package internal

import (
	"io"
)

type StreamReader struct {
	dataChan   <-chan []byte
	cancelChan chan<- interface{}
	extraData  []byte
}

func NewStreamReader(stream *Stream) io.ReadCloser {

	r, w := io.Pipe()

	stream.Subscribe(w)

	return r
}

func (reader *StreamReader) Close() error {
	reader.cancelChan <- nil
	return nil
}

func (reader *StreamReader) Read(data []byte) (n int, err error) {
	n = 0
	ok := false

	// Do we have a buffer to read data from?
	if reader.extraData == nil {
		// Fill our buffer with new data.
		reader.extraData, ok = <-reader.dataChan
		if !ok { // EOF?
			err = io.EOF
			return
		}
	}

	// Target array too small to fit all of our data? Keep the rest.
	if len(reader.extraData) > len(data) {
		copy(data, reader.extraData[0:len(data)])
		reader.extraData = reader.extraData[len(data):]
		n = len(data)
		return
	}

	// Copy all of the buffer and reset the buffer.
	copy(data, reader.extraData)
	n = len(reader.extraData)
	reader.extraData = nil
	return
}