package notify

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

// SMTPNotifier sends a plaintext email. Authentication is left at zero
// (LAN-only relay assumed); if the configured server requires auth the
// Send call will return an error and the Registry will log it.
//
// SendMailFn is overridable so tests can capture the outgoing message
// without needing a live SMTP server.
type SMTPNotifier struct {
	NameStr    string
	Host       string
	Port       int
	From       string
	To         []string
	SendMailFn func(addr string, a smtp.Auth, from string, to []string, msg []byte) error
}

func NewSMTP(name, host string, port int, from string, to []string) *SMTPNotifier {
	if port == 0 {
		port = 25
	}
	return &SMTPNotifier{
		NameStr:    name,
		Host:       host,
		Port:       port,
		From:       from,
		To:         to,
		SendMailFn: smtp.SendMail,
	}
}

func (s *SMTPNotifier) Name() string { return s.NameStr }

func (s *SMTPNotifier) Send(ctx context.Context, ev Event) error {
	if s.Host == "" || s.From == "" || len(s.To) == 0 {
		return fmt.Errorf("smtp: incomplete config (host/from/to required)")
	}
	// We intentionally don't honour ctx here — net/smtp.SendMail doesn't
	// accept a context; for a LAN relay with a short TCP timeout the
	// Registry's goroutine will outlive the timeout but only by seconds.
	addr := s.Host + ":" + strconv.Itoa(s.Port)
	msg := buildEmail(s.From, s.To, ev)
	return s.SendMailFn(addr, nil, s.From, s.To, msg)
}

// buildEmail produces an RFC 5322 minimal message. Body is plaintext;
// the URL is appended so the recipient can click through from a text
// mail client. No MIME for now — keeps it robust.
func buildEmail(from string, to []string, ev Event) []byte {
	var b strings.Builder
	b.WriteString("From: ")
	b.WriteString(from)
	b.WriteString("\r\n")
	b.WriteString("To: ")
	b.WriteString(strings.Join(to, ", "))
	b.WriteString("\r\n")
	subject := ev.Title
	if subject == "" {
		subject = "[vetting] " + string(ev.Kind)
	}
	b.WriteString("Subject: ")
	b.WriteString(subject)
	b.WriteString("\r\n")
	b.WriteString("Content-Type: text/plain; charset=UTF-8\r\n")
	b.WriteString("\r\n")
	b.WriteString(ev.Body)
	if ev.URL != "" {
		b.WriteString("\r\n\r\nLink: ")
		b.WriteString(ev.URL)
	}
	b.WriteString("\r\n")
	return []byte(b.String())
}