#include "synth.h"

Synth::Synth(double sampleRate){
    setSampleRate(48000.0, sampleRate);
}

#define frac(x) ((x) - ((long)x))
constexpr double MIN_VOLUME = 0.00001;

static constexpr double amin = 50;
static constexpr double apiq = 500;
static constexpr double amax = 10000;
//Volume of voice as a function of sample rate independent frequency.
static constexpr inline float getAmplitude( double hz )
{
  if( hz < amin )       return 0.0;
  if( hz < apiq )      {
        double a = (hz - amin) / (apiq - amin);
        return a * a;}
  if( hz < amax )     {
        double a  = 1.0 - (hz - apiq) / (amax - apiq);
        return a * a;
  }
  return 0.0;
}

//Interpolation function on unit interval with good regularity as a function on S^1.
static constexpr inline float smooth( double x )
{
    return x * x * x;//(3.0 * x - 2.0);
}

//Sanity checks: voices should become silent outside audible frequencies.
static_assert( MIN_VOLUME > getAmplitude(10.0) );
static_assert( MIN_VOLUME > getAmplitude(20000.0));

//New fundamental is twice as high as old fundamental.
//Even overtones become plain overtones.
void Synth::shiftUp()
{
    tablePhase *= 2.0;
    spectrumPhase += 1.0;
}

//New fundamental is half as high as old fundamental.
//Overtones become even overtones.
void Synth::shiftDown()
{
    tablePhase /= 2.0;
    spectrumPhase -= 1.0;
}

void Synth::process(float* output, const uint32_t frames)
{
    //Render.
    for(uint32_t i = 0; i < frames; i++){

        //Set pitch.
        hzFund = exp2(spectrumPhase) * fMin;
        
        tablePhase += hzFund * sampleInterval;
        tablePhase = frac(tablePhase);

        bool isOddHarmonic = true;
        
        for(uint voice = 0; voice < NUM_VOICES; ++voice){

            double voicePhase = 2.0 * M_PI * tablePhase * (voice + 1.0);
            //Anti-aliasing: don't bother rendering anything over the Nyquist rate.
            if( hzFund * (voice + 1.0) > hzNyq ) break;

            output[i] += (!isOddHarmonic + isOddHarmonic * smooth(spectrumPhase))   //Fade in odd harmonics.
            * getAmplitude(hzFund * (voice + 1.0))                                  //Frequency response.
            * sinf(static_cast<float>(voicePhase));                                 //Additives.

            isOddHarmonic = !isOddHarmonic;
        }

        output[i] *= fMin * volume / static_cast<float>(8 * NUM_VOICES);

        //Wrapping.
        spectrumPhase += spectrumPhaseVelocity * sampleInterval;
        if( spectrumPhase > 1.0) shiftDown();
        if( spectrumPhase < 0.0)   shiftUp();
    }

}

void Synth::setSampleRate(double oldRate, double newRate){
    sampleInterval = 1.0 / newRate;
    hzNyq = newRate / 2;
}

//Takes value from 0 to 1 representing rate of wrapping pitch increase.
//0 : lower one octave per second
//1 : raise one octave per second
void Synth::setPhaseVelocity(double in){
    spectrumPhaseVelocity = 2.0 * (in - 0.5);
}

//Vary pitch of fundamental in a non-wrapping kinda way.
//Current range is six octaves, current bottom is 13.75 Hz (A0)
void Synth::setPitchOffset(double in){
    fMin = exp2(in * 6.0) * 13.75;
}


void Synth::setVolume(double in){
    volume = in;
}