// Copyright 2025 linux.do
// Copyright 2026 Arctel.net
// SPDX-License-Identifier: Apache-2.0

package mail

import (
	"bytes"
	"context"
	"crypto/tls"
	"fmt"
	"net"
	"net/smtp"
	"strconv"
	"time"
)

const (
	smtpSSLPort         = 465              // SMTP SSL 端口
	smtpDialTimeout     = 5 * time.Second  // SMTP 连接超时
	smtpSessionDeadline = 10 * time.Second // SMTP 会话截止时间
)

// Config represents SMTP mail configuration
type Config struct {
	Host     string
	Port     int
	Username string
	Password string
}

// SendMail sends an HTML email using the provided config and message details
func SendMail(ctx context.Context, cfg Config, to string, subject, body string) error {
	return SendMailHTML(ctx, cfg, to, subject, body)
}

// SendMailHTML sends an HTML format email
func SendMailHTML(ctx context.Context, cfg Config, to string, subject, body string) error {
	addr := net.JoinHostPort(cfg.Host, strconv.Itoa(cfg.Port))

	// Header & MIME settings for HTML email
	header := make(map[string]string)
	header["From"] = cfg.Username
	header["To"] = to
	header["Subject"] = subject
	header["MIME-Version"] = "1.0"
	header["Content-Type"] = "text/html; charset=UTF-8"

	message := ""
	for k, v := range header {
		message += fmt.Sprintf("%s: %s\r\n", k, v)
	}
	message += "\r\n" + body

	auth := smtp.PlainAuth("", cfg.Username, cfg.Password, cfg.Host)

	// If using SSL port 465, we connection via TLS dial
	if cfg.Port == smtpSSLPort {
		return sendMailViaSSL(ctx, addr, auth, cfg, to, message)
	}

	// For standard port (587 / 25), use smtp.SendMail directly (handles STARTTLS automatically if server supports it)
	err := smtp.SendMail(addr, auth, cfg.Username, []string{to}, []byte(message))
	if err != nil {
		return fmt.Errorf(errSendMailFailed, err)
	}

	return nil
}

// sendMailViaSSL 通过 TLS 直接连接 SMTP SSL 端口发送邮件
func sendMailViaSSL(ctx context.Context, addr string, auth smtp.Auth, cfg Config, to, message string) error {
	tlsConfig := &tls.Config{
		InsecureSkipVerify: true, //nolint:gosec // SMTP servers might use self-signed certificates
		ServerName:         cfg.Host,
	}
	dialer := &net.Dialer{Timeout: smtpDialTimeout}
	tlsDialer := &tls.Dialer{
		NetDialer: dialer,
		Config:    tlsConfig,
	}
	conn, err := tlsDialer.DialContext(ctx, "tcp", addr)
	if err != nil {
		return fmt.Errorf(errDialTLSFailed, err)
	}
	defer func() { _ = conn.Close() }()
	_ = conn.SetDeadline(time.Now().Add(smtpSessionDeadline))

	client, err := smtp.NewClient(conn, cfg.Host)
	if err != nil {
		return fmt.Errorf(errSMTPClientCreationFailed, err)
	}
	defer func() { _ = client.Close() }()

	if err = client.Auth(auth); err != nil {
		return fmt.Errorf(errSMTPAuthFailed, err)
	}
	if err = client.Mail(cfg.Username); err != nil {
		return fmt.Errorf(errSMTPMailCommandFailed, err)
	}
	if err = client.Rcpt(to); err != nil {
		return fmt.Errorf(errSMTPRcptCommandFailed, err)
	}

	w, err := client.Data()
	if err != nil {
		return fmt.Errorf(errSMTPDataCommandFailed, err)
	}
	defer func() { _ = w.Close() }()

	_, err = w.Write([]byte(message))
	if err != nil {
		return fmt.Errorf(errSMTPWritingBodyFailed, err)
	}
	return nil
}

