/*
- http://codereview.stackexchange.com/questions/41086/play-some-sine-waves-with-sdl2
- http://stackoverflow.com/questions/10110905/simple-wave-generator-with-sdl-in-c
- http://stackoverflow.com/questions/9137297/generating-sounds-without-a-library
- http://stackoverflow.com/questions/7678470/generating-sound-of-a-particular-frequency-using-gcc-in-ubuntu
- http://gamedev.stackexchange.com/questions/47009/is-there-a-sound-library-for-c-to-generate-sound-samples-from-code
- https://www.youtube.com/watch?v=0Q8VB5oZJVM

TODO minimize, clean up.
*/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <SDL2/SDL.h>

const double ChromaticRatio = 1.059463094359295264562;
const double Tao = 6.283185307179586476925;

Uint32 sampleRate = 48000;
Uint32  frameRate =    60;
Uint32 floatStreamLength = 1024;
Uint32 samplesPerFrame;
Uint32 msPerFrame;
double practicallySilent = 0.001;

Uint32 audioBufferLength = 48000;
float *audioBuffer;

SDL_atomic_t audioCallbackLeftOff;
Sint32 audioMainLeftOff;
Uint8 audioMainAccumulator;

SDL_AudioDeviceID AudioDevice;
SDL_AudioSpec audioSpec;

SDL_Event event;
SDL_bool running = SDL_TRUE;

typedef struct {
    float *waveform;
    Uint32 waveformLength;
    double volume;
    double pan;
    double frequency;
    double phase;
} voice;

void speak(voice *v) {
    float sample;
    Uint32 sourceIndex;
    double phaseIncrement = v->frequency/sampleRate;
    Uint32 i;
    if (v->volume > practicallySilent) {
        for (i = 0; (i + 1) < samplesPerFrame; i += 2) {
            v->phase += phaseIncrement;
            if (v->phase > 1)
                v->phase -= 1;

            sourceIndex = v->phase*v->waveformLength;
            sample = v->waveform[sourceIndex]*v->volume;

            audioBuffer[audioMainLeftOff+i] += sample*(1-v->pan);
            audioBuffer[audioMainLeftOff+i+1] += sample*v->pan;
        }
    }
    else {
        for (i=0; i<samplesPerFrame; i+=1)
            audioBuffer[audioMainLeftOff+i] = 0;
    }
    audioMainAccumulator++;
}

double getFrequency(double pitch) {
    return pow(ChromaticRatio, pitch-57)*440;
}

int getWaveformLength(double pitch) {
    return sampleRate / getFrequency(pitch)+0.5f;
}

void buildSineWave(float *data, Uint32 length) {
    Uint32 i;
    for (i=0; i < length; i++)
        data[i] = sin(i*(Tao/length));
}

void logSpec(SDL_AudioSpec *as) {
    printf(
        " freq______%5d\n"
        " format____%5d\n"
        " channels__%5d\n"
        " silence___%5d\n"
        " samples___%5d\n"
        " size______%5d\n\n",
        (int) as->freq,
        (int) as->format,
        (int) as->channels,
        (int) as->silence,
        (int) as->samples,
        (int) as->size
    );
}

void logVoice(voice *v) {
    printf(
        " waveformLength__%d\n"
        " volume__________%f\n"
        " pan_____________%f\n"
        " frequency_______%f\n"
        " phase___________%f\n",
        v->waveformLength,
        v->volume,
        v->pan,
        v->frequency,
        v->phase
    );
}

void logWavedata(float *floatStream, Uint32 floatStreamLength, Uint32 increment) {
    printf("\n\nwaveform data:\n\n");
    Uint32 i=0;
    for (i = 0; i < floatStreamLength; i += increment)
        printf("%4d:%2.16f\n", i, floatStream[i]);
    printf("\n\n");
}

void audioCallback(void *unused, Uint8 *byteStream, int byteStreamLength) {
    float* floatStream = (float*) byteStream;
    Sint32 localAudioCallbackLeftOff = SDL_AtomicGet(&audioCallbackLeftOff);
    Uint32 i;
    for (i = 0; i < floatStreamLength; i++) {
        floatStream[i] = audioBuffer[localAudioCallbackLeftOff];
        localAudioCallbackLeftOff++;
        if (localAudioCallbackLeftOff == audioBufferLength)
            localAudioCallbackLeftOff = 0;
    }
    SDL_AtomicSet(&audioCallbackLeftOff, localAudioCallbackLeftOff);
}

int init(void) {
    SDL_Init(SDL_INIT_AUDIO | SDL_INIT_TIMER);
    SDL_AudioSpec want;
    SDL_zero(want);

    want.freq = sampleRate;
    want.format = AUDIO_F32;
    want.channels = 2;
    want.samples = floatStreamLength;
    want.callback = audioCallback;

