// Command fakeark pretends to be an ARK server's RCON and query ports, so Megalodon can be tried
// (and its dashboard looked at) without a real server. Players come and go, and chat appears.
package main

import (
	"encoding/binary"
	"flag"
	"fmt"
	"io"
	"log"
	"math/rand"
	"net"
	"strings"
	"sync"
	"time"
)

type server struct {
	mu       sync.Mutex
	name     string
	password string
	online   map[string]string // steam id -> name
	chat     []string
	pool     [][2]string
}

func main() {
	rconAddr := flag.String("rcon", "127.0.0.1:27020", "RCON listen address")
	query := flag.String("query", "127.0.0.1:27015", "query (UDP) listen address, empty to disable")
	password := flag.String("password", "secret", "RCON password")
	name := flag.String("name", "Fake Island", "server name")
	flag.Parse()

	s := &server{name: *name, password: *password, online: map[string]string{}}
	for i, n := range []string{"Alex", "Bo", "Casey", "Dana", "Eli", "Fern", "Gus", "Hana"} {
		s.pool = append(s.pool, [2]string{fmt.Sprintf("7656119800000%04d", i+1), n})
	}
	go s.simulate()
	if *query != "" {
		go s.serveQuery(*query)
	}
	ln, err := net.Listen("tcp", *rconAddr)
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("fake ARK server %q: RCON %s (password %q), query %s", *name, *rconAddr, *password, *query)
	for {
		c, err := ln.Accept()
		if err != nil {
			log.Fatal(err)
		}
		go s.handle(c)
	}
}

func (s *server) simulate() {
	lines := []string{"hello everyone", "anyone want to breed rexes?", "my base got raided", "gg", "brb food"}
	for range time.Tick(6 * time.Second) {
		s.mu.Lock()
		p := s.pool[rand.Intn(len(s.pool))]
		if _, on := s.online[p[0]]; on {
			if rand.Intn(2) == 0 {
				delete(s.online, p[0])
			} else {
				s.chat = append(s.chat, fmt.Sprintf("%s (%s the Tamer): %s", p[1], p[1], lines[rand.Intn(len(lines))]))
			}
		} else {
			s.online[p[0]] = p[1]
		}
		s.mu.Unlock()
	}
}

func (s *server) run(cmd string) string {
	s.mu.Lock()
	defer s.mu.Unlock()
	verb, rest, _ := strings.Cut(cmd, " ")
	switch strings.ToLower(verb) {
	case "listplayers":
		if len(s.online) == 0 {
			return "No Players Connected \n"
		}
		var sb strings.Builder
		n := 0
		for id, name := range s.online {
			fmt.Fprintf(&sb, "%d. %s, %s\n", n, name, id)
			n++
		}
		return sb.String()
	case "getchat":
		if len(s.chat) == 0 {
			return "Server received, But no response!!\n"
		}
		out := strings.Join(s.chat, "\n") + "\n"
		s.chat = nil
		return out
	case "saveworld":
		return "World Saved\n"
	case "broadcast", "serverchat":
		if strings.ToLower(verb) == "serverchat" {
			s.chat = append(s.chat, "SERVER: "+rest)
		}
		return "Server received, But no response!!\n"
	case "kickplayer", "banplayer":
		delete(s.online, strings.TrimSpace(rest))
		return fmt.Sprintf("%s %s\n", verb, rest)
	}
	return "Server received, But no response!!\n"
}

func (s *server) handle(c net.Conn) {
	defer c.Close()
	id, typ, body, err := read(c)
	if err != nil || typ != 3 {
		return
	}
	write(c, id, 0, "")
	if body != s.password {
		write(c, -1, 2, "")
		return
	}
	write(c, id, 2, "")
	for {
		id, _, cmd, err := read(c)
		if err != nil {
			return
		}
		write(c, id, 0, s.run(cmd))
	}
}

func write(w io.Writer, id, typ int32, body string) {
	buf := make([]byte, 12+len(body)+2)
	binary.LittleEndian.PutUint32(buf, uint32(10+len(body)))
	binary.LittleEndian.PutUint32(buf[4:], uint32(id))
	binary.LittleEndian.PutUint32(buf[8:], uint32(typ))
	copy(buf[12:], body)
	w.Write(buf)
}

func read(r io.Reader) (id, typ int32, body string, err error) {
	var h [4]byte
	if _, err = io.ReadFull(r, h[:]); err != nil {
		return
	}
	n := binary.LittleEndian.Uint32(h[:])
	if n < 10 || n > 1<<16 {
		return 0, 0, "", io.ErrUnexpectedEOF
	}
	buf := make([]byte, n)
	if _, err = io.ReadFull(r, buf); err != nil {
		return
	}
	return int32(binary.LittleEndian.Uint32(buf)), int32(binary.LittleEndian.Uint32(buf[4:])), string(buf[8 : n-2]), nil
}

// serveQuery answers A2S_INFO with a challenge first, like a real server.
func (s *server) serveQuery(addr string) {
	pc, err := net.ListenPacket("udp", addr)
	if err != nil {
		log.Print("query: ", err)
		return
	}
	buf := make([]byte, 100)
	for {
		n, from, err := pc.ReadFrom(buf)
		if err != nil {
			return
		}
		if n <= 25 {
			pc.WriteTo([]byte{0xff, 0xff, 0xff, 0xff, 0x41, 1, 2, 3, 4}, from)
			continue
		}
		s.mu.Lock()
		players := len(s.online)
		s.mu.Unlock()
		reply := []byte{0xff, 0xff, 0xff, 0xff, 0x49, 17}
		for _, v := range []string{s.name + " - (v350.2)", "TheIsland", "ark_survival_evolved", "ARK: Survival Evolved"} {
			reply = append(append(reply, v...), 0)
		}
		reply = append(reply, 0, 0, byte(players), 70, 0, 'd', 'w', 0, 1, '1', '.', '0', 0)
		pc.WriteTo(reply, from)
	}
}