package runtime

import (
	"context"
	"encoding/base64"
	"fmt"
	"net"
	"net/http"
	"net/textproto"
	"strconv"
	"strings"
	"sync"
	"time"

	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/grpclog"
	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/status"
)

// MetadataHeaderPrefix is the http prefix that represents custom metadata
// parameters to or from a gRPC call.
const MetadataHeaderPrefix = "Grpc-Metadata-"

// MetadataPrefix is prepended to permanent HTTP header keys (as specified
// by the IANA) when added to the gRPC context.
const MetadataPrefix = "grpcgateway-"

// MetadataTrailerPrefix is prepended to gRPC metadata as it is converted to
// HTTP headers in a response handled by grpc-gateway
const MetadataTrailerPrefix = "Grpc-Trailer-"

const metadataGrpcTimeout = "Grpc-Timeout"
const metadataHeaderBinarySuffix = "-Bin"

const xForwardedFor = "X-Forwarded-For"
const xForwardedHost = "X-Forwarded-Host"

// DefaultContextTimeout is used for gRPC call context.WithTimeout whenever a Grpc-Timeout inbound
// header isn't present. If the value is 0 the sent `context` will not have a timeout.
var DefaultContextTimeout = 0 * time.Second

// malformedHTTPHeaders lists the headers that the gRPC server may reject outright as malformed.
// See https://github.com/grpc/grpc-go/pull/4803#issuecomment-986093310 for more context.
var malformedHTTPHeaders = map[string]struct{}{
	"connection": {},
}

type (
	rpcMethodKey       struct{}
	httpPathPatternKey struct{}

	AnnotateContextOption func(ctx context.Context) context.Context
)

func WithHTTPPathPattern(pattern string) AnnotateContextOption {
	return func(ctx context.Context) context.Context {
		return withHTTPPathPattern(ctx, pattern)
	}
}

func decodeBinHeader(v string) ([]byte, error) {
	if len(v)%4 == 0 {
		// Input was padded, or padding was not necessary.
		return base64.StdEncoding.DecodeString(v)
	}
	return base64.RawStdEncoding.DecodeString(v)
}

/*
AnnotateContext adds context information such as metadata from the request.

At a minimum, the RemoteAddr is included in the fashion of "X-Forwarded-For",
except that the forwarded destination is not another HTTP service but rather
a gRPC service.
*/
func AnnotateContext(ctx context.Context, mux *ServeMux, req *http.Request, rpcMethodName string, options ...AnnotateContextOption) (context.Context, error) {
	ctx, md, err := annotateContext(ctx, mux, req, rpcMethodName, options...)
	if err != nil {
		return nil, err
	}
	if md == nil {
		return ctx, nil
	}

	return metadata.NewOutgoingContext(ctx, md), nil
}

// AnnotateIncomingContext adds context information such as metadata from the request.
// Attach metadata as incoming context.
func AnnotateIncomingContext(ctx context.Context, mux *ServeMux, req *http.Request, rpcMethodName string, options ...AnnotateContextOption) (context.Context, error) {
	ctx, md, err := annotateContext(ctx, mux, req, rpcMethodName, options...)
	if err != nil {
		return nil, err
	}
	if md == nil {
		return ctx, nil
	}

	return metadata.NewIncomingContext(ctx, md), nil
}

func isValidGRPCMetadataKey(key string) bool {
	// Must be a valid gRPC "Header-Name" as defined here:
	//   https://github.com/grpc/grpc/blob/4b05dc88b724214d0c725c8e7442cbc7a61b1374/doc/PROTOCOL-HTTP2.md
	// This means 0-9 a-z _ - .
	// Only lowercase letters are valid in the wire protocol, but the client library will normalize
	// uppercase ASCII to lowercase, so uppercase ASCII is also acceptable.
	bytes := []byte(key) // gRPC validates strings on the byte level, not Unicode.
	for _, ch := range bytes {
		validLowercaseLetter := ch >= 'a' && ch <= 'z'
		validUppercaseLetter := ch >= 'A' && ch <= 'Z'
		validDigit := ch >= '0' && ch <= '9'
		validOther := ch == '.' || ch == '-' || ch == '_'
		if !validLowercaseLetter && !validUppercaseLetter && !validDigit && !validOther {
			return false
		}
	}
	return true
}

