import("math.lib");


freqSlider = hslider("Freq", 1000.0, 1, 20000, 0.1);
qSlider = hslider("Q", 0.1, 0.001, 1, 0.001);
gainSlider = hslider("Volume", 1.0, 0.1, 6.0, 0.025);

kLowPass = 0;
kHighPass = 1;
kBandPass = 2;
kNotch = 3;
kPeak = 4;
kBell = 5;
kLowPassShelf = 6;
kHighPassShelf = 7;
kNumModes = 8;

modeSlider = hslider("Mode", 0, 0, kNumModes, 1);

SAMPLERATE = 48000;
M_PI = 3.1415926535897932384626433832795028841;

class SVF(int mode, float freq, float Q, float gain){

    float mV1 = 0.;
    float mV2 = 0.;
    float mV3 = 0.;
    float mIc1eq = 0.;
    float mIc2eq = 0.;

    process(input){


        float w = tan(M_PI * freq / SAMPLERATE);

        float m_a1;
        float m_a2;
        float m_a3;
        float m_m0;
        float m_m1;
        float m_m2;

        if (mode == kLowPass)
            {
                float g = w;
                float k = 1. / Q;
                m_a1 = 1./(1. + g * (g + k));
                m_a2 = g * m_a1;
                m_a3 = g * m_a2;
                m_m0 = 0;
                m_m1 = 0;
                m_m2 = 1.;
            }

        else if (mode == kHighPass)
            {
                float g = w;
                float k = 1. / Q;
                m_a1 = 1./(1. + g * (g + k));
                m_a2 = g * m_a1;
                m_a3 = g * m_a2;
                m_m0 = 1.;
                m_m1 = -k;
                m_m2 = -1.;
            }


        else if (mode == kBandPass)
            {
                float g = w;
                float k = 1. / Q;
                m_a1 = 1./(1. + g * (g + k));
                m_a2 = g * m_a1;
                m_a3 = g * m_a2;
                m_m0 = 0.;
                m_m1 = 1.;
                m_m2 = 0.;
            }

        else if (mode == kNotch)
            {
                float g = w;
                float k = 1. / Q;
                m_a1 = 1./(1. + g * (g + k));
                m_a2 = g * m_a1;
                m_a3 = g * m_a2;
                m_m0 = 1.;
                m_m1 = -k;
                m_m2 = 0.;
            }

        else if (mode == kPeak)
            {
                float g = w;
                float k = 1. / Q;
                m_a1 = 1./(1. + g * (g + k));
                m_a2 = g * m_a1;
                m_a3 = g * m_a2;
                m_m0 = 1.;
                m_m1 = -k;
                m_m2 = -2.;
            }

        else if (mode == kBell)
            {
                float A = pow(10., gain/40.);
                float g = w;
                float k = 1 / Q;
                m_a1 = 1./(1. + g * (g + k));
                m_a2 = g * m_a1;
                m_a3 = g * m_a2;
                m_m0 = 1.;
                m_m1 = k * (A * A - 1.);
                m_m2 = 0.;
            }

        else if (mode == kLowPassShelf)
            {
                float A = pow(10., gain/40.);
                float g = w / sqrt(A);
                float k = 1. / Q;
                m_a1 = 1./(1. + g * (g + k));
                m_a2 = g * m_a1;
                m_a3 = g * m_a2;
                m_m0 = 1.;
                m_m1 = k * (A - 1.);
                m_m2 = (A * A - 1.);
            }

        else if (mode == kHighPassShelf)
            {
                float A = pow(10., gain/40.);
                float g = w / sqrt(A);
                float k = 1. / Q;
                m_a1 = 1./(1. + g * (g + k));
                m_a2 = g * m_a1;
                m_a3 = g * m_a2;
                m_m0 = A*A;
                m_m1 = k*(1. - A)*A;
                m_m2 = (1. - A*A);
            }

        float v0 = input;

        mV3 = v0 - mIc2eq;
        mV1 = m_a1 * mIc1eq + m_a2*mV3;
        mV2 = mIc2eq + m_a2 * mIc1eq + m_a3 * mV3;
        mIc1eq = 2. * mV1 - mIc1eq;
        mIc2eq = 2. * mV2 - mIc2eq;

        return m_m0 * v0 + m_m1 * mV1 + m_m2 * mV2;
    }

}

process = SVF(modeSlider, freqSlider, qSlider, gainSlider);