package vless

import (
	"bytes"
	"crypto/rand"
	"crypto/tls"
	"io"
	"math/big"
	"net"
	"reflect"
	"time"
	"unsafe"

	C "github.com/sagernet/sing-box/constant"
	"github.com/sagernet/sing/common"
	"github.com/sagernet/sing/common/buf"
	"github.com/sagernet/sing/common/bufio"
	E "github.com/sagernet/sing/common/exceptions"
	"github.com/sagernet/sing/common/logger"
	N "github.com/sagernet/sing/common/network"
)

var tlsRegistry []func(conn net.Conn) (loaded bool, netConn net.Conn, reflectType reflect.Type, reflectPointer uintptr)

func init() {
	tlsRegistry = append(tlsRegistry, func(conn net.Conn) (loaded bool, netConn net.Conn, reflectType reflect.Type, reflectPointer uintptr) {
		tlsConn, loaded := conn.(*tls.Conn)
		if !loaded {
			return
		}
		return true, tlsConn.NetConn(), reflect.TypeOf(tlsConn).Elem(), uintptr(unsafe.Pointer(tlsConn))
	})
}

type VisionConn struct {
	net.Conn
	writer   N.VectorisedWriter
	input    *bytes.Reader
	rawInput *bytes.Buffer
	netConn  net.Conn
	logger   logger.Logger

	userUUID               [16]byte
	isTLS                  bool
	numberOfPacketToFilter int
	isTLS12orAbove         bool
	remainingServerHello   int32
	cipher                 uint16
	enableXTLS             bool
	isPadding              bool
	directWrite            bool
	writeUUID              bool
	withinPaddingBuffers   bool
	remainingContent       int
	remainingPadding       int
	currentCommand         int
	directRead             bool
	remainingReader        io.Reader
}

func NewVisionConn(conn net.Conn, userUUID [16]byte, logger logger.Logger) (*VisionConn, error) {
	var (
		loaded         bool
		reflectType    reflect.Type
		reflectPointer uintptr
		netConn        net.Conn
	)
	for _, tlsCreator := range tlsRegistry {
		loaded, netConn, reflectType, reflectPointer = tlsCreator(conn)
		if loaded {
			break
		}
	}
	if !loaded {
		return nil, C.ErrTLSRequired
	}
	input, _ := reflectType.FieldByName("input")
	rawInput, _ := reflectType.FieldByName("rawInput")
	return &VisionConn{
		Conn:     conn,
		writer:   bufio.NewVectorisedWriter(conn),
		input:    (*bytes.Reader)(unsafe.Pointer(reflectPointer + input.Offset)),
		rawInput: (*bytes.Buffer)(unsafe.Pointer(reflectPointer + rawInput.Offset)),
		netConn:  netConn,
		logger:   logger,

		userUUID:               userUUID,
		numberOfPacketToFilter: 8,
		remainingServerHello:   -1,
		isPadding:              true,
		writeUUID:              true,
		withinPaddingBuffers:   true,
		remainingContent:       -1,
		remainingPadding:       -1,
	}, nil
}

func (c *VisionConn) Read(p []byte) (n int, err error) {
	if c.remainingReader != nil {
		n, err = c.remainingReader.Read(p)
		if err == io.EOF {
			c.remainingReader = nil
			if n > 0 {
				err = nil
				return
			}
		}
	}
	if c.directRead {
		return c.netConn.Read(p)
	}
	n, err = c.Conn.Read(p)
	if err != nil {
		return
	}
	buffer := p[:n]
	if c.withinPaddingBuffers || c.numberOfPacketToFilter > 0 {
		buffers := c.unPadding(buffer)
		if c.remainingContent == 0 && c.remainingPadding == 0 {
			if c.currentCommand == 1 {
				c.withinPaddingBuffers = false
				c.remainingContent = -1
				c.remainingPadding = -1
			} else if c.currentCommand == 2 {
				c.withinPaddingBuffers = false
				c.directRead = true

				inputBuffer, err := io.ReadAll(c.input)
				if err != nil {
					return 0, err
				}
				buffers = append(buffers, inputBuffer)