// SendMailWithLog sends a test email and records a detailed SMTP connection log
func SendMailWithLog(ctx context.Context, cfg Config, to string, subject, body string) (string, error) {
	var logBuf bytes.Buffer
	logLine := func(dir string, format string, args ...interface{}) {
		fmt.Fprintf(&logBuf, "[%s] %s\n", dir, fmt.Sprintf(format, args...))
	}

	addr := net.JoinHostPort(cfg.Host, strconv.Itoa(cfg.Port))
	logLine("System", "Connecting to %s...", addr)

	var conn net.Conn
	var err error
	dialer := &net.Dialer{Timeout: smtpDialTimeout}
	if cfg.Port == smtpSSLPort {
		tlsConfig := &tls.Config{
			InsecureSkipVerify: true, //nolint:gosec // SMTP servers might use self-signed certificates
			ServerName:         cfg.Host,
		}
		tlsDialer := &tls.Dialer{
			NetDialer: dialer,
			Config:    tlsConfig,
		}
		conn, err = tlsDialer.DialContext(ctx, "tcp", addr)
	} else {
		conn, err = dialer.DialContext(ctx, "tcp", addr)
	}
	if err != nil {
		logLine("Error", "Connection failed: %v", err)
		return logBuf.String(), err
	}
	defer func() { _ = conn.Close() }()
	logLine("System", "Connected successfully.")

	// Set a 10-second session deadline for read/write operations
	_ = conn.SetDeadline(time.Now().Add(smtpSessionDeadline))

	client, err := smtp.NewClient(conn, cfg.Host)
	if err != nil {
		logLine("Error", "SMTP client handshake failed: %v", err)
		return logBuf.String(), err
	}
	defer func() { _ = client.Close() }()

	// If not 465, support STARTTLS if available
	if cfg.Port != smtpSSLPort {
		if ok, _ := client.Extension("STARTTLS"); ok {
			logLine("C", "STARTTLS")
			tlsConfig := &tls.Config{
				InsecureSkipVerify: true, //nolint:gosec // SMTP servers might use self-signed certificates
				ServerName:         cfg.Host,
			}
			if err = client.StartTLS(tlsConfig); err != nil {
				logLine("Error", "STARTTLS failed: %v", err)
				return logBuf.String(), err
			}
			logLine("S", "220 Ready to start TLS")
		}
	}

	// Authentication
	if cfg.Username != "" && cfg.Password != "" {
		auth := smtp.PlainAuth("", cfg.Username, cfg.Password, cfg.Host)
		logLine("C", "AUTH PLAIN **********")
		if err = client.Auth(auth); err != nil {
			logLine("Error", "Authentication failed: %v", err)
			return logBuf.String(), err
		}
		logLine("S", "235 Authentication successful")
	}

	// Mail command
	logLine("C", "MAIL FROM:<%s>", cfg.Username)
	if err = client.Mail(cfg.Username); err != nil {
		logLine("Error", "MAIL FROM command failed: %v", err)
		return logBuf.String(), err
	}
	logLine("S", "250 OK")

	// Rcpt command
	logLine("C", "RCPT TO:<%s>", to)
	if err = client.Rcpt(to); err != nil {
		logLine("Error", "RCPT TO command failed: %v", err)
		return logBuf.String(), err
	}
	logLine("S", "250 OK")

	// Data command
	logLine("C", "DATA")
	w, err := client.Data()
	if err != nil {
		logLine("Error", "DATA command failed: %v", err)
		return logBuf.String(), err
	}
	logLine("S", "354 Start mail input")

	// Header & MIME settings for HTML email
	header := make(map[string]string)
	header["From"] = cfg.Username
	header["To"] = to
	header["Subject"] = subject
	header["MIME-Version"] = "1.0"
	header["Content-Type"] = "text/html; charset=UTF-8"

	message := ""
	for k, v := range header {
		message += fmt.Sprintf("%s: %s\r\n", k, v)
	}
	message += "\r\n" + body

	logLine("System", "Sending message body...")
	if _, err = w.Write([]byte(message)); err != nil {
		_ = w.Close()
		logLine("Error", "Writing message body failed: %v", err)
		return logBuf.String(), err
	}
	_ = w.Close()
	logLine("S", "250 OK")

	logLine("C", "QUIT")
	_ = client.Quit()
	logLine("System", "Mail sent successfully!")

	return logBuf.String(), nil
}