package main

import (
	"bufio"
	"encoding/base64"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/kardianos/service"
)

type Config struct {
	ListenAddress  string `json:"listen_address"`
	ListenPort     int    `json:"listen_port"`
	StorageDir     string `json:"storage_dir"`
	DomainName     string `json:"domain_name"`
	MaxMessageSize int64  `json:"max_message_size"`
	EnableAuth     bool   `json:"enable_auth"`
}

type SMTPState struct {
	heloName         string
	from             string
	to               []string
	authenticated    bool
	mailFromReceived bool
	authType         string
	authStep         int // for LOGIN: 0=waiting username, 1=waiting password
}

type FakeSMTPServer struct {
	config Config
	logger service.Logger
}

type Program struct {
	server *FakeSMTPServer
}

func getExecutableDir() (string, error) {
	exe, err := os.Executable()
	if err != nil {
		return "", err
	}
	return filepath.Dir(exe), nil
}

func loadConfig(configPath string) (Config, error) {
	var cfg Config
	data, err := os.ReadFile(configPath)
	if err != nil {
		if os.IsNotExist(err) {
			cfg = Config{
				ListenAddress:  "0.0.0.0",
				ListenPort:     25,
				StorageDir:     "emails",
				DomainName:     "m.ric930.ru",
				MaxMessageSize: 50 * 1024 * 1024, // 50MB
				EnableAuth:     true,
			}
			cfgData, _ := json.MarshalIndent(cfg, "", "  ")
			os.WriteFile(configPath, cfgData, 0644)
			log.Printf("Created default config at %s", configPath)
			return cfg, nil
		}
		return cfg, err
	}
	err = json.Unmarshal(data, &cfg)
	return cfg, err
}

func (s *FakeSMTPServer) ensureStorageDir() error {
	return os.MkdirAll(s.config.StorageDir, 0755)
}

func (s *FakeSMTPServer) getEmailFilePath(from string, to []string, receivedTime time.Time) (string, error) {
	yearMonthDay := receivedTime.Format("2006-01-02")
	dir := filepath.Join(s.config.StorageDir, yearMonthDay)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return "", err
	}

	fromClean := strings.ReplaceAll(from, "<", "")
	fromClean = strings.ReplaceAll(fromClean, ">", "")
	fromClean = strings.ReplaceAll(fromClean, "@", "_")
	if len(fromClean) > 30 {
		fromClean = fromClean[:30]
	}

	timestamp := receivedTime.Format("20060102_150405")
	filename := fmt.Sprintf("%s_%s.eml", timestamp, fromClean)
	return filepath.Join(dir, filename), nil
}

func (s *FakeSMTPServer) saveEmail(from string, to []string, data []byte, receivedTime time.Time) error {
	filePath, err := s.getEmailFilePath(from, to, receivedTime)
	if err != nil {
		return err
	}

	receivedHeader := fmt.Sprintf("Received: from %s\r\n\tby %s (ric930-fake-smtp)\r\n\tfor <%s>;\r\n\t%s\r\n",
		s.config.DomainName, s.config.DomainName, strings.Join(to, ","), receivedTime.Format(time.RFC1123Z))

	finalData := []byte(receivedHeader + string(data))
	return os.WriteFile(filePath, finalData, 0644)
}

func (s *FakeSMTPServer) sendReply(writer *bufio.Writer, code int, message string) {
	response := fmt.Sprintf("%d %s\r\n", code, message)
	writer.WriteString(response)
	writer.Flush()
	s.logger.Infof("S: %d %s", code, message)
}

func parseAddress(arg string) (string, error) {
	start := strings.Index(arg, ":")
	if start == -1 {
		return "", fmt.Errorf("invalid address format")
	}

	addr := strings.TrimSpace(arg[start+1:])
	addr = strings.Trim(addr, "<>")

	if !strings.Contains(addr, "@") {
		return "", fmt.Errorf("invalid email address")
	}

	return addr, nil
}

func (s *FakeSMTPServer) handleConnection(conn net.Conn) {
	defer conn.Close()

	state := &SMTPState{
		to:               make([]string, 0),
		authenticated:    !s.config.EnableAuth,
		mailFromReceived: false,
		authStep:         0,
	}

	reader := bufio.NewReader(conn)
	writer := bufio.NewWriter(conn)

	s.sendReply(writer, 220, fmt.Sprintf("%s ESMTP ric930-fake-smtp", s.config.DomainName))

	for {
		line, err := reader.ReadString('\n')
		if err != nil {
			if err != io.EOF {
				s.logger.Warningf("Read error: %v", err)
			}
			break
		}

		line = strings.TrimRight(line, "\r\n")
		if line == "" {
			continue
		}

		s.logger.Infof("C: %s", line)

