package rpc

import (
	"bytes"
	"crypto/rand"
	"encoding/binary"
	"net"

	"github.com/juju/errors"

	"github.com/9seconds/mtg/mtproto"
)

const (
	rpcProxyRequestConnectionIDLength = 8
	rpcProxyRequestIPPortLength       = 16 + 4
)

var (
	rpcProxyRequestTag       = []byte{0xee, 0xf1, 0xce, 0x36}
	rpcProxyRequestExtraSize = []byte{0x18, 0x00, 0x00, 0x00}
	rpcProxyRequestProxyTag  = []byte{0xae, 0x26, 0x1e, 0xdb}
)

type RPCProxyRequest struct {
	Flags        RPCProxyRequestFlags
	ConnectionID [rpcProxyRequestConnectionIDLength]byte
	OurIPPort    [rpcProxyRequestIPPortLength]byte
	ClientIPPort [rpcProxyRequestIPPortLength]byte
	ADTag        []byte
	Options      *mtproto.ConnectionOpts
}

func (r *RPCProxyRequest) Bytes(message []byte) []byte {
	buf := &bytes.Buffer{}

	flags := r.Flags
	if r.Options.QuickAck {
		flags |= RPCProxyRequestFlagsQuickAck
	}

	if bytes.HasPrefix(message, rpcProxyRequestFlagsEncryptedPrefix[:]) {
		flags |= RPCProxyRequestFlagsEncrypted
	}

	buf.Write(rpcProxyRequestTag)
	buf.Write(flags.Bytes())
	buf.Write(r.ConnectionID[:])
	buf.Write(r.ClientIPPort[:])
	buf.Write(r.OurIPPort[:])
	buf.Write(rpcProxyRequestExtraSize)
	buf.Write(rpcProxyRequestProxyTag)
	buf.WriteByte(byte(len(r.ADTag)))
	buf.Write(r.ADTag)
	buf.Write(bytes.Repeat([]byte{0x00}, buf.Len()%4))
	buf.Write(message)

	return buf.Bytes()
}

func NewRPCProxyRequest(clientAddr, ownAddr *net.TCPAddr, opts *mtproto.ConnectionOpts, adTag []byte) (*RPCProxyRequest, error) {
	flags := RPCProxyRequestFlagsHasAdTag | RPCProxyRequestFlagsMagic | RPCProxyRequestFlagsExtMode2

	switch opts.ConnectionType {
	case mtproto.ConnectionTypeAbridged:
		flags |= RPCProxyRequestFlagsAbdridged
	case mtproto.ConnectionTypeIntermediate:
		flags |= RPCProxyRequestFlagsIntermediate
	}

	request := RPCProxyRequest{
		Flags:   flags,
		ADTag:   adTag,
		Options: opts,
	}

	if _, err := rand.Read(request.ConnectionID[:]); err != nil {
		return nil, errors.Annotate(err, "Cannot generate connection ID")
	}

	port := make([]byte, 4)
	copy(request.ClientIPPort[:16], clientAddr.IP.To16())
	binary.LittleEndian.PutUint32(port, uint32(clientAddr.Port))
	copy(request.ClientIPPort[16:], port)

	copy(request.OurIPPort[:16], ownAddr.IP.To16())
	binary.LittleEndian.PutUint32(port, uint32(ownAddr.Port))
	copy(request.OurIPPort[16:], port)

	return &request, nil
}