/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2017 - ROLI Ltd.

   JUCE is an open source library subject to commercial or open-source
   licensing.

   The code included in this file is provided under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
   To use, copy, modify, and/or distribute this software for any purpose with or
   without fee is hereby granted provided that the above copyright notice and
   this permission notice appear in all copies.

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace
{
    static forcedinline void pushInterpolationSample (float* lastInputSamples, const float newValue) noexcept
    {
        lastInputSamples[4] = lastInputSamples[3];
        lastInputSamples[3] = lastInputSamples[2];
        lastInputSamples[2] = lastInputSamples[1];
        lastInputSamples[1] = lastInputSamples[0];
        lastInputSamples[0] = newValue;
    }

    static forcedinline void pushInterpolationSamples (float* lastInputSamples, const float* input, int numOut) noexcept
    {
        if (numOut >= 5)
        {
            for (int i = 0; i < 5; ++i)
                lastInputSamples[i] = input[--numOut];
        }
        else
        {
            for (int i = 0; i < numOut; ++i)
                pushInterpolationSample (lastInputSamples, input[i]);
        }
    }

    template <typename InterpolatorType>
    static int interpolate (float* lastInputSamples, double& subSamplePos, const double actualRatio,
                            const float* in, float* out, const int numOut) noexcept
    {
        if (actualRatio == 1.0)
        {
            memcpy (out, in, (size_t) numOut * sizeof (float));
            pushInterpolationSamples (lastInputSamples, in, numOut);
            return numOut;
        }

        const float* const originalIn = in;
        double pos = subSamplePos;

        if (actualRatio < 1.0)
        {
            for (int i = numOut; --i >= 0;)
            {
                if (pos >= 1.0)
                {
                    pushInterpolationSample (lastInputSamples, *in++);
                    pos -= 1.0;
                }

                *out++ = InterpolatorType::valueAtOffset (lastInputSamples, (float) pos);
                pos += actualRatio;
            }
        }
        else
        {
            for (int i = numOut; --i >= 0;)
            {
                while (pos < actualRatio)
                {
                    pushInterpolationSample (lastInputSamples, *in++);
                    pos += 1.0;
                }

                pos -= actualRatio;
                *out++ = InterpolatorType::valueAtOffset (lastInputSamples, jmax (0.0f, 1.0f - (float) pos));
            }
        }

        subSamplePos = pos;
        return (int) (in - originalIn);
    }

    template <typename InterpolatorType>
    static int interpolateAdding (float* lastInputSamples, double& subSamplePos, const double actualRatio,
                                  const float* in, float* out, const int numOut, const float gain) noexcept
    {
        if (actualRatio == 1.0)
        {
            FloatVectorOperations::addWithMultiply (out, in, gain, numOut);
            pushInterpolationSamples (lastInputSamples, in, numOut);
            return numOut;
        }

        const float* const originalIn = in;
        double pos = subSamplePos;

        if (actualRatio < 1.0)
        {
            for (int i = numOut; --i >= 0;)
            {
                if (pos >= 1.0)
                {
                    pushInterpolationSample (lastInputSamples, *in++);
                    pos -= 1.0;
                }

                *out++ += gain * InterpolatorType::valueAtOffset (lastInputSamples, (float) pos);
                pos += actualRatio;
            }
        }
        else
        {
            for (int i = numOut; --i >= 0;)
            {
                while (pos < actualRatio)
                {
                    pushInterpolationSample (lastInputSamples, *in++);
                    pos += 1.0;
                }

                pos -= actualRatio;
                *out++ += gain * InterpolatorType::valueAtOffset (lastInputSamples, jmax (0.0f, 1.0f - (float) pos));
            }
        }

        subSamplePos = pos;
        return (int) (in - originalIn);
    }
}

//==============================================================================
template <int k>
struct LagrangeResampleHelper
{
    static forcedinline void calc (float& a, float b) noexcept   { a *= b * (1.0f / k); }
};

template<>
struct LagrangeResampleHelper<0>
{
    static forcedinline void calc (float&, float) noexcept {}
};

struct LagrangeAlgorithm
{
    static forcedinline float valueAtOffset (const float* const inputs, const float offset) noexcept
    {
        return calcCoefficient<0> (inputs[4], offset)
             + calcCoefficient<1> (inputs[3], offset)
             + calcCoefficient<2> (inputs[2], offset)
             + calcCoefficient<3> (inputs[1], offset)
             + calcCoefficient<4> (inputs[0], offset);
    }

    template <int k>
    static forcedinline float calcCoefficient (float input, const float offset) noexcept
    {
        LagrangeResampleHelper<0 - k>::calc (input, -2.0f - offset);
        LagrangeResampleHelper<1 - k>::calc (input, -1.0f - offset);
        LagrangeResampleHelper<2 - k>::calc (input,  0.0f - offset);
        LagrangeResampleHelper<3 - k>::calc (input,  1.0f - offset);
        LagrangeResampleHelper<4 - k>::calc (input,  2.0f - offset);
        return input;
    }
};

LagrangeInterpolator::LagrangeInterpolator() noexcept  { reset(); }
LagrangeInterpolator::~LagrangeInterpolator() noexcept {}

void LagrangeInterpolator::reset() noexcept
{
    subSamplePos = 1.0;

    for (int i = 0; i < numElementsInArray (lastInputSamples); ++i)
        lastInputSamples[i] = 0;
}

int LagrangeInterpolator::process (double actualRatio, const float* in, float* out, int numOut) noexcept
{
    return interpolate<LagrangeAlgorithm> (lastInputSamples, subSamplePos, actualRatio, in, out, numOut);
}

int LagrangeInterpolator::processAdding (double actualRatio, const float* in, float* out, int numOut, float gain) noexcept
{
    return interpolateAdding<LagrangeAlgorithm> (lastInputSamples, subSamplePos, actualRatio, in, out, numOut, gain);
}
