/*
 * Copyright (C) 2021  Christopher J. Howard
 *
 * This file is part of Antkeeper source code.
 *
 * Antkeeper source code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Antkeeper source code 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef ANTKEEPER_COLOR_CCT_HPP
#define ANTKEEPER_COLOR_CCT_HPP

#include "math/math.hpp"
#include "ucs.hpp"
#include "xyy.hpp"

namespace color {

/// Functions which operate on correlated color temperature (CCT).
namespace cct {

/**
 * Calculates CIE 1960 UCS colorspace chromaticity coordinates given a correlated color temperature using Krystek's algorithm.
 *
 * @param t Correlated color temperature, in Kelvin.
 * @return CIE 1960 UCS colorspace chromaticity coordinates.
 *
 * @see Krystek, M. (1985), An algorithm to calculate correlated colour temperature. Color Res. Appl., 10: 38-40.
 */
template <class T>
math::vector2<T> to_ucs(T t);

/**
 * Calculates CIE xyY colorspace chromaticity coordinates given a correlated color temperature using Krystek's algorithm.
 *
 * @param t Correlated color temperature, in Kelvin.
 * @return CIE xyY color with `Y = 1`.
 */
template <class T>
math::vector3<T> to_xyy(T t);

/**
 * Calculates CIE XYZ colorspace chromaticity coordinates given a correlated color temperature using Krystek's algorithm.
 *
 * @param t Correlated color temperature, in Kelvin.
 * @return CIE XYZ color with `Y = 1`.
 */
template <class T>
math::vector3<T> to_xyz(T t);

template <class T>
math::vector2<T> to_ucs(T t)
{
	// Approximate the Planckian locus in CIE 1960 UCS colorspace (Krystek's algorithm)
	const T tt = t * t;
	return math::vector2<T>
		{
			(T(0.860117757) + T(1.54118254e-4) * t + T(1.28641212e-7) * tt) / (T(1.0) + T(8.42420235e-4) * t + T(7.08145163e-7) * tt),
			(T(0.317398726) + T(4.22806245e-5) * t + T(4.20481691e-8) * tt) / (T(1.0) - T(2.89741816e-5) * t + T(1.61456053e-7) * tt)
		};
}

template <class T>
math::vector3<T> to_xyy(T t)
{
	return ucs::to_xyy(to_ucs(t), T(1.0));
}

template <class T>
math::vector3<T> to_xyz(T t)
{
	return xyy::to_xyz(to_xyy(t));
}

} // namespace cct
} // namespace color

#endif // ANTKEEPER_COLOR_CCT_HPP