package testsupport

import (
	"context"
	"errors"
	"io"
	"log"
)

type ChannelReadWriter struct {
	ctx      context.Context
	receiver <-chan []byte
	// bytes that were read and that did not fit
	readBuf []byte
	sender  chan<- []byte
	closed  bool
}

func NewChannelReadWriter(ctx context.Context, receiver <-chan []byte,
	sender chan<- []byte) *ChannelReadWriter {
	return &ChannelReadWriter{
		ctx:      ctx,
		receiver: receiver,
		sender:   sender,
		closed:   false,
	}
}

func (rw *ChannelReadWriter) Read(p []byte) (n int, err error) {
	nread := copy(p, rw.readBuf)
	if nread > 0 {
		log.Printf("Read %v bytes", nread)
		rw.readBuf = rw.readBuf[nread:]
		return nread, nil
	}

	select {
	case <-rw.ctx.Done():
		return 0, io.EOF
	case data, ok := <-rw.receiver:
		if !ok {
			return 0, io.EOF
		}
		nread = copy(p, data)
		rw.readBuf = data[nread:]
		return nread, nil
	}

}
func (rw *ChannelReadWriter) Write(p []byte) (n int, err error) {
	if rw.closed {
		return 0, errors.New("Write on closed channel")
	}
	select {
	case <-rw.ctx.Done():
		rw.Close()
		return 0, io.EOF
	case rw.sender <- p:
	}
	return len(p), nil
}

func (rw *ChannelReadWriter) Close() error {
	if !rw.closed {
		close(rw.sender)
		rw.closed = true
	}
	return nil
}