package vision

import (
	"bytes"
	"crypto/subtle"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"net"

	"github.com/metacubex/mihomo/common/buf"
	N "github.com/metacubex/mihomo/common/net"
	"github.com/metacubex/mihomo/log"

	"github.com/gofrs/uuid/v5"
)

var (
	_ N.ExtendedConn = (*Conn)(nil)
)

type Conn struct {
	net.Conn // should be *vless.Conn
	N.ExtendedReader
	N.ExtendedWriter
	userUUID *uuid.UUID

	// tlsConn and it's internal variables
	tlsConn  net.Conn      // maybe [*tls.Conn] or other tls-like conn
	netConn  net.Conn      // tlsConn.NetConn()
	input    *bytes.Reader // &tlsConn.input or nil
	rawInput *bytes.Buffer // &tlsConn.rawInput or nil

	needHandshake              bool
	packetsToFilter            int
	isTLS                      bool
	isTLS12orAbove             bool
	enableXTLS                 bool
	cipher                     uint16
	remainingServerHello       uint16
	readRemainingContent       int
	readRemainingPadding       int
	readProcess                bool
	readFilterUUID             bool
	readLastCommand            byte
	writeFilterApplicationData bool
	writeDirect                bool
}

func (vc *Conn) Read(b []byte) (int, error) {
	if vc.readProcess {
		buffer := buf.With(b)
		err := vc.ReadBuffer(buffer)
		return buffer.Len(), err
	}
	return vc.ExtendedReader.Read(b)
}

func (vc *Conn) ReadBuffer(buffer *buf.Buffer) error {
	toRead := buffer.FreeBytes()
	if vc.readRemainingContent > 0 {
		if vc.readRemainingContent < buffer.FreeLen() {
			toRead = toRead[:vc.readRemainingContent]
		}
		n, err := vc.ExtendedReader.Read(toRead)
		buffer.Truncate(n)
		vc.readRemainingContent -= n
		vc.FilterTLS(toRead)
		return err
	}
	if vc.readRemainingPadding > 0 {
		_, err := io.CopyN(io.Discard, vc.ExtendedReader, int64(vc.readRemainingPadding))
		if err != nil {
			return err
		}
		vc.readRemainingPadding = 0
	}
	if vc.readProcess {
		switch vc.readLastCommand {
		case commandPaddingContinue:
			//if vc.isTLS || vc.packetsToFilter > 0 {
			headerUUIDLen := 0
			if vc.readFilterUUID {
				headerUUIDLen = uuid.Size
			}
			var header []byte
			if need := headerUUIDLen + PaddingHeaderLen - uuid.Size; buffer.FreeLen() < need {
				header = make([]byte, need)
			} else {
				header = buffer.FreeBytes()[:need]
			}
			_, err := io.ReadFull(vc.ExtendedReader, header)
			if err != nil {
				return err
			}
			if vc.readFilterUUID {
				vc.readFilterUUID = false
				if subtle.ConstantTimeCompare(vc.userUUID.Bytes(), header[:uuid.Size]) != 1 {
					err = fmt.Errorf("XTLS Vision server responded unknown UUID: %s",
						uuid.FromBytesOrNil(header[:uuid.Size]).String())
					log.Errorln(err.Error())
					return err
				}
				header = header[uuid.Size:]
			}
			vc.readRemainingPadding = int(binary.BigEndian.Uint16(header[3:]))
			vc.readRemainingContent = int(binary.BigEndian.Uint16(header[1:]))
			vc.readLastCommand = header[0]
			log.Debugln("XTLS Vision read padding: command=%d, payloadLen=%d, paddingLen=%d",
				vc.readLastCommand, vc.readRemainingContent, vc.readRemainingPadding)
			return vc.ReadBuffer(buffer)
			//}
		case commandPaddingEnd:
			vc.readProcess = false
			return vc.ReadBuffer(buffer)
		case commandPaddingDirect:
			needReturn := false
			if vc.input != nil {
				_, err := buffer.ReadOnceFrom(vc.input)
				if err != nil {
					if !errors.Is(err, io.EOF) {
						return err
					}
				}
				if vc.input.Len() == 0 {
					needReturn = true
					vc.input = nil
				} else { // buffer is full
					return nil
				}
			}
			if vc.rawInput != nil {
				_, err := buffer.ReadOnceFrom(vc.rawInput)
				if err != nil {
					if !errors.Is(err, io.EOF) {
						return err
					}
				}
				needReturn = true
				if vc.rawInput.Len() == 0 {
					vc.rawInput = nil
				}
			}
			if vc.input == nil && vc.rawInput == nil {
				vc.readProcess = false
				vc.ExtendedReader = N.NewExtendedReader(vc.netConn)
				log.Debugln("XTLS Vision direct read start")
			}
			if needReturn {
				return nil
			}
		default:
			err := fmt.Errorf("XTLS Vision read unknown command: %d", vc.readLastCommand)
			log.Debugln(err.Error())
			return err
		}
	}
	return vc.ExtendedReader.ReadBuffer(buffer)
}

