package main

import (
	"bytes"
	"encoding/binary"
	"flag"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	silk "github.com/git-jiadong/go-silk"
)

const sampleRate = 24000

func main() {
	in := flag.String("in", "", "input .silk file")
	out := flag.String("out", "", "output .wav file")
	flag.Parse()
	if strings.TrimSpace(*in) == "" || strings.TrimSpace(*out) == "" {
		fatalf("missing -in or -out")
	}
	if err := decodeSilkToWav(*in, *out); err != nil {
		fatalf("%v", err)
	}
}

func fatalf(format string, args ...interface{}) {
	_, _ = fmt.Fprintf(os.Stderr, format+"\n", args...)
	os.Exit(1)
}

func decodeSilkToWav(inputPath string, outputPath string) error {
	input, err := os.Open(inputPath)
	if err != nil {
		return fmt.Errorf("open silk failed: %w", err)
	}
	defer input.Close()
	var pcm bytes.Buffer
	writer := silk.NewWriter(&pcm)
	writer.Decoder.SetSampleRate(sampleRate)
	if _, err := io.Copy(writer, input); err != nil {
		_ = writer.Close()
		return fmt.Errorf("silk decode failed: %w", err)
	}
	if err := writer.Close(); err != nil {
		return fmt.Errorf("silk decode close failed: %w", err)
	}
	if pcm.Len() == 0 {
		return fmt.Errorf("silk decode returned empty pcm")
	}
	return writeWAV(outputPath, pcm.Bytes())
}

func writeWAV(path string, pcm []byte) error {
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return err
	}
	file, err := os.Create(path)
	if err != nil {
		return fmt.Errorf("create wav failed: %w", err)
	}
	defer file.Close()
	dataSize := uint32(len(pcm))
	header := &bytes.Buffer{}
	header.WriteString("RIFF")
	_ = binary.Write(header, binary.LittleEndian, uint32(36)+dataSize)
	header.WriteString("WAVEfmt ")
	_ = binary.Write(header, binary.LittleEndian, uint32(16))
	_ = binary.Write(header, binary.LittleEndian, uint16(1))
	_ = binary.Write(header, binary.LittleEndian, uint16(1))
	_ = binary.Write(header, binary.LittleEndian, uint32(sampleRate))
	_ = binary.Write(header, binary.LittleEndian, uint32(sampleRate*2))
	_ = binary.Write(header, binary.LittleEndian, uint16(2))
	_ = binary.Write(header, binary.LittleEndian, uint16(16))
	header.WriteString("data")
	_ = binary.Write(header, binary.LittleEndian, dataSize)
	if _, err := file.Write(header.Bytes()); err != nil {
		return err
	}
	_, err = file.Write(pcm)
	return err
}