Refactor {{ UnsubURL }} into a global function (breaking change)

main.go

@@ -33,7 +33,7 @@ type constants struct {
 	RootURL      string `koanf:"root"`
 	LogoURL      string `koanf:"logo_url"`
 	FaviconURL   string `koanf:"favicon_url"`
-	UnsubscribeURL string
+	UnsubURL     string
 	LinkTrackURL string
 	ViewTrackURL string
 	OptinURL     string
@@ -309,7 +309,7 @@ func main() {
 
 	// Static URLS.
 	// url.com/subscription/{campaign_uuid}/{subscriber_uuid}
-	c.UnsubscribeURL = fmt.Sprintf("%s/subscription/%%s/%%s", app.Constants.RootURL)
+	c.UnsubURL = fmt.Sprintf("%s/subscription/%%s/%%s", app.Constants.RootURL)
 
 	// url.com/subscription/optin/{subscriber_uuid}
 	c.OptinURL = fmt.Sprintf("%s/subscription/optin/%%s?%%s", app.Constants.RootURL)
@@ -328,7 +328,7 @@ func main() {
 		Concurrency:   ko.Int("app.concurrency"),
 		MaxSendErrors: ko.Int("app.max_send_errors"),
 		FromEmail:     app.Constants.FromEmail,
-		UnsubURL:      c.UnsubscribeURL,
+		UnsubURL:      c.UnsubURL,
 		OptinURL:      c.OptinURL,
 		LinkTrackURL:  c.LinkTrackURL,
 		ViewTrackURL:  c.ViewTrackURL,

manager/manager.go

@@ -65,6 +65,7 @@ type Message struct {
 
 	from     string
 	to       string
+	unsubURL string
 }
 
 // Config has parameters for configuring the manager.
@@ -110,6 +111,7 @@ func (m *Manager) NewMessage(c *models.Campaign, s *models.Subscriber) *Message
 
 		from:     c.FromEmail,
 		to:       s.Email,
+		unsubURL: fmt.Sprintf(m.cfg.UnsubURL, c.UUID, s.UUID),
 	}
 }
 
@@ -422,7 +424,7 @@ func (m *Manager) TemplateFuncs(c *models.Campaign) template.FuncMap {
 				fmt.Sprintf(m.cfg.ViewTrackURL, msg.Campaign.UUID, msg.Subscriber.UUID)))
 		},
 		"UnsubscribeURL": func(msg *Message) string {
-			return fmt.Sprintf(m.cfg.UnsubURL, c.UUID, msg.Subscriber.UUID)
+			return msg.unsubURL
 		},
 		"OptinURL": func(msg *Message) string {
 			// Add list IDs.