package main

import (
	"bufio"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"log/syslog"
	"os"
	"os/exec"
	"os/signal"
	"os/user"
	"path"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"tunnel/pkg/config"
	"tunnel/pkg/server"
)

var BuildVersion string

const trimSize = 32

type programArgs struct {
	debug    bool
	force    bool
	syslog   bool
	output   string
	config   string
	ctlrpath string
	ctlrname string
	version  bool
}

func parseArgs() programArgs {
	var args programArgs
	flag.BoolVar(&args.debug, "d", false, "debug: print time and source info")
	flag.BoolVar(&args.force, "f", false, "try start with force")
	flag.BoolVar(&args.syslog, "syslog", false, "write log to syslog instead of stdout")
	flag.StringVar(&args.output, "o", "", "write log to file instead of stdout")
	flag.StringVar(&args.config, "c", "", "path to configuration file")
	flag.StringVar(&args.ctlrpath, "S", "", "path to control socket")
	flag.StringVar(&args.ctlrname, "s", "", "name of control socket")
	flag.BoolVar(&args.version, "version", false, "print version and exit")

	flag.Parse()
	return args
}

func initLog(args programArgs) {
	if args.output != "" && args.syslog {
		log.Fatal("bad usage: duplicate log write flag")
	}

	if args.debug && args.syslog {
		log.Fatal("bad usage: debug with syslog is out of sense")
	}

	if args.output != "" {
		const fileFlags = os.O_APPEND | os.O_CREATE | os.O_WRONLY

		f, err := os.OpenFile(args.output, fileFlags, 0644)
		if err != nil {
			log.Fatalf("log: %s", err)
		}

		log.SetOutput(f)
	}

	if args.syslog {
		sysLog, err := syslog.New(syslog.LOG_INFO, "tunneld")
		if err != nil {
			log.Fatalf("log: %s", err)
		}

		log.SetOutput(sysLog)
	}

	var logFlags int

	if args.debug {
		logFlags |= log.Ldate | log.Ltime | log.Lshortfile
	}

	if args.output != "" {
		logFlags |= log.Ldate | log.Ltime
	}

	log.SetFlags(logFlags)
}

func sighandler(c chan os.Signal, s *server.Server) {
	var try bool

	for sig := range c {
		if try {
			log.Fatal("force exit")
		}

		log.Printf("catch signal: %s", sig)
		try = true
		s.Stop()
	}
}

func initSignals(s *server.Server) {
	var c = make(chan os.Signal, 1)

	signal.Notify(c, syscall.SIGINT, syscall.SIGTERM)

	go sighandler(c, s)
}

func getSocketPath(args programArgs) string {
	if args.ctlrpath != "" {
		return args.ctlrpath
	}

	s := config.GetSocketPath(args.ctlrname)

	if err := os.Mkdir(path.Dir(s), 0700); err != nil {
		if !errors.Is(err, syscall.EEXIST) {
			log.Fatal(err)
		}
	}

	return s
}

type parser struct {
	s *server.Server
	m map[string]bool
	f []string
}

func newParser(s *server.Server) *parser {
	return &parser{s: s, m: map[string]bool{}}
}

func (p *parser) parse(file string, skip bool) error {
	if p.m[file] {
		log.Printf("skip reading '%s' twice", file)
		return nil
	}

	p.m[file] = true
	p.f = append(p.f, file)

	defer func() {
		p.f = p.f[:len(p.f)-1]
	}()

	log.Println("read config", file)

	fp, err := os.Open(file)
	if err != nil {
		if skip && errors.Is(err, syscall.ENOENT) {
			return nil
		}
		return err
	}

	defer fp.Close()

	return p.read(fp)
}

func (p *parser) read(fp *os.File) error {
	scanner := bufio.NewScanner(fp)

	var args []string
	var line int

	var block bool

	for n := 1; scanner.Scan(); n++ {
		if line == 0 {
			line = n
		}

		parts := strings.SplitN(scanner.Text(), "#", 2)
		s := strings.TrimSpace(parts[0])

		if strings.HasSuffix(s, " --") {
			if block {
				return fmt.Errorf("%s:%d: duplicate block", fp.Name(), n)
			}
			s = s[:len(s)-3]
			block = true
		}

		if s == "--" {
			if !block {
				return fmt.Errorf("%s:%d: no block context", fp.Name(), n)
			}
			block = false
			s = ""
		}

		args = append(args, strings.Fields(s)...)

