package smux

import (
	"bytes"
	"sync"
	"sync/atomic"

	"github.com/pkg/errors"
)

// Stream implements io.ReadWriteCloser
type Stream struct {
	id          uint32
	rstflag     int32
	sess        *Session
	frameSize   int
	chReadEvent chan struct{} // notify a read event
	die         chan struct{} // flag the stream has closed
	dieLock     sync.Mutex
}

// newStream initiates a Stream struct
func newStream(id uint32, frameSize int, sess *Session) *Stream {
	s := new(Stream)
	s.id = id
	s.chReadEvent = make(chan struct{}, 1)
	s.frameSize = frameSize
	s.sess = sess
	s.die = make(chan struct{})
	return s
}

// Read implements io.ReadWriteCloser
func (s *Stream) Read(b []byte) (n int, err error) {
READ:
	select {
	case <-s.die:
		return 0, errors.New(errBrokenPipe)
	default:
	}

	if n = s.sess.nioread(s.id, b); n > 0 {
		return n, err
	} else if atomic.LoadInt32(&s.rstflag) == 1 {
		s.Close()
		return 0, errors.New(errBrokenPipe)
	}

	select {
	case <-s.chReadEvent:
		goto READ
	case <-s.die:
		return 0, errors.New(errBrokenPipe)
	}
}

// Write implements io.ReadWriteCloser
func (s *Stream) Write(b []byte) (n int, err error) {
	select {
	case <-s.die:
		return 0, errors.New(errBrokenPipe)
	default:
	}

	frames := s.split(b, cmdPSH, s.id)
	// combine the frames
	var buffer bytes.Buffer
	for k := range frames {
		bts, _ := frames[k].MarshalBinary()
		buffer.Write(bts)
	}

	if _, err = s.sess.writeBinary(buffer.Bytes()); err != nil {
		return 0, err
	}
	return len(b), nil
}

// Close implements io.ReadWriteCloser
func (s *Stream) Close() error {
	s.dieLock.Lock()
	defer s.dieLock.Unlock()

	select {
	case <-s.die:
		return errors.New(errBrokenPipe)
	default:
		close(s.die)
		s.sess.streamClosed(s.id)
		s.sess.writeFrame(newFrame(cmdRST, s.id))
	}
	return nil
}

// notify the stream that the session has closed
func (s *Stream) sessionClose() error {
	s.dieLock.Lock()
	defer s.dieLock.Unlock()

	select {
	case <-s.die:
		return errors.New(errBrokenPipe)
	default:
		close(s.die)
	}
	return nil
}

// split large byte buffer into smaller frames
func (s *Stream) split(bts []byte, cmd byte, sid uint32) []Frame {
	var frames []Frame
	for len(bts) > int(s.frameSize) {
		frame := newFrame(cmd, sid)
		frame.data = make([]byte, s.frameSize)
		n := copy(frame.data, bts)
		bts = bts[n:]
		frames = append(frames, frame)
	}
	if len(bts) > 0 {
		frame := newFrame(cmd, sid)
		frame.data = make([]byte, len(bts))
		copy(frame.data, bts)
		frames = append(frames, frame)
	}
	return frames
}

// notify read event
func (s *Stream) notifyReadEvent() {
	select {
	case s.chReadEvent <- struct{}{}:
	default:
	}
}

// mark this stream has benn reset
func (s *Stream) markRST() {
	atomic.StoreInt32(&s.rstflag, 1)
}