				rawInputBuffer, err := io.ReadAll(c.rawInput)
				if err != nil {
					return 0, err
				}

				buffers = append(buffers, rawInputBuffer)

				c.logger.Trace("XtlsRead readV")
			} else if c.currentCommand == 0 {
				c.withinPaddingBuffers = true
			} else {
				return 0, E.New("unknown command ", c.currentCommand)
			}
		} else if c.remainingContent > 0 || c.remainingPadding > 0 {
			c.withinPaddingBuffers = true
		} else {
			c.withinPaddingBuffers = false
		}
		if c.numberOfPacketToFilter > 0 {
			c.filterTLS(buffers)
		}
		c.remainingReader = io.MultiReader(common.Map(buffers, func(it []byte) io.Reader { return bytes.NewReader(it) })...)
		return c.remainingReader.Read(p)
	} else {
		if c.numberOfPacketToFilter > 0 {
			c.filterTLS([][]byte{buffer})
		}
		return
	}
}

func (c *VisionConn) Write(p []byte) (n int, err error) {
	if c.numberOfPacketToFilter > 0 {
		c.filterTLS([][]byte{p})
	}
	if c.isPadding {
		inputLen := len(p)
		buffers := reshapeBuffer(p)
		var specIndex int
		for i, buffer := range buffers {
			if c.isTLS && buffer.Len() > 6 && bytes.Equal(tlsApplicationDataStart, buffer.To(3)) {
				var command byte = commandPaddingEnd
				if c.enableXTLS {
					c.directWrite = true
					specIndex = i
					command = commandPaddingDirect
				}
				c.isPadding = false
				buffers[i] = c.padding(buffer, command)
				break
			} else if !c.isTLS12orAbove && c.numberOfPacketToFilter <= 1 {
				c.isPadding = false
				buffers[i] = c.padding(buffer, commandPaddingEnd)
				break
			}
			buffers[i] = c.padding(buffer, commandPaddingContinue)
		}
		if c.directWrite {
			encryptedBuffer := buffers[:specIndex+1]
			err = c.writer.WriteVectorised(encryptedBuffer)
			if err != nil {
				return
			}
			buffers = buffers[specIndex+1:]
			c.writer = bufio.NewVectorisedWriter(c.netConn)
			c.logger.Trace("XtlsWrite writeV ", specIndex, " ", buf.LenMulti(encryptedBuffer), " ", len(buffers))
			time.Sleep(5 * time.Millisecond) // wtf
		}
		err = c.writer.WriteVectorised(buffers)
		if err == nil {
			n = inputLen
		}
		return
	}
	if c.directWrite {
		return c.netConn.Write(p)
	} else {
		return c.Conn.Write(p)
	}
}

func (c *VisionConn) filterTLS(buffers [][]byte) {
	for _, buffer := range buffers {
		c.numberOfPacketToFilter--
		if len(buffer) > 6 {
			if buffer[0] == 22 && buffer[1] == 3 && buffer[2] == 3 {
				c.isTLS = true
				if buffer[5] == 2 {
					c.isTLS12orAbove = true
					c.remainingServerHello = (int32(buffer[3])<<8 | int32(buffer[4])) + 5
					if len(buffer) >= 79 && c.remainingServerHello >= 79 {
						sessionIdLen := int32(buffer[43])
						cipherSuite := buffer[43+sessionIdLen+1 : 43+sessionIdLen+3]
						c.cipher = uint16(cipherSuite[0])<<8 | uint16(cipherSuite[1])
					} else {
						c.logger.Trace("XtlsFilterTls short server hello, tls 1.2 or older? ", len(buffer), " ", c.remainingServerHello)
					}
				}
			} else if bytes.Equal(tlsClientHandShakeStart, buffer[:2]) && buffer[5] == 1 {
				c.isTLS = true
				c.logger.Trace("XtlsFilterTls found tls client hello! ", len(buffer))
			}
		}
		if c.remainingServerHello > 0 {
			end := int(c.remainingServerHello)
			if end > len(buffer) {
				end = len(buffer)
			}
			c.remainingServerHello -= int32(end)
			if bytes.Contains(buffer[:end], tls13SupportedVersions) {
				cipher, ok := tls13CipherSuiteDic[c.cipher]
				if ok && cipher != "TLS_AES_128_CCM_8_SHA256" {
					c.enableXTLS = true
				}
				c.logger.Trace("XtlsFilterTls found tls 1.3! ", len(buffer), " ", c.cipher, " ", c.enableXTLS)
				c.numberOfPacketToFilter = 0
				return
			} else if c.remainingServerHello == 0 {
				c.logger.Trace("XtlsFilterTls found tls 1.2! ", len(buffer))
				c.numberOfPacketToFilter = 0
				return
			}
		}
		if c.numberOfPacketToFilter == 0 {
			c.logger.Trace("XtlsFilterTls stop filtering ", len(buffer))
		}
	}
}