		var cmd string
		var arg string

		if idx := strings.Index(line, " "); idx != -1 {
			cmd = strings.ToUpper(line[:idx])
			arg = strings.TrimSpace(line[idx+1:])
		} else {
			cmd = strings.ToUpper(line)
			arg = ""
		}

		switch cmd {
		case "EHLO":
			if state.heloName != "" {
				s.sendReply(writer, 503, "Bad sequence")
				continue
			}

			state.heloName = arg

			fmt.Fprintf(writer, "250-%s Hello %s\r\n", s.config.DomainName, arg)
			fmt.Fprintf(writer, "250-PIPELINING\r\n")
			fmt.Fprintf(writer, "250-SIZE %d\r\n", s.config.MaxMessageSize)

			if s.config.EnableAuth {
				// libcurl ожидает именно AUTH PLAIN LOGIN
				fmt.Fprintf(writer, "250-AUTH PLAIN LOGIN\r\n")
			}

			fmt.Fprintf(writer, "250-8BITMIME\r\n")
			fmt.Fprintf(writer, "250 SMTPUTF8\r\n")
			writer.Flush()

		case "HELO":
			if state.heloName != "" {
				s.sendReply(writer, 503, "Bad sequence")
				continue
			}

			state.heloName = arg
			s.sendReply(writer, 250, fmt.Sprintf("%s Hello %s", s.config.DomainName, arg))

		case "AUTH":
			if !s.config.EnableAuth {
				s.logger.Infof("AUTH ignored because enable_auth=false")
				state.authenticated = true
				s.sendReply(writer, 235, "Authentication successful (bypass)")
				continue
			}

			parts := strings.SplitN(arg, " ", 2)
			method := strings.ToUpper(parts[0])

			switch method {
			case "PLAIN":
				var authResp string
				if len(parts) == 2 {
					authResp = parts[1]
				} else {
					s.sendReply(writer, 334, "")
					respLine, err := reader.ReadString('\n')
					if err != nil {
						s.sendReply(writer, 501, "Auth failed")
						continue
					}
					authResp = strings.TrimSpace(respLine)
					s.logger.Infof("C: %s", authResp)
				}

				decoded, err := base64.StdEncoding.DecodeString(authResp)
				if err != nil {
					s.sendReply(writer, 535, "Auth failed")
					continue
				}

				authParts := strings.Split(string(decoded), "\x00")
				if len(authParts) >= 3 {
					username := authParts[1]
					password := authParts[2]
					s.logger.Infof("AUTH PLAIN - Username: %s, Password: %s", username, password)
				}

				state.authenticated = true
				s.sendReply(writer, 235, "Authentication successful")

			case "LOGIN":
				state.authType = "LOGIN"
				state.authStep = 0
				s.sendReply(writer, 334, "VXNlcm5hbWU6") // "Username:" in base64

				usernameLine, err := reader.ReadString('\n')
				if err != nil {
					s.sendReply(writer, 535, "Auth failed")
					continue
				}
				usernameLine = strings.TrimSpace(usernameLine)
				s.logger.Infof("C: %s", usernameLine)

				usernameBytes, err := base64.StdEncoding.DecodeString(usernameLine)
				if err != nil {
					s.sendReply(writer, 535, "Auth failed")
					continue
				}
				username := string(usernameBytes)

				s.sendReply(writer, 334, "UGFzc3dvcmQ6") // "Password:" in base64

				passwordLine, err := reader.ReadString('\n')
				if err != nil {
					s.sendReply(writer, 535, "Auth failed")
					continue
				}
				passwordLine = strings.TrimSpace(passwordLine)
				s.logger.Infof("C: %s", passwordLine)

				passwordBytes, err := base64.StdEncoding.DecodeString(passwordLine)
				if err != nil {
					s.sendReply(writer, 535, "Auth failed")
					continue
				}
				password := string(passwordBytes)

				s.logger.Infof("AUTH LOGIN - Username: %s, Password: %s (accepted)", username, password)
				state.authenticated = true
				s.sendReply(writer, 235, "Authentication successful")

			default:
				s.sendReply(writer, 504, "Unsupported auth mechanism")
			}

		case "MAIL":
			if !state.authenticated && s.config.EnableAuth {
				s.sendReply(writer, 530, "Authentication required")
				continue
			}

			if !strings.HasPrefix(strings.ToUpper(arg), "FROM:") {
				s.sendReply(writer, 501, "Syntax error")
				continue
			}

			from, err := parseAddress(arg)
			if err != nil {
				s.sendReply(writer, 501, "Invalid address")
				continue
			}

			state.from = from
			state.mailFromReceived = true
			state.to = make([]string, 0)
			s.sendReply(writer, 250, "OK")

