package transport

import (
	"bufio"
	"bytes"
	"encoding/base64"
	"fmt"
	"io"
	"math"
	"net"
	"net/http"
	"strconv"
	"strings"
	"time"
	"unicode/utf8"

	"github.com/golang/protobuf/proto"
	"golang.org/x/net/http2"
	"golang.org/x/net/http2/hpack"
	spb "google.golang.org/genproto/googleapis/rpc/status"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/grpclog"
	"google.golang.org/grpc/internal/grpcutil"
	"google.golang.org/grpc/status"
)

)

var (
	clientPreface   = []byte(http2.ClientPreface)
	http2ErrConvTab = map[http2.ErrCode]codes.Code{
		http2.ErrCodeNo:                 codes.Internal,
		http2.ErrCodeProtocol:           codes.Internal,
		http2.ErrCodeInternal:           codes.Internal,
		http2.ErrCodeFlowControl:        codes.ResourceExhausted,
		http2.ErrCodeSettingsTimeout:    codes.Internal,
		http2.ErrCodeStreamClosed:       codes.Internal,
		http2.ErrCodeFrameSize:          codes.Internal,
		http2.ErrCodeRefusedStream:      codes.Unavailable,
		http2.ErrCodeCancel:             codes.Canceled,
		http2.ErrCodeCompression:        codes.Internal,
		http2.ErrCodeConnect:            codes.Internal,
		http2.ErrCodeEnhanceYourCalm:    codes.ResourceExhausted,
		http2.ErrCodeInadequateSecurity: codes.PermissionDenied,
		http2.ErrCodeHTTP11Required:     codes.Internal,
	}
	statusCodeConvTab = map[codes.Code]http2.ErrCode{
		codes.Internal:          http2.ErrCodeInternal,
		codes.Canceled:          http2.ErrCodeCancel,
		codes.Unavailable:       http2.ErrCodeRefusedStream,
		codes.ResourceExhausted: http2.ErrCodeEnhanceYourCalm,
		codes.PermissionDenied:  http2.ErrCodeInadequateSecurity,

		http.StatusGatewayTimeout: codes.Unavailable,
	}
	logger = grpclog.Component("transport")
)

type parsedHeaderData struct {

	rawStatusCode *int
	rawStatusMsg  string

	timeoutSet bool
	timeout    time.Duration

	mdata          map[string][]string
	statsTags      []byte
	statsTrace     []byte
	contentSubtype string

	isGRPC         bool
	grpcErr        error
	httpErr        error
	contentTypeErr string
}

	serverSide bool

	data parsedHeaderData
}

func isReservedHeader(hdr string) bool {
	if hdr != "" && hdr[0] == ':' {
		return true
	}
	switch hdr {
	case "content-type",
		"user-agent",
		"grpc-message-type",
		"grpc-encoding",
		"grpc-message",
		"grpc-status",
		"grpc-timeout",

		"te":
		return true
	default:
		return false
	}
}

func isWhitelistedHeader(hdr string) bool {
	switch hdr {
	case ":authority", "user-agent":
		return true
	default:
		return false
	}
}

func (d *decodeState) status() *status.Status {

		d.data.statusGen = status.New(codes.Code(int32(*(d.data.rawStatusCode))), d.data.rawStatusMsg)
	}
	return d.data.statusGen
}

const binHdrSuffix = "-bin"

func encodeBinHeader(v []byte) string {
	return base64.RawStdEncoding.EncodeToString(v)
}

func decodeBinHeader(v string) ([]byte, error) {

		return base64.StdEncoding.DecodeString(v)
	}
	return base64.RawStdEncoding.DecodeString(v)
}

func encodeMetadataHeader(k, v string) string {
	if strings.HasSuffix(k, binHdrSuffix) {
		return encodeBinHeader(([]byte)(v))
	}
	return v
}

func decodeMetadataHeader(k, v string) (string, error) {
	if strings.HasSuffix(k, binHdrSuffix) {
		b, err := decodeBinHeader(v)
		return string(b), err
	}
	return v, nil
}

	if frame.Truncated {
		return status.Error(codes.Internal, "peer header list size exceeded limit")
	}

	for _, hf := range frame.Fields {
		d.processHeaderField(hf)
	}

	if d.data.isGRPC {
		if d.data.grpcErr != nil {
			return d.data.grpcErr
		}
		if d.serverSide {
			return nil
		}

			code := int(codes.Unknown)
			d.data.rawStatusCode = &code
		}
		return nil
	}

	if d.data.httpErr != nil {
		return d.data.httpErr
	}

	var (
		code = codes.Internal // when header does not include HTTP status, return INTERNAL
		ok   bool
	)

