AppError {
 	return nil
 }
 
-func createUserActivitySystemMessage(channel *model.Channel, user *model.User, otherUsername, messageType, message string) *model.AppError {
-	props := model.StringInterface{"username": user.Username}
-	if messageType == model.POST_ADD_TO_CHANNEL {
-		props["addedUsername"] = otherUsername
-	}
-
-	if messageType == model.POST_REMOVE_FROM_CHANNEL {
-		props["removedUsername"] = user.Username
-		delete(props, "username")
-	}
-
+func postJoinChannelMessage(user *model.User, channel *model.Channel) *model.AppError {
 	post := &model.Post{
 		ChannelId: channel.Id,
-		Message:   message,
-		Type:      messageType,
+		Message:   fmt.Sprintf(utils.T("api.channel.join_channel.post_and_forget"), user.Username),
+		Type:      model.POST_JOIN_CHANNEL,
 		UserId:    user.Id,
-		Props:     props,
+		Props: model.StringInterface{
+			"username": user.Username,
+		},
 	}
 
 	if _, err := CreatePost(post, channel.TeamId, false); err != nil {
-		return model.NewLocAppError("createUserActivitySystemMessage", "api.channel.create_user_activity_post.error", nil, err.Error())
-	}
-
-	return nil
-}
-
-func updateUserActivitySystemMessage(post *model.Post, username, otherUsername, messageType, messageToAdd string) *model.AppError {
-	post.Message += " " + messageToAdd
-	props := model.StringMap{"type": messageType, "username": username}
-	if messageType == model.POST_ADD_TO_CHANNEL {
-		props["addedUsername"] = otherUsername
-	}
-
-	if messageType == model.POST_REMOVE_FROM_CHANNEL {
-		props["removedUsername"] = username
-		delete(props, "username")
-	}
-
-	if val, ok := post.Props["messages"]; ok {
-		post.Props["messages"] = append(val.([]interface{}), props)
-	} else {
-		oldProps := make(model.StringInterface)
-		for key, value := range post.Props {
-			oldProps[key] = value
-		}
-		oldProps["type"] = post.Type
-		post.Props["messages"] = []interface{}{oldProps, props}
-	}
-
-	if _, err := UpdatePost(post, false); err != nil {
-		return model.NewLocAppError("updateUserActivitySystemMessage", "api.channel.update_user_activity_post.error", nil, err.Error())
-	}
-
-	return nil
-}
-
-func postJoinChannelMessage(user *model.User, channel *model.Channel) *model.AppError {
-	message := fmt.Sprintf(utils.T("api.channel.join_channel.post_and_forget"), user.Username)
-
-	if post, err := GetLastPostForChannel(channel.Id); err != nil {
-		return err
-	} else if post.IsUserActivitySystemMessage() {
-		if err := updateUserActivitySystemMessage(post, user.Username, "", model.POST_JOIN_CHANNEL, message); err != nil {
-			return err
-		}
-	} else {
-		if err := createUserActivitySystemMessage(channel, user, "", model.POST_JOIN_CHANNEL, message); err != nil {
-			return err
-		}
+		return model.NewLocAppError("postJoinChannelMessage", "api.channel.post_user_add_remove_message_and_forget.error", nil, err.Error())
 	}
 
 	return nil
@@ -1010,64 +954,55 @@ func LeaveChannel(channelId string, userId string) *model.AppError {
 }
 
 func postLeaveChannelMessage(user *model.User, channel *model.Channel) *model.AppError {
-	message := fmt.Sprintf(utils.T("api.channel.leave.left"), user.Username)
+	post := &model.Post{
+		ChannelId: channel.Id,
+		Message:   fmt.Sprintf(utils.T("api.channel.leave.left"), user.Username),
+		Type:      model.POST_LEAVE_CHANNEL,
+		UserId:    user.Id,
+		Props: model.StringInterface{
+			"username": user.Username,
+		},
+	}
 
