#include "Filter.h"

namespace serum
{

namespace
{
    constexpr double kPi = 3.14159265358979323846;

    inline float clampF (float v, float lo, float hi) noexcept
    {
        return v < lo ? lo : (v > hi ? hi : v);
    }

    inline double clampD (double v, double lo, double hi) noexcept
    {
        return v < lo ? lo : (v > hi ? hi : v);
    }
}

void Filter::prepare (double sampleRate, int maxBlockSize)
{
    sr = sampleRate;
    combLine.assign ((size_t) sampleRate, 0.0f);   // 1 second of delay
    combWrite = 0;
    combDamp  = 0.0;
    reset();
    (void) maxBlockSize;
}

void Filter::reset()
{
    ic1eq = ic2eq = 0.0;
    lastG = lastK = 0.0;
    a1 = a2 = a3 = 0.0;
    stage.fill (0.0);
    for (auto& s : formantState) s.fill (0.0);
    std::fill (combLine.begin(), combLine.end(), 0.0f);
    combWrite = 0;
    combDamp  = 0.0;
}

void Filter::updateSvf (double g, double k) noexcept
{
    if (g == lastG && k == lastK)
        return;
    lastG = g;
    lastK = k;
    a1 = 1.0 / (1.0 + g * (g + k));
    a2 = g * a1;
    a3 = g * a2;
}

double Filter::svfLow (double in, double g, double k) noexcept
{
    updateSvf (g, k);
    const double v3 = in - ic2eq;
    const double v1 = a1 * ic1eq + a2 * v3;
    const double v2 = ic2eq + a2 * ic1eq + a3 * v3;
    ic1eq = 2.0 * v1 - ic1eq;
    ic2eq = 2.0 * v2 - ic2eq;
    return v2;
}

double Filter::svfBand (double in, double g, double k) noexcept
{
    updateSvf (g, k);
    const double v3 = in - ic2eq;
    const double v1 = a1 * ic1eq + a2 * v3;
    const double v2 = ic2eq + a2 * ic1eq + a3 * v3;
    ic1eq = 2.0 * v1 - ic1eq;
    ic2eq = 2.0 * v2 - ic2eq;
    return v1;
}

double Filter::svfHigh (double in, double g, double k) noexcept
{
    updateSvf (g, k);
    const double v3 = in - ic2eq;
    const double v1 = a1 * ic1eq + a2 * v3;
    const double v2 = ic2eq + a2 * ic1eq + a3 * v3;
    ic1eq = 2.0 * v1 - ic1eq;
    ic2eq = 2.0 * v2 - ic2eq;
    return in - k * v1 - v2;
}

double Filter::ladder (double in, double g, double res, double drive, int stages, bool diode) noexcept
{
    stages = juce::jlimit (1, 4, stages);
    res    = clampD (res, 0.0, 0.97);

    double x;
    if (diode)
    {
        // Diode ladder: softer, asymmetric feedback and diode clipping.
        x = in - 3.0 * res * (stage[(size_t) (stages - 1)] - in * 0.5);
        x = x / (1.0 + std::abs (x));               // diode curve
        x = x * (1.0 + drive * 3.0);
    }
    else
    {
        x = in - 4.0 * res * stage[(size_t) (stages - 1)];
        x = std::tanh (x * (1.0 + drive * 6.0));    // Moog-ish input saturation
    }

    for (int i = 0; i < stages; ++i)
    {
        stage[(size_t) i] += g * (x - stage[(size_t) i]);
        x = stage[(size_t) i];
    }

    x = clampD (x, -8.0, 8.0);
    return x;
}

double Filter::comb (double in, double freqHz, double res, double drive) noexcept
{
    const int len = (int) combLine.size();
    if (len < 4)
        return in;

    const double freq = clampD (freqHz, 20.0, sr * 0.45);
    double delay = sr / freq;
    delay = clampD (delay, 2.0, (double) len - 2.0);

    int    readPos = combWrite - (int) delay;
    if (readPos < 0) readPos += len;
    const int readPos2 = (readPos + 1) % len;
    const float frac = (float) (delay - std::floor (delay));

    const float y0 = combLine[(size_t) readPos];
    const float y1 = combLine[(size_t) readPos2];
    float y = y0 + (y1 - y0) * frac;

