/*
 * 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_PHYSICS_LIGHT_PHOTOMETRY_HPP
#define ANTKEEPER_PHYSICS_LIGHT_PHOTOMETRY_HPP

#include "math/constants.hpp"
#include "math/quadrature.hpp"

namespace physics {
namespace light {

/**
 * Calculates the luminous efficiency of a light source.
 *
 * @param spd Unary function object that returns spectral radiance given a wavelength.
 * @param lef Unary function object that returns luminous efficiency given a wavelength.
 * @param first,last Range of sample wavelengths.
 * @return Luminous efficiency, on `[0, 1]`.
 *
 * @see physics::light::blackbody::spectral_radiance
 * @see physics::light::luminosity::photopic
 */
template <class T, class UnaryOp1, class UnaryOp2, class InputIt>
T luminous_efficiency(UnaryOp1 spd, UnaryOp2 lef, InputIt first, InputIt last)
{
	auto spd_lef = [spd, lef](T x) -> T
	{
		return spd(x) * lef(x);
	};
	
	const T num = math::quadrature::trapezoid(spd_lef, first, last);
	const T den = math::quadrature::trapezoid(spd, first, last);
	
	return num / den;
}

/**
 * Calculates luminous efficacy given luminous efficiency.
 *
 * @param efficiency Luminous efficiency, on `[0, 1]`.
 * @return Luminous flux, in lumens.
 */
template <class T>
T luminous_efficacy(T efficiency)
{
	return T(683.002) * efficiency;
}

/**
 * Converts watts (radiant flux) to lumens (luminous flux).
 *
 * @param radient_flux Radiance flux, in watts.
 * @param efficiency Luminous efficiency, on `[0, 1]`.
 * @return Luminous flux, in lumens.
 */
template <class T>
T watts_to_lumens(T radient_flux, T efficiency)
{
	return radient_flux * luminous_efficacy(efficiency);
}

} // namespace light
} // namespace physics

#endif // ANTKEEPER_PHYSICS_LIGHT_PHOTOMETRY_HPP