package trojan

import (
	"context"
	"crypto/sha256"
	"crypto/tls"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"io"
	"net"
	"net/http"
	"sync"

	N "github.com/Dreamacro/clash/common/net"
	"github.com/Dreamacro/clash/common/pool"
	"github.com/Dreamacro/clash/component/ca"
	tlsC "github.com/Dreamacro/clash/component/tls"
	C "github.com/Dreamacro/clash/constant"
	"github.com/Dreamacro/clash/transport/socks5"
	"github.com/Dreamacro/clash/transport/vmess"
)

const (
	// max packet length
	maxLength = 8192
)

var (
	defaultALPN          = []string{"h2", "http/1.1"}
	defaultWebsocketALPN = []string{"http/1.1"}

	crlf = []byte{'\r', '\n'}
)

type Command = byte

const (
	CommandTCP byte = 1
	CommandUDP byte = 3

	// deprecated XTLS commands, as souvenirs
	commandXRD byte = 0xf0 // XTLS direct mode
	commandXRO byte = 0xf1 // XTLS origin mode
)

type Option struct {
	Password          string
	ALPN              []string
	ServerName        string
	SkipCertVerify    bool
	Fingerprint       string
	ClientFingerprint string
	Reality           *tlsC.RealityConfig
}

type WebsocketOption struct {
	Host             string
	Port             string
	Path             string
	Headers          http.Header
	V2rayHttpUpgrade bool
}

type Trojan struct {
	option      *Option
	hexPassword []byte
}

func (t *Trojan) StreamConn(ctx context.Context, conn net.Conn) (net.Conn, error) {
	alpn := defaultALPN
	if len(t.option.ALPN) != 0 {
		alpn = t.option.ALPN
	}
	tlsConfig := &tls.Config{
		NextProtos:         alpn,
		MinVersion:         tls.VersionTLS12,
		InsecureSkipVerify: t.option.SkipCertVerify,
		ServerName:         t.option.ServerName,
	}

	var err error
	tlsConfig, err = ca.GetSpecifiedFingerprintTLSConfig(tlsConfig, t.option.Fingerprint)
	if err != nil {
		return nil, err
	}

	if len(t.option.ClientFingerprint) != 0 {
		if t.option.Reality == nil {
			utlsConn, valid := vmess.GetUTLSConn(conn, t.option.ClientFingerprint, tlsConfig)
			if valid {
				ctx, cancel := context.WithTimeout(context.Background(), C.DefaultTLSTimeout)
				defer cancel()

				err := utlsConn.(*tlsC.UConn).HandshakeContext(ctx)
				return utlsConn, err
			}
		} else {
			ctx, cancel := context.WithTimeout(context.Background(), C.DefaultTLSTimeout)
			defer cancel()
			return tlsC.GetRealityConn(ctx, conn, t.option.ClientFingerprint, tlsConfig, t.option.Reality)
		}
	}
	if t.option.Reality != nil {
		return nil, errors.New("REALITY is based on uTLS, please set a client-fingerprint")
	}

	tlsConn := tls.Client(conn, tlsConfig)

	// fix tls handshake not timeout
	ctx, cancel := context.WithTimeout(context.Background(), C.DefaultTLSTimeout)
	defer cancel()

	err = tlsConn.HandshakeContext(ctx)
	return tlsConn, err
}

func (t *Trojan) StreamWebsocketConn(ctx context.Context, conn net.Conn, wsOptions *WebsocketOption) (net.Conn, error) {
	alpn := defaultWebsocketALPN
	if len(t.option.ALPN) != 0 {
		alpn = t.option.ALPN
	}

	tlsConfig := &tls.Config{
		NextProtos:         alpn,
		MinVersion:         tls.VersionTLS12,
		InsecureSkipVerify: t.option.SkipCertVerify,
		ServerName:         t.option.ServerName,
	}

	return vmess.StreamWebsocketConn(ctx, conn, &vmess.WebsocketConfig{
		Host:              wsOptions.Host,
		Port:              wsOptions.Port,
		Path:              wsOptions.Path,
		Headers:           wsOptions.Headers,
		V2rayHttpUpgrade:  wsOptions.V2rayHttpUpgrade,
		TLS:               true,
		TLSConfig:         tlsConfig,
		ClientFingerprint: t.option.ClientFingerprint,
	})
}

func (t *Trojan) WriteHeader(w io.Writer, command Command, socks5Addr []byte) error {
	buf := pool.GetBuffer()
	defer pool.PutBuffer(buf)

	buf.Write(t.hexPassword)
	buf.Write(crlf)

	buf.WriteByte(command)
	buf.Write(socks5Addr)
	buf.Write(crlf)

