package audio

import (
	"bytes"
	"encoding/binary"
	"encoding/json"
	"errors"
	"io"
	"time"
)

// Skip riff header and `fmt ` just 16 bytes
const (
	FmtHeaderOffset        = 0x0c
	FmtHeaderIDSize        = 4
	FmtHeaderChunkSizeSize = 4
	FmtHeaderSizeDefault   = 16
)

type WavHeader struct {
	ID            [4]byte
	Size          uint32
	AudioFormat   uint16
	NumChannels   uint16
	SampleRate    uint32
	ByteRate      uint32
	BlockAlign    uint16
	BitsPerSample uint16
}

func NewHeader(f io.Reader) (*WavHeader, error) {
	w := &WavHeader{}
	if err := w.Parse(f); err != nil {
		return nil, err
	}
	return w, nil
}

func DefaultHeader() *WavHeader {
	return &WavHeader{
		Size:          uint32(FmtHeaderSizeDefault),
		AudioFormat:   1,
		NumChannels:   2,
		SampleRate:    48000, // opus only support 48kHz
		BlockAlign:    4,
		BitsPerSample: 16,
	}
}

func (w *WavHeader) Parse(f io.Reader) error {
	// skip headers
	var headers [FmtHeaderOffset]byte
	if _, err := f.Read(headers[:]); err != nil {
		return err
	}

	var id [4]byte
	if _, err := f.Read(id[:]); err != nil {
		return err
	}
	if bytes.Equal(id[:], []byte{'f', 'm', 't', '0'}[:]) {
		return errors.New("bad header")
	}
	w.ID = id

	var size [4]byte
	if _, err := f.Read(size[:]); err != nil {
		return err
	}
	w.Size = binary.LittleEndian.Uint32(size[:])

	var af [2]byte
	if _, err := f.Read(af[:]); err != nil {
		return err
	}
	w.AudioFormat = binary.LittleEndian.Uint16(af[:])

	var nc [2]byte
	if _, err := f.Read(nc[:]); err != nil {
		return err
	}
	w.NumChannels = binary.LittleEndian.Uint16(nc[:])

	var sr [4]byte
	if _, err := f.Read(sr[:]); err != nil {
		return err
	}
	w.SampleRate = binary.LittleEndian.Uint32(sr[:])

	var br [4]byte
	if _, err := f.Read(br[:]); err != nil {
		return err
	}
	w.ByteRate = binary.LittleEndian.Uint32(br[:])

	var ba [2]byte
	if _, err := f.Read(ba[:]); err != nil {
		return err
	}
	w.BlockAlign = binary.LittleEndian.Uint16(ba[:])

	var bps [2]byte
	if _, err := f.Read(bps[:]); err != nil {
		return err
	}
	w.BitsPerSample = binary.LittleEndian.Uint16(bps[:])

	return nil
}

func (w *WavHeader) String() string {
	b, _ := json.Marshal(w)
	return string(b)
}

func (w *WavHeader) GetLatnecy(bufferSizeByBytes uint16) time.Duration {
	bytesPerSample := w.BitsPerSample / BitsPerByte
	bufferLength := bufferSizeByBytes / bytesPerSample

	return time.Second *
		time.Duration(bufferLength) /
		time.Duration(w.NumChannels) /
		time.Duration(w.SampleRate)
}