package flac

import (
	"bytes"
	"errors"
	"io"

	"github.com/go-audio/audio"
	"github.com/go-audio/wav"
	"github.com/mewkiz/flac"
)

const wavAudioFormat = 1

type buffer struct {
	Buffer bytes.Buffer
	Index  int64
}

func (b *buffer) Bytes() []byte {
	return b.Buffer.Bytes()
}

func (b *buffer) Read(p []byte) (int, error) {
	n, err := bytes.NewBuffer(b.Buffer.Bytes()[b.Index:]).Read(p)

	if err == nil {
		if b.Index+int64(len(p)) < int64(b.Buffer.Len()) {
			b.Index += int64(len(p))
		} else {
			b.Index = int64(b.Buffer.Len())
		}
	}

	return n, err
}

func (b *buffer) Write(p []byte) (int, error) {
	n, err := b.Buffer.Write(p)

	if err == nil {
		b.Index = int64(b.Buffer.Len())
	}

	return n, err
}

func (b *buffer) Seek(offset int64, whence int) (int64, error) {
	var err error
	var Index int64 = 0

	switch whence {
	case 0:
		if offset >= int64(b.Buffer.Len()) || offset < 0 {
			err = errors.New("Invalid Offset.")
		} else {
			b.Index = offset
			Index = offset
		}
	default:
		err = errors.New("Unsupported Seek Method.")
	}

	return Index, err
}

// Decode takes a slice of flac and decodes to wav
func Decode(buf []byte) ([]byte, error) {
	r := bytes.NewReader(buf)
	stream, err := flac.Parse(r)
	if err != nil {
		return nil, errors.New("Could not parse FLAC")
	}
	fb := &buffer{}
	enc := wav.NewEncoder(fb, int(stream.Info.SampleRate), int(stream.Info.BitsPerSample), int(stream.Info.NChannels), wavAudioFormat)
	defer enc.Close()
	var data []int
	for {
		// Decode FLAC audio samples.
		frame, err := stream.ParseNext()
		if err != nil {
			if err == io.EOF {
				break
			}
			return nil, err
		}

		// Encode WAV audio samples.
		data = data[:0]
		for i := 0; i < frame.Subframes[0].NSamples; i++ {
			for _, subframe := range frame.Subframes {
				data = append(data, int(subframe.Samples[i]))
			}
		}
		buf := &audio.IntBuffer{
			Format: &audio.Format{
				NumChannels: int(stream.Info.NChannels),
				SampleRate:  int(stream.Info.SampleRate),
			},
			Data:           data,
			SourceBitDepth: int(stream.Info.BitsPerSample),
		}
		if err := enc.Write(buf); err != nil {
			return nil, err
		}
	}
	return fb.Bytes(), nil
}