func (vc *Conn) Write(p []byte) (int, error) {
	if vc.writeFilterApplicationData {
		return N.WriteBuffer(vc, buf.As(p))
	}
	return vc.ExtendedWriter.Write(p)
}

func (vc *Conn) WriteBuffer(buffer *buf.Buffer) (err error) {
	if vc.needHandshake {
		vc.needHandshake = false
		if buffer.IsEmpty() {
			ApplyPadding(buffer, commandPaddingContinue, vc.userUUID, true) // we do a long padding to hide vless header
		} else {
			vc.FilterTLS(buffer.Bytes())
			ApplyPadding(buffer, commandPaddingContinue, vc.userUUID, vc.isTLS)
		}
		err = vc.ExtendedWriter.WriteBuffer(buffer)
		if err != nil {
			buffer.Release()
			return err
		}
		err = vc.checkTLSVersion()
		if err != nil {
			buffer.Release()
			return err
		}
		vc.tlsConn = nil
		return nil
	}

	if vc.writeFilterApplicationData {
		vc.FilterTLS(buffer.Bytes())
		buffers := vc.ReshapeBuffer(buffer)
		applyPadding := true
		for i, buffer := range buffers {
			command := commandPaddingContinue
			if applyPadding {
				if vc.isTLS && buffer.Len() > 6 && bytes.Equal(buffer.To(3), tlsApplicationDataStart) {
					command = commandPaddingEnd
					if vc.enableXTLS {
						command = commandPaddingDirect
						vc.writeDirect = true
					}
					vc.writeFilterApplicationData = false
					applyPadding = false
				} else if !vc.isTLS12orAbove && vc.packetsToFilter <= 1 {
					command = commandPaddingEnd
					vc.writeFilterApplicationData = false
					applyPadding = false
				}
				ApplyPadding(buffer, command, nil, vc.isTLS)
			}

			err = vc.ExtendedWriter.WriteBuffer(buffer)
			if err != nil {
				buf.ReleaseMulti(buffers[i:]) // release unwritten buffers
				return
			}
			if command == commandPaddingDirect {
				vc.ExtendedWriter = N.NewExtendedWriter(vc.netConn)
				log.Debugln("XTLS Vision direct write start")
				//time.Sleep(5 * time.Millisecond)
			}
		}
		return err
	}
	/*if vc.writeDirect {
		log.Debugln("XTLS Vision Direct write, payloadLen=%d", buffer.Len())
	}*/
	return vc.ExtendedWriter.WriteBuffer(buffer)
}

func (vc *Conn) FrontHeadroom() int {
	if vc.readFilterUUID {
		return PaddingHeaderLen
	}
	return PaddingHeaderLen - uuid.Size
}

func (vc *Conn) RearHeadroom() int {
	return 500 + 900
}

func (vc *Conn) NeedHandshake() bool {
	return vc.needHandshake
}

func (vc *Conn) Upstream() any {
	if vc.writeDirect ||
		vc.readLastCommand == commandPaddingDirect {
		return vc.netConn
	}
	return vc.Conn
}

func (vc *Conn) ReaderPossiblyReplaceable() bool {
	return vc.readProcess
}

func (vc *Conn) ReaderReplaceable() bool {
	if !vc.readProcess &&
		vc.readLastCommand == commandPaddingDirect {
		return true
	}
	return false
}

func (vc *Conn) WriterPossiblyReplaceable() bool {
	return vc.writeFilterApplicationData
}

func (vc *Conn) WriterReplaceable() bool {
	if vc.writeDirect {
		return true
	}
	return false
}

func (vc *Conn) Close() error {
	if vc.ReaderReplaceable() || vc.WriterReplaceable() { // ignore send closeNotify alert in tls.Conn
		return vc.netConn.Close()
	}
	return vc.Conn.Close()
}