package slicewriter

import "io"

type SliceWriter struct {
	off int
	buf []byte
}

func (w *SliceWriter) Write(p []byte) (int, error) {
	if len(p)+w.off <= len(w.buf) {
		copy(w.buf[w.off:], p)
		w.off += len(p)
		return len(p), nil
	}

	space := len(w.buf) - w.off
	copy(w.buf[:w.off], p[:space])
	w.off += space
	return space, io.ErrShortWrite
}

func (w *SliceWriter) Reset() {
	w.off = 0
}

func (w *SliceWriter) Bytes() []byte {
	return w.buf[:w.off]
}

func NewSliceWriter(b []byte) *SliceWriter {
	return &SliceWriter{
		off: 0,
		buf: b,
	}
}