[MM-382] Add feature to use struct fields in the channel welcome message

README.md

@@ -83,7 +83,15 @@ The preview of the configured messages, as well as the creation of a channel wel
 * `/welcomebot help` - Displays usage information.
 * `/welcomebot list` - Lists the teams for which greetings were defined.
 * `/welcomebot preview [team-name]` - Sends ephemeral messages to the user calling the command, with the preview of the welcome message[s] for the given team name and the user that requested the preview.
-* `/welcomebot set_channel_welcome [welcome-message]` - Sets the given text as current's channel welcome message.
+* `/welcomebot set_channel_welcome [welcome-message]` - Sets the given text as current's channel welcome message. You can also include `{{.UserDisplayName}}` and `{{.Channel.DisplayName}}` in the command to print the user joined and the channel display name in the message, respectively. You can insert any variable from the `MessageTemplate` struct, which has the following fields:
+    ```go
+    type MessageTemplate struct {
+        WelcomeBot      *model.User
+        User            *model.User
+        DirectMessage   *model.Channel
+        UserDisplayName string
+    }
+    ```
 * `/welcomebot get_channel_welcome` - Gets the current channel's welcome message.
 * `/welcomebot delete_channel_welcome` - Deletes the current channel's welcome message.
 

server/hooks.go

@@ -69,13 +69,20 @@ func (p *Plugin) UserHasJoinedChannel(c *plugin.Context, channelMember *model.Ch
 		return
 	}
 
+	templateData := p.constructChannelMessageTemplate(channelMember.UserId, channelMember.ChannelId)
+	if templateData == nil {
+		return
+	}
+
+	message := p.getTemplateMessage([]string{string(data)}, templateData)
+
 	// We send a DM and an opportunistic ephemeral message to the channel. See
 	// the discussion at the link below for more details:
 	// https://github.com/mattermost/mattermost-plugin-welcomebot/pull/31#issuecomment-611691023
 	postDM := &model.Post{
 		UserId:    p.botUserID,
 		ChannelId: dmChannel.Id,
-		Message:   string(data),
+		Message:   message,
 	}
 	if _, appErr := p.API.CreatePost(postDM); appErr != nil {
 		mlog.Error("failed to post welcome message to the channel",
@@ -87,7 +94,7 @@ func (p *Plugin) UserHasJoinedChannel(c *plugin.Context, channelMember *model.Ch
 	postChannel := &model.Post{
 		UserId:    p.botUserID,
 		ChannelId: channelMember.ChannelId,
-		Message:   string(data),
+		Message:   message,
 	}
 	time.Sleep(1 * time.Second)
 	_ = p.API.SendEphemeralPost(channelMember.UserId, postChannel)

server/message_template.go

@@ -11,3 +11,11 @@ type MessageTemplate struct {
 	DirectMessage   *model.Channel
 	UserDisplayName string
 }
+
+type ChannelMessageTemplate struct {
+	WelcomeBot      *model.User
+	User            *model.User
+	Channel         *model.Channel
+	DirectMessage   *model.Channel
+	UserDisplayName string
+}

server/welcomebot.go

@@ -45,6 +45,37 @@ func (p *Plugin) constructMessageTemplate(userID, teamID string) *MessageTemplat
 	return data
 }
 
+func (p *Plugin) constructChannelMessageTemplate(userID, channelID string) *ChannelMessageTemplate {
+	data := &ChannelMessageTemplate{}
+	var err *model.AppError
+
+	if len(userID) > 0 {
+		if data.User, err = p.API.GetUser(userID); err != nil {
+			p.API.LogError("failed to query user", "UserID", userID)
+			return nil
+		}
+	}
+
+	if data.User != nil {
+		if data.DirectMessage, err = p.API.GetDirectChannel(userID, p.botUserID); err != nil {
+			p.API.LogError("failed to query direct message channel", "UserID", userID)
+			return nil
+		}
+	}
+
+	if len(channelID) > 0 {
+		data.Channel, err = p.API.GetChannel(channelID)
+		if err != nil {
+			p.API.LogError("failed to query channel", "ChannelID", channelID)
+			return nil
+		}
+	}
+
+	data.UserDisplayName = data.User.GetDisplayName(model.ShowNicknameFullName)
+
+	return data
+}
+
 func (p *Plugin) getSiteURL() string {
 	siteURL := "http://localhost:8065"
 
@@ -133,18 +164,10 @@ func (p *Plugin) renderWelcomeMessage(messageTemplate MessageTemplate, configMes
 		}
 	}
 
-	tmpMsg, _ := template.New("Response").Parse(strings.Join(configMessage.Message, "\n"))
-	var message bytes.Buffer
-	err := tmpMsg.Execute(&message, messageTemplate)
-	if err != nil {
-		p.API.LogError(
-			"Failed to execute message template",
-			"err", err.Error(),
-		)
-	}
+	message := p.getTemplateMessage(configMessage.Message, messageTemplate)
 
 	post := &model.Post{
-		Message: message.String(),
+		Message: message,
 		UserId:  p.botUserID,
 	}
 
@@ -177,6 +200,17 @@ func (p *Plugin) renderWelcomeMessage(messageTemplate MessageTemplate, configMes
 	return post
 }
 
+func (p *Plugin) getTemplateMessage(data []string, messageTemplate interface{}) string {
+	tmpMsg, _ := template.New("Response").Parse(strings.Join(data, "\n"))
+	var message bytes.Buffer
+	if appErr := tmpMsg.Execute(&message, messageTemplate); appErr != nil {
+		p.API.LogError("Failed to execute channel message template", "Error", appErr.Error())
+		return ""
+	}
+
+	return message.String()
+}
+
 func (p *Plugin) processWelcomeMessage(messageTemplate MessageTemplate, configMessage ConfigMessage) {
 	time.Sleep(time.Second * time.Duration(configMessage.DelayInSeconds))