// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

//go:build !plan9

// Package spdy contains functionality for parsing SPDY streaming sessions. This
// is used for 'kubectl exec' session recording.
package spdy

import (
	"bytes"
	"encoding/binary"
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"sync"
	"sync/atomic"

	"go.uber.org/zap"
	corev1 "k8s.io/api/core/v1"
	"tailscale.com/k8s-operator/sessionrecording/tsrecorder"
	"tailscale.com/sessionrecording"
)

// New wraps the provided network connection and returns a connection whose reads and writes will get triggered as data is received on the hijacked connection.
// The connection must be a hijacked connection for a 'kubectl exec' session using SPDY.
// The hijacked connection is used to transmit SPDY streams between Kubernetes client ('kubectl') and the destination container.
// Data read from the underlying network connection is data sent via one of the SPDY streams from the client to the container.
// Data written to the underlying connection is data sent from the container to the client.
// We parse the data and send everything for the STDOUT/STDERR streams to the configured tsrecorder as an asciinema recording with the provided header.
// https://github.com/kubernetes/enhancements/tree/master/keps/sig-api-machinery/4006-transition-spdy-to-websockets#background-remotecommand-subprotocol
func New(nc net.Conn, rec *tsrecorder.Client, ch sessionrecording.CastHeader, log *zap.SugaredLogger) net.Conn {
	return &conn{
		Conn: nc,
		rec:  rec,
		ch:   ch,
		log:  log,
	}
}

// conn is a wrapper around net.Conn. It reads the bytestream for a 'kubectl
// exec' session streamed using SPDY protocol, sends session recording data to
// the configured recorder and forwards the raw bytes to the original
// destination.
type conn struct {
	net.Conn
	// rec knows how to send data written to it to a tsrecorder instance.
	rec *tsrecorder.Client
	ch  sessionrecording.CastHeader

	stdoutStreamID atomic.Uint32
	stderrStreamID atomic.Uint32
	resizeStreamID atomic.Uint32

	wmu    sync.Mutex // sequences writes
	closed bool

	rmu                 sync.Mutex // sequences reads
	writeCastHeaderOnce sync.Once

	zlibReqReader zlibReader
	// writeBuf is used to store data written to the connection that has not
	// yet been parsed as SPDY frames.
	writeBuf bytes.Buffer
	// readBuf is used to store data read from the connection that has not
	// yet been parsed as SPDY frames.
	readBuf bytes.Buffer
	log     *zap.SugaredLogger
}

// Read reads bytes from the original connection and parses them as SPDY frames.
// If the frame is a data frame for resize stream, sends resize message to the
// recorder. If the frame is a SYN_STREAM control frame that starts stdout,
// stderr or resize stream, store the stream ID.
func (c *conn) Read(b []byte) (int, error) {
	c.rmu.Lock()
	defer c.rmu.Unlock()
	n, err := c.Conn.Read(b)
	if err != nil {
		return n, fmt.Errorf("error reading from connection: %w", err)
	}
	c.readBuf.Write(b[:n])

	var sf spdyFrame
	ok, err := sf.Parse(c.readBuf.Bytes(), c.log)
	if err != nil {
		return 0, fmt.Errorf("error parsing data read from connection: %w", err)
	}
	if !ok {
		// The parsed data in the buffer will be processed together with
		// the new data on the next call to Read.
		return n, nil
	}
	c.readBuf.Next(len(sf.Raw)) // advance buffer past the parsed frame

	if !sf.Ctrl { // data frame
		switch sf.StreamID {
		case c.resizeStreamID.Load():
			var err error
			var msg spdyResizeMsg
			if err = json.Unmarshal(sf.Payload, &msg); err != nil {
				return 0, fmt.Errorf("error umarshalling resize msg: %w", err)
			}
			c.ch.Width = msg.Width
			c.ch.Height = msg.Height
		}
		return n, nil
	}
	// We always want to parse the headers, even if we don't care about the
	// frame, as we need to advance the zlib reader otherwise we will get
	// garbage.
	header, err := sf.parseHeaders(&c.zlibReqReader, c.log)
	if err != nil {
		return 0, fmt.Errorf("error parsing frame headers: %w", err)
	}
	if sf.Type == SYN_STREAM {
		c.storeStreamID(sf, header)
	}
	return n, nil
}

// Write forwards the raw data of the latest parsed SPDY frame to the original
// destination. If the frame is an SPDY data frame, it also sends the payload to
// the connected session recorder.
func (c *conn) Write(b []byte) (int, error) {
	c.wmu.Lock()
	defer c.wmu.Unlock()
	c.writeBuf.Write(b)

	var sf spdyFrame
	ok, err := sf.Parse(c.writeBuf.Bytes(), c.log)
	if err != nil {
		return 0, fmt.Errorf("error parsing data: %w", err)
	}
	if !ok {
		// The parsed data in the buffer will be processed together with
		// the new data on the next call to Write.
		return len(b), nil
	}
	c.writeBuf.Next(len(sf.Raw)) // advance buffer past the parsed frame

	// If this is a stdout or stderr data frame, send its payload to the
	// session recorder.
	if !sf.Ctrl {
		switch sf.StreamID {
		case c.stdoutStreamID.Load(), c.stderrStreamID.Load():
			var err error
			c.writeCastHeaderOnce.Do(func() {
				var j []byte
				j, err = json.Marshal(c.ch)
				if err != nil {
					return
				}
				j = append(j, '\n')
				err = c.rec.WriteCastLine(j)
				if err != nil {
					c.log.Errorf("received error from recorder: %v", err)
				}
			})
			if err != nil {
				return 0, fmt.Errorf("error writing CastHeader: %w", err)
			}
			if err := c.rec.Write(sf.Payload); err != nil {
				return 0, fmt.Errorf("error sending payload to session recorder: %w", err)
			}
		}
	}
	// Forward the whole frame to the original destination.
	_, err = c.Conn.Write(sf.Raw) // send to net.Conn
	return len(b), err
}

func (c *conn) Close() error {
	c.wmu.Lock()
	defer c.wmu.Unlock()
	if c.closed {
		return nil
	}
	c.writeBuf.Reset()
	c.closed = true
	err := c.Conn.Close()
	c.rec.Close()
	return err
}

// storeStreamID parses SYN_STREAM SPDY control frame and updates
// conn to store the newly created stream's ID if it is one of
// the stream types we care about. Storing stream_id:stream_type mapping allows
// us to parse received data frames (that have stream IDs) differently depening
// on which stream they belong to (i.e send data frame payload for stdout stream
// to session recorder).
func (c *conn) storeStreamID(sf spdyFrame, header http.Header) {
	const (
		streamTypeHeaderKey = "Streamtype"
	)
	id := binary.BigEndian.Uint32(sf.Payload[0:4])
	switch header.Get(streamTypeHeaderKey) {
	case corev1.StreamTypeStdout:
		c.stdoutStreamID.Store(id)
	case corev1.StreamTypeStderr:
		c.stderrStreamID.Store(id)
	case corev1.StreamTypeResize:
		c.resizeStreamID.Store(id)
	}
}

type spdyResizeMsg struct {
	Width  int `json:"width"`
	Height int `json:"height"`
}