package ark

import (
	"bytes"
	"errors"
	"net"
	"regexp"
	"time"
)

// Info is what a server tells the Steam server browser (A2S_INFO).
type Info struct {
	Name       string `json:"name"`
	Map        string `json:"map"`
	Game       string `json:"game"`
	Version    string `json:"version,omitempty"`
	Players    int    `json:"players"`
	MaxPlayers int    `json:"max_players"`
	PingMS     int64  `json:"ping_ms"`
}

var a2sRequest = []byte("\xff\xff\xff\xffTSource Engine Query\x00")

// ARK puts its version in the server name: "My Server - (v349.7)".
var nameVersion = regexp.MustCompile(`\(v(\d+(?:\.\d+)*)\)`)

// Query asks the game's query port (UDP, usually 27015) who is on the server, without needing the
// RCON password.
func Query(addr string, timeout time.Duration) (*Info, error) {
	conn, err := net.Dial("udp", addr)
	if err != nil {
		return nil, err
	}
	defer conn.Close()
	start := time.Now()
	conn.SetDeadline(start.Add(timeout))
	if _, err := conn.Write(a2sRequest); err != nil {
		return nil, err
	}
	buf := make([]byte, 1400)
	n, err := conn.Read(buf)
	if err != nil {
		return nil, err
	}
	if n >= 9 && buf[4] == 0x41 { // challenge: ask again with the number it gave
		req := append(append([]byte{}, a2sRequest...), buf[5:9]...)
		if _, err := conn.Write(req); err != nil {
			return nil, err
		}
		if n, err = conn.Read(buf); err != nil {
			return nil, err
		}
	}
	info, err := parseInfo(buf[:n])
	if err != nil {
		return nil, err
	}
	info.PingMS = time.Since(start).Milliseconds()
	return info, nil
}

func parseInfo(b []byte) (*Info, error) {
	if len(b) < 6 || !bytes.Equal(b[:4], []byte{0xff, 0xff, 0xff, 0xff}) || b[4] != 0x49 {
		return nil, errors.New("not an A2S_INFO reply")
	}
	r := b[6:] // skip the header and the protocol byte
	str := func() string {
		i := bytes.IndexByte(r, 0)
		if i < 0 {
			s := string(r)
			r = nil
			return s
		}
		s := string(r[:i])
		r = r[i+1:]
		return s
	}
	var in Info
	in.Name, in.Map = str(), str()
	str() // folder
	in.Game = str()
	if len(r) < 9 {
		return nil, errors.New("short A2S_INFO reply")
	}
	in.Players, in.MaxPlayers = int(r[2]), int(r[3])
	r = r[9:] // app id (2), players, max, bots, type, environment, visibility, VAC
	in.Version = str()
	if m := nameVersion.FindStringSubmatch(in.Name); m != nil {
		in.Version = m[1]
	}
	return &in, nil
}