package mailer

import (
	"bytes"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"
	"github.com/emersion/go-message"
	"github.com/emersion/go-sasl"
	"github.com/emersion/go-smtp"
	"io"
	"os"
	"strings"
)

type Mailer struct {
	auth sasl.Client
	conf SmtpConfig
	pool *x509.CertPool
}

func NewMailer(conf SmtpConfig) (*Mailer, error) {
	var pool *x509.CertPool = nil
	if conf.Cert != "" {
		pool = x509.NewCertPool()
		open, err := os.Open(conf.Cert)
		if err != nil {
			return nil, err
		}
		all, err := io.ReadAll(open)
		if err != nil {
			return nil, err
		}
		if !pool.AppendCertsFromPEM(all) {
			return nil, errors.New("invalid SMTP certificate")
		}
	}
	return &Mailer{
		auth: sasl.NewPlainClient("", conf.Username, conf.Password),
		conf: conf,
		pool: pool,
	}, nil
}

func (m *Mailer) MailHtml(subject string, to []string, body io.Reader) error {
	h := message.Header{}
	h.SetContentType("multipart/alternative", nil)
	h.SetText("From", m.conf.From)
	h.SetText("To", strings.Join(to, ", "))
	h.SetText("Subject", subject)
	h.SetText("MIME-version", "1.0")

	msg := new(bytes.Buffer)
	w, err := message.CreateWriter(msg, h)
	if err != nil {
		return fmt.Errorf("failed to create message writer: %w", err)
	}

	h2 := message.Header{}
	h2.SetContentType("text/html", map[string]string{"charset": "UTF-8"})

	part, err := w.CreatePart(h2)
	if err != nil {
		return fmt.Errorf("failed to create part: %w", err)
	}
	_, err = io.Copy(part, body)
	if err != nil {
		return fmt.Errorf("failed to copy body into part: %w", err)
	}
	err = part.Close()
	if err != nil {
		return fmt.Errorf("failed to close part: %w", err)
	}
	err = w.Close()
	if err != nil {
		return fmt.Errorf("failed to close message writer: %w", err)
	}

	return m.sendMail(to, msg)
}

func (m *Mailer) sendMail(to []string, body io.Reader) error {
	var err error
	var client *smtp.Client
	if m.conf.Tls {
		client, err = smtp.DialTLS(m.conf.Server, &tls.Config{RootCAs: m.pool})
		if err != nil {
			return fmt.Errorf("failed to dial tls: %w", err)
		}
	} else {
		client, err = smtp.Dial(m.conf.Server)
		if err != nil {
			return fmt.Errorf("failed to dial: %w", err)
		}
	}
	if m.conf.StartTls {
		if ok, _ := client.Extension("STARTTLS"); ok {
			if err = client.StartTLS(nil); err != nil {
				return fmt.Errorf("failed to start tls: %w", err)
			}
		}
	}
	if err = client.Auth(m.auth); err != nil {
		return fmt.Errorf("failed to add auth: %w", err)
	}
	if err = client.Mail(m.conf.Username, nil); err != nil {
		return fmt.Errorf("failed to start mail: %w", err)
	}
	for _, i := range to {
		if err = client.Rcpt(i); err != nil {
			return fmt.Errorf("failed to add recipient: %w", err)
		}
	}
	wc, err := client.Data()
	if err != nil {
		return fmt.Errorf("failed to start mail data: %w", err)
	}
	if _, err = io.Copy(wc, body); err != nil {
		return fmt.Errorf("failed to : %w", err)
	}
	if err = wc.Close(); err != nil {
		return fmt.Errorf("failed to close: %w", err)
	}
	if err = client.Quit(); err != nil {
		return fmt.Errorf("failed to quit: %w", err)
	}
	return nil
}