package encoding

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/md5"
	"crypto/rand"
	"hash/fnv"
	"io"

	"golang.org/x/crypto/chacha20poly1305"

	"v2ray.com/core/common"
	"v2ray.com/core/common/bitmask"
	"v2ray.com/core/common/buf"
	"v2ray.com/core/common/crypto"
	"v2ray.com/core/common/dice"
	"v2ray.com/core/common/protocol"
	"v2ray.com/core/common/serial"
	"v2ray.com/core/proxy/vmess"
)

func hashTimestamp(t protocol.Timestamp) []byte {
	bytes := make([]byte, 0, 32)
	bytes = t.Bytes(bytes)
	bytes = t.Bytes(bytes)
	bytes = t.Bytes(bytes)
	bytes = t.Bytes(bytes)
	return bytes
}

// ClientSession stores connection session info for VMess client.
type ClientSession struct {
	requestBodyKey  []byte
	requestBodyIV   []byte
	responseHeader  byte
	responseBodyKey []byte
	responseBodyIV  []byte
	responseReader  io.Reader
	idHash          protocol.IDHash
}

// NewClientSession creates a new ClientSession.
func NewClientSession(idHash protocol.IDHash) *ClientSession {
	randomBytes := make([]byte, 33) // 16 + 16 + 1
	common.Must2(rand.Read(randomBytes))

	session := &ClientSession{}
	session.requestBodyKey = randomBytes[:16]
	session.requestBodyIV = randomBytes[16:32]
	session.responseHeader = randomBytes[32]
	responseBodyKey := md5.Sum(session.requestBodyKey)
	responseBodyIV := md5.Sum(session.requestBodyIV)
	session.responseBodyKey = responseBodyKey[:]
	session.responseBodyIV = responseBodyIV[:]
	session.idHash = idHash

	return session
}

func (c *ClientSession) EncodeRequestHeader(header *protocol.RequestHeader, writer io.Writer) error {
	timestamp := protocol.NewTimestampGenerator(protocol.NowTime(), 30)()
	account, err := header.User.GetTypedAccount()
	if err != nil {
		return newError("failed to get user account: ", err).AtError()
	}
	idHash := c.idHash(account.(*vmess.InternalAccount).AnyValidID().Bytes())
	common.Must2(idHash.Write(timestamp.Bytes(nil)))
	common.Must2(writer.Write(idHash.Sum(nil)))

	buffer := buf.New()
	defer buffer.Release()

	buffer.AppendBytes(Version)
	buffer.Append(c.requestBodyIV)
	buffer.Append(c.requestBodyKey)
	buffer.AppendBytes(c.responseHeader, byte(header.Option))

	padingLen := dice.Roll(16)
	security := byte(padingLen<<4) | byte(header.Security)
	buffer.AppendBytes(security, byte(0), byte(header.Command))

	if header.Command != protocol.RequestCommandMux {
		if err := addrParser.WriteAddressPort(buffer, header.Address, header.Port); err != nil {
			return newError("failed to writer address and port").Base(err)
		}
	}

	if padingLen > 0 {
		common.Must(buffer.AppendSupplier(buf.ReadFullFrom(rand.Reader, padingLen)))
	}

	fnv1a := fnv.New32a()
	common.Must2(fnv1a.Write(buffer.Bytes()))

	common.Must(buffer.AppendSupplier(func(b []byte) (int, error) {
		fnv1a.Sum(b[:0])
		return fnv1a.Size(), nil
	}))

	timestampHash := md5.New()
	common.Must2(timestampHash.Write(hashTimestamp(timestamp)))
	iv := timestampHash.Sum(nil)
	aesStream := crypto.NewAesEncryptionStream(account.(*vmess.InternalAccount).ID.CmdKey(), iv)
	aesStream.XORKeyStream(buffer.Bytes(), buffer.Bytes())
	common.Must2(writer.Write(buffer.Bytes()))
	return nil
}

func (c *ClientSession) EncodeRequestBody(request *protocol.RequestHeader, writer io.Writer) buf.Writer {
	var sizeParser crypto.ChunkSizeEncoder = crypto.PlainChunkSizeParser{}
	if request.Option.Has(protocol.RequestOptionChunkMasking) {
		sizeParser = NewShakeSizeParser(c.requestBodyIV)
	}
	switch request.Security {
	case protocol.SecurityType_NONE:
		if request.Option.Has(protocol.RequestOptionChunkStream) {
			if request.Command.TransferType() == protocol.TransferTypeStream {
				return crypto.NewChunkStreamWriter(sizeParser, writer)
			}
			auth := &crypto.AEADAuthenticator{
				AEAD:                    new(NoOpAuthenticator),
				NonceGenerator:          crypto.NoOpBytesGenerator{},
				AdditionalDataGenerator: crypto.NoOpBytesGenerator{},
			}
			return crypto.NewAuthenticationWriter(auth, sizeParser, writer, protocol.TransferTypePacket)
		}

		return buf.NewWriter(writer)
	case protocol.SecurityType_LEGACY:
		aesStream := crypto.NewAesEncryptionStream(c.requestBodyKey, c.requestBodyIV)
		cryptionWriter := crypto.NewCryptionWriter(aesStream, writer)
		if request.Option.Has(protocol.RequestOptionChunkStream) {
			auth := &crypto.AEADAuthenticator{
				AEAD:                    new(FnvAuthenticator),
				NonceGenerator:          crypto.NoOpBytesGenerator{},
				AdditionalDataGenerator: crypto.NoOpBytesGenerator{},
			}
			return crypto.NewAuthenticationWriter(auth, sizeParser, cryptionWriter, request.Command.TransferType())
		}

