package buf

type MergingReader struct {
	reader        Reader
	timeoutReader TimeoutReader
	leftover      *Buffer
}

func NewMergingReader(reader Reader) Reader {
	return &MergingReader{
		reader:        reader,
		timeoutReader: reader.(TimeoutReader),
	}
}

func (r *MergingReader) Read() (*Buffer, error) {
	if r.leftover != nil {
		b := r.leftover
		r.leftover = nil
		return b, nil
	}

	b, err := r.reader.Read()
	if err != nil {
		return nil, err
	}

	if b.IsFull() {
		return b, nil
	}

	if r.timeoutReader == nil {
		return b, nil
	}

	for {
		b2, err := r.timeoutReader.ReadTimeout(0)
		if err != nil {
			break
		}

		nBytes := b.Append(b2.Bytes())
		b2.SliceFrom(nBytes)
		if b2.IsEmpty() {
			b2.Release()
		} else {
			r.leftover = b2
			break
		}
	}

	return b, nil
}