package email

import (
	"context"
	"crypto/tls"
	"fmt"
	"math/rand"
	"net"
	"net/smtp"
	"time"

	"cloudnest/internal/config"
	"cloudnest/internal/infrastructure/database"
	"cloudnest/internal/pkg/logger"
)

// EmailService provides email sending and verification code management.
// EmailService 提供邮件发送和验证码管理功能。
type EmailService struct {
	cfg   *config.EmailConfig
	redis *database.RedisClient
}

// NewEmailService creates a new EmailService.
// NewEmailService 创建一个新的 EmailService。
func NewEmailService(cfg *config.EmailConfig, redis *database.RedisClient) *EmailService {
	return &EmailService{cfg: cfg, redis: redis}
}

// SendVerifyCode generates a 6-digit verification code, sends it via email, and stores it in Redis.
// SendVerifyCode 生成6位数字验证码，通过邮件发送，并存入 Redis。
//
// Returns:
//   - code: The generated verification code.
//   - err: Any error that occurred.
func (s *EmailService) SendVerifyCode(toEmail string) (code string, err error) {
	if s.cfg.SMTPUsername == "" {
		return "", fmt.Errorf("邮件服务未配置")
	}

	code = generateCode(6)
	subject := "CloudNest 邮箱验证码"
	body := fmt.Sprintf("您的验证码是：%s，有效期10分钟，请勿泄露给他人。", code)

	if err = s.sendMail(toEmail, subject, body); err != nil {
		logger.Error("failed to send email", "error", err, "to", toEmail)
		return "", err
	}

	ctx := context.Background()
	key := fmt.Sprintf("email_code:%s", toEmail)
	if err = s.redis.Client.Set(ctx, key, code, 10*time.Minute).Err(); err != nil {
		return "", err
	}

	return code, nil
}

// VerifyCode checks the email verification code and deletes it from Redis on success.
// VerifyCode 检查邮箱验证码，成功时从 Redis 中删除。
func (s *EmailService) VerifyCode(email, code string) bool {
	ctx := context.Background()
	key := fmt.Sprintf("email_code:%s", email)
	val, err := s.redis.Client.Get(ctx, key).Result()
	if err != nil {
		return false
	}
	if val != code {
		return false
	}
	s.redis.Client.Del(ctx, key)
	return true
}

func generateCode(length int) string {
	b := make([]byte, length)
	for i := range b {
		b[i] = byte(rand.Intn(10)) + '0'
	}
	return string(b)
}

func (s *EmailService) sendMail(to, subject, body string) error {
	from := s.cfg.SMTPUsername
	addr := fmt.Sprintf("%s:%d", s.cfg.SMTPHost, s.cfg.SMTPPort)

	msg := []byte(fmt.Sprintf("To: %s\r\nFrom: %s <%s>\r\nSubject: %s\r\nContent-Type: text/plain; charset=UTF-8\r\n\r\n%s",
		to, s.cfg.FromName, from, subject, body))

	if s.cfg.SMTPPort == 587 {
		return sendMailSTARTTLS(addr, s.cfg.SMTPHost, from, s.cfg.SMTPPassword, []string{to}, msg)
	}

	auth := smtp.PlainAuth("", from, s.cfg.SMTPPassword, s.cfg.SMTPHost)
	return smtp.SendMail(addr, auth, from, []string{to}, msg)
}

func sendMailSTARTTLS(addr, host, from, password string, to []string, msg []byte) error {
	conn, err := net.Dial("tcp", addr)
	if err != nil {
		return err
	}
	defer conn.Close()

	client, err := smtp.NewClient(conn, host)
	if err != nil {
		return err
	}
	defer client.Close()

	tlsConfig := &tls.Config{ServerName: host}
	if err := client.StartTLS(tlsConfig); err != nil {
		return err
	}

	auth := smtp.PlainAuth("", from, password, host)
	if err := client.Auth(auth); err != nil {
		return err
	}

	if err := client.Mail(from); err != nil {
		return err
	}
	for _, addr := range to {
		if err := client.Rcpt(addr); err != nil {
			return err
		}
	}

	w, err := client.Data()
	if err != nil {
		return err
	}
	_, err = w.Write(msg)
	if err != nil {
		return err
	}
	err = w.Close()
	if err != nil {
		return err
	}

	return client.Quit()
}