func isValidGRPCMetadataTextValue(textValue string) bool {
	// Must be a valid gRPC "ASCII-Value" as defined here:
	//   https://github.com/grpc/grpc/blob/4b05dc88b724214d0c725c8e7442cbc7a61b1374/doc/PROTOCOL-HTTP2.md
	// This means printable ASCII (including/plus spaces); 0x20 to 0x7E inclusive.
	bytes := []byte(textValue) // gRPC validates strings on the byte level, not Unicode.
	for _, ch := range bytes {
		if ch < 0x20 || ch > 0x7E {
			return false
		}
	}
	return true
}

func annotateContext(ctx context.Context, mux *ServeMux, req *http.Request, rpcMethodName string, options ...AnnotateContextOption) (context.Context, metadata.MD, error) {
	ctx = withRPCMethod(ctx, rpcMethodName)
	for _, o := range options {
		ctx = o(ctx)
	}
	timeout := DefaultContextTimeout
	if tm := req.Header.Get(metadataGrpcTimeout); tm != "" {
		var err error
		timeout, err = timeoutDecode(tm)
		if err != nil {
			return nil, nil, status.Errorf(codes.InvalidArgument, "invalid grpc-timeout: %s", tm)
		}
	}
	var pairs []string
	for key, vals := range req.Header {
		key = textproto.CanonicalMIMEHeaderKey(key)
		switch key {
		case xForwardedFor, xForwardedHost:
			// Handled separately below
			continue
		}

		for _, val := range vals {
			// For backwards-compatibility, pass through 'authorization' header with no prefix.
			if key == "Authorization" {
				pairs = append(pairs, "authorization", val)
			}
			if h, ok := mux.incomingHeaderMatcher(key); ok {
				if !isValidGRPCMetadataKey(h) {
					grpclog.Errorf("HTTP header name %q is not valid as gRPC metadata key; skipping", h)
					continue
				}
				// Handles "-bin" metadata in grpc, since grpc will do another base64
				// encode before sending to server, we need to decode it first.
				if strings.HasSuffix(key, metadataHeaderBinarySuffix) {
					b, err := decodeBinHeader(val)
					if err != nil {
						return nil, nil, status.Errorf(codes.InvalidArgument, "invalid binary header %s: %s", key, err)
					}

					val = string(b)
				} else if !isValidGRPCMetadataTextValue(val) {
					grpclog.Errorf("Value of HTTP header %q contains non-ASCII value (not valid as gRPC metadata): skipping", h)
					continue
				}
				pairs = append(pairs, h, val)
			}
		}
	}
	if host := req.Header.Get(xForwardedHost); host != "" {
		pairs = append(pairs, strings.ToLower(xForwardedHost), host)
	} else if req.Host != "" {
		pairs = append(pairs, strings.ToLower(xForwardedHost), req.Host)
	}

	xff := req.Header.Values(xForwardedFor)
	if addr := req.RemoteAddr; addr != "" {
		if remoteIP, _, err := net.SplitHostPort(addr); err == nil {
			xff = append(xff, remoteIP)
		}
	}
	if len(xff) > 0 {
		pairs = append(pairs, strings.ToLower(xForwardedFor), strings.Join(xff, ", "))
	}

	if timeout != 0 {
		ctx, _ = context.WithTimeout(ctx, timeout)
	}
	if len(pairs) == 0 {
		return ctx, nil, nil
	}
	md := metadata.Pairs(pairs...)
	for _, mda := range mux.metadataAnnotators {
		md = metadata.Join(md, mda(ctx, req))
	}
	return ctx, md, nil
}

// ServerMetadata consists of metadata sent from gRPC server.
type ServerMetadata struct {
	HeaderMD  metadata.MD
	TrailerMD metadata.MD
}

type serverMetadataKey struct{}

// NewServerMetadataContext creates a new context with ServerMetadata
func NewServerMetadataContext(ctx context.Context, md ServerMetadata) context.Context {
	if ctx == nil {
		ctx = context.Background()
	}
	return context.WithValue(ctx, serverMetadataKey{}, md)
}

// ServerMetadataFromContext returns the ServerMetadata in ctx
func ServerMetadataFromContext(ctx context.Context) (md ServerMetadata, ok bool) {
	if ctx == nil {
		return md, false
	}
	md, ok = ctx.Value(serverMetadataKey{}).(ServerMetadata)
	return
}