	if d.data.httpStatus != nil {
		code, ok = HTTPStatusConvTab[*(d.data.httpStatus)]
		if !ok {
			code = codes.Unknown
		}
	}

	return status.Error(code, d.constructHTTPErrMsg())
}

func (d *decodeState) constructHTTPErrMsg() string {
	var errMsgs []string

	if d.data.httpStatus == nil {
		errMsgs = append(errMsgs, "malformed header: missing HTTP status")
	} else {
		errMsgs = append(errMsgs, fmt.Sprintf("%s: HTTP status code %d", http.StatusText(*(d.data.httpStatus)), *d.data.httpStatus))
	}

	if d.data.contentTypeErr == "" {
		errMsgs = append(errMsgs, "transport: missing content-type field")
	} else {
		errMsgs = append(errMsgs, d.data.contentTypeErr)
	}

	return strings.Join(errMsgs, "; ")
}

func (d *decodeState) addMetadata(k, v string) {
	if d.data.mdata == nil {
		d.data.mdata = make(map[string][]string)
	}
	d.data.mdata[k] = append(d.data.mdata[k], v)
}

func (d *decodeState) processHeaderField(f hpack.HeaderField) {
	switch f.Name {
	case "content-type":
		contentSubtype, validContentType := grpcutil.ContentSubtype(f.Value)
		if !validContentType {
			d.data.contentTypeErr = fmt.Sprintf("transport: received the unexpected content-type %q", f.Value)
			return
		}

		d.addMetadata(f.Name, f.Value)
		d.data.isGRPC = true
	case "grpc-encoding":
		d.data.encoding = f.Value
	case "grpc-status":
		code, err := strconv.Atoi(f.Value)
		if err != nil {
			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-status: %v", err)
			return
		}
		d.data.rawStatusCode = &code
	case "grpc-message":
		d.data.rawStatusMsg = decodeGrpcMessage(f.Value)
	case "grpc-status-details-bin":
		v, err := decodeBinHeader(f.Value)
		if err != nil {
			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-status-details-bin: %v", err)
			return
		}
		s := &spb.Status{}
		if err := proto.Unmarshal(v, s); err != nil {
			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-status-details-bin: %v", err)
			return
		}
		d.data.statusGen = status.FromProto(s)
	case "grpc-timeout":
		d.data.timeoutSet = true
		var err error
		if d.data.timeout, err = decodeTimeout(f.Value); err != nil {
			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed time-out: %v", err)
		}
	case ":path":
		d.data.method = f.Value
	case ":status":
		code, err := strconv.Atoi(f.Value)
		if err != nil {
			d.data.httpErr = status.Errorf(codes.Internal, "transport: malformed http-status: %v", err)
			return
		}
		d.data.httpStatus = &code
	case "grpc-tags-bin":
		v, err := decodeBinHeader(f.Value)
		if err != nil {
			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-tags-bin: %v", err)
			return
		}
		d.data.statsTags = v
		d.addMetadata(f.Name, string(v))
	case "grpc-trace-bin":
		v, err := decodeBinHeader(f.Value)
		if err != nil {
			d.data.grpcErr = status.Errorf(codes.Internal, "transport: malformed grpc-trace-bin: %v", err)
			return
		}
		d.data.statsTrace = v
		d.addMetadata(f.Name, string(v))
	default:
		if isReservedHeader(f.Name) && !isWhitelistedHeader(f.Name) {
			break
		}
		v, err := decodeMetadataHeader(f.Name, f.Value)
		if err != nil {
			if logger.V(logLevel) {
				logger.Errorf("Failed to decode metadata header (%q, %q): %v", f.Name, f.Value, err)
			}
			return
		}
		d.addMetadata(f.Name, v)
	}
}

type timeoutUnit uint8

const (
	hour        timeoutUnit = 'H'
	minute      timeoutUnit = 'M'
	second      timeoutUnit = 'S'
	millisecond timeoutUnit = 'm'
	microsecond timeoutUnit = 'u'
	nanosecond  timeoutUnit = 'n'
)

func timeoutUnitToDuration(u timeoutUnit) (d time.Duration, ok bool) {
	switch u {
	case hour:
		return time.Hour, true
	case minute:
		return time.Minute, true
	case second:
		return time.Second, true
	case millisecond:
		return time.Millisecond, true
	case microsecond:
		return time.Microsecond, true
	case nanosecond:
		return time.Nanosecond, true
	default:
	}
	return
}

