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

   This file is part of the JUCE library.
   Copyright (c) 2015 - ROLI Ltd.

   Permission is granted to use this software under the terms of either:
   a) the GPL v2 (or any later version)
   b) the Affero GPL v3

   Details of these licenses can be found at: www.gnu.org/licenses

   JUCE is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
   A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

   ------------------------------------------------------------------------------

   To release a closed-source product which uses JUCE, commercial licenses are
   available: visit www.juce.com for more information.

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

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);
}