import sdl2
import sdl2/audio
import math

const BufferSizeInSamples = 2048
const BytesPerSample = 2   # 16 bit PCM
const BufferSizeInBytes = BufferSizeInSamples * BytesPerSample
const SampleRate = 44100   # Hz
const Frequence = 1000     # Hz
const Volume = 0.1         # 0..1
const x = (Frequence * 2000 / SampleRate)

var counter = 0

proc AudioCallback(userdata: pointer; stream: ptr uint8; len: cint) {.cdecl.} =
  var buffer: array[BufferSizeInSamples, int16]
  for i in 0..BufferSizeInSamples - 1:
      buffer[i] = int16(sin(float((counter + i) mod int(x)) / x * 2 * PI) * 32767)
  MixAudio(stream, cast[ptr uint8](addr(buffer[0])), BufferSizeInBytes, cint(SDL_MIX_MAXVOLUME * 0.1))
  counter = counter + BufferSizeInSamples

proc main() =
  if Init(INIT_AUDIO) != SdlSuccess:
    echo("Init() failed")
    return
  var AudioSpec: TAudioSpec
  AudioSpec.freq = 44100
  AudioSpec.format = AUDIO_S16 # 16 bit PCM
  AudioSpec.channels = 1
  AudioSpec.samples = BufferSizeInBytes
  AudioSpec.padding = 0
  AudioSpec.callback = AudioCallback
  AudioSpec.userdata = nil
  if OpenAudio(addr(AudioSpec), nil) < 0:
    echo("OpenAudio() failed")
    return
  PauseAudio(0)
  # run program for 2 seconds
  var t = 2000
  while t > 0:
    Delay(100)
    t = t - 100

main()