/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2020, Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include <algorithm>

#include "../../extent.hpp"
#include "../../region.hpp"
#include "../../random.hpp"


namespace cruft::geom::sample {
    /// Given a desired subregion shape, and a possible field of locations,
    /// select a random location for surface placement.
    ///
    /// Valid placements allow for rotations, but are exclusive of far edges
    /// for integer types.
    ///
    /// The largest axis of the shape must not be larger than the smallest
    /// axis of the placement field otherwise the chosen region may fall
    /// outside the field.
    class subregion {
    public:
        subregion (cruft::extent2i _shape, cruft::extent2i _field)
            : m_shape (_shape)
            , m_field (_field)
        {
            CHECK (all (m_shape <= m_field));
        }


        // Choose placements by looking at each axis in turn.
        //
        // We support rotations by randomising the axis ordering for the shape
        // but not the field.
        template <typename GeneratorT>
        cruft::region2i
        operator() (GeneratorT &&gen)
        {
            int axes[] = { 0, 1 };
            std::shuffle (std::begin (axes), std::end (axes), gen);

            cruft::region2i res;

            for (int i = 0; i < std::ssize (axes); ++i) {
                res.e[i] = m_shape[axes[i]];
                res.p[i] = cruft::random::uniform (m_field[i] - res.e[i]);
            }

            return res;
        }

    private:
        cruft::extent2i m_shape;
        cruft::extent2i m_field;
    };
}