    AudioDevice = SDL_OpenAudioDevice(NULL, 0, &want, &audioSpec, SDL_AUDIO_ALLOW_FORMAT_CHANGE);
    if (AudioDevice == 0) {
        printf("\nFailed to open audio: %s\n", SDL_GetError());
        return 1;
    }

    printf("want:\n");
    logSpec(&want);
    printf("audioSpec:\n");
    logSpec(&audioSpec);

    if (audioSpec.format != want.format) {
        printf("\nCouldn't get Float32 audio format.\n");
        return 2;
    }

    sampleRate = audioSpec.freq;
    floatStreamLength = audioSpec.size / 4;
    samplesPerFrame = sampleRate / frameRate;
    msPerFrame = 1000 / frameRate;
    audioMainLeftOff = samplesPerFrame * 8;
    SDL_AtomicSet(&audioCallbackLeftOff, 0);

    if (audioBufferLength % samplesPerFrame)
        audioBufferLength += samplesPerFrame - (audioBufferLength % samplesPerFrame);
    audioBuffer = malloc(sizeof(float) * audioBufferLength);

    return 0;
}

int onExit(void) {
    SDL_CloseAudioDevice(AudioDevice);
    SDL_Quit();
    return 0;
}

int main(int argc, char *argv[]) {
    float  syncCompensationFactor = 0.0016;
    Sint32 mainAudioLead;
    Uint32 i;

    voice testVoiceA;
    voice testVoiceB;
    voice testVoiceC;
    testVoiceA.volume = 1;
    testVoiceB.volume = 1;
    testVoiceC.volume = 1;
    testVoiceA.pan = 0.5;
    testVoiceB.pan = 0;
    testVoiceC.pan = 1;
    testVoiceA.phase = 0;
    testVoiceB.phase = 0;
    testVoiceC.phase = 0;
    testVoiceA.frequency = getFrequency(45);
    testVoiceB.frequency = getFrequency(49);
    testVoiceC.frequency = getFrequency(52);
    Uint16 C0waveformLength = getWaveformLength(0);
    testVoiceA.waveformLength = C0waveformLength;
    testVoiceB.waveformLength = C0waveformLength;
    testVoiceC.waveformLength = C0waveformLength;
    float sineWave[C0waveformLength];
    buildSineWave(sineWave, C0waveformLength);
    testVoiceA.waveform = sineWave;
    testVoiceB.waveform = sineWave;
    testVoiceC.waveform = sineWave;

    if (init())
        return 1;

    SDL_Delay(42);
    SDL_PauseAudioDevice(AudioDevice, 0);
    while (running) {
        while (SDL_PollEvent(&event) != 0) {
            if (event.type == SDL_QUIT) {
                running = SDL_FALSE;
            }
        }
        for (i = 0; i < samplesPerFrame; i++)
            audioBuffer[audioMainLeftOff+i] = 0;
        speak(&testVoiceA);
        speak(&testVoiceB);
        speak(&testVoiceC);
        if (audioMainAccumulator > 1) {
            for (i=0; i<samplesPerFrame; i++) {
                audioBuffer[audioMainLeftOff+i] /= audioMainAccumulator;
            }
        }
        audioMainAccumulator = 0;
        audioMainLeftOff += samplesPerFrame;
        if (audioMainLeftOff == audioBufferLength)
            audioMainLeftOff = 0;
        mainAudioLead = audioMainLeftOff - SDL_AtomicGet(&audioCallbackLeftOff);
        if (mainAudioLead < 0)
            mainAudioLead += audioBufferLength;
        if (mainAudioLead < floatStreamLength)
            printf("An audio collision may have occurred!\n");
        SDL_Delay(mainAudioLead * syncCompensationFactor);
    }
    onExit();
    return 0;
}