[MM-36457] - Send email when license is up for renewal (#17816)

* [MM-36457] - Send email when license is up for renewal

* i18n-extract

* feedback impl

* feedback impl

* fix translations

* Change license key to test for testing purposes

* Revert license key

* Trying test license key once more

* revert license change

Co-authored-by: marianunez <maria.nunez@mattermost.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/server.go

@@ -1781,6 +1781,52 @@ func (s *Server) startMetricsServer() {
 	s.Log.Info("Metrics and profiling server is started", mlog.String("address", l.Addr().String()))
 }
 
+func (s *Server) sendLicenseUpForRenewalEmail(users map[string]*model.User, license *model.License) *model.AppError {
+	key := model.LICENSE_UP_FOR_RENEWAL_EMAIL_SENT + license.Id
+	if _, err := s.Store.System().GetByName(key); err == nil {
+		// return early because the key already exists and that means we already executed the code below to send email successfully
+		return nil
+	}
+
+	daysToExpiration := license.DaysToExpiration()
+
+	renewalLink, appErr := s.GenerateLicenseRenewalLink()
+	if appErr != nil {
+		return model.NewAppError("s.sendLicenseUpForRenewalEmail", "api.server.license_up_for_renewal.error_generating_link", nil, appErr.Error(), http.StatusInternalServerError)
+	}
+
+	// we want to at least have one email sent out to an admin
+	countNotOks := 0
+
+	for _, user := range users {
+		name := user.FirstName
+		if name == "" {
+			name = user.Username
+		}
+		ok, err := s.EmailService.SendLicenseUpForRenewalEmail(user.Email, name, user.Locale, *s.Config().ServiceSettings.SiteURL, renewalLink, daysToExpiration)
+		if !ok || err != nil {
+			mlog.Error("Error sending license up for renewal email to", mlog.String("user_email", user.Email))
+			countNotOks++
+		}
+	}
+
+	// if not even one admin got an email, we consider that this operation errored
+	if countNotOks == len(users) {
+		return model.NewAppError("s.sendLicenseUpForRenewalEmail", "api.server.license_up_for_renewal.error_sending_email", nil, "", http.StatusInternalServerError)
+	}
+
+	system := model.System{
+		Name:  key,
+		Value: "true",
+	}
+
+	if err := s.Store.System().Save(&system); err != nil {
+		mlog.Debug("Failed to mark license up for renewal email sending as completed.", mlog.Err(err))
+	}
+
+	return nil
+}
+
 func (s *Server) doLicenseExpirationCheck() {
 	s.LoadLicense()
 	license := s.License()
@@ -1790,17 +1836,24 @@ func (s *Server) doLicenseExpirationCheck() {
 		return
 	}
 
-	if !license.IsPastGracePeriod() {
-		mlog.Debug("License is not past the grace period.")
-		return
-	}
-
 	users, err := s.Store.User().GetSystemAdminProfiles()
 	if err != nil {
 		mlog.Error("Failed to get system admins for license expired message from Mattermost.")
 		return
 	}
 
+	if license.IsWithinExpirationPeriod() {
+		appErr := s.sendLicenseUpForRenewalEmail(users, license)
+		if appErr != nil {
+			mlog.Debug(appErr.Error())
+		}
+	}
+
+	if !license.IsPastGracePeriod() {
+		mlog.Debug("License is not past the grace period.")
+		return
+	}
+
 	//send email to admin(s)
 	for _, user := range users {
 		user := user