package websocket

import (
	"crypto/sha1"
	"encoding/base64"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"net/http"
	"runtime/debug"
	"sync/atomic"
	"time"

	"github.com/gorilla/websocket"
	"github.com/rs/zerolog"
)

// IsWebSocketUpgrade checks to see if the request is a WebSocket connection.
func IsWebSocketUpgrade(req *http.Request) bool {
	return websocket.IsWebSocketUpgrade(req)
}

// NewResponseHeader returns headers needed to return to origin for completing handshake
func NewResponseHeader(req *http.Request) http.Header {
	header := http.Header{}
	header.Add("Connection", "Upgrade")
	header.Add("Sec-Websocket-Accept", generateAcceptKey(req.Header.Get("Sec-WebSocket-Key")))
	header.Add("Upgrade", "websocket")
	return header
}

type bidirectionalStreamStatus struct {
	doneChan chan struct{}
	anyDone  uint32
}

func newBiStreamStatus() *bidirectionalStreamStatus {
	return &bidirectionalStreamStatus{
		doneChan: make(chan struct{}, 2),
		anyDone:  0,
	}
}

func (s *bidirectionalStreamStatus) markUniStreamDone() {
	atomic.StoreUint32(&s.anyDone, 1)
	s.doneChan <- struct{}{}
}

func (s *bidirectionalStreamStatus) waitAnyDone() {
	<-s.doneChan
}
func (s *bidirectionalStreamStatus) isAnyDone() bool {
	return atomic.LoadUint32(&s.anyDone) > 0
}

// Stream copies copy data to & from provided io.ReadWriters.
func Stream(tunnelConn, originConn io.ReadWriter, log *zerolog.Logger) {
	status := newBiStreamStatus()

	go unidirectionalStream(tunnelConn, originConn, "origin->tunnel", status, log)
	go unidirectionalStream(originConn, tunnelConn, "tunnel->origin", status, log)

	// If one side is done, we are done.
	status.waitAnyDone()
}

func unidirectionalStream(dst io.Writer, src io.Reader, dir string, status *bidirectionalStreamStatus, log *zerolog.Logger) {
	defer func() {
		// The bidirectional streaming spawns 2 goroutines to stream each direction.
		// If any ends, the callstack returns, meaning the Tunnel request/stream (depending on http2 vs quic) will
		// close. In such case, if the other direction did not stop (due to application level stopping, e.g., if a
		// server/origin listens forever until closure), it may read/write from the underlying ReadWriter (backed by
		// the Edge<->cloudflared transport) in an unexpected state.

		if status.isAnyDone() {
			// Because of this, we set this recover() logic, which kicks-in *only* if any stream is known to have
			// exited. In such case, we stop a possible panic from propagating upstream.
			if r := recover(); r != nil {
				// We handle such unexpected errors only when we detect that one side of the streaming is done.
				log.Debug().Msgf("Gracefully handled error %v in Streaming for %s, error %s", r, dir, debug.Stack())
			}
		}
	}()

	_, err := copyData(dst, src, dir)
	if err != nil {
		log.Debug().Msgf("%s copy: %v", dir, err)
	}
	status.markUniStreamDone()
}

// when set to true, enables logging of content copied to/from origin and tunnel
const debugCopy = false

func copyData(dst io.Writer, src io.Reader, dir string) (written int64, err error) {
	if debugCopy {
		// copyBuffer is based on stdio Copy implementation but shows copied data
		copyBuffer := func(dst io.Writer, src io.Reader, dir string) (written int64, err error) {
			var buf []byte
			size := 32 * 1024
			buf = make([]byte, size)
			for {
				t := time.Now()
				nr, er := src.Read(buf)
				if nr > 0 {
					fmt.Println(dir, t.UnixNano(), "\n"+hex.Dump(buf[0:nr]))
					nw, ew := dst.Write(buf[0:nr])
					if nw < 0 || nr < nw {
						nw = 0
						if ew == nil {
							ew = errors.New("invalid write")
						}
					}
					written += int64(nw)
					if ew != nil {
						err = ew
						break
					}
					if nr != nw {
						err = io.ErrShortWrite
						break
					}
				}
				if er != nil {
					if er != io.EOF {
						err = er
					}
					break
				}
			}
			return written, err
		}
		return copyBuffer(dst, src, dir)
	} else {
		return io.Copy(dst, src)
	}
}

// from RFC-6455
var keyGUID = []byte("258EAFA5-E914-47DA-95CA-C5AB0DC85B11")

func generateAcceptKey(challengeKey string) string {
	h := sha1.New()
	h.Write([]byte(challengeKey))
	h.Write(keyGUID)
	return base64.StdEncoding.EncodeToString(h.Sum(nil))
}