		case "RCPT":
			if !state.mailFromReceived {
				s.sendReply(writer, 503, "MAIL FROM required first")
				continue
			}

			if !strings.HasPrefix(strings.ToUpper(arg), "TO:") {
				s.sendReply(writer, 501, "Syntax error")
				continue
			}

			to, err := parseAddress(arg)
			if err != nil {
				s.sendReply(writer, 501, "Invalid address")
				continue
			}

			state.to = append(state.to, to)
			s.sendReply(writer, 250, "OK")

		case "DATA":
			if !state.mailFromReceived || len(state.to) == 0 {
				s.sendReply(writer, 503, "MAIL and RCPT required")
				continue
			}

			s.sendReply(writer, 354, "Start mail input; end with <CRLF>.<CRLF>")

			var messageBody strings.Builder
			var dotEncountered bool

			for {
				line, err := reader.ReadString('\n')
				if err != nil {
					s.logger.Errorf("Error reading body: %v", err)
					break
				}

				if strings.TrimRight(line, "\r\n") == "." {
					dotEncountered = true
					break
				}

				if len(line) > 0 && line[0] == '.' {
					line = line[1:]
				}

				messageBody.WriteString(line)
			}

			if !dotEncountered {
				s.sendReply(writer, 554, "No termination dot")
				continue
			}

			receivedTime := time.Now()
			if err := s.saveEmail(state.from, state.to, []byte(messageBody.String()), receivedTime); err != nil {
				s.logger.Errorf("Save failed: %v", err)
				s.sendReply(writer, 554, "Transaction failed")
			} else {
				s.logger.Infof("Email saved: %d bytes", messageBody.Len())
				// КРИТИЧЕСКИ ВАЖНО для libcurl - отправляем 250
				s.sendReply(writer, 250, "OK: message accepted")
			}

			state.mailFromReceived = false
			state.from = ""
			state.to = make([]string, 0)

		case "RSET":
			state.mailFromReceived = false
			state.from = ""
			state.to = make([]string, 0)
			s.sendReply(writer, 250, "OK")

		case "NOOP":
			s.sendReply(writer, 250, "OK")

		case "QUIT":
			s.sendReply(writer, 221, "Bye")
			return

		default:
			s.sendReply(writer, 502, "Command not implemented")
		}
	}
}

func (s *FakeSMTPServer) Start() error {
	if err := s.ensureStorageDir(); err != nil {
		return err
	}

	addr := fmt.Sprintf("%s:%d", s.config.ListenAddress, s.config.ListenPort)
	listener, err := net.Listen("tcp", addr)
	if err != nil {
		return fmt.Errorf("failed to listen: %v", err)
	}

	s.logger.Infof("SMTP server listening on %s", addr)
	s.logger.Infof("Storage: %s", s.config.StorageDir)
	s.logger.Infof("Auth enabled: %v", s.config.EnableAuth)

	go func() {
		for {
			conn, err := listener.Accept()
			if err != nil {
				s.logger.Errorf("Accept error: %v", err)
				continue
			}
			go s.handleConnection(conn)
		}
	}()

	return nil
}

func (p *Program) Start(s service.Service) error {
	go p.server.Start()
	return nil
}

func (p *Program) Stop(s service.Service) error {
	return nil
}

func main() {
	exeDir, err := getExecutableDir()
	if err != nil {
		log.Printf("Warning: cannot get executable directory: %v, using current directory", err)
		exeDir = "."
	}

	defaultConfigPath := filepath.Join(exeDir, "config.json")
	configPath := flag.String("config", defaultConfigPath, "Path to config file")
	flag.Parse()

	finalConfigPath := *configPath
	if !filepath.IsAbs(finalConfigPath) {
		finalConfigPath = filepath.Join(exeDir, finalConfigPath)
	}

	cfg, err := loadConfig(finalConfigPath)
	if err != nil {
		log.Fatalf("Failed to load config: %v", err)
	}

	if !filepath.IsAbs(cfg.StorageDir) {
		cfg.StorageDir = filepath.Join(exeDir, cfg.StorageDir)
	}

	svcConfig := &service.Config{
		Name:        "ric930-fake-smtp",
		DisplayName: "Ric930 Fake SMTP Server",
		Description: "RIC930 Fake SMTP server for Consultant IV",
	}

	server := &FakeSMTPServer{config: cfg}
	prg := &Program{server: server}

	s, err := service.New(prg, svcConfig)
	if err != nil {
		log.Fatal(err)
	}

	logger, err := s.Logger(nil)
	if err != nil {
		log.Fatal(err)
	}
	server.logger = logger

	if len(os.Args) > 1 {
		service.Control(s, os.Args[1])
		return
	}

	s.Run()
}