Implement notifications service with shared messaging and email drivers (#36)

backend/notifications/email/sendgrid.go

@@ -0,0 +1,28 @@
+package email
+
+// Adapted from Sendico's SendGrid notifier (see PROVENANCE.md). The SDK mail
+// construction is retained; templates, retries and logging belong to our service.
+import (
+	"context"
+
+	"git.sendico.io/tech/sxchnge/notifications/model"
+	"github.com/sendgrid/sendgrid-go/helpers/mail"
+)
+
+type sendgrid struct{ client }
+
+func (s *sendgrid) Send(ctx context.Context, _ string, email model.Email) Outcome {
+	m := mail.NewV3Mail()
+	m.SetFrom(mail.NewEmail(s.settings.SenderName, s.settings.SenderAddress))
+	m.Subject = email.Subject
+	p := mail.NewPersonalization()
+	p.AddTos(mail.NewEmail("", email.Address))
+	m.AddPersonalizations(p)
+	if email.Text != "" {
+		m.AddContent(mail.NewContent("text/plain", email.Text))
+	}
+	if email.HTML != "" {
+		m.AddContent(mail.NewContent("text/html", email.HTML))
+	}
+	return s.post(ctx, "", m)
+}