/*
 * 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 2010-2017 Danny Robson <danny@nerdcruft.net>
 */


#ifndef CRUFT_UTIL_REGION_HPP
#define CRUFT_UTIL_REGION_HPP

#include "./extent.hpp"
#include "./point.hpp"
#include "./vector.hpp"
#include "./types/traits.hpp"

#include <iosfwd>

namespace util {
    /**
     * A two-dimensional rectangle, with size and position.
     */
    template <size_t S, typename T>
    struct region {
        using extent_t = util::extent<S,T>;
        using point_t  = util::point<S,T>;

        using value_type = T;

        //---------------------------------------------------------------------
        static constexpr size_t dimension = S;
        static constexpr size_t elements = extent_t::elements + point_t::elements;

        point_t  p;
        extent_t e;

        //---------------------------------------------------------------------
        region () = default;
        explicit region (extent_t);
        region (point_t, extent_t);
        region (point_t, point_t);

        //---------------------------------------------------------------------
        template <typename U>
        constexpr region<S,U>
        cast (void) const
        {
            return {
                p.template cast<U> (),
                e.template cast<U> ()
            };
        }

        //---------------------------------------------------------------------
        T area (void) const;
        T diameter (void) const;
        extent_t magnitude (void) const;
        extent_t magnitude (extent_t);

        bool empty (void) const;

        //---------------------------------------------------------------------
        point_t base    (void) const;
        point_t away    (void) const;
        point_t centre  (void) const;
        point_t closest (point_t) const;

        //---------------------------------------------------------------------
        // exclusive of borders
        bool intersects (region<S,T>) const;

        // Compute binary region combinations
        region intersection (region<S,T>) const;

        // Test if a region lies completely within our space
        bool covers (region<S,T>) const noexcept;

        /// Test if a point lies within our space. Inclusive of borders
        constexpr
        bool
        inclusive (point<S,T> q) const noexcept
        {
            return all (p <= q && p + e >= q);
        }

        /// test if a point lies within our space, exclusive of the
        /// bottom-right border
        constexpr bool
        exclusive (point<S,T> q) const noexcept
        {
            return all (p <= q && p + e > q);
        }

        // Move a point to be within the region bounds
        point_t constrain (point_t) const noexcept;

        //---------------------------------------------------------------------
        // Compute a region `mag` units into the region
        region inset (T mag) const;
        region inset (vector<S,T> mag) const;

        region expand (T mag) const;
        region expand (vector<S,T>) const;

        // arithmetic operators
        region operator+ (vector<S,T>) const;
        region operator- (vector<S,T>) const;

        // Logical comparison operators
        bool operator ==(region<S,T> rhs) const;
        bool operator !=(region<S,T> rhs) const
            { return !(*this == rhs); }

        // Utility constants
        static constexpr region<S,T> max  (void)
        {
            return {
                util::point <S,T> {std::numeric_limits<T>::lowest () / 2},
                util::extent<S,T> {std::numeric_limits<T>::max ()}
            };
        }

        static constexpr region<S,T> unit (void)
        {
            return {
                point_t::origin (),
                extent_t {1}
            };
        }

        static constexpr region<S,T> zero (void)
        { return { point_t {0}, extent_t {0} }; }


        class iterator {
        public:
            using iterator_category = std::forward_iterator_tag;
            using difference_type = std::size_t;
            using value_type = point_t;
            using pointer = value_type*;
            using reference = value_type&;

            iterator (point_t _lo, point_t _hi):
                cursor (_lo),
                lo (_lo),
                hi (_hi)
            { ; }


            const point_t& operator* (void) const& { return cursor; }

            iterator&
            operator++ (void)
            {
                cursor[0] += 1;

                for (size_t s = 0; s < S-1; ++s) {
                    if (cursor[s] <= hi[s])
                        return *this;

                    cursor[s] = lo[s];
                    cursor[s+1]++;
                }

                return *this;
            }

            bool operator== (const iterator &rhs) const { return cursor == rhs.cursor; }
            bool operator!= (const iterator &rhs) const { return cursor != rhs.cursor; }

        private:
            point_t cursor, lo, hi;
        };

        auto step (void) const
        {
            point_t last = p;
            last[S-1] = (p + e)[S-1] + 1;

            return util::view {
                iterator { p,    p + e },
                iterator { last, p + e }
            };
        };


        void sanity (void) const;
    };


    ///////////////////////////////////////////////////////////////////////////
    /// constructs the minimal region that encompasses a region and a point.
    template <typename T, size_t S>
    region<S,T>
    make_union (region<S,T> r, point<S,T> p)
    {
        const auto p0 = select (r.p < p,       r.p,       p);
        const auto p1 = select (r.away () > p, r.away (), p);
        return { p0, p1 };
    }


    template <size_t S, typename T>
    T
    distance2 (region<S,T> r, point<S,T> p)
    {
        auto const clamped = util::max (
            util::min (p, r.p + r.e),
            r.p
        );

        return distance2 (r.p, clamped);
    }


    template <size_t S, typename T>
    T
    distance2 (point<S,T> p, region<S,T> r)
    {
        return distance2 (r, p);
    }


    template <size_t S, typename T>
    bool
    intersects (util::region<S,T> const area,
                util::point<S,T> const query)
    {
        return area.inclusive (query);
    }


    ///------------------------------------------------------------------------
    /// returns true if the supplied point lies within the supplied region
    /// inclusive of borders.
    template <size_t S, typename T>
    bool
    intersects (util::point<S,T> const query,
                util::region<S,T> const area)
    {
        return intersects (area, query);
    }


    ///////////////////////////////////////////////////////////////////////////
    /// returns a uniformly randomly sampled point within the supplied region
    template <size_t S, typename T, typename GeneratorT>
    util::point<S,T>
    sample (region<S,T> shape, GeneratorT &&gen)
    {
        return shape.p + sample (shape.e, std::forward<GeneratorT> (gen)).template as<util::vector> ();
    }


    ///////////////////////////////////////////////////////////////////////////
    template <typename T> using region2 = region<2,T>;
    template <typename T> using region3 = region<3,T>;


    using region2u = region2<unsigned>;
    using region2i = region2<int>;
    using region2f = region2<float>;
    using region2d = region2<double>;


    ///////////////////////////////////////////////////////////////////////////
    template <size_t S, typename T>
    std::ostream& operator<< (std::ostream&, const util::region<S,T>&);
}

#endif