    // Damping lowpass in the feedback path (drive controls damping).
    const double dampCoef = 1.0 - clampD (drive, 0.0, 0.99);
    combDamp = y * (1.0 - dampCoef) + combDamp * dampCoef;

    const float feedback = clampF ((float) res * 0.9f, 0.0f, 0.98f);
    combLine[(size_t) combWrite] = (float) in + (float) combDamp * feedback;
    combWrite = (combWrite + 1) % len;

    return (double) y;
}

double Filter::formant (double in, double morph, double res) noexcept
{
    // morph (0..1) sweeps the three bandpass centres to produce vowel-like spectra.
    const double m = clampD (morph, 0.0, 1.0);
    const double base[3] = { 400.0, 1200.0, 2600.0 };
    const double k = clampD (2.0 * (1.0 - res), 0.05, 2.0);

    double out = 0.0;
    const double gains[3] = { 1.0, 0.8, 0.5 };
    for (int i = 0; i < 3; ++i)
    {
        const double fc = base[i] * (0.7 + 1.6 * m) * (i == 2 ? 0.9 : 1.0);
        const double g  = std::tan (kPi * clampD (fc, 30.0, sr * 0.45) / sr);
        const double a1 = 1.0 / (1.0 + g * (g + k));
        const double a2 = g * a1;
        const double a3 = g * a2;
        const double v3 = in - formantState[(size_t) i][1];
        const double v1 = a1 * formantState[(size_t) i][0] + a2 * v3;
        const double v2 = formantState[(size_t) i][1] + a2 * formantState[(size_t) i][0] + a3 * v3;
        formantState[(size_t) i][0] = 2.0 * v1 - formantState[(size_t) i][0];
        formantState[(size_t) i][1] = 2.0 * v2 - formantState[(size_t) i][1];
        out += v1 * gains[i];
    }
    return clampD (out * 0.5, -8.0, 8.0);
}

double Filter::screamer (double in, double cutoffHz, double res, double drive) noexcept
{
    const double g = std::tan (kPi * clampD (cutoffHz, 30.0, sr * 0.45) / sr);
    const double k = clampD (2.0 * (1.0 - res), 0.05, 2.0);
    const double band = svfBand (in, g, k);
    const double driven = std::tanh (band * (1.0 + drive * 12.0));
    return driven * (1.0 - drive * 0.4);
}

float Filter::processSample (float in, float cutoffHz, float res, float drive, int type, int slope) noexcept
{
    res   = clampF (res, 0.0f, 0.98f);
    drive = clampF (drive, 0.0f, 1.0f);

    // Ladder stages are cascaded one-poles, which need an exponential coefficient
    // (always in (0,1]) for unconditional stability. The TPT SVF (formant/screamer)
    // computes its own tan()-based g internally.
    const double fc = clampD (cutoffHz, 20.0, sr * 0.45);
    const double g = 1.0 - std::exp (-2.0 * kPi * fc / sr);
    double out = (double) in;

    switch ((FilterModel) type)
    {
        case FilterModel::LadderLP:
        {
            const int stages = (slope == 0) ? 1 : (slope == 1) ? 2 : 4;
            out = ladder (in, g, res, drive, stages, false);
            break;
        }
        case FilterModel::LadderHP:
        {
            const int stages = (slope == 0) ? 1 : (slope == 1) ? 2 : 4;
            out = (double) in - ladder (in, g, res, drive, stages, false);
            break;
        }
        case FilterModel::LadderBP:
        {
            int stages = (slope == 0) ? 2 : (slope == 1) ? 2 : 4;
            out = ladder (in, g, res, drive, stages, false);
            out = stage[0] - stage[(size_t) (stages - 1)];
            break;
        }
        case FilterModel::Diode:
        {
            const int stages = (slope == 0) ? 1 : (slope == 1) ? 2 : 4;
            out = ladder (in, g, res, drive, stages, true);
            break;
        }
        case FilterModel::Comb:
            out = comb (in, cutoffHz, res, drive);
            break;
        case FilterModel::Formant:
            out = formant (in, maps::hzToCutoff (cutoffHz), res);
            break;
        case FilterModel::Screamer:
            out = screamer (in, cutoffHz, res, drive);
            break;
        default:
            break;
    }

    return (float) clampD (out, -8.0, 8.0);
}

void Filter::process (float* samples, int numSamples, float cutoffNorm, float res,
                      float drive, float keytrack, float noteHz, int type, int slope) noexcept
{
    if (samples == nullptr || numSamples <= 0)
        return;

    // Keytrack shifts the cutoff with note pitch.
    const float noteNumber = (noteHz > 0.0f) ? (69.0f + 12.0f * std::log2f (noteHz / 440.0f)) : 60.0f;
    const float baseHz = maps::cutoffToHz (cutoffNorm);
    const float keyFactor = std::pow (2.0f, keytrack * (noteNumber - 60.0f) / 12.0f);
    const float cutoffHz = clampF (baseHz * keyFactor, 20.0f, 18000.0f);

    for (int i = 0; i < numSamples; ++i)
        samples[i] = processSample (samples[i], cutoffHz, res, drive, type, slope);
}

} // namespace serum