package main

import (
	"bytes"
	"crypto/tls"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"net/smtp"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type Mailer struct {
	Host     string `json:"host"`
	Port     int    `json:"port"`
	User     string `json:"user"`
	Password string `json:"password"`
	From     string `json:"from"`
	StartTLS bool   `json:"starttls"`
	Insecure bool   `json:"insecure"`
	API      string `json:"api"`
	Key      string `json:"key"`
}

func loadMailer(root string) *Mailer {
	b, err := os.ReadFile(filepath.Join(root, "smtp.json"))
	if err != nil {
		return nil
	}
	var m Mailer
	if json.Unmarshal(b, &m) != nil || (m.Host == "" && m.API == "") || m.From == "" {
		return nil
	}
	if m.Port == 0 {
		m.Port = 465
	}
	return &m
}

func (m *Mailer) Send(to, subject, body string) error {
	if m == nil {
		return errors.New("mail is not configured")
	}
	if m.API != "" {
		return m.post(to, subject, body)
	}
	addr := net.JoinHostPort(m.Host, fmt.Sprint(m.Port))
	tlsConfig := &tls.Config{ServerName: m.Host, InsecureSkipVerify: m.Insecure}
	var client *smtp.Client
	var err error
	if m.StartTLS {
		client, err = smtp.Dial(addr)
		if err == nil {
			err = client.StartTLS(tlsConfig)
		}
	} else if m.Insecure && m.Port != 465 {
		client, err = smtp.Dial(addr)
	} else {
		var conn net.Conn
		conn, err = tls.DialWithDialer(&net.Dialer{Timeout: 15 * time.Second}, "tcp", addr, tlsConfig)
		if err == nil {
			client, err = smtp.NewClient(conn, m.Host)
		}
	}
	if err != nil {
		return err
	}
	defer client.Close()
	if m.User != "" {
		if err := client.Auth(smtp.PlainAuth("", m.User, m.Password, m.Host)); err != nil {
			return err
		}
	}
	if err := client.Mail(m.From); err != nil {
		return err
	}
	if err := client.Rcpt(to); err != nil {
		return err
	}
	w, err := client.Data()
	if err != nil {
		return err
	}
	msg := fmt.Sprintf("From: %s\r\nTo: %s\r\nSubject: %s\r\nDate: %s\r\nMessage-ID: <%d.%s>\r\nMIME-Version: 1.0\r\nContent-Type: text/plain; charset=utf-8\r\n\r\n%s\r\n",
		m.From, to, headerText(subject), time.Now().Format(time.RFC1123Z), time.Now().UnixNano(), m.domain(), body)
	if _, err := w.Write([]byte(msg)); err != nil {
		return err
	}
	if err := w.Close(); err != nil {
		return err
	}
	return client.Quit()
}

func (s *Server) notify(to, subject, body string) {
	if to == "" || s.mailer == nil {
		return
	}
	go func() {
		if err := s.mailer.Send(to, subject, body); err != nil {
			log.Printf("mail to %s: %v", to, err)
		}
	}()
}

func (m *Mailer) domain() string {
	from := m.From
	if i := strings.LastIndex(from, "<"); i >= 0 {
		from = strings.TrimSuffix(from[i+1:], ">")
	}
	_, d, _ := strings.Cut(from, "@")
	return d
}

func (m *Mailer) post(to, subject, body string) error {
	payload, _ := json.Marshal(map[string]any{"from": m.From, "to": []string{to}, "subject": headerText(subject), "text": body})
	req, err := http.NewRequest("POST", m.API, bytes.NewReader(payload))
	if err != nil {
		return err
	}
	req.Header.Set("Authorization", "Bearer "+m.Key)
	req.Header.Set("Content-Type", "application/json")
	resp, err := (&http.Client{Timeout: 20 * time.Second}).Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode/100 != 2 {
		msg, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
		return fmt.Errorf("mail api: %s: %s", resp.Status, strings.TrimSpace(string(msg)))
	}
	return nil
}

func headerText(s string) string {
	return strings.Map(func(r rune) rune {
		if r < 0x20 || r == 0x7f {
			return ' '
		}
		return r
	}, s)
}