#include "Buzzer.hpp"

#include <cmath>
#include <limits>
#include <stdexcept>
#include <cstring>

void SDLCALL Buzzer::audioCallback(void *userdata, Uint8 *stream, int len) {
  static_cast<Buzzer*>(userdata)->copySamples(stream, len);
}

Buzzer::Buzzer(unsigned buzzerFrequency) {
  SDL_AudioSpec desired;
  SDL_AudioSpec obtained;

  SDL_zero(desired);
  desired.channels = 1;
  desired.freq = 44000;
  desired.format = AUDIO_S16SYS;
  desired.samples = 4096;
  desired.callback = audioCallback;
  desired.userdata = this;
  
  mAudioDevice = SDL_OpenAudioDevice(NULL, SDL_FALSE, &desired, &obtained, SDL_AUDIO_ALLOW_FREQUENCY_CHANGE | SDL_AUDIO_ALLOW_SAMPLES_CHANGE);
  if(mAudioDevice == 0) {
    throw std::runtime_error(SDL_GetError());
  }

  // period of the sine wave, in samples, to obtained the desired
  // buffer buzzer frequency at a particular audio sample rate
  double waveLength = double(obtained.freq) / buzzerFrequency;
  // buffer size that fits a whole number of sine waves and is roughly the same size of obtained.samples
  size_t numSamples = waveLength * std::max(std::floor(obtained.samples / waveLength), 1.0);
  mSamples.resize(numSamples);

  // generate the sine wave
  auto amplitude = std::numeric_limits<sample_t>::max();
  auto angularFreq = 2.0 * M_PI / waveLength;
  for(size_t iSample = 0; iSample < numSamples; iSample++) {
    mSamples[iSample] = amplitude * std::sin(angularFreq * iSample);
  }
  miCurrentSample = 0;
}

Buzzer::~Buzzer() {
  SDL_CloseAudioDevice(mAudioDevice);
}

void Buzzer::on() {
  SDL_PauseAudioDevice(mAudioDevice, SDL_FALSE);
}

void Buzzer::off() {
  SDL_PauseAudioDevice(mAudioDevice, SDL_TRUE);
}

void Buzzer::copySamples(Uint8 *stream, int len) {
  // Copy len samples from the current position of the buffer,
  // looping back to the start of the buffer when needed.
  while(len > 0) {
    size_t numBytes = std::min(sizeof(sample_t) * (mSamples.size() - miCurrentSample), size_t(len));
    size_t numSamples = numBytes / sizeof(sample_t);
    std::memcpy(stream, mSamples.data() + miCurrentSample, numBytes);
    stream += numBytes;
    len -= numBytes;
    miCurrentSample += numSamples;
    if(miCurrentSample >= mSamples.size()) {
      miCurrentSample = 0;
    }
  }
}