// ServerTransportStream implements grpc.ServerTransportStream.
// It should only be used by the generated files to support grpc.SendHeader
// outside of gRPC server use.
type ServerTransportStream struct {
	mu      sync.Mutex
	header  metadata.MD
	trailer metadata.MD
}

// Method returns the method for the stream.
func (s *ServerTransportStream) Method() string {
	return ""
}

// Header returns the header metadata of the stream.
func (s *ServerTransportStream) Header() metadata.MD {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.header.Copy()
}

// SetHeader sets the header metadata.
func (s *ServerTransportStream) SetHeader(md metadata.MD) error {
	if md.Len() == 0 {
		return nil
	}

	s.mu.Lock()
	s.header = metadata.Join(s.header, md)
	s.mu.Unlock()
	return nil
}

// SendHeader sets the header metadata.
func (s *ServerTransportStream) SendHeader(md metadata.MD) error {
	return s.SetHeader(md)
}

// Trailer returns the cached trailer metadata.
func (s *ServerTransportStream) Trailer() metadata.MD {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.trailer.Copy()
}

// SetTrailer sets the trailer metadata.
func (s *ServerTransportStream) SetTrailer(md metadata.MD) error {
	if md.Len() == 0 {
		return nil
	}

	s.mu.Lock()
	s.trailer = metadata.Join(s.trailer, md)
	s.mu.Unlock()
	return nil
}

func timeoutDecode(s string) (time.Duration, error) {
	size := len(s)
	if size < 2 {
		return 0, fmt.Errorf("timeout string is too short: %q", s)
	}
	d, ok := timeoutUnitToDuration(s[size-1])
	if !ok {
		return 0, fmt.Errorf("timeout unit is not recognized: %q", s)
	}
	t, err := strconv.ParseInt(s[:size-1], 10, 64)
	if err != nil {
		return 0, err
	}
	return d * time.Duration(t), nil
}

func timeoutUnitToDuration(u uint8) (d time.Duration, ok bool) {
	switch u {
	case 'H':
		return time.Hour, true
	case 'M':
		return time.Minute, true
	case 'S':
		return time.Second, true
	case 'm':
		return time.Millisecond, true
	case 'u':
		return time.Microsecond, true
	case 'n':
		return time.Nanosecond, true
	default:
		return
	}
}

// isPermanentHTTPHeader checks whether hdr belongs to the list of
// permanent request headers maintained by IANA.
// http://www.iana.org/assignments/message-headers/message-headers.xml
func isPermanentHTTPHeader(hdr string) bool {
	switch hdr {
	case
		"Accept",
		"Accept-Charset",
		"Accept-Language",
		"Accept-Ranges",
		"Authorization",
		"Cache-Control",
		"Content-Type",
		"Cookie",
		"Date",
		"Expect",
		"From",
		"Host",
		"If-Match",
		"If-Modified-Since",
		"If-None-Match",
		"If-Schedule-Tag-Match",
		"If-Unmodified-Since",
		"Max-Forwards",
		"Origin",
		"Pragma",
		"Referer",
		"User-Agent",
		"Via",
		"Warning":
		return true
	}
	return false
}

// isMalformedHTTPHeader checks whether header belongs to the list of
// "malformed headers" and would be rejected by the gRPC server.
func isMalformedHTTPHeader(header string) bool {
	_, isMalformed := malformedHTTPHeaders[strings.ToLower(header)]
	return isMalformed
}

// RPCMethod returns the method string for the server context. The returned
// string is in the format of "/package.service/method".
func RPCMethod(ctx context.Context) (string, bool) {
	m := ctx.Value(rpcMethodKey{})
	if m == nil {
		return "", false
	}
	ms, ok := m.(string)
	if !ok {
		return "", false
	}
	return ms, true
}

func withRPCMethod(ctx context.Context, rpcMethodName string) context.Context {
	return context.WithValue(ctx, rpcMethodKey{}, rpcMethodName)
}

// HTTPPathPattern returns the HTTP path pattern string relating to the HTTP handler, if one exists.
// The format of the returned string is defined by the google.api.http path template type.
func HTTPPathPattern(ctx context.Context) (string, bool) {
	m := ctx.Value(httpPathPatternKey{})
	if m == nil {
		return "", false
	}
	ms, ok := m.(string)
	if !ok {
		return "", false
	}
	return ms, true
}

func withHTTPPathPattern(ctx context.Context, httpPathPattern string) context.Context {
	return context.WithValue(ctx, httpPathPatternKey{}, httpPathPattern)
}