emailing/mailer.go

package emailing

import (
	"bytes"
	"fmt"
	"html/template"
	"net/smtp"

	"github.com/spf13/viper"
)

type Mailer struct {
	TemplatesDir    string
	TemplatesConfig *viper.Viper

	From     string
	Host     string
	Port     int
	Username string
	Password string
}

func NewMailer(templates_dir string, tplcfg *viper.Viper, smtpconfig *viper.Viper) (*Mailer, error) {
	var (
		from     = smtpconfig.GetString("from")
		host     = smtpconfig.GetString("host")
		port     = smtpconfig.GetInt("port")
		username = smtpconfig.GetString("username")
		password = smtpconfig.GetString("password")
	)

	return &Mailer{
		TemplatesDir:    templates_dir,
		TemplatesConfig: tplcfg,
		From:            from,
		Host:            host,
		Port:            port,
		Username:        username,
		Password:        password,
	}, nil
}

func (m *Mailer) Send(emailcfg string, to string, data any) error {
	cfg := m.TemplatesConfig.Sub(emailcfg)
	subject := cfg.GetString("subject")

	files := cfg.GetStringSlice("files")

	auth := smtp.PlainAuth("", m.Username, m.Password, m.Host)

	var body bytes.Buffer

	mimeHeaders := "MIME-version: 1.0;\nContent-Type: text/html; charset=\"UTF-8\";\n\n"
	body.Write([]byte(fmt.Sprintf("Subject: %s \n%s\n\n", subject, mimeHeaders)))

	if err := executeTemplate(&body, files, data, m.TemplatesDir); err != nil {
		return fmt.Errorf("failed executing email template : %w", err)
	}

	smtpserver := fmt.Sprintf("%s:%d", m.Host, m.Port)

	err := smtp.SendMail(smtpserver, auth, m.From, []string{to}, body.Bytes())
	if err != nil {
		return fmt.Errorf("isser sending email: %w", err)
	}

	return nil
}

func executeTemplate(body *bytes.Buffer, files []string, data any, templatesdir string) error {
	prefixed_files := []string{}
	for _, f := range files {
		prefixed_files = append(prefixed_files, templatesdir+f)
	}

	t := template.New("email").Funcs(
		template.FuncMap{
			"unescapeHTML": UnescapeHTML,
		},
	)
	t = template.Must(t.ParseFiles(prefixed_files...))
	if err := t.ExecuteTemplate(body, "main", data); err != nil {
		return fmt.Errorf("failed execute mail template : %w", err)
	}
	return nil
}

func UnescapeHTML(s string) template.HTML {
	return template.HTML(s)
}