-	if post, err := GetLastPostForChannel(channel.Id); err != nil {
-		return err
-	} else if post.IsUserActivitySystemMessage() {
-		if err := updateUserActivitySystemMessage(post, user.Username, "", model.POST_LEAVE_CHANNEL, message); err != nil {
-			return err
-		}
-	} else {
-		if err := createUserActivitySystemMessage(channel, user, "", model.POST_LEAVE_CHANNEL, message); err != nil {
-			return err
-		}
+	if _, err := CreatePost(post, channel.TeamId, false); err != nil {
+		return model.NewLocAppError("postLeaveChannelMessage", "api.channel.post_user_add_remove_message_and_forget.error", nil, err.Error())
 	}
 
 	return nil
 }
 
 func PostAddToChannelMessage(user *model.User, addedUser *model.User, channel *model.Channel) *model.AppError {
-	message := fmt.Sprintf(utils.T("api.channel.add_member.added"), user.Username, addedUser.Username)
-
-	if post, err := GetLastPostForChannel(channel.Id); err != nil {
-		return err
-	} else if post.IsUserActivitySystemMessage() {
-		if err := updateUserActivitySystemMessage(post, user.Username, addedUser.Username, model.POST_ADD_TO_CHANNEL, message); err != nil {
-			return err
-		}
+	post := &model.Post{
+		ChannelId: channel.Id,
+		Message:   fmt.Sprintf(utils.T("api.channel.add_member.added"), addedUser.Username, user.Username),
+		Type:      model.POST_ADD_TO_CHANNEL,
+		UserId:    user.Id,
+		Props: model.StringInterface{
+			"username":      user.Username,
+			"addedUsername": addedUser.Username,
+		},
+	}
 
-		SendNotificationsForSystemMessageAddRemove(user, addedUser, channel, post)
-	} else {
-		if err := createUserActivitySystemMessage(channel, user, addedUser.Username, model.POST_ADD_TO_CHANNEL, message); err != nil {
-			return err
-		}
+	if _, err := CreatePost(post, channel.TeamId, false); err != nil {
+		return model.NewLocAppError("postAddToChannelMessage", "api.channel.post_user_add_remove_message_and_forget.error", nil, err.Error())
 	}
 
 	return nil
 }
 
 func PostRemoveFromChannelMessage(removerUserId string, removedUser *model.User, channel *model.Channel) *model.AppError {
-	message := fmt.Sprintf(utils.T("api.channel.remove_member.removed"), removedUser.Username)
-
-	removerUser, err := GetUser(removerUserId)
-	if err != nil {
-		fmt.Printf("err: %+v\n", err)
-		return err
+	post := &model.Post{
+		ChannelId: channel.Id,
+		Message:   fmt.Sprintf(utils.T("api.channel.remove_member.removed"), removedUser.Username),
+		Type:      model.POST_REMOVE_FROM_CHANNEL,
+		UserId:    removerUserId,
+		Props: model.StringInterface{
+			"removedUsername": removedUser.Username,
+		},
 	}
 
-	if post, err := GetLastPostForChannel(channel.Id); err != nil {
-		return err
-	} else if post.IsUserActivitySystemMessage() {
-		if err := updateUserActivitySystemMessage(post, removedUser.Username, removerUser.Username, model.POST_REMOVE_FROM_CHANNEL, message); err != nil {
-			return err
-		}
-
-		SendNotificationsForSystemMessageAddRemove(removerUser, removedUser, channel, post)
-	} else {
-		if err := createUserActivitySystemMessage(channel, removedUser, removerUser.Username, model.POST_ADD_TO_CHANNEL, message); err != nil {
-			return err
-		}
+	if _, err := CreatePost(post, channel.TeamId, false); err != nil {
+		return model.NewLocAppError("postRemoveFromChannelMessage", "api.channel.post_user_add_remove_message_and_forget.error", nil, err.Error())
 	}
 
 	return nil
@@ -1111,28 +1046,20 @@ func RemoveUserFromChannel(userIdToRemove string, removerUserId string, channel
 		return err
 	}
 
-	var userToRemove *model.User
-	if userToRemove, err = GetUser(userIdToRemove); err != nil {
+	var user *model.User
+	if user, err = GetUser(userIdToRemove); err != nil {
 		return err
 	}
 
 	if userIdToRemove == removerUserId {
-		postLeaveChannelMessage(userToRemove, channel)
+		postLeaveChannelMessage(user, channel)
 	} else {
-		go PostRemoveFromChannelMessage(removerUserId, userToRemove, channel)
+		go PostRemoveFromChannelMessage(removerUserId, user, channel)
 	}
 
