// Package vmess contains protocol definition, io lib for VMess.
package vmess

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	_ "log"
	mrand "math/rand"

	"github.com/v2ray/v2ray-core"
	v2io "github.com/v2ray/v2ray-core/io"
	v2net "github.com/v2ray/v2ray-core/net"
)

const (
	addrTypeIPv4   = byte(0x01)
	addrTypeIPv6   = byte(0x03)
	addrTypeDomain = byte(0x02)

	Version = byte(0x01)
)

var (
	ErrorInvalidUser = errors.New("Invalid User")
)

// VMessRequest implements the request message of VMess protocol. It only contains
// the header of a request message. The data part will be handled by conection
// handler directly, in favor of data streaming.

type VMessRequest struct {
	Version        byte
	UserId         core.ID
	RequestIV      [16]byte
	RequestKey     [16]byte
	ResponseHeader [4]byte
	Command        byte
	Address        v2net.Address
}

type VMessRequestReader struct {
	vUserSet *core.UserSet
}

func NewVMessRequestReader(vUserSet *core.UserSet) *VMessRequestReader {
	reader := new(VMessRequestReader)
	reader.vUserSet = vUserSet
	return reader
}

func (r *VMessRequestReader) Read(reader io.Reader) (*VMessRequest, error) {
	request := new(VMessRequest)

	buffer := make([]byte, 256)
	nBytes, err := reader.Read(buffer[0:1])
	if err != nil {
		return nil, err
	}
	// TODO: verify version number
	request.Version = buffer[0]

	nBytes, err = reader.Read(buffer[:len(request.UserId)])
	if err != nil {
		return nil, err
	}

	userId, valid := r.vUserSet.IsValidUserId(buffer[:nBytes])
	if !valid {
		return nil, ErrorInvalidUser
	}
	request.UserId = *userId

	decryptor, err := NewDecryptionReader(reader, userId.Hash([]byte("PWD")), make([]byte, blockSize))
	if err != nil {
		return nil, err
	}

	nBytes, err = decryptor.Read(buffer[0:1])
	if err != nil {
		return nil, err
	}

	randomLength := buffer[0]
	if randomLength <= 0 || randomLength > 32 {
		return nil, fmt.Errorf("Unexpected random length %d", randomLength)
	}
	_, err = decryptor.Read(buffer[:randomLength])
	if err != nil {
		return nil, err
	}

	// TODO: check number of bytes returned
	_, err = decryptor.Read(request.RequestIV[:])
	if err != nil {
		return nil, err
	}
	_, err = decryptor.Read(request.RequestKey[:])
	if err != nil {
		return nil, err
	}
	_, err = decryptor.Read(request.ResponseHeader[:])
	if err != nil {
		return nil, err
	}
	_, err = decryptor.Read(buffer[0:1])
	if err != nil {
		return nil, err
	}
	request.Command = buffer[0]

	_, err = decryptor.Read(buffer[0:2])
	if err != nil {
		return nil, err
	}
	port := binary.BigEndian.Uint16(buffer[0:2])

	_, err = decryptor.Read(buffer[0:1])
	if err != nil {
		return nil, err
	}
	switch buffer[0] {
	case addrTypeIPv4:
		_, err = decryptor.Read(buffer[1:5])
		if err != nil {
			return nil, err
		}
		request.Address = v2net.IPAddress(buffer[1:5], port)
	case addrTypeIPv6:
		_, err = decryptor.Read(buffer[1:17])
		if err != nil {
			return nil, err
		}
		request.Address = v2net.IPAddress(buffer[1:17], port)
	case addrTypeDomain:
		_, err = decryptor.Read(buffer[1:2])
		if err != nil {
			return nil, err
		}
		domainLength := buffer[1]
		_, err = decryptor.Read(buffer[2 : 2+domainLength])
		if err != nil {
			return nil, err
		}
		request.Address = v2net.DomainAddress(string(buffer[2:2+domainLength]), port)
	}
	_, err = decryptor.Read(buffer[0:1])
	if err != nil {
		return nil, err
	}
	randomLength = buffer[0]
	_, err = decryptor.Read(buffer[:randomLength])
	if err != nil {
		return nil, err
	}

	return request, nil
}

type VMessRequestWriter struct {
}

func NewVMessRequestWriter() *VMessRequestWriter {
	writer := new(VMessRequestWriter)
	return writer
}

func (w *VMessRequestWriter) Write(writer io.Writer, request *VMessRequest) error {
	buffer := make([]byte, 0, 300)
	buffer = append(buffer, request.Version)
	buffer = append(buffer, request.UserId.Hash([]byte("ASK"))...)

	encryptionBegin := len(buffer)

	randomLength := mrand.Intn(32) + 1
	randomContent := make([]byte, randomLength)
	_, err := rand.Read(randomContent)
	if err != nil {
		return err
	}
	buffer = append(buffer, byte(randomLength))
	buffer = append(buffer, randomContent...)

	buffer = append(buffer, request.RequestIV[:]...)
	buffer = append(buffer, request.RequestKey[:]...)
	buffer = append(buffer, request.ResponseHeader[:]...)
	buffer = append(buffer, request.Command)

	portBytes := make([]byte, 2)
	binary.BigEndian.PutUint16(portBytes, request.Address.Port)
	buffer = append(buffer, portBytes...)

	switch {
	case request.Address.IsIPv4():
		buffer = append(buffer, addrTypeIPv4)
		buffer = append(buffer, request.Address.IP...)
	case request.Address.IsIPv6():
		buffer = append(buffer, addrTypeIPv6)
		buffer = append(buffer, request.Address.IP...)
	case request.Address.IsDomain():
		buffer = append(buffer, addrTypeDomain)
		buffer = append(buffer, byte(len(request.Address.Domain)))
		buffer = append(buffer, []byte(request.Address.Domain)...)
	}

	paddingLength := blockSize - 1 - (len(buffer)-encryptionBegin)%blockSize
	if paddingLength == 0 {
		paddingLength = blockSize
	}
	paddingBuffer := make([]byte, paddingLength)
	_, err = rand.Read(paddingBuffer)
	if err != nil {
		return err
	}
	buffer = append(buffer, byte(paddingLength))
	buffer = append(buffer, paddingBuffer...)
	encryptionEnd := len(buffer)

	aesCipher, err := aes.NewCipher(request.UserId.Hash([]byte("PWD")))
	if err != nil {
		return err
	}
	aesStream := cipher.NewCFBEncrypter(aesCipher, make([]byte, blockSize))
	cWriter := v2io.NewCryptionWriter(aesStream, writer)

	_, err = writer.Write(buffer[0:encryptionBegin])
	if err != nil {
		return err
	}
	_, err = cWriter.Write(buffer[encryptionBegin:encryptionEnd])
	if err != nil {
		return err
	}

	return nil
}

type VMessResponse [4]byte

func NewVMessResponse(request *VMessRequest) *VMessResponse {
	response := new(VMessResponse)
	copy(response[:], request.ResponseHeader[:])
	return response
}