package infra

import (
	"crypto/tls"
	"fmt"
	"net"
	"net/smtp"
	"strings"
)

// SMTPMailConfig SMTP 发信参数
type SMTPMailConfig struct {
	Host      string
	Port      int
	User      string
	Password  string
	FromEmail string
	FromName  string
}

// SendSMTPMail 通过 SMTP 发送纯文本邮件（支持 465 SSL / 587 STARTTLS）
func SendSMTPMail(cfg SMTPMailConfig, to, subject, body string) error {
	if cfg.Host == "" || cfg.FromEmail == "" {
		return fmt.Errorf("SMTP 未配置完整")
	}
	to = strings.TrimSpace(to)
	if to == "" {
		return fmt.Errorf("收件人邮箱为空")
	}
	port := cfg.Port
	if port <= 0 {
		port = 465
	}

	from := cfg.FromEmail
	fromHeader := from
	if cfg.FromName != "" {
		fromHeader = fmt.Sprintf("%s <%s>", cfg.FromName, from)
	}

	msg := buildPlainTextMessage(fromHeader, to, subject, body)
	addr := fmt.Sprintf("%s:%d", cfg.Host, port)

	if port == 465 {
		return sendSMTPSImplicitTLS(addr, cfg, from, to, msg)
	}
	return sendSMTPStartTLS(addr, cfg, from, to, msg)
}

func buildPlainTextMessage(from, to, subject, body string) []byte {
	var b strings.Builder
	b.WriteString("From: " + from + "\r\n")
	b.WriteString("To: " + to + "\r\n")
	b.WriteString("Subject: " + subject + "\r\n")
	b.WriteString("MIME-Version: 1.0\r\n")
	b.WriteString("Content-Type: text/plain; charset=UTF-8\r\n")
	b.WriteString("\r\n")
	b.WriteString(body)
	return []byte(b.String())
}

func sendSMTPSImplicitTLS(addr string, cfg SMTPMailConfig, from, to string, msg []byte) error {
	tlsCfg := &tls.Config{ServerName: cfg.Host}
	conn, err := tls.Dial("tcp", addr, tlsCfg)
	if err != nil {
		return fmt.Errorf("连接 SMTP 失败: %w", err)
	}
	defer conn.Close()

	client, err := smtp.NewClient(conn, cfg.Host)
	if err != nil {
		return fmt.Errorf("创建 SMTP 客户端失败: %w", err)
	}
	defer client.Close()

	if cfg.User != "" {
		if err := client.Auth(smtp.PlainAuth("", cfg.User, cfg.Password, cfg.Host)); err != nil {
			return fmt.Errorf("SMTP 认证失败: %w", err)
		}
	}
	if err := client.Mail(from); err != nil {
		return fmt.Errorf("设置发件人失败: %w", err)
	}
	if err := client.Rcpt(to); err != nil {
		return fmt.Errorf("设置收件人失败: %w", err)
	}
	w, err := client.Data()
	if err != nil {
		return fmt.Errorf("打开邮件正文失败: %w", err)
	}
	if _, err := w.Write(msg); err != nil {
		return fmt.Errorf("写入邮件正文失败: %w", err)
	}
	if err := w.Close(); err != nil {
		return fmt.Errorf("关闭邮件正文失败: %w", err)
	}
	return client.Quit()
}

func sendSMTPStartTLS(addr string, cfg SMTPMailConfig, from, to string, msg []byte) error {
	conn, err := net.Dial("tcp", addr)
	if err != nil {
		return fmt.Errorf("连接 SMTP 失败: %w", err)
	}
	defer conn.Close()

	host := cfg.Host
	client, err := smtp.NewClient(conn, host)
	if err != nil {
		return fmt.Errorf("创建 SMTP 客户端失败: %w", err)
	}
	defer client.Close()

	if ok, _ := client.Extension("STARTTLS"); ok {
		if err := client.StartTLS(&tls.Config{ServerName: host}); err != nil {
			return fmt.Errorf("STARTTLS 失败: %w", err)
		}
	}
	if cfg.User != "" {
		if err := client.Auth(smtp.PlainAuth("", cfg.User, cfg.Password, host)); err != nil {
			return fmt.Errorf("SMTP 认证失败: %w", err)
		}
	}
	if err := client.Mail(from); err != nil {
		return fmt.Errorf("设置发件人失败: %w", err)
	}
	if err := client.Rcpt(to); err != nil {
		return fmt.Errorf("设置收件人失败: %w", err)
	}
	w, err := client.Data()
	if err != nil {
		return fmt.Errorf("打开邮件正文失败: %w", err)
	}
	if _, err := w.Write(msg); err != nil {
		return fmt.Errorf("写入邮件正文失败: %w", err)
	}
	if err := w.Close(); err != nil {
		return fmt.Errorf("关闭邮件正文失败: %w", err)
	}
	return client.Quit()
}