 	return nil
 }
 
-func GetLastPostForChannel(channelId string) (*model.Post, *model.AppError) {
-	result := <-Srv.Store.Post().GetLastPostForChannel(channelId)
-	if result.Err != nil {
-		return nil, result.Err
-	}
-	return result.Data.(*model.Post), nil
-}
-
 func GetNumberOfChannelsOnTeam(teamId string) (int, *model.AppError) {
 	// Get total number of channels on current team
 	if result := <-Srv.Store.Channel().GetTeamChannels(teamId); result.Err != nil {
diff --git a/app/channel_test.go b/app/channel_test.go
index 167e1b0ae..438eb959b 100644
--- a/app/channel_test.go
+++ b/app/channel_test.go
@@ -1,11 +1,6 @@
-// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
-// See License.txt for license information.
-
 package app
 
 import (
-	"fmt"
-	"reflect"
 	"testing"
 
 	"github.com/mattermost/platform/model"
@@ -69,193 +64,3 @@ func TestPermanentDeleteChannel(t *testing.T) {
 		t.Error("outgoing webhook wasn't deleted")
 	}
 }
-
-func PostUserActivitySystemMessage(t *testing.T, testFunc func(user *model.User, channel *model.Channel) *model.AppError, postType string, messageKey string) {
-	th := Setup().InitBasic()
-
-	// Test when last post was a leave/join post
-	user := &model.User{Id: model.NewId(), Email: "test@example.com", Username: "test"}
-
-	post := &model.Post{
-		ChannelId: th.BasicChannel.Id, UserId: user.Id, Type: postType, Message: "message",
-		Props: model.StringInterface{"username": user.Username},
-	}
-	post = (<-Srv.Store.Post().Save(post)).Data.(*model.Post)
-
-	testFunc(user, th.BasicChannel)
-	post = (<-Srv.Store.Post().GetSingle(post.Id)).Data.(*model.Post)
-	if post.Message != "message "+fmt.Sprintf(utils.T(messageKey), user.Username) {
-		t.Fatal("Leave/join a channel message wasn't appended to last leave/join post")
-	}
-
-	if !reflect.DeepEqual(
-		post.Props["messages"].([]interface{}),
-		[]interface{}{
-			map[string]interface{}{"type": postType, "username": user.Username},
-			map[string]interface{}{"type": postType, "username": user.Username},
-		},
-	) {
-		t.Fatal("Invalid leave/join a channel props")
-	}
-
-	// Test when last post was not a leave/join post
-	post.Id = ""
-	post.Message = "message1"
-	post.Type = model.POST_DEFAULT
-	post.Props = nil
-	post = (<-Srv.Store.Post().Save(post)).Data.(*model.Post)
-
-	testFunc(user, th.BasicChannel)
-	post = (<-Srv.Store.Post().GetSingle(post.Id)).Data.(*model.Post)
-	if post.Message == "message1 "+fmt.Sprintf(utils.T(messageKey), user.Username) {
-		t.Fatal("Leave/join a channel message was appended to last non leave/join post")
-	}
-
-	if _, ok := post.Props["messages"]; ok {
-		t.Fatal("Invalid leave/join a channel props. \"message\" shouldn't be present")
-	}
-}
-
-func TestPostJoinChannelMessage(t *testing.T) {
-	PostUserActivitySystemMessage(t, postJoinChannelMessage, model.POST_JOIN_CHANNEL, "api.channel.join_channel.post_and_forget")
-}
-
-func TestPostLeaveChannelMessage(t *testing.T) {
-	PostUserActivitySystemMessage(t, postLeaveChannelMessage, model.POST_LEAVE_CHANNEL, "api.channel.leave.left")
-}
-
-func TestPostAddToChannelMessage(t *testing.T) {
-	th := Setup().InitBasic()
-
-	// Test when last post was a user activity system message post
-	user := &model.User{Id: model.NewId(), Email: "test@example.com", Username: "test"}
-	addedUser := &model.User{Id: model.NewId(), Email: "test1@example.com", Username: "test1"}
-
-	post := &model.Post{
-		ChannelId: th.BasicChannel.Id, UserId: user.Id, Type: model.POST_ADD_TO_CHANNEL, Message: "message",
-		Props: model.StringInterface{"username": user.Username, "addedUsername": addedUser.Username},
-	}
-	post = (<-Srv.Store.Post().Save(post)).Data.(*model.Post)
-
-	PostAddToChannelMessage(user, addedUser, th.BasicChannel)
-	post = (<-Srv.Store.Post().GetSingle(post.Id)).Data.(*model.Post)
-	if post.Message != "message "+fmt.Sprintf(utils.T("api.channel.add_member.added"), user.Username, addedUser.Username) {
-		t.Fatal("Add message wasn't appended to last user activity system message post")
-	}
-
-	if !reflect.DeepEqual(
-		post.Props["messages"].([]interface{}),
-		[]interface{}{
-			map[string]interface{}{"type": model.POST_ADD_TO_CHANNEL, "username": user.Username, "addedUsername": addedUser.Username},
-			map[string]interface{}{"type": model.POST_ADD_TO_CHANNEL, "username": user.Username, "addedUsername": addedUser.Username},