		return buf.NewWriter(cryptionWriter)
	case protocol.SecurityType_AES128_GCM:
		block, _ := aes.NewCipher(c.requestBodyKey)
		aead, _ := cipher.NewGCM(block)

		auth := &crypto.AEADAuthenticator{
			AEAD: aead,
			NonceGenerator: &ChunkNonceGenerator{
				Nonce: append([]byte(nil), c.requestBodyIV...),
				Size:  aead.NonceSize(),
			},
			AdditionalDataGenerator: crypto.NoOpBytesGenerator{},
		}
		return crypto.NewAuthenticationWriter(auth, sizeParser, writer, request.Command.TransferType())
	case protocol.SecurityType_CHACHA20_POLY1305:
		aead, _ := chacha20poly1305.New(GenerateChacha20Poly1305Key(c.requestBodyKey))

		auth := &crypto.AEADAuthenticator{
			AEAD: aead,
			NonceGenerator: &ChunkNonceGenerator{
				Nonce: append([]byte(nil), c.requestBodyIV...),
				Size:  aead.NonceSize(),
			},
			AdditionalDataGenerator: crypto.NoOpBytesGenerator{},
		}
		return crypto.NewAuthenticationWriter(auth, sizeParser, writer, request.Command.TransferType())
	default:
		panic("Unknown security type.")
	}
}

func (c *ClientSession) DecodeResponseHeader(reader io.Reader) (*protocol.ResponseHeader, error) {
	aesStream := crypto.NewAesDecryptionStream(c.responseBodyKey, c.responseBodyIV)
	c.responseReader = crypto.NewCryptionReader(aesStream, reader)

	buffer := buf.New()
	defer buffer.Release()

	if err := buffer.AppendSupplier(buf.ReadFullFrom(c.responseReader, 4)); err != nil {
		return nil, newError("failed to read response header").Base(err)
	}

	if buffer.Byte(0) != c.responseHeader {
		return nil, newError("unexpected response header. Expecting ", int(c.responseHeader), " but actually ", int(buffer.Byte(0)))
	}

	header := &protocol.ResponseHeader{
		Option: bitmask.Byte(buffer.Byte(1)),
	}

	if buffer.Byte(2) != 0 {
		cmdID := buffer.Byte(2)
		dataLen := int(buffer.Byte(3))

		if err := buffer.Reset(buf.ReadFullFrom(c.responseReader, dataLen)); err != nil {
			return nil, newError("failed to read response command").Base(err)
		}
		command, err := UnmarshalCommand(cmdID, buffer.Bytes())
		if err == nil {
			header.Command = command
		}
	}

	return header, nil
}

func (c *ClientSession) DecodeResponseBody(request *protocol.RequestHeader, reader io.Reader) buf.Reader {
	var sizeParser crypto.ChunkSizeDecoder = crypto.PlainChunkSizeParser{}
	if request.Option.Has(protocol.RequestOptionChunkMasking) {
		sizeParser = NewShakeSizeParser(c.responseBodyIV)
	}
	switch request.Security {
	case protocol.SecurityType_NONE:
		if request.Option.Has(protocol.RequestOptionChunkStream) {
			if request.Command.TransferType() == protocol.TransferTypeStream {
				return crypto.NewChunkStreamReader(sizeParser, reader)
			}

			auth := &crypto.AEADAuthenticator{
				AEAD:                    new(NoOpAuthenticator),
				NonceGenerator:          crypto.NoOpBytesGenerator{},
				AdditionalDataGenerator: crypto.NoOpBytesGenerator{},
			}

			return crypto.NewAuthenticationReader(auth, sizeParser, reader, protocol.TransferTypePacket)
		}

		return buf.NewReader(reader)
	case protocol.SecurityType_LEGACY:
		if request.Option.Has(protocol.RequestOptionChunkStream) {
			auth := &crypto.AEADAuthenticator{
				AEAD:                    new(FnvAuthenticator),
				NonceGenerator:          crypto.NoOpBytesGenerator{},
				AdditionalDataGenerator: crypto.NoOpBytesGenerator{},
			}
			return crypto.NewAuthenticationReader(auth, sizeParser, c.responseReader, request.Command.TransferType())
		}

		return buf.NewReader(c.responseReader)
	case protocol.SecurityType_AES128_GCM:
		block, _ := aes.NewCipher(c.responseBodyKey)
		aead, _ := cipher.NewGCM(block)

		auth := &crypto.AEADAuthenticator{
			AEAD: aead,
			NonceGenerator: &ChunkNonceGenerator{
				Nonce: append([]byte(nil), c.responseBodyIV...),
				Size:  aead.NonceSize(),
			},
			AdditionalDataGenerator: crypto.NoOpBytesGenerator{},
		}
		return crypto.NewAuthenticationReader(auth, sizeParser, reader, request.Command.TransferType())
	case protocol.SecurityType_CHACHA20_POLY1305:
		aead, _ := chacha20poly1305.New(GenerateChacha20Poly1305Key(c.responseBodyKey))

		auth := &crypto.AEADAuthenticator{
			AEAD: aead,
			NonceGenerator: &ChunkNonceGenerator{
				Nonce: append([]byte(nil), c.responseBodyIV...),
				Size:  aead.NonceSize(),
			},
			AdditionalDataGenerator: crypto.NoOpBytesGenerator{},
		}
		return crypto.NewAuthenticationReader(auth, sizeParser, reader, request.Command.TransferType())
	default:
		panic("Unknown security type.")
	}
}

type ChunkNonceGenerator struct {
	Nonce []byte
	Size  int
	count uint16
}

func (g *ChunkNonceGenerator) Next() []byte {
	serial.Uint16ToBytes(g.count, g.Nonce[:0])
	g.count++
	return g.Nonce[:g.Size]
}
