From 64d44707c2828b8f6442d42d2fe8b7b966607310 Mon Sep 17 00:00:00 2001
From: Kailash Nadh <kailash@nadh.in>
Date: Sun, 5 Jul 2020 18:39:24 +0530
Subject: [PATCH] Add {{ templating }} support to e-mail subjects

---
 campaigns.go                |  5 ++++-
 internal/manager/manager.go | 19 ++++++++++++++++++-
 models/models.go            | 14 ++++++++++++++
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/campaigns.go b/campaigns.go
index 31ae615..ceb4bd3 100644
--- a/campaigns.go
+++ b/campaigns.go
@@ -558,7 +558,10 @@ func sendTestMessage(sub models.Subscriber, camp *models.Campaign, app *App) err
 			fmt.Sprintf("Error rendering message: %v", err))
 	}
 
-	if err := app.messenger.Push(camp.FromEmail, []string{sub.Email}, camp.Subject, m.Body(), nil); err != nil {
+	if err := app.messenger.Push(camp.FromEmail,
+		[]string{sub.Email},
+		m.Subject(),
+		m.Body(), nil); err != nil {
 		return err
 	}
 
diff --git a/internal/manager/manager.go b/internal/manager/manager.go
index 9af267c..e9804f3 100644
--- a/internal/manager/manager.go
+++ b/internal/manager/manager.go
@@ -68,6 +68,7 @@ type CampaignMessage struct {
 
 	from     string
 	to       string
+	subject  string
 	body     []byte
 	unsubURL string
 }
@@ -126,6 +127,7 @@ func (m *Manager) NewCampaignMessage(c *models.Campaign, s models.Subscriber) Ca
 		Campaign:   c,
 		Subscriber: s,
 
+		subject:  c.Subject,
 		from:     c.FromEmail,
 		to:       s.Email,
 		unsubURL: fmt.Sprintf(m.cfg.UnsubURL, c.UUID, s.UUID),
@@ -271,7 +273,7 @@ func (m *Manager) SpawnWorkers() {
 					numMsg++
 
 					err := m.messengers[msg.Campaign.MessengerID].Push(
-						msg.from, []string{msg.to}, msg.Campaign.Subject, msg.body, nil)
+						msg.from, []string{msg.to}, msg.subject, msg.body, nil)
 					if err != nil {
 						m.logger.Printf("error sending message in campaign %s: %v", msg.Campaign.Name, err)
 
@@ -480,6 +482,16 @@ func (m *Manager) sendNotif(c *models.Campaign, status, reason string) error {
 // and applies the resultant bytes to Message.body to be used in messages.
 func (m *CampaignMessage) Render() error {
 	out := bytes.Buffer{}
+
+	// Render the subject if it's a template.
+	if m.Campaign.SubjectTpl != nil {
+		if err := m.Campaign.SubjectTpl.ExecuteTemplate(&out, models.ContentTpl, m); err != nil {
+			return err
+		}
+		m.subject = out.String()
+		out.Reset()
+	}
+
 	if err := m.Campaign.Tpl.ExecuteTemplate(&out, models.BaseTpl, m); err != nil {
 		return err
 	}
@@ -487,6 +499,11 @@ func (m *CampaignMessage) Render() error {
 	return nil
 }
 
+// Subject returns a copy of the message subject
+func (m *CampaignMessage) Subject() string {
+	return m.subject
+}
+
 // Body returns a copy of the message body.
 func (m *CampaignMessage) Body() []byte {
 	out := make([]byte, len(m.body))
diff --git a/models/models.go b/models/models.go
index 1423068..22477c7 100644
--- a/models/models.go
+++ b/models/models.go
@@ -169,6 +169,7 @@ type Campaign struct {
 	// TemplateBody is joined in from templates by the next-campaigns query.
 	TemplateBody string             `db:"template_body" json:"-"`
 	Tpl          *template.Template `json:"-"`
+	SubjectTpl   *template.Template `json:"-"`
 
 	// Pseudofield for getting the total number of subscribers
 	// in searches and queries.
@@ -310,6 +311,19 @@ func (c *Campaign) CompileTemplate(f template.FuncMap) error {
 		return fmt.Errorf("error inserting child template: %v", err)
 	}
 
+	// If the subject line has a template string, compile it.
+	if strings.Contains(c.Subject, "{{") {
+		subj := c.Subject
+		for _, r := range regTplFuncs {
+			subj = r.regExp.ReplaceAllString(subj, r.replace)
+		}
+		subjTpl, err := template.New(ContentTpl).Funcs(f).Parse(subj)
+		if err != nil {
+			return fmt.Errorf("error compiling subject: %v", err)
+		}
+		c.SubjectTpl = subjTpl
+	}
+
 	c.Tpl = out
 	return nil
 }