-		},
-	) {
-		t.Fatal("Invalid added to channel props")
-	}
-
-	// Test when last post was not a user activity system message post
-	post.Id = ""
-	post.Message = "message1"
-	post.Type = model.POST_DEFAULT
-	post.Props = nil
-	post = (<-Srv.Store.Post().Save(post)).Data.(*model.Post)
-
-	PostAddToChannelMessage(user, addedUser, th.BasicChannel)
-	post = (<-Srv.Store.Post().GetSingle(post.Id)).Data.(*model.Post)
-	if post.Message == "message1\n"+fmt.Sprintf(utils.T("api.channel.add_member.added"), addedUser.Username, user.Username) {
-		t.Fatal("Added to channel message was appended to last non user activity system message post")
-	}
-
-	if _, ok := post.Props["messages"]; ok {
-		t.Fatal("Invalid added to channel props. \"message\" shouldn't be present")
-	}
-}
-
-func TestPostRemoveFromChannelMessage(t *testing.T) {
-	th := Setup().InitBasic()
-	user := th.BasicUser
-
-	// // Test when last post was a user activity system message post
-	removedUser := &model.User{Id: model.NewId(), Email: "test1@example.com", Username: "test1"}
-
-	post := &model.Post{
-		ChannelId: th.BasicChannel.Id, UserId: user.Id, Type: model.POST_REMOVE_FROM_CHANNEL, Message: "message",
-		Props: model.StringInterface{"removedUsername": removedUser.Username},
-	}
-	post = (<-Srv.Store.Post().Save(post)).Data.(*model.Post)
-
-	PostRemoveFromChannelMessage(user.Id, removedUser, th.BasicChannel)
-	post = (<-Srv.Store.Post().GetSingle(post.Id)).Data.(*model.Post)
-	if post.Message != "message "+fmt.Sprintf(utils.T("api.channel.remove_member.removed"), removedUser.Username) {
-		t.Fatal("Post removed from a channel message wasn't appended to last user activity system message post")
-	}
-
-	if !reflect.DeepEqual(
-		post.Props["messages"].([]interface{}),
-		[]interface{}{
-			map[string]interface{}{"type": model.POST_REMOVE_FROM_CHANNEL, "removedUsername": removedUser.Username},
-			map[string]interface{}{"type": model.POST_REMOVE_FROM_CHANNEL, "removedUsername": removedUser.Username},
-		},
-	) {
-		t.Fatal("Invalid removed from a channel props")
-	}
-
-	// Test when last post was not a user activity system message post
-	post.Id = ""
-	post.Message = "message1"
-	post.Type = model.POST_DEFAULT
-	post.Props = nil
-	post = (<-Srv.Store.Post().Save(post)).Data.(*model.Post)
-
-	PostRemoveFromChannelMessage(user.Id, removedUser, th.BasicChannel)
-	post = (<-Srv.Store.Post().GetSingle(post.Id)).Data.(*model.Post)
-	if post.Message == "message1 "+fmt.Sprintf(utils.T("api.channel.remove_member.removed"), removedUser.Username) {
-		t.Fatal("Post removed from a channel message was appended to last non user activity system message post")
-	}
-
-	if _, ok := post.Props["messages"]; ok {
-		t.Fatal("Invalid removed from a channel props. \"message\" shouldn't be present")
-	}
-}
-
-func TestGetLastPostForChannel(t *testing.T) {
-	th := Setup().InitBasic()
-	user := th.BasicUser
-
-	post1 := &model.Post{
-		ChannelId: th.BasicChannel.Id,
-		UserId:    user.Id,
-		Message:   "message",
-	}
-	post1 = (<-Srv.Store.Post().Save(post1)).Data.(*model.Post)
-
-	rpost1, err := GetLastPostForChannel(th.BasicChannel.Id)
-	if err != nil {
-		t.Fatal("Last post should have been returned")
-	}
-
-	if post1.Message != rpost1.Message {
-		t.Fatal("Should match post message")
-	}
-
-	post2 := &model.Post{
-		ChannelId: th.BasicChannel.Id,
-		UserId:    user.Id,
-		Message:   "message",
-	}
-	post2 = (<-Srv.Store.Post().Save(post2)).Data.(*model.Post)
-
-	rpost2, err := GetLastPostForChannel(th.BasicChannel.Id)
-	if err != nil {
-		t.Fatal("Last post should have been returned")
-	}
-
-	if post2.Message != rpost2.Message {
-		t.Fatal("Should match post message")
-	}
-
-	_, err = GetLastPostForChannel(model.NewId())
-	if err != nil {
-		t.Fatal("Should not return err")
-	}
-}
diff --git a/app/notification.go b/app/notification.go
index e5a43b4e8..d145b21b3 100644
--- a/app/notification.go
+++ b/app/notification.go
@@ -306,91 +306,6 @@ 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 {
diff --git a/app/post.go b/app/post.go
index ee28fbbf7..055f98373 100644
--- a/app/post.go
+++ b/app/post.go
@@ -250,8 +250,8 @@ func UpdatePost(post *model.Post, safeUpdate bool) (*model.Post, *model.AppError
 			return nil, err
 		}
 
