//go:build !disable_format_alac
// +build !disable_format_alac

package alac

import (
	"bytes"
	"errors"
	"github.com/edgeware/mp4ff/mp4"
	"io"
)

type mp4Decoder struct {
	mp4     *mp4.File
	reader  io.ReadSeekCloser
	trackId uint32
	cookie  []byte

	currentSegment  int
	currentFragment int
	currentSample   uint32
}

func tryDecodeMP4(r io.ReadSeekCloser) (*mp4Decoder, error) {
	//TODO: mp4.DecModeLazyMdat errors in segmented files
	parsedMp4, err := mp4.DecodeFile(r, mp4.WithDecodeMode(mp4.DecModeNormal))
	if err != nil {
		return nil, err
	}

	var trackId uint32
	var magicCookie []byte

	for _, trak := range parsedMp4.Moov.Traks {
		if box, err := trak.Mdia.Minf.Stbl.Stsd.GetSampleDescription(0); err == nil && box.Type() == "alac" {
			trackId = trak.Tkhd.TrackID

			buf := new(bytes.Buffer)
			box.Encode(buf)

			boxBytes := buf.Bytes()

			boxOffset := 36 + 12

			magicCookie = boxBytes[boxOffset:]
			break

		}
	}

	if magicCookie == nil {
		return nil, errors.New("could not find track entry")
	}

	return &mp4Decoder{
		reader:        r,
		mp4:           parsedMp4,
		cookie:        magicCookie,
		trackId:       trackId,
		currentSample: 1,
	}, nil
}

func (d *mp4Decoder) Read() (samples [][]byte) {
	if d.mp4.IsFragmented() {
		if d.currentSegment >= len(d.mp4.Segments) {
			//EOF
			return nil
		}
		segment := d.mp4.Segments[d.currentSegment]

		if d.currentFragment >= len(segment.Fragments) {
			d.currentSegment++
			d.currentFragment = 0
			return d.Read()
		}

		frag := segment.Fragments[d.currentFragment]

		fullSamples, err := frag.GetFullSamples(&mp4.TrexBox{
			TrackID: d.trackId,
		})
		if err != nil {
			return nil
		}

		for _, sample := range fullSamples {
			samples = append(samples, sample.Data)
		}
		d.currentFragment++

		return
	} else {
		for _, trak := range d.mp4.Moov.Traks {
			if trak.Tkhd.TrackID == d.trackId {
				buf := new(bytes.Buffer)
				if err := d.mp4.CopySampleData(buf, d.reader, trak, d.currentSample, d.currentSample); err != nil {
					return nil
				}
				d.currentSample++

				return [][]byte{buf.Bytes()}
			}
		}
		return
	}
}