package auth

import (
	"context"
	"fmt"
	"io"
	"net/smtp"
	"strings"
)

// Mailer sends magic-link emails. The interface keeps the auth flow
// decoupled from any concrete delivery backend.
type Mailer interface {
	SendMagicLink(ctx context.Context, email, link string) error
}

// LogMailer writes the magic link to a writer instead of sending an
// email. Useful for development and tests.
type LogMailer struct{ W io.Writer }

func (m LogMailer) SendMagicLink(_ context.Context, email, link string) error {
	if m.W == nil {
		return nil
	}
	_, err := fmt.Fprintf(m.W, "magic link for %s: %s\n", email, link)
	return err
}

// SMTPMailer delivers via plain SMTP with optional auth. TLS is the
// caller's responsibility (use submission port 587 with STARTTLS or 465
// with implicit TLS — the stdlib smtp package handles STARTTLS via
// SendMail when the server supports it).
type SMTPMailer struct {
	Host     string
	Port     string
	Username string
	Password string
	From     string
}

func (m SMTPMailer) SendMagicLink(_ context.Context, to, link string) error {
	if m.Host == "" || m.From == "" {
		return fmt.Errorf("smtp not configured")
	}
	addr := m.Host + ":" + m.Port
	var auth smtp.Auth
	if m.Username != "" {
		auth = smtp.PlainAuth("", m.Username, m.Password, m.Host)
	}
	subject := "Your librenotes login link"
	body := fmt.Sprintf("Click to sign in to librenotes:\n\n%s\n\nThis link is valid for 15 minutes and can be used once.\n", link)
	msg := strings.Join([]string{
		"From: " + m.From,
		"To: " + to,
		"Subject: " + subject,
		"MIME-Version: 1.0",
		"Content-Type: text/plain; charset=utf-8",
		"",
		body,
	}, "\r\n")
	return smtp.SendMail(addr, auth, m.From, []string{to}, []byte(msg))
}