-		if oldPost.IsSystemMessage() && !oldPost.IsUserActivitySystemMessage() {
-			err := model.NewAppError("updatePost", "api.post.update_post.system_message.app_error", nil, "id="+post.Id, http.StatusBadRequest)
+		if oldPost.IsSystemMessage() {
+			err := model.NewAppError("UpdatePost", "api.post.update_post.system_message.app_error", nil, "id="+post.Id, http.StatusBadRequest)
 			return nil, err
 		}
 
diff --git a/i18n/en.json b/i18n/en.json
index 01bde8f12..c4940295b 100644
--- a/i18n/en.json
+++ b/i18n/en.json
@@ -153,7 +153,7 @@
   },
   {
     "id": "api.channel.add_member.added",
-    "translation": "%v added %v to the channel."
+    "translation": "%v added to the channel by %v"
   },
   {
     "id": "api.channel.add_member.find_channel.app_error",
@@ -297,7 +297,7 @@
   },
   {
     "id": "api.channel.join_channel.post_and_forget",
-    "translation": "%v joined the channel."
+    "translation": "%v has joined the channel."
   },
   {
     "id": "api.channel.leave.default.app_error",
@@ -313,7 +313,7 @@
   },
   {
     "id": "api.channel.leave.left",
-    "translation": "%v left the channel."
+    "translation": "%v has left the channel."
   },
   {
     "id": "api.channel.post_update_channel_displayname_message_and_forget.create_post.error",
@@ -348,14 +348,6 @@
     "translation": "%s updated the channel header to: %s"
   },
   {
-    "id": "api.channel.create_user_activity_post.error",
-    "translation": "Failed to create user activity system message like add, remove, join or leave"
-  },
-  {
-    "id": "api.channel.update_user_activity_post.error",
-    "translation": "Failed to update user activity system message like add, remove, join or leave"
-  },
-  {
     "id": "api.channel.post_user_add_remove_message_and_forget.error",
     "translation": "Failed to post join/leave message"
   },
diff --git a/model/post.go b/model/post.go
index 67a418700..55e6f591d 100644
--- a/model/post.go
+++ b/model/post.go
@@ -205,15 +205,6 @@ func (o *Post) IsSystemMessage() bool {
 	return len(o.Type) >= len(POST_SYSTEM_MESSAGE_PREFIX) && o.Type[:len(POST_SYSTEM_MESSAGE_PREFIX)] == POST_SYSTEM_MESSAGE_PREFIX
 }
 
