// Copyright 2024 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package nat

import (
	"fmt"
	"net"
	"time"

	stunV2 "github.com/pion/stun/v2"
)

// The code are from erigon p2p/nat/nat_stun.go
// This stun server is part of the mainnet infrastructure.
// The addr are from https://github.com/ethereum/trin/blob/master/portalnet/src/socket.rs
const stunDefaultServerAddr = "159.223.0.83:3478"

type stun struct {
	server *net.UDPAddr
}

func newSTUN(serverAddr string) (Interface, error) {
	if serverAddr == "default" {
		serverAddr = stunDefaultServerAddr
	}
	addr, err := net.ResolveUDPAddr("udp4", serverAddr)
	if err != nil {
		return nil, err
	}
	return stun{server: addr}, nil
}

func (s stun) String() string {
	return fmt.Sprintf("STUN(%s)", s.server)
}

func (stun) SupportsMapping() bool {
	return false
}

func (stun) AddMapping(protocol string, extport, intport int, name string, lifetime time.Duration) (uint16, error) {
	return uint16(extport), nil
}

func (stun) DeleteMapping(string, int, int) error {
	return nil
}

func (s stun) ExternalIP() (net.IP, error) {
	conn, err := stunV2.Dial("udp4", s.server.String())
	if err != nil {
		return nil, err
	}
	defer conn.Close()

	message, err := stunV2.Build(stunV2.TransactionID, stunV2.BindingRequest)
	if err != nil {
		return nil, err
	}
	var response *stunV2.Event
	err = conn.Do(message, func(event stunV2.Event) {
		response = &event
	})
	if err != nil {
		return nil, err
	}
	if response.Error != nil {
		return nil, response.Error
	}

	var mappedAddr stunV2.XORMappedAddress
	if err := mappedAddr.GetFrom(response.Message); err != nil {
		return nil, err
	}

	return mappedAddr.IP, nil
}