package alerts

import (
	"crypto/tls"
	"fmt"
	"net/smtp"
	"strings"
)

func sendMail(addr, user, pass, from string, to []string, subject, body string) error {
	host := addr
	for i, c := range addr {
		if c == ':' {
			host = addr[:i]
			break
		}
	}

	msg := fmt.Sprintf("From: %s\r\nTo: %s\r\nSubject: %s\r\nMIME-Version: 1.0\r\nContent-Type: text/plain; charset=UTF-8\r\n\r\n%s",
		from, strings.Join(to, ", "), subject, body)

	auth := newLoginAuth(user, pass)

	c, err := smtp.Dial(addr)
	if err != nil {
		return fmt.Errorf("dial: %w", err)
	}
	defer c.Close()

	if err := c.StartTLS(&tls.Config{ServerName: host}); err != nil {
		return fmt.Errorf("starttls: %w", err)
	}

	if user != "" {
		if err := c.Auth(auth); err != nil {
			return fmt.Errorf("auth: %w", err)
		}
	}

	if err := c.Mail(from); err != nil {
		return fmt.Errorf("mail from: %w", err)
	}
	for _, addr := range to {
		if err := c.Rcpt(addr); err != nil {
			return fmt.Errorf("rcpt %s: %w", addr, err)
		}
	}

	w, err := c.Data()
	if err != nil {
		return fmt.Errorf("data: %w", err)
	}
	if _, err := fmt.Fprint(w, msg); err != nil {
		return fmt.Errorf("write: %w", err)
	}
	if err := w.Close(); err != nil {
		return fmt.Errorf("close: %w", err)
	}
	return c.Quit()
}

type loginAuth struct {
	user, pass string
}

func newLoginAuth(user, pass string) smtp.Auth {
	return &loginAuth{user, pass}
}

func (a *loginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
	return "LOGIN", []byte(a.user), nil
}

func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
	if more {
		msg := string(fromServer)
		switch {
		case strings.EqualFold(msg, "Username:"):
			return []byte(a.user), nil
		case strings.EqualFold(msg, "Password:"):
			return []byte(a.pass), nil
		}
	}
	return nil, nil
}