-func (o *Post) IsUserActivitySystemMessage() bool {
-	return o.Type == POST_JOIN_LEAVE ||
-		o.Type == POST_JOIN_CHANNEL ||
-		o.Type == POST_LEAVE_CHANNEL ||
-		o.Type == POST_ADD_REMOVE ||
-		o.Type == POST_ADD_TO_CHANNEL ||
-		o.Type == POST_REMOVE_FROM_CHANNEL
-}
-
 func (p *Post) Patch(patch *PostPatch) {
 	if patch.IsPinned != nil {
 		p.IsPinned = *patch.IsPinned
diff --git a/model/post_test.go b/model/post_test.go
index 64c8a2f3d..1096ccbd8 100644
--- a/model/post_test.go
+++ b/model/post_test.go
@@ -113,48 +113,3 @@ func TestPostIsSystemMessage(t *testing.T) {
 		t.Fatalf("TestPostIsSystemMessage failed, expected post2.IsSystemMessage() to be true")
 	}
 }
-
-func TestPostIsUserActivitySystemMessage(t *testing.T) {
-	post1 := Post{Message: "test_1"}
-	post1.PreSave()
-
-	if post1.IsUserActivitySystemMessage() {
-		t.Fatalf("TestPostIsUserActivitySystemMessage failed, expected post1.IsSystemMessage() to be false")
-	}
-
-	post2 := Post{Message: "test_2", Type: POST_JOIN_LEAVE}
-	post2.PreSave()
-	if !post2.IsUserActivitySystemMessage() {
-		t.Fatalf("TestPostIsUserActivitySystemMessage failed, expected post2.IsSystemMessage() to be true")
-	}
-
-	post3 := Post{Message: "test_3", Type: POST_JOIN_CHANNEL}
-	post3.PreSave()
-	if !post3.IsUserActivitySystemMessage() {
-		t.Fatalf("TestPostIsUserActivitySystemMessage failed, expected post3.IsSystemMessage() to be true")
-	}
-
-	post4 := Post{Message: "test_4", Type: POST_LEAVE_CHANNEL}
-	post4.PreSave()
-	if !post4.IsUserActivitySystemMessage() {
-		t.Fatalf("TestPostIsUserActivitySystemMessage failed, expected post4.IsSystemMessage() to be true")
-	}
-
-	post5 := Post{Message: "test_5", Type: POST_ADD_REMOVE}
-	post5.PreSave()
-	if !post5.IsUserActivitySystemMessage() {
-		t.Fatalf("TestPostIsUserActivitySystemMessage failed, expected post5.IsSystemMessage() to be true")
-	}
-
-	post6 := Post{Message: "test_6", Type: POST_ADD_TO_CHANNEL}
-	post6.PreSave()
-	if !post6.IsUserActivitySystemMessage() {
-		t.Fatalf("TestPostIsUserActivitySystemMessage failed, expected post6.IsSystemMessage() to be true")
-	}
-
-	post7 := Post{Message: "test_7", Type: POST_REMOVE_FROM_CHANNEL}
-	post7.PreSave()
-	if !post7.IsUserActivitySystemMessage() {
-		t.Fatalf("TestPostIsUserActivitySystemMessage failed, expected post7.IsSystemMessage() to be true")
-	}
-}
diff --git a/store/sql_post_store.go b/store/sql_post_store.go
index c66e44274..e89b5e042 100644
--- a/store/sql_post_store.go
+++ b/store/sql_post_store.go
@@ -97,7 +97,8 @@ func (s SqlPostStore) Save(post *model.Post) StoreChannel {
 		} else {
 			time := post.UpdateAt
 
-			if !post.IsUserActivitySystemMessage() {
+			if post.Type != model.POST_JOIN_LEAVE && post.Type != model.POST_JOIN_CHANNEL && post.Type != model.POST_LEAVE_CHANNEL &&
+				post.Type != model.POST_ADD_REMOVE && post.Type != model.POST_ADD_TO_CHANNEL && post.Type != model.POST_REMOVE_FROM_CHANNEL {
 				s.GetMaster().Exec("UPDATE Channels SET LastPostAt = :LastPostAt, TotalMsgCount = TotalMsgCount + 1 WHERE Id = :ChannelId", map[string]interface{}{"LastPostAt": time, "ChannelId": post.ChannelId})
 			} else {
 				// don't update TotalMsgCount for unimportant messages so that the channel isn't marked as unread
@@ -1354,29 +1355,3 @@ func (s SqlPostStore) GetPostsBatchForIndexing(startTime int64, limit int) Store
 
