// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

//go:build linux || freebsd

package email

import (
	"bytes"
	"fmt"
	"net/smtp"
	"time"

	"sourcedock.dev/petrbalvin/nuntius/internal/config"
)

// SendConfirmation mails the double opt-in link directly to the subscriber.
// It uses the form's SMTP identity so replies land at the owner address,
// which is set as Reply-To.
func (s *FormSender) SendConfirmation(to, link string) error {
	auth := smtp.PlainAuth("", s.form.SMTP.User, s.form.SMTP.Password, s.form.SMTP.Host)
	msg := composeConfirmation(s.form.From, to, s.form.To, s.form, link)
	return sendMail(s.form.SMTP, auth, s.form.From, []string{to}, msg, s.form.SMTP.Timeout(), s.TLSConfig)
}

// composeConfirmation builds a single-part plain-text message. Transactional
// confirmations stay deliberately simple: one link, no tracking, no HTML.
// The subject prefix and the footer brand come from the form's
// configuration; the defaults reproduce the earlier wording.
func composeConfirmation(from, to, replyToOwner string, form *config.Form, link string) []byte {
	subject := "Confirm your subscription"
	if prefix := form.EmailSubjectPrefix(); prefix != "" {
		subject = fmt.Sprintf("[%s/%s] %s", prefix, form.Name, subject)
	}

	var body bytes.Buffer
	fmt.Fprintf(&body, "Hi,\r\n\r\n")
	fmt.Fprintf(&body, "someone signed this address up for the \"%s\" form.\r\n", form.Name)
	fmt.Fprintf(&body, "If that was you, please confirm the subscription by opening:\r\n\r\n")
	fmt.Fprintf(&body, "  %s\r\n\r\n", link)
	fmt.Fprintf(&body, "If it was not you, ignore this message and nothing will happen:\r\n")
	fmt.Fprintf(&body, "the request expires automatically without any action from you.\r\n\r\n")
	if brand := form.Brand(); brand != "" {
		fmt.Fprintf(&body, "Delivered by %s\r\n", brand)
	}

	var msg bytes.Buffer
	msg.WriteString(fmt.Sprintf("From: %s\r\n", sanitizeHeaderValue(from)))
	msg.WriteString(fmt.Sprintf("To: %s\r\n", sanitizeHeaderValue(to)))
	msg.WriteString(fmt.Sprintf("Subject: %s\r\n", sanitizeHeaderValue(subject)))
	msg.WriteString(fmt.Sprintf("Date: %s\r\n", time.Now().UTC().Format(time.RFC1123Z)))
	msg.WriteString(fmt.Sprintf("Reply-To: %s\r\n", sanitizeHeaderValue(replyToOwner)))
	msg.WriteString("MIME-Version: 1.0\r\n")
	msg.WriteString("Content-Type: text/plain; charset=UTF-8\r\n")
	msg.WriteString("Content-Transfer-Encoding: 8bit\r\n")
	msg.WriteString("\r\n")
	msg.Write(body.Bytes())
	return msg.Bytes()
}