/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Copyright 2015 Danny Robson <danny@nerdcruft.net>
 */

#ifndef __UTIL_GEOM_RAY_HPP
#define __UTIL_GEOM_RAY_HPP

#include "aabb.hpp"
#include "plane.hpp"
#include "sphere.hpp"
#include "../vector.hpp"
#include "../point.hpp"


///////////////////////////////////////////////////////////////////////////////
namespace util::geom {
    template <size_t S, typename T>
    struct ray {
        constexpr ray () = default;

        constexpr ray (point<S,T> _origin, vector<S,T> _direction) noexcept:
            origin (_origin),
            direction (_direction)
        {
            CHECK (is_normalised (direction));
        }

        constexpr ray (point<S,T> _origin, point <S,T> _distant) noexcept:
            ray (_origin, _origin.to (_distant ))
        {
            CHECK (is_normalised (direction));
        }


        // queries
        T closest (point<S,T>) const;

        util::point<S,T> at (T) const;

        // data members
        point<S,T>  origin;
        vector<S,T> direction;
    };


    ///////////////////////////////////////////////////////////////////////////
    /// returns the distance along the ray in a ray-plane intersection
    ///
    /// returns inf if parallel
    /// returns 0   if coplanar
    template <size_t S, typename T>
    constexpr T
    distance (const ray<S,T> r, const plane<S,T> p)
    {
        return dot (p.coefficients, r.origin.   template redim<S+1> (1)) /
               dot (p.coefficients, r.direction.template redim<S+1> (0));

    }


    //-------------------------------------------------------------------------
    template <size_t S, typename T>
    constexpr bool
    intersects (const ray<S,T> r, const plane<S,T> p)
    {
        const auto d = distance (r, p);
        return d >= 0 && std::isfinite (d);
    }


    ///////////////////////////////////////////////////////////////////////////
    // returns the distance along a ray to an aabb
    //
    // the return value may be negative if the plane lies behind the ray.
    // the return value may be NaN in the case the ray and plane are parallel
    template <size_t S, typename T>
    constexpr T
    distance (const ray<S,T> r, const aabb<S,T> b)
    {
        const auto t1 = (b.lo - r.origin) / r.direction;
        const auto t2 = (b.hi - r.origin) / r.direction;

        const auto tmin = max (min (t1, t2));
        const auto tmax = min (max (t1, t2));

        // did not intersect
        if (tmin > tmax)
            return std::numeric_limits<T>::quiet_NaN ();

        // closest is behind us
        if (tmax < 0)
            return tmax;

        // closest is in front of us
        return tmin;
    }


    ///////////////////////////////////////////////////////////////////////////
    /// returns the smallest distance from a ray to a sphere intersection
    ///
    /// returns NaN on miss
    /// returns NaN if behind
    template <size_t S, typename T>
    constexpr T
    distance (const ray<S,T> r, const sphere<S,T> s)
    {
        const T b = dot (r.direction, r.origin - s.centre);
        const T c = dot (r.origin - s.centre, r.origin - s.centre) - s.radius * s.radius;

        const T D = b * b - c;

        // no intersection
        if (D < 0)
            return std::numeric_limits<T>::quiet_NaN ();

        auto t_ = std::sqrt (D);
        auto t0 = -b + t_;
        auto t1 = -b - t_;

        return t1 >= 0 ? t1 :
               t0 >= 0 ? t0 :
               std::numeric_limits<T>::quiet_NaN ();
    }


    //-------------------------------------------------------------------------
    // convenience method to test a ray intersects an aabb
    template <size_t S, typename T>
    constexpr bool
    intersects (const ray<S,T> r, const aabb<S,T> b)
    {
        return distance (r, b) >= 0;
    }


    ///////////////////////////////////////////////////////////////////////////
    typedef ray<2,float> ray2f;
    typedef ray<3,float> ray3f;
}

#endif