 	return storeChannel
 }
-
-func (s SqlPostStore) GetLastPostForChannel(channelId string) StoreChannel {
-	storeChannel := make(StoreChannel, 1)
-
-	go func() {
-		result := StoreResult{}
-
-		var post model.Post
-		query := `
-			SELECT * FROM Posts 
-			WHERE ChannelId = :channelId AND DeleteAt = 0
-			ORDER BY CreateAt DESC
-			LIMIT 1
-		`
-
-		if err := s.GetReplica().SelectOne(&post, query, map[string]interface{}{"channelId": channelId}); err != nil {
-			l4g.Error(err)
-		}
-
-		result.Data = &post
-		storeChannel <- result
-		close(storeChannel)
-	}()
-
-	return storeChannel
-}
diff --git a/store/sql_post_store_test.go b/store/sql_post_store_test.go
index 761e0dcdf..27e816996 100644
--- a/store/sql_post_store_test.go
+++ b/store/sql_post_store_test.go
@@ -1661,37 +1661,3 @@ func TestPostStoreGetPostsBatchForIndexing(t *testing.T) {
 		}
 	}
 }
-
-func TestGetLastPostForChannel(t *testing.T) {
-	Setup()
-
-	o1 := &model.Post{}
-	o1.ChannelId = model.NewId()
-	o1.UserId = model.NewId()
-	o1.Message = ""
-	o1.Type = model.POST_JOIN_CHANNEL
-
-	o1 = (<-store.Post().Save(o1)).Data.(*model.Post)
-
-	if r1 := <-store.Post().GetLastPostForChannel(o1.ChannelId); r1.Err != nil {
-		t.Fatal(r1.Err)
-	} else {
-		if r1.Data.(*model.Post).Id != o1.Id {
-			t.Fatal("invalid returned post")
-		}
-	}
-
-	o2 := &model.Post{}
-	o2.ChannelId = o1.ChannelId
-	o2.UserId = model.NewId()
-	o2.Message = ""
-
-	o2 = (<-store.Post().Save(o2)).Data.(*model.Post)
-	if r2 := <-store.Post().GetLastPostForChannel(o2.ChannelId); r2.Err != nil {
-		t.Fatal(r2.Err)
-	} else {
-		if r2.Data.(*model.Post).Id != o2.Id {
-			t.Fatal("invalid returned post")
-		}
-	}
-}
diff --git a/store/store.go b/store/store.go
index 9824ec213..d883ea5a2 100644
--- a/store/store.go
+++ b/store/store.go
@@ -170,7 +170,6 @@ type PostStore interface {
 	Overwrite(post *model.Post) StoreChannel
 	GetPostsByIds(postIds []string) StoreChannel
 	GetPostsBatchForIndexing(startTime int64, limit int) StoreChannel
-	GetLastPostForChannel(channelId string) StoreChannel
 }
 
 type UserStore interface {
diff --git a/webapp/components/post_view/post_message_view/system_message_helpers.jsx b/webapp/components/post_view/post_message_view/system_message_helpers.jsx
index c215ddb59..c134e1a7a 100644
--- a/webapp/components/post_view/post_message_view/system_message_helpers.jsx
+++ b/webapp/components/post_view/post_message_view/system_message_helpers.jsx
@@ -7,13 +7,6 @@ import {FormattedMessage} from 'react-intl';
 import {PostTypes} from 'utils/constants.jsx';
 import {formatText} from 'utils/text_formatting.jsx';
 
-const joinLeaveMessageGetters = {
-    [PostTypes.JOIN_CHANNEL]: getJoinChannelMessage,
-    [PostTypes.LEAVE_CHANNEL]: getLeaveChannelMessage,
-    [PostTypes.ADD_TO_CHANNEL]: getAddToChannelMessage,
-    [PostTypes.REMOVE_FROM_CHANNEL]: getRemoveFromChannelMessage
-};
-
 function renderUsername(value, options) {
     return renderFormattedText(value, {...options, markdown: false});
 }
@@ -22,60 +15,38 @@ function renderFormattedText(value, options) {
     return <span dangerouslySetInnerHTML={{__html: formatText(value, options)}}/>;
 }
 
