// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package email

import (
	"bytes"
	"errors"
	"fmt"
	"net/smtp"
	"os"
	"path/filepath"
	"strings"
	"text/template"

	"github.com/superseriousbusiness/gotosocial/internal/config"
	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
)

func (s *sender) sendTemplate(template string, subject string, data any, toAddresses ...string) error {
	buf := &bytes.Buffer{}
	if err := s.template.ExecuteTemplate(buf, template, data); err != nil {
		return err
	}

	msg, err := assembleMessage(subject, buf.String(), s.from, toAddresses...)
	if err != nil {
		return err
	}

	if err := smtp.SendMail(s.hostAddress, s.auth, s.from, toAddresses, msg); err != nil {
		return gtserror.SetSMTP(err)
	}

	return nil
}

func loadTemplates(templateBaseDir string) (*template.Template, error) {
	if !filepath.IsAbs(templateBaseDir) {
		cwd, err := os.Getwd()
		if err != nil {
			return nil, fmt.Errorf("error getting current working directory: %s", err)
		}
		templateBaseDir = filepath.Join(cwd, templateBaseDir)
	}

	// look for all templates that start with 'email_'
	return template.ParseGlob(filepath.Join(templateBaseDir, "email_*"))
}

// assembleMessage assembles a valid email message following:
//   - https://datatracker.ietf.org/doc/html/rfc2822
//   - https://pkg.go.dev/net/smtp#SendMail
func assembleMessage(mailSubject string, mailBody string, mailFrom string, mailTo ...string) ([]byte, error) {
	if strings.ContainsAny(mailSubject, "\r\n") {
		return nil, errors.New("email subject must not contain newline characters")
	}

	if strings.ContainsAny(mailFrom, "\r\n") {
		return nil, errors.New("email from address must not contain newline characters")
	}

	for _, to := range mailTo {
		if strings.ContainsAny(to, "\r\n") {
			return nil, errors.New("email to address must not contain newline characters")
		}
	}

	// Normalize the message body to use CRLF line endings
	const CRLF = "\r\n"
	mailBody = strings.ReplaceAll(mailBody, CRLF, "\n")
	mailBody = strings.ReplaceAll(mailBody, "\n", CRLF)

	msg := bytes.Buffer{}
	switch {
	case len(mailTo) == 1:
		// Address email directly to the one recipient.
		msg.WriteString("To: " + mailTo[0] + CRLF)
	case config.GetSMTPDiscloseRecipients():
		// Simply address To all recipients.
		msg.WriteString("To: " + strings.Join(mailTo, ", ") + CRLF)
	default:
		// Address To anonymous group.
		//
		// Email will be sent to all recipients but we shouldn't include Bcc header.
		//
		// From the smtp.SendMail function: 'Sending "Bcc" messages is accomplished by
		// including an email address in the to parameter but not including it in the
		// msg headers.'
		msg.WriteString("To: Undisclosed Recipients:;" + CRLF)
	}
	msg.WriteString("From: " + mailFrom + CRLF)
	msg.WriteString("Subject: " + mailSubject + CRLF)
	msg.WriteString(CRLF)
	msg.WriteString(mailBody)
	msg.WriteString(CRLF)

	return msg.Bytes(), nil
}