package server

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"strings"
	"sync"
	"time"
	"tunnel/pkg/netstring"
	"tunnel/pkg/server/env"
)

type Server struct {
	listen net.Listener
	since  time.Time

	wg sync.WaitGroup
	mu sync.Mutex

	once sync.Once
	done chan struct{}

	tunnels automap
	env     env.Env

	nextCid int
}

type client struct {
	id int

	s *Server

	conn net.Conn
	r    *netstring.Decoder
	w    *netstring.Encoder

	nextRid int
}

type request struct {
	id int

	c *client

	cmd *cmd

	argc int
	args []string

	fail bool

	out bytes.Buffer
}

type requestError string

var errNotImplemented = errors.New("not implemented")

func (c *client) String() string {
	return fmt.Sprintf("client:%d", c.id)
}

func (r *request) String() string {
	return fmt.Sprintf("request:%d", r.id)
}

func (r *request) Write(p []byte) (int, error) {
	return r.out.Write(p)
}

func (r *request) Print(v ...interface{}) {
	fmt.Fprint(&r.out, v...)
}

func (r *request) Printf(format string, v ...interface{}) {
	fmt.Fprintf(&r.out, format, v...)
}

func (r *request) Println(v ...interface{}) {
	fmt.Fprintln(&r.out, v...)
}

func (r *request) Fatal(v ...interface{}) {
	panic(requestError(fmt.Sprint(v...)))
}

func (r *request) Fatalf(format string, v ...interface{}) {
	panic(requestError(fmt.Sprintf(format, v...)))
}

func (r *request) expect(c ...int) {
	desc := func(n int) string {
		var sep string

		if n == 1 {
			sep = " is "
		} else {
			sep = " are "
		}

		return fmt.Sprint(n, sep, "expected")
	}

	check := func(cond bool, args ...interface{}) {
		if cond {
			r.Fatal(args...)
		}
	}

	switch len(c) {
	case 0:
		check(r.argc > 0, "args are not expected")
	case 1:
		check(r.argc < c[0], "not enough args: ", desc(c[0]))
		check(r.argc > c[0], "too many args: ", desc(c[0]))
	case 2:
		check(r.argc < c[0], "not enough args: at least ", desc(c[0]))
		check(r.argc > c[1], "too many args: no more than ", desc(c[1]))
	}
}

func (s *Server) isDone() bool {
	select {
	case <-s.done:
		return true
	default:
		return false
	}
}

func New(path string) (*Server, error) {
	listen, err := net.Listen("unix", path)
	if err != nil {
		return nil, err
	}

	log.Println("listen at", path)

	s := &Server{
		env:     env.New(),
		listen:  listen,
		since:   time.Now(),
		done:    make(chan struct{}),
		tunnels: make(automap),
	}

	return s, nil
}

func (s *Server) Env() env.Env {
	return s.env
}

func (s *Server) Socket() string {
	return s.listen.Addr().String()
}

func (s *Server) Run() {
	for {
		conn, err := s.listen.Accept()
		if err != nil {
			if s.isDone() {
				break
			}

			log.Print(err)
			continue
		}

		c := s.newClient(conn)

		log.Println(c, "accept")

		s.wg.Add(1)

		go c.handle()
	}

	s.wg.Wait()
}

func (s *Server) Stop() {
	s.once.Do(func() {
		close(s.done)
		s.listen.Close()
	})
}

func (s *Server) newClient(conn net.Conn) *client {
	c := &client{
		s:    s,
		conn: conn,
		r:    netstring.NewDecoder(conn),
		w:    netstring.NewEncoder(conn),
		id:   s.nextCid,
	}

	s.nextCid++

	return c
}

func (s *Server) Command(query string) error {
	args := strings.Split(query, " ")

	r := &request{c: &client{s: s}}

	r.run(args)

	if r.fail {
		if r.out.Len() == 0 {
			return errors.New("failed")
		}

		return errors.New(r.out.String())
	}

	return nil
}

func (c *client) newRequest() *request {
	r := &request{
		c:  c,
		id: c.nextRid,
	}

	c.nextRid++

	return r
}

func (c *client) handle() {
	defer c.close()

	for {
		req, er := c.r.Decode()
		if er != nil {
			if !errors.Is(er, io.EOF) {
				log.Println(c, "handle:", er)
			}
			break
		}

		args, err := c.decode([]byte(req))
		if err != nil {
			log.Println(c, "decode:", err)
			break
		}

		r := c.newRequest()

		r.run(args)

		if r.out.Len() == 0 {
			r.out.Write([]byte("\n"))
		}

		ew := c.w.Encode(r.out.String())
		if ew != nil {
			log.Println(c, "handle:", ew)
			break
		}
	}
}

func (c *client) decode(b []byte) ([]string, error) {
	dec := netstring.NewDecoder(bytes.NewReader(b))
	var t []string

	for {
		if s, err := dec.Decode(); err == nil {
			t = append(t, s)
		} else {
			if !errors.Is(err, io.EOF) {
				return nil, err
			}

			break
		}
	}

	return t, nil
}

func (r *request) eval(args []string) []string {
	var out []string

	for _, s := range args {
		var t string

		if strings.HasPrefix(s, ":") {
			t = s[1:]
		} else {
			t = r.c.s.env.Eval(s)
		}

		out = append(out, t)
	}

	return out
}

func (r *request) parse(args []string) {
	if c, args := getCmd(r.eval(args)); c == nil {
		r.Fatal("command not found")
	} else {
		r.args = args
		r.argc = len(args)
		r.cmd = c
	}
}

func (r *request) run(args []string) {
	defer func() {
		switch err := recover().(type) {
		case requestError:
			r.Print(err)
			r.fail = true
		default:
			panic(err)
		case nil:
		}
	}()

	log.Println(r.c, r, ">", strings.Join(args, " "))

	r.parse(args)

	r.c.s.mu.Lock()
	defer r.c.s.mu.Unlock()

	r.cmd.f(r)
}

func (c *client) close() {
	log.Println(c, "close")

	c.conn.Close()
	c.s.wg.Done()
}