package exif

import "io"

type (
	writerSkipper struct {
		io.Writer
		bytesToSkip int
	}
)

func NewWriterExif(w io.Writer, exif []byte) (io.Writer, error) {
	writer := &writerSkipper{
		Writer:      w,
		bytesToSkip: 2,
	}
	soi := []byte{0xff, 0xd8}
	if _, err := w.Write(soi); err != nil {
		return nil, err
	}

	if exif != nil {
		app1Marker := 0xe1
		markerlen := 2 + len(exif)
		marker := []byte{0xff, uint8(app1Marker), uint8(markerlen >> 8), uint8(markerlen & 0xff)}
		if _, err := w.Write(marker); err != nil {
			return nil, err
		}

		if _, err := w.Write(exif); err != nil {
			return nil, err
		}
	}

	return writer, nil
}

func (w *writerSkipper) Write(data []byte) (int, error) {
	if w.bytesToSkip <= 0 {
		return w.Writer.Write(data)
	}

	if dataLen := len(data); dataLen < w.bytesToSkip {
		w.bytesToSkip -= dataLen
		return dataLen, nil
	}

	if n, err := w.Writer.Write(data[w.bytesToSkip:]); err == nil {
		n += w.bytesToSkip
		w.bytesToSkip = 0
		return n, nil
	} else {
		return n, err
	}
}