package vnc

import (
	"crypto/des"
	"encoding/binary"
	"fmt"
)

type SecurityType uint8

const (
	SecTypeUnknown  = SecurityType(0)
	SecTypeNone     = SecurityType(1)
	SecTypeVNC      = SecurityType(2)
	SecTypeVeNCrypt = SecurityType(19)
)

type SecuritySubType uint32

const (
	SecSubTypeUnknown = SecuritySubType(0)
)

const (
	SecSubTypeVeNCrypt01Unknown   = SecuritySubType(0)
	SecSubTypeVeNCrypt01Plain     = SecuritySubType(19)
	SecSubTypeVeNCrypt01TLSNone   = SecuritySubType(20)
	SecSubTypeVeNCrypt01TLSVNC    = SecuritySubType(21)
	SecSubTypeVeNCrypt01TLSPlain  = SecuritySubType(22)
	SecSubTypeVeNCrypt01X509None  = SecuritySubType(23)
	SecSubTypeVeNCrypt01X509VNC   = SecuritySubType(24)
	SecSubTypeVeNCrypt01X509Plain = SecuritySubType(25)
)

const (
	SecSubTypeVeNCrypt02Unknown   = SecuritySubType(0)
	SecSubTypeVeNCrypt02Plain     = SecuritySubType(256)
	SecSubTypeVeNCrypt02TLSNone   = SecuritySubType(257)
	SecSubTypeVeNCrypt02TLSVNC    = SecuritySubType(258)
	SecSubTypeVeNCrypt02TLSPlain  = SecuritySubType(259)
	SecSubTypeVeNCrypt02X509None  = SecuritySubType(260)
	SecSubTypeVeNCrypt02X509VNC   = SecuritySubType(261)
	SecSubTypeVeNCrypt02X509Plain = SecuritySubType(262)
)

type SecurityHandler interface {
	Type() SecurityType
	SubType() SecuritySubType
	Auth(Conn) error
}

type ClientAuthNone struct{}

func (*ClientAuthNone) Type() SecurityType {
	return SecTypeNone
}

func (*ClientAuthNone) SubType() SecuritySubType {
	return SecSubTypeUnknown
}

func (*ClientAuthNone) Auth(conn Conn) error {
	return nil
}

// ServerAuthNone is the "none" authentication. See 7.2.1.
type ServerAuthNone struct{}

func (*ServerAuthNone) Type() SecurityType {
	return SecTypeNone
}

func (*ServerAuthNone) Auth(c Conn) error {
	return nil
}

func (*ClientAuthVeNCrypt02Plain) SubType() SecuritySubType {
	return SecSubTypeVeNCrypt02Plain
}

// ClientAuthVeNCryptPlain see https://www.berrange.com/~dan/vencrypt.txt
type ClientAuthVeNCrypt02Plain struct {
	Username []byte
	Password []byte
}

func (auth *ClientAuthVeNCrypt02Plain) Auth(c Conn) error {
	if len(auth.Password) == 0 || len(auth.Username) == 0 {
		return fmt.Errorf("Security Handshake failed; no username and/or password provided for VeNCryptAuth.")
	}

	if err := binary.Write(c, binary.BigEndian, uint32(len(auth.Username))); err != nil {
		return err
	}

	if err := binary.Write(c, binary.BigEndian, uint32(len(auth.Password))); err != nil {
		return err
	}

	if err := binary.Write(c, binary.BigEndian, auth.Username); err != nil {
		return err
	}

	if err := binary.Write(c, binary.BigEndian, auth.Password); err != nil {
		return err
	}

	return c.Flush()
}

// ServerAuthVNC is the standard password authentication. See 7.2.2.
type ServerAuthVNC struct{}

func (*ServerAuthVNC) Type() SecurityType {
	return SecTypeVNC
}
func (*ServerAuthVNC) SubType() SecuritySubType {
	return SecSubTypeUnknown
}

func (auth *ServerAuthVNC) Auth(c Conn) error {
	return nil
}

// ClientAuthVNC is the standard password authentication. See 7.2.2.
type ClientAuthVNC struct {
	Challenge [16]byte
	Password  []byte
}

func (*ClientAuthVNC) Type() SecurityType {
	return SecTypeVNC
}
func (*ClientAuthVNC) SubType() SecuritySubType {
	return SecSubTypeUnknown
}

func (auth *ClientAuthVNC) Auth(c Conn) error {
	if len(auth.Password) == 0 {
		return fmt.Errorf("Security Handshake failed; no password provided for VNCAuth.")
	}

	if err := binary.Read(c, binary.BigEndian, auth.Challenge); err != nil {
		return err
	}

	auth.encode()

	// Send the encrypted challenge back to server
	if err := binary.Write(c, binary.BigEndian, auth.Challenge); err != nil {
		return err
	}

	return c.Flush()
}

func (auth *ClientAuthVNC) encode() error {
	// Copy password string to 8 byte 0-padded slice
	key := make([]byte, 8)
	copy(key, auth.Password)

	// Each byte of the password needs to be reversed. This is a
	// non RFC-documented behaviour of VNC clients and servers
	for i := range key {
		key[i] = (key[i]&0x55)<<1 | (key[i]&0xAA)>>1 // Swap adjacent bits
		key[i] = (key[i]&0x33)<<2 | (key[i]&0xCC)>>2 // Swap adjacent pairs
		key[i] = (key[i]&0x0F)<<4 | (key[i]&0xF0)>>4 // Swap the 2 halves
	}

	// Encrypt challenge with key.
	cipher, err := des.NewCipher(key)
	if err != nil {
		return err
	}
	for i := 0; i < len(auth.Challenge); i += cipher.BlockSize() {
		cipher.Encrypt(auth.Challenge[i:i+cipher.BlockSize()], auth.Challenge[i:i+cipher.BlockSize()])
	}

	return nil
}