package notify

import (
	"context"
	"crypto/tls"
	"fmt"
	"log"
	"net/smtp"
	"os"
	"strconv"
	"strings"
)

type Message struct {
	To      []string
	Subject string
	Body    string
}

type Sender interface {
	Send(context.Context, Message) error
}

type SMTP struct {
	Host     string
	Port     int
	Username string
	Password string
	From     string
	TLS      bool
}

type LogSender struct {
	Logger *log.Logger
}

func NewFromEnv(logger *log.Logger) Sender {
	host := strings.TrimSpace(os.Getenv("SCOUT_SMTP_HOST"))
	if host == "" {
		return LogSender{Logger: logger}
	}
	port, err := strconv.Atoi(envOr("SCOUT_SMTP_PORT", "587"))
	if err != nil || port <= 0 || port > 65535 {
		port = 587
	}
	return SMTP{
		Host:     host,
		Port:     port,
		Username: os.Getenv("SCOUT_SMTP_USERNAME"),
		Password: os.Getenv("SCOUT_SMTP_PASSWORD"),
		From:     envOr("SCOUT_SMTP_FROM", os.Getenv("SCOUT_SMTP_USERNAME")),
		TLS:      strings.EqualFold(os.Getenv("SCOUT_SMTP_TLS"), "true"),
	}
}

func (sender LogSender) Send(_ context.Context, message Message) error {
	if sender.Logger != nil {
		sender.Logger.Printf("邮箱通知未配置 SMTP，记录待发送邮件：收件人=%s，主题=%s", strings.Join(message.To, ","), message.Subject)
	}
	return nil
}

func (sender SMTP) Send(ctx context.Context, message Message) error {
	if len(message.To) == 0 {
		return nil
	}
	if sender.Host == "" || sender.From == "" {
		return fmt.Errorf("SMTP 配置不完整")
	}
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}
	address := fmt.Sprintf("%s:%d", sender.Host, sender.Port)
	headers := []string{
		"From: " + sender.From,
		"To: " + strings.Join(message.To, ", "),
		"Subject: " + message.Subject,
		"MIME-Version: 1.0",
		"Content-Type: text/plain; charset=UTF-8",
	}
	data := []byte(strings.Join(headers, "\r\n") + "\r\n\r\n" + message.Body)
	if sender.TLS {
		connection, err := tls.Dial("tcp", address, &tls.Config{ServerName: sender.Host, MinVersion: tls.VersionTLS12})
		if err != nil {
			return fmt.Errorf("连接 SMTP TLS 服务失败: %w", err)
		}
		defer connection.Close()
		client, err := smtp.NewClient(connection, sender.Host)
		if err != nil {
			return fmt.Errorf("创建 SMTP 客户端失败: %w", err)
		}
		defer client.Close()
		if sender.Username != "" {
			if err := client.Auth(smtp.PlainAuth("", sender.Username, sender.Password, sender.Host)); err != nil {
				return fmt.Errorf("SMTP 认证失败: %w", err)
			}
		}
		if err := sendWithClient(client, sender.From, message.To, data); err != nil {
			return err
		}
		return client.Quit()
	}
	auth := smtp.PlainAuth("", sender.Username, sender.Password, sender.Host)
	if sender.Username == "" {
		auth = nil
	}
	if err := smtp.SendMail(address, auth, sender.From, message.To, data); err != nil {
		return fmt.Errorf("发送邮件失败: %w", err)
	}
	return nil
}

func sendWithClient(client *smtp.Client, from string, recipients []string, data []byte) error {
	if err := client.Mail(from); err != nil {
		return fmt.Errorf("设置发件人失败: %w", err)
	}
	for _, recipient := range recipients {
		if err := client.Rcpt(recipient); err != nil {
			return fmt.Errorf("设置收件人失败: %w", err)
		}
	}
	writer, err := client.Data()
	if err != nil {
		return fmt.Errorf("打开邮件正文失败: %w", err)
	}
	if _, err := writer.Write(data); err != nil {
		writer.Close()
		return fmt.Errorf("写入邮件正文失败: %w", err)
	}
	if err := writer.Close(); err != nil {
		return fmt.Errorf("关闭邮件正文失败: %w", err)
	}
	return nil
}

func envOr(name, fallback string) string {
	if value := os.Getenv(name); value != "" {
		return value
	}
	return fallback
}