#include "AudioBackend.h"

#include <iostream>

#include "../../audio/AudioPlayer.h"

AudioBackend audioBackend;

AudioBackend::AudioBackend() {
}

AudioBackend::~AudioBackend() {
    terminate();
}

void AudioBackend::init() {
    SDL_AudioSpec desired;
    desired.freq = 44100;
    desired.format = AUDIO_S16LSB;
    desired.channels = 2;
    desired.samples = 1024;
    desired.padding = 0;
    desired.userdata = this;
    desired.callback = [] (void *userdata, Uint8 *stream, int len) {
        static_cast<AudioBackend*>(userdata)->generate(stream, len);
    };

    _audioDevice = SDL_OpenAudioDevice(nullptr, 0, &desired, &_audioSpec, 0);
    if (!_audioDevice) {
        std::cerr << "Failed to open audio device: " << SDL_GetError() << std::endl;
        abort();
    }

    _audioStream = SDL_NewAudioStream(AUDIO_S8, 1, 8000, AUDIO_S16LSB, _audioSpec.channels, _audioSpec.freq);

    SDL_PauseAudioDevice(_audioDevice, 0);
}

void AudioBackend::terminate() {
    if (_audioDevice) {
        SDL_PauseAudioDevice(_audioDevice, 1);
        SDL_FreeAudioStream(_audioStream);
        SDL_CloseAudioDevice(_audioDevice);
    }
}

void AudioBackend::generate(Uint8 *stream, int len) {
    auto s = reinterpret_cast<int16_t *>(stream);

    // Convert sample rate (8000->44100) for SDL output
    int8_t mixerSample = 0;
    while (SDL_AudioStreamAvailable(_audioStream) < len) {
        audioPlayer.generateSamples(&mixerSample, 1);
        SDL_AudioStreamPut(_audioStream, &mixerSample, 1);
    }

    for (int i = 0; i < len/4; i++) {
        int16_t convertedMixerSample[2]{};
        SDL_AudioStreamGet(_audioStream, &convertedMixerSample, sizeof convertedMixerSample);

        int16_t l = 0, r = 0;
        Opl::generateSample(&l, &r);
        *s++ = l + convertedMixerSample[0];
        *s++ = r + convertedMixerSample[1];
    }
}