/*
 * SPDX-FileCopyrightText: 2006 Cyrille Berger <cberger@cberger.net>
 * SPDX-FileCopyrightText: 2011 Silvio Heinrich <plassy@web.de>
 *
 * SPDX-License-Identifier: LGPL-2.0-or-later
 */

#ifndef KOCOMPOSITEOPALPHADARKEN_H_
#define KOCOMPOSITEOPALPHADARKEN_H_

#include "KoColorSpaceMaths.h"
#include "KoCompositeOpBase.h"
#include <KoCompositeOpRegistry.h>

/**
 * A template version of the alphadarken composite operation to use in colorspaces
 */
template<class Traits, class ParamsWrapper>
class KoCompositeOpAlphaDarken: public KoCompositeOp
{
    typedef typename Traits::channels_type channels_type;

    static const qint32 channels_nb = Traits::channels_nb;
    static const qint32 alpha_pos   = Traits::alpha_pos;

public:
    KoCompositeOpAlphaDarken(const KoColorSpace* cs):
        KoCompositeOp(cs, COMPOSITE_ALPHA_DARKEN, KoCompositeOp::categoryMix()) { }

    using KoCompositeOp::composite;

    void composite(const KoCompositeOp::ParameterInfo& params) const override
    {
        if(params.maskRowStart != 0)
            genericComposite<true>(params);
        else
            genericComposite<false>(params);
    }

    template<bool useMask>
    void genericComposite(const KoCompositeOp::ParameterInfo& params) const
    {
        using namespace Arithmetic;

        ParamsWrapper paramsWrapper(params);

        qint32        srcInc       = (params.srcRowStride == 0) ? 0 : channels_nb;
        channels_type flow         = scale<channels_type>(paramsWrapper.flow);
        channels_type opacity      = scale<channels_type>(paramsWrapper.opacity);
        quint8*       dstRowStart  = params.dstRowStart;
        const quint8* srcRowStart  = params.srcRowStart;
        const quint8* maskRowStart = params.maskRowStart;

        for (qint32 r = params.rows; r > 0; --r) {
            const channels_type* src  = reinterpret_cast<const channels_type*>(srcRowStart);
            channels_type*       dst  = reinterpret_cast<channels_type*>(dstRowStart);
            const quint8*        mask = maskRowStart;

            for(qint32 c=params.cols; c>0; --c) {
                channels_type srcAlpha = (alpha_pos == -1) ? unitValue<channels_type>() : src[alpha_pos];
                channels_type dstAlpha = (alpha_pos == -1) ? unitValue<channels_type>() : dst[alpha_pos];
                channels_type mskAlpha = useMask ? mul(scale<channels_type>(*mask), srcAlpha) : srcAlpha;

                srcAlpha = mul(mskAlpha, opacity);

                if(dstAlpha != zeroValue<channels_type>()) {
                    for(qint32 i=0; i <channels_nb; i++) {
                        if(i != alpha_pos)
                            dst[i] = lerp(dst[i], src[i], srcAlpha);
                    }
                }
                else {
                    for(qint32 i=0; i <channels_nb; i++) {
                        if(i != alpha_pos)
                            dst[i] = src[i];
                    }
                }

                if(alpha_pos != -1) {
                    channels_type fullFlowAlpha;
                    channels_type averageOpacity = scale<channels_type>(paramsWrapper.averageOpacity);

                    /**
                     * Here we calculate fullFlowAlpha, which shuold strive either to
                     * averageOpacity or opacity (whichever is the greater) or just keep old dstAlpha
                     * value, if both opacity values are not bit enough
                     */
                    if (averageOpacity > opacity) {
                        /**
                         * This crypty code is basically an optimized version of the following:
                         * fullFlowAlpha = averageOpacity *
                         *                     unionShapeOpacity(srcAlpha / averageOpacity,
                         *                                       dstAlpha / averageOpacity);
                         *
                         * The main idea is: fullFlowAlpha should be as near to averageOpacity as
                         * maximum of srcAlpha and dstAlpha and a bit more. So that in consequent
                         * applications of the blending operation alpha channel would aim to
                         * averageOpacity.
                         */

                        channels_type reverseBlend = KoColorSpaceMaths<channels_type>::divide(dstAlpha, averageOpacity);
                        fullFlowAlpha = averageOpacity > dstAlpha ? lerp(srcAlpha, averageOpacity, reverseBlend) : dstAlpha;
                    } else {
                        fullFlowAlpha = opacity > dstAlpha ? lerp(dstAlpha, opacity, mskAlpha) : dstAlpha;
                    }

                    if (params.flow == 1.0f) {
                        dstAlpha = fullFlowAlpha;
                    } else {
                        channels_type zeroFlowAlpha = ParamsWrapper::calculateZeroFlowAlphaLegacy(srcAlpha, dstAlpha);
                        dstAlpha = lerp(zeroFlowAlpha, fullFlowAlpha, flow);
                    }

                    dst[alpha_pos] = dstAlpha;
                }

                src += srcInc;
                dst += channels_nb;

                if(useMask)
                    ++mask;
            }

            srcRowStart  += params.srcRowStride;
            dstRowStart  += params.dstRowStride;
            maskRowStart += params.maskRowStride;
        }
    }
};

#endif // KOCOMPOSITEOPALPHADARKEN_H_