	_, err := w.Write(buf.Bytes())
	return err
}

func (t *Trojan) PacketConn(conn net.Conn) net.PacketConn {
	return &PacketConn{
		Conn: conn,
	}
}

func writePacket(w io.Writer, socks5Addr, payload []byte) (int, error) {
	buf := pool.GetBuffer()
	defer pool.PutBuffer(buf)

	buf.Write(socks5Addr)
	binary.Write(buf, binary.BigEndian, uint16(len(payload)))
	buf.Write(crlf)
	buf.Write(payload)

	return w.Write(buf.Bytes())
}

func WritePacket(w io.Writer, socks5Addr, payload []byte) (int, error) {
	if len(payload) <= maxLength {
		return writePacket(w, socks5Addr, payload)
	}

	offset := 0
	total := len(payload)
	for {
		cursor := offset + maxLength
		if cursor > total {
			cursor = total
		}

		n, err := writePacket(w, socks5Addr, payload[offset:cursor])
		if err != nil {
			return offset + n, err
		}

		offset = cursor
		if offset == total {
			break
		}
	}

	return total, nil
}

func ReadPacket(r io.Reader, payload []byte) (net.Addr, int, int, error) {
	addr, err := socks5.ReadAddr(r, payload)
	if err != nil {
		return nil, 0, 0, errors.New("read addr error")
	}
	uAddr := addr.UDPAddr()
	if uAddr == nil {
		return nil, 0, 0, errors.New("parse addr error")
	}

	if _, err = io.ReadFull(r, payload[:2]); err != nil {
		return nil, 0, 0, errors.New("read length error")
	}

	total := int(binary.BigEndian.Uint16(payload[:2]))
	if total > maxLength {
		return nil, 0, 0, errors.New("packet invalid")
	}

	// read crlf
	if _, err = io.ReadFull(r, payload[:2]); err != nil {
		return nil, 0, 0, errors.New("read crlf error")
	}

	length := len(payload)
	if total < length {
		length = total
	}

	if _, err = io.ReadFull(r, payload[:length]); err != nil {
		return nil, 0, 0, errors.New("read packet error")
	}

	return uAddr, length, total - length, nil
}

func New(option *Option) *Trojan {
	return &Trojan{option, hexSha224([]byte(option.Password))}
}

var _ N.EnhancePacketConn = (*PacketConn)(nil)

type PacketConn struct {
	net.Conn
	remain int
	rAddr  net.Addr
	mux    sync.Mutex
}

func (pc *PacketConn) WriteTo(b []byte, addr net.Addr) (int, error) {
	return WritePacket(pc, socks5.ParseAddr(addr.String()), b)
}

func (pc *PacketConn) ReadFrom(b []byte) (int, net.Addr, error) {
	pc.mux.Lock()
	defer pc.mux.Unlock()
	if pc.remain != 0 {
		length := len(b)
		if pc.remain < length {
			length = pc.remain
		}

		n, err := pc.Conn.Read(b[:length])
		if err != nil {
			return 0, nil, err
		}

		pc.remain -= n
		addr := pc.rAddr
		if pc.remain == 0 {
			pc.rAddr = nil
		}

		return n, addr, nil
	}

	addr, n, remain, err := ReadPacket(pc.Conn, b)
	if err != nil {
		return 0, nil, err
	}

	if remain != 0 {
		pc.remain = remain
		pc.rAddr = addr
	}

	return n, addr, nil
}

func (pc *PacketConn) WaitReadFrom() (data []byte, put func(), addr net.Addr, err error) {
	pc.mux.Lock()
	defer pc.mux.Unlock()

	destination, err := socks5.ReadAddr0(pc.Conn)
	if err != nil {
		return nil, nil, nil, err
	}
	addr = destination.UDPAddr()

	data = pool.Get(pool.UDPBufferSize)
	put = func() {
		_ = pool.Put(data)
	}

	_, err = io.ReadFull(pc.Conn, data[:2+2]) // u16be length + CR LF
	if err != nil {
		if put != nil {
			put()
		}
		return nil, nil, nil, err
	}
	length := binary.BigEndian.Uint16(data)

	if length > 0 {
		data = data[:length]
		_, err = io.ReadFull(pc.Conn, data)
		if err != nil {
			if put != nil {
				put()
			}
			return nil, nil, nil, err
		}
	} else {
		if put != nil {
			put()
		}
		return nil, nil, addr, nil
	}

	return
}

func hexSha224(data []byte) []byte {
	buf := make([]byte, 56)
	hash := sha256.Sum224(data)
	hex.Encode(buf, hash[:])
	return buf
}