		if block {
			continue
		}

		t := strings.Join(args, " ")
		if err := p.apply(args); err != nil {
			return fmt.Errorf("%s:%d: %s: %w", fp.Name(), line, t, err)
		}

		args = []string{}
		line = 0
	}

	if len(args) > 0 {
		return fmt.Errorf("%s:%d: unexpected end of file", fp.Name(), line)
	}

	return nil
}

func (p *parser) apply(args []string) error {
	if len(args) == 0 {
		return nil
	}

	if args[0] == "read" {
		if len(args) < 2 {
			return errors.New("argument expected")
		}

		file := args[1]

		if !path.IsAbs(file) {
			now := p.f[len(p.f)-1]
			file = path.Join(path.Dir(now), file)
		}

		return p.parse(file, false)
	}

	return p.s.Command(args)
}

func updateSocketGroup(s *server.Server, group string) error {
	var gid int

	if g, err := user.LookupGroup(group); err != nil {
		return err
	} else {
		var err error

		if gid, err = strconv.Atoi(g.Gid); err != nil {
			return fmt.Errorf("bad group id %s: %w", g.Gid, err)
		}
	}

	f := s.Socket()
	d := path.Dir(f)

	if err := os.Chown(d, -1, gid); err != nil {
		return err
	}

	if err := os.Chmod(d, 0750); err != nil {
		return err
	}

	if err := os.Chown(f, -1, gid); err != nil {
		return err
	}

	if err := os.Chmod(f, 0770); err != nil {
		return err
	}

	return nil
}

func runCommand(s *server.Server, name string) error {
	cmd := s.Env().Value(name)
	if cmd == "" {
		return nil
	}

	log.Printf("cmd \"%s\" try", cmd)

	args := strings.Fields(cmd)
	c := exec.Command(args[0], args[1:]...)

	if env := s.Env().Value("cmd.env"); env != "" {
		c.Env = append(os.Environ(), strings.Split(env, ",")...)
	}

	stdout, _ := c.StdoutPipe()
	stderr, _ := c.StderrPipe()

	if err := c.Start(); err != nil {
		return fmt.Errorf("cmd \"%s\" start failed: %w", cmd, err)
	}

	var wg sync.WaitGroup

	logger := func(s string, r io.Reader) {
		for scanner := bufio.NewScanner(r); scanner.Scan(); {
			log.Println(s, ">", scanner.Text())
		}
		wg.Done()
	}

	wg.Add(2)

	go logger(args[0], stdout)
	go logger(args[0], stderr)

	if err := c.Wait(); err != nil {
		return fmt.Errorf("cmd \"%s\" failed: %w", cmd, err)
	}

	wg.Wait()

	log.Printf("cmd \"%s\" ok", cmd)

	return nil
}

func configure(s *server.Server, args programArgs) error {
	var file string
	var skip bool

	if args.config != "" {
		file = args.config
	} else {
		file = config.GetConfigPath()
		skip = true
	}

	if err := newParser(s).parse(file, skip); err != nil {
		return err
	}

	return postconfigure(s)
}

func postconfigure(s *server.Server) error {
	if group, ok := s.Env().Find("server.socket.group"); ok {
		if err := updateSocketGroup(s, group); err != nil {
			return err
		}
	}

	if err := runCommand(s, "cmd.init"); err != nil {
		return err
	}

	return nil
}

func deconfigure(s *server.Server) error {
	return runCommand(s, "cmd.fini")
}

func main() {
	log.SetFlags(0)

	args := parseArgs()

	if args.version {
		fmt.Fprintln(os.Stderr, BuildVersion)
		os.Exit(1)
	}

	initLog(args)

	if flag.NArg() > 0 {
		log.Fatal("bad usage: extra args")
	}

	socket := getSocketPath(args)
	if args.force {
		if err := os.Remove(socket); err != nil {
			if !errors.Is(err, syscall.ENOENT) {
				log.Fatal(err)
			}
		}
	}

	s, err := server.New(socket, BuildVersion)
	if err != nil {
		log.Fatal(err)
	}

	if err := configure(s, args); err != nil {
		s.Stop()
		log.Fatal(err)
	}

	initSignals(s)

	log.Print("ready")

	s.Serve()

	if err := deconfigure(s); err != nil {
		log.Println(err)
	}

	log.Print("exit")
}