/**
 * \file
 *
 * \author Mattia Basaglia
 *
 * \copyright Copyright (C) 2013-2020 Mattia Basaglia
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
#ifndef GRADIENT_HELPER_HPP
#define GRADIENT_HELPER_HPP

#include "colorwidgets_global.hpp"

#include <QGradient>

namespace color_widgets {

inline QColor blendColors(const QColor& a, const QColor& b, qreal ratio)
{
    return QColor::fromRgbF(
        a.redF()   * (1-ratio) + b.redF()   * ratio,
        a.greenF() * (1-ratio) + b.greenF() * ratio,
        a.blueF()  * (1-ratio) + b.blueF()  * ratio,
        a.alphaF() * (1-ratio) + b.alphaF() * ratio
    );
}


/**
 * \brief Get an insertion point in the gradient
 * \param gradient  Gradient stops to look into (must be properly set up)
 * \param factor    Value in [0, 1] to get the color for
 * \return A pair whose first element is the index to insert the new value at, and a GradientStop
 */
inline QPair<int, QGradientStop> Q_DECL_EXPORT gradientBlendedColorInsert(const QGradientStops& gradient, qreal factor)
{
    if ( gradient.empty() )
        return {0, {0, QColor()}};

    if ( gradient.size() == 1 || factor <= 0 )
        return {0, gradient.front()};

    int i = 0;
    QGradientStop s1;
    for ( auto s2 : gradient )
    {
        if ( factor < s2.first )
        {
            qreal ratio = (factor - s1.first) / (s2.first - s1.first);
            return {i, {factor, blendColors(s1.second, s2.second, ratio)}};
        }
        s1 = s2;
        ++i;
    }

    return {gradient.size(), gradient.back()};
}

/**
 * \brief Returns a color in the gradient
 * \param gradient  Gradient stops to look into (must be properly set up)
 * \param factor    Value in [0, 1] to get the color for
 */
inline QColor Q_DECL_EXPORT gradientBlendedColor(const QGradientStops& gradient, qreal factor)
{
    return gradientBlendedColorInsert(gradient, factor).second.second;
}

/**
 * \brief Returns a color in the gradient
 * \param gradient  Gradient to look into
 * \param factor    Value in [0, 1] to get the color for
 */
inline QColor Q_DECL_EXPORT gradientBlendedColor(const QGradient& gradient, qreal factor)
{
    return gradientBlendedColor(gradient.stops(), factor);
}

} // namespace color_widgets




#endif // GRADIENT_HELPER_HPP