func decodeTimeout(s string) (time.Duration, error) {
	size := len(s)
	if size < 2 {
		return 0, fmt.Errorf("transport: timeout string is too short: %q", s)
	}

		return 0, fmt.Errorf("transport: timeout string is too long: %q", s)
	}
	unit := timeoutUnit(s[size-1])
	d, ok := timeoutUnitToDuration(unit)
	if !ok {
		return 0, fmt.Errorf("transport: timeout unit is not recognized: %q", s)
	}
	t, err := strconv.ParseInt(s[:size-1], 10, 64)
	if err != nil {
		return 0, err
	}
	const maxHours = math.MaxInt64 / int64(time.Hour)

		return time.Duration(math.MaxInt64), nil
	}
	return d * time.Duration(t), nil
}

const (
	spaceByte   = ' '
	tildeByte   = '~'
	percentByte = '%'
)

func encodeGrpcMessage(msg string) string {
	if msg == "" {
		return ""
	}
	lenMsg := len(msg)
	for i := 0; i < lenMsg; i++ {
		c := msg[i]
		if !(c >= spaceByte && c <= tildeByte && c != percentByte) {
			return encodeGrpcMessageUnchecked(msg)
		}
	}
	return msg
}

func encodeGrpcMessageUnchecked(msg string) string {
	var buf bytes.Buffer
	for len(msg) > 0 {
		r, size := utf8.DecodeRuneInString(msg)
		for _, b := range []byte(string(r)) {

				buf.WriteString(fmt.Sprintf("%%%02X", b))
				continue
			}

			if b >= spaceByte && b <= tildeByte && b != percentByte {
				buf.WriteByte(b)
			} else {
				buf.WriteString(fmt.Sprintf("%%%02X", b))
			}
		}
		msg = msg[size:]
	}
	return buf.String()
}

func decodeGrpcMessage(msg string) string {
	if msg == "" {
		return ""
	}
	lenMsg := len(msg)
	for i := 0; i < lenMsg; i++ {
		if msg[i] == percentByte && i+2 < lenMsg {
			return decodeGrpcMessageUnchecked(msg)
		}
	}
	return msg
}

func decodeGrpcMessageUnchecked(msg string) string {
	var buf bytes.Buffer
	lenMsg := len(msg)
	for i := 0; i < lenMsg; i++ {
		c := msg[i]
		if c == percentByte && i+2 < lenMsg {
			parsed, err := strconv.ParseUint(msg[i+1:i+3], 16, 8)
			if err != nil {
				buf.WriteByte(c)
			} else {
				buf.WriteByte(byte(parsed))
				i += 2
			}
		} else {
			buf.WriteByte(c)
		}
	}
	return buf.String()
}

type bufWriter struct {
	buf       []byte
	offset    int
	batchSize int
	conn      net.Conn
	err       error

	onFlush func()
}

func newBufWriter(conn net.Conn, batchSize int) *bufWriter {
	return &bufWriter{
		buf:       make([]byte, batchSize*2),
		batchSize: batchSize,
		conn:      conn,
	}
}

func (w *bufWriter) Write(b []byte) (n int, err error) {
	if w.err != nil {
		return 0, w.err
	}
	if w.batchSize == 0 { // Buffer has been disabled.
		return w.conn.Write(b)
	}
	for len(b) > 0 {
		nn := copy(w.buf[w.offset:], b)
		b = b[nn:]
		w.offset += nn
		n += nn
		if w.offset >= w.batchSize {
			err = w.Flush()
		}
	}
	return n, err
}

func (w *bufWriter) Flush() error {
	if w.err != nil {
		return w.err
	}
	if w.offset == 0 {
		return nil
	}
	if w.onFlush != nil {
		w.onFlush()
	}
	_, w.err = w.conn.Write(w.buf[:w.offset])
	w.offset = 0
	return w.err
}

type framer struct {
	writer *bufWriter
	fr     *http2.Framer
}

func newFramer(conn net.Conn, writeBufferSize, readBufferSize int, maxHeaderListSize uint32) *framer {
	if writeBufferSize < 0 {
		writeBufferSize = 0
	}
	var r io.Reader = conn
	if readBufferSize > 0 {
		r = bufio.NewReaderSize(r, readBufferSize)
	}
	w := newBufWriter(conn, writeBufferSize)
	f := &framer{
		writer: w,
		fr:     http2.NewFramer(w, r),
	}

	f.fr.SetReuseFrames()
	f.fr.MaxHeaderListSize = maxHeaderListSize
	f.fr.ReadMetaHeaders = hpack.NewDecoder(http2InitHeaderTableSize, nil)
	return f