Initial commit

internal/mailer/mailer.go

@@ -0,0 +1,163 @@
+package mailer
+
+import (
+	"bytes"
+	"embed"
+	"errors"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/wneessen/go-mail"
+
+	ht "html/template"
+	tt "text/template"
+)
+
+//go:embed "templates"
+var templateFS embed.FS
+
+// Mailer renders embedded templates and delivers the resulting message.
+type Mailer struct {
+	client   *mail.Client
+	mode     Mode
+	filePath string
+	sender   string
+	fileMu   sync.Mutex
+}
+
+// Mode selects the delivery backend used by a Mailer.
+type Mode string
+
+const (
+	// ModeSMTP sends messages through an SMTP server.
+	ModeSMTP Mode = "smtp"
+	// ModeFile appends rendered messages to a local development file.
+	ModeFile Mode = "file"
+)
+
+// Config contains SMTP or development-file delivery settings.
+type Config struct {
+	Mode     Mode
+	Host     string
+	Port     int
+	Username string
+	Password string
+	Sender   string
+	FilePath string
+}
+
+// New validates config and creates a Mailer.
+func New(config Config) (*Mailer, error) {
+	mailer := &Mailer{
+		mode:     config.Mode,
+		filePath: config.FilePath,
+		sender:   config.Sender,
+	}
+
+	switch config.Mode {
+	case ModeSMTP:
+		client, err := mail.NewClient(
+			config.Host,
+			mail.WithSMTPAuth(mail.SMTPAuthLogin),
+			mail.WithPort(config.Port),
+			mail.WithUsername(config.Username),
+			mail.WithPassword(config.Password),
+			mail.WithTimeout(5*time.Second),
+		)
+		if err != nil {
+			return nil, err
+		}
+		mailer.client = client
+	case ModeFile:
+		if config.FilePath == "" {
+			return nil, errors.New("mailer: file path must not be empty in file mode")
+		}
+	default:
+		return nil, fmt.Errorf("mailer: unsupported mode %q", config.Mode)
+	}
+
+	return mailer, nil
+}
+
+// Send renders templateFile with data and delivers it to recipient.
+func (m *Mailer) Send(recipient string, templateFile string, data any) error {
+	textTmpl, err := tt.New("").ParseFS(templateFS, "templates/"+templateFile)
+	if err != nil {
+		return err
+	}
+
+	subject := new(bytes.Buffer)
+	err = textTmpl.ExecuteTemplate(subject, "subject", data)
+	if err != nil {
+		return err
+	}
+
+	plainBody := new(bytes.Buffer)
+	err = textTmpl.ExecuteTemplate(plainBody, "plainBody", data)
+	if err != nil {
+		return err
+	}
+
+	htmlTmpl, err := ht.New("").ParseFS(templateFS, "templates/"+templateFile)
+	if err != nil {
+		return err
+	}
+
+	htmlBody := new(bytes.Buffer)
+	err = htmlTmpl.ExecuteTemplate(htmlBody, "htmlBody", data)
+	if err != nil {
+		return err
+	}
+
+	msg := mail.NewMsg()
+
+	err = msg.To(recipient)
+	if err != nil {
+		return err
+	}
+
+	err = msg.From(m.sender)
+	if err != nil {
+		return err
+	}
+
+	msg.Subject(subject.String())
+	msg.SetBodyString(mail.TypeTextPlain, plainBody.String())
+	msg.AddAlternativeString(mail.TypeTextHTML, htmlBody.String())
+
+	if m.mode == ModeFile {
+		return m.appendToFile(msg)
+	}
+
+	return m.client.DialAndSend(msg)
+}
+
+func (m *Mailer) appendToFile(msg *mail.Msg) error {
+	var content bytes.Buffer
+	if _, err := msg.WriteTo(&content); err != nil {
+		return fmt.Errorf("mailer: format message: %w", err)
+	}
+
+	m.fileMu.Lock()
+	defer m.fileMu.Unlock()
+
+	file, err := os.OpenFile(m.filePath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o600)
+	if err != nil {
+		return fmt.Errorf("mailer: open output file: %w", err)
+	}
+	defer file.Close()
+
+	if _, err = file.WriteString("\n=== gardomatic mail ===\n"); err != nil {
+		return fmt.Errorf("mailer: append separator: %w", err)
+	}
+	if _, err = content.WriteTo(file); err != nil {
+		return fmt.Errorf("mailer: append message: %w", err)
+	}
+	if _, err = file.WriteString("\n"); err != nil {
+		return fmt.Errorf("mailer: finish message: %w", err)
+	}
+
+	return nil
+}