// Command gentone writes the WAV test pack's tone (0.8 s at 440 Hz, then
// 0.2 s at 880 Hz as an end marker) as integer PCM, optionally with the
// WAVE_FORMAT_EXTENSIBLE header many audio tools write.
//
//	go run ./tools/checkpoint-a/gentone -rate 48000 -bits 24 -channels 2 -extensible out.wav
package main

import (
	"bytes"
	"encoding/binary"
	"flag"
	"fmt"
	"math"
	"os"
)

func main() {
	rate := flag.Int("rate", 44100, "sample rate")
	bits := flag.Int("bits", 16, "bits per sample: 16 or 24")
	channels := flag.Int("channels", 1, "1 or 2")
	ext := flag.Bool("extensible", false, "write a WAVE_FORMAT_EXTENSIBLE header (PCM sub-format)")
	flag.Parse()
	if flag.NArg() != 1 || (*bits != 16 && *bits != 24) || *channels < 1 || *channels > 2 {
		fmt.Fprintln(os.Stderr, "usage: gentone [-rate N] [-bits 16|24] [-channels 1|2] [-extensible] out.wav")
		os.Exit(2)
	}
	if err := os.WriteFile(flag.Arg(0), tone(*rate, *bits, *channels, *ext), 0o644); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func tone(rate, bits, channels int, ext bool) []byte {
	le := binary.LittleEndian
	width := bits / 8
	var data bytes.Buffer
	fade := 0.005 * float64(rate)
	for i := 0; i < rate; i++ {
		t := float64(i) / float64(rate)
		f := 440.0
		if t >= 0.8 {
			f = 880
		}
		env := math.Min(1, math.Min(float64(i)/fade, float64(rate-1-i)/fade))
		v := 0.5 * env * math.Sin(2*math.Pi*f*t)
		s := int32(math.Round(v * float64(int32(1)<<(bits-1)-1)))
		var b [4]byte
		le.PutUint32(b[:], uint32(s))
		for c := 0; c < channels; c++ {
			data.Write(b[:width])
		}
	}

	align := channels * width
	var fmtc bytes.Buffer
	tag := uint16(1)
	if ext {
		tag = 0xFFFE
	}
	for _, v := range []any{tag, uint16(channels), uint32(rate), uint32(rate * align), uint16(align), uint16(bits)} {
		binary.Write(&fmtc, le, v)
	}
	if ext {
		mask := uint32(4) // front centre
		if channels == 2 {
			mask = 3 // front left, front right
		}
		for _, v := range []any{uint16(22), uint16(bits), mask} {
			binary.Write(&fmtc, le, v)
		}
		// KSDATAFORMAT_SUBTYPE_PCM 00000001-0000-0010-8000-00aa00389b71
		fmtc.Write([]byte{1, 0, 0, 0, 0, 0, 0x10, 0, 0x80, 0, 0, 0xaa, 0, 0x38, 0x9b, 0x71})
	}

	var body bytes.Buffer
	body.WriteString("WAVEfmt ")
	binary.Write(&body, le, uint32(fmtc.Len()))
	body.Write(fmtc.Bytes())
	body.WriteString("data")
	binary.Write(&body, le, uint32(data.Len()))
	body.Write(data.Bytes())
	if data.Len()%2 == 1 {
		body.WriteByte(0)
	}
	var out bytes.Buffer
	out.WriteString("RIFF")
	binary.Write(&out, le, uint32(body.Len()))
	out.Write(body.Bytes())
	return out.Bytes()
}