-function renderJoinLeaveMessage(post, options, messageFunction) {
-    if (post.props.messages) {
-        return (
-            <div>
-                {post.props.messages.map((message, key) => <span key={key}> {joinLeaveMessageGetters[message.type](message, options)}</span>)}
-            </div>
-        );
-    }
-    return messageFunction(post.props, options);
-}
-
 function renderJoinChannelMessage(post, options) {
-    return renderJoinLeaveMessage(post, options, getJoinChannelMessage);
-}
-
-function getJoinChannelMessage(messageProps, options) {
-    const username = renderUsername(messageProps.username, options);
+    const username = renderUsername(post.props.username, options);
 
     return (
         <FormattedMessage
             id='api.channel.join_channel.post_and_forget'
-            defaultMessage='{username} joined the channel.'
+            defaultMessage='{username} has joined the channel.'
             values={{username}}
         />
     );
 }
 
 function renderLeaveChannelMessage(post, options) {
-    return renderJoinLeaveMessage(post, options, getLeaveChannelMessage);
-}
-
-function getLeaveChannelMessage(messageProps, options) {
-    const username = renderUsername(messageProps.username, options);
+    const username = renderUsername(post.props.username, options);
 
     return (
         <FormattedMessage
             id='api.channel.leave.left'
-            defaultMessage='{username} left the channel.'
+            defaultMessage='{username} has left the channel.'
             values={{username}}
         />
     );
 }
 
 function renderAddToChannelMessage(post, options) {
-    return renderJoinLeaveMessage(post, options, getAddToChannelMessage);
-}
+    const username = renderUsername(post.props.username, options);
+    const addedUsername = renderUsername(post.props.addedUsername, options);
 
-function getAddToChannelMessage(messageProps, options) {
-    const username = renderUsername(messageProps.username, options);
-    const addedUsername = renderUsername(messageProps.addedUsername, options);
     return (
         <FormattedMessage
             id='api.channel.add_member.added'
-            defaultMessage='{username} added {addedUsername} to the channel.'
+            defaultMessage='{addedUsername} added to the channel by {username}'
             values={{
                 username,
                 addedUsername
@@ -85,16 +56,12 @@ function getAddToChannelMessage(messageProps, options) {
 }
 
 function renderRemoveFromChannelMessage(post, options) {
-    return renderJoinLeaveMessage(post, options, getRemoveFromChannelMessage);
-}
-
-function getRemoveFromChannelMessage(messageProps, options) {
-    const removedUsername = renderUsername(messageProps.removedUsername, options);
+    const removedUsername = renderUsername(post.props.removedUsername, options);
 
     return (
         <FormattedMessage
             id='api.channel.remove_member.removed'
-            defaultMessage='{removedUsername} was removed from the channel.'
+            defaultMessage='{removedUsername} was removed from the channel'
             values={{
                 removedUsername
             }}
diff --git a/webapp/i18n/en.json b/webapp/i18n/en.json
index 55fc3cd74..79d291e47 100755
--- a/webapp/i18n/en.json
+++ b/webapp/i18n/en.json
@@ -1042,15 +1042,15 @@
   "analytics.team.title": "Team Statistics for {team}",
   "analytics.team.totalPosts": "Total Posts",
   "analytics.team.totalUsers": "Total Users",
-  "api.channel.add_member.added": " {username} added {addedUsername} to the channel.",
+  "api.channel.add_member.added": "{addedUsername} added to the channel by {username}",
   "api.channel.delete_channel.archived": "{username} has archived the channel.",
-  "api.channel.join_channel.post_and_forget": "{username} joined the channel.",
-  "api.channel.leave.left": "{username} left the channel.",
+  "api.channel.join_channel.post_and_forget": "{username} has joined the channel.",
+  "api.channel.leave.left": "{username} has left the channel.",
   "api.channel.post_update_channel_displayname_message_and_forget.updated_from": "{username} updated the channel display name from: {old} to: {new}",
   "api.channel.post_update_channel_header_message_and_forget.removed": "{username} removed the channel header (was: {old})",
   "api.channel.post_update_channel_header_message_and_forget.updated_from": "{username} updated the channel header from: {old} to: {new}",
   "api.channel.post_update_channel_header_message_and_forget.updated_to": "{username} updated the channel header to: {new}",
-  "api.channel.remove_member.removed": "{removedUsername} was removed from the channel.",
+  "api.channel.remove_member.removed": "{removedUsername} was removed from the channel",
   "app.channel.post_update_channel_purpose_message.removed": "{username} removed the channel purpose (was: {old})",
   "app.channel.post_update_channel_purpose_message.updated_from": "{username} updated the channel purpose from: {old} to: {new}",
   "app.channel.post_update_channel_purpose_message.updated_to": "{username} updated the channel purpose to: {new}",