func (c *VisionConn) padding(buffer *buf.Buffer, command byte) *buf.Buffer {
	contentLen := 0
	paddingLen := 0
	if buffer != nil {
		contentLen = buffer.Len()
	}
	if contentLen < 900 && c.isTLS {
		l, _ := rand.Int(rand.Reader, big.NewInt(500))
		paddingLen = int(l.Int64()) + 900 - contentLen
	} else {
		l, _ := rand.Int(rand.Reader, big.NewInt(256))
		paddingLen = int(l.Int64())
	}
	newBuffer := buf.New()
	if c.writeUUID {
		newBuffer.Write(c.userUUID[:])
		c.writeUUID = false
	}
	newBuffer.Write([]byte{command, byte(contentLen >> 8), byte(contentLen), byte(paddingLen >> 8), byte(paddingLen)})
	if buffer != nil {
		newBuffer.Write(buffer.Bytes())
		buffer.Release()
	}
	newBuffer.Extend(paddingLen)
	c.logger.Trace("XtlsPadding ", contentLen, " ", paddingLen, " ", command)
	return newBuffer
}

func (c *VisionConn) unPadding(buffer []byte) [][]byte {
	var bufferIndex int
	if c.remainingContent == -1 && c.remainingPadding == -1 {
		if len(buffer) >= 21 && bytes.Equal(c.userUUID[:], buffer[:16]) {
			bufferIndex = 16
			c.remainingContent = 0
			c.remainingPadding = 0
			c.currentCommand = 0
		}
	}
	if c.remainingContent == -1 && c.remainingPadding == -1 {
		return [][]byte{buffer}
	}
	var buffers [][]byte
	for bufferIndex < len(buffer) {
		if c.remainingContent <= 0 && c.remainingPadding <= 0 {
			if c.currentCommand == 1 {
				buffers = append(buffers, buffer[bufferIndex:])
				break
			} else {
				paddingInfo := buffer[bufferIndex : bufferIndex+5]
				c.currentCommand = int(paddingInfo[0])
				c.remainingContent = int(paddingInfo[1])<<8 | int(paddingInfo[2])
				c.remainingPadding = int(paddingInfo[3])<<8 | int(paddingInfo[4])
				bufferIndex += 5
				c.logger.Trace("Xtls Unpadding new block ", bufferIndex, " ", c.remainingContent, " padding ", c.remainingPadding, " ", c.currentCommand)
			}
		} else if c.remainingContent > 0 {
			end := c.remainingContent
			if end > len(buffer)-bufferIndex {
				end = len(buffer) - bufferIndex
			}
			buffers = append(buffers, buffer[bufferIndex:bufferIndex+end])
			c.remainingContent -= end
			bufferIndex += end
		} else {
			end := c.remainingPadding
			if end > len(buffer)-bufferIndex {
				end = len(buffer) - bufferIndex
			}
			c.remainingPadding -= end
			bufferIndex += end
		}
		if bufferIndex == len(buffer) {
			break
		}
	}
	return buffers
}

func (c *VisionConn) Upstream() any {
	return c.Conn
}