    // Copyright (C) 2011  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_BORDER_EnUMERATOR_H_
    #define DLIB_BORDER_EnUMERATOR_H_

    #include "border_enumerator_abstract.h"
    #include "rectangle.h"

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        class border_enumerator
        {
        public:
            border_enumerator(
            )
            {
                reset();
            }

            border_enumerator(
                const rectangle& rect_,
                unsigned long border_size
            ) :
                rect(rect_),
                inner_rect(shrink_rect(rect_, border_size))
            {
                reset();
            }

            border_enumerator(
                const rectangle& rect_,
                const rectangle& non_border_region
            ) :
                rect(rect_),
                inner_rect(non_border_region.intersect(rect))
            {
                reset();
            }

            void reset (
            )
            {
                // make the four rectangles that surround inner_rect and intersect them
                // with rect.
                bleft   = rect.intersect(rectangle(std::numeric_limits<long>::min(),
                                                   std::numeric_limits<long>::min(),
                                                   inner_rect.left()-1,
                                                   std::numeric_limits<long>::max()));

                bright  = rect.intersect(rectangle(inner_rect.right()+1,
                                                   std::numeric_limits<long>::min(),
                                                   std::numeric_limits<long>::max(),
                                                   std::numeric_limits<long>::max()));

                btop    = rect.intersect(rectangle(inner_rect.left(),
                                                   std::numeric_limits<long>::min(),
                                                   inner_rect.right(),
                                                   inner_rect.top()-1));

                bbottom = rect.intersect(rectangle(inner_rect.left(),
                                                   inner_rect.bottom()+1,
                                                   inner_rect.right(),
                                                   std::numeric_limits<long>::max()));

                p = bleft.tl_corner();
                p.x() -= 1;

                mode = atleft;
            }

            bool at_start (
            ) const
            {
                point temp = bleft.tl_corner();
                temp.x() -=1;
                return temp == p;
            }

            bool current_element_valid(
            ) const
            {
                return rect.contains(p);
            }

            bool move_next()
            {
                if (mode == atleft)
                {
                    if (advance_point(bleft, p))
                        return true;

                    mode = attop;
                    p = btop.tl_corner();
                    p.x() -= 1;
                }
                if (mode == attop)
                {
                    if (advance_point(btop, p))
                        return true;

                    mode = atright;
                    p = bright.tl_corner();
                    p.x() -= 1;
                }
                if (mode == atright)
                {
                    if (advance_point(bright, p))
                        return true;

                    mode = atbottom;
                    p = bbottom.tl_corner();
                    p.x() -= 1;
                }

                if (advance_point(bbottom, p))
                    return true;

                // put p outside rect since there are no more points to enumerate
                p = rect.br_corner();
                p.x() += 1;

                return false;
            }

            unsigned long size (
            ) const
            {
                return rect.area() - inner_rect.area();
            }

            const point& element (
            ) const
            {
                // make sure requires clause is not broken
                DLIB_ASSERT(current_element_valid(),
                    "\t point border_enumerator::element()"
                    << "\n\t This function can't be called unless the element is valid."
                    << "\n\t this: " << this
                    );

                return p;
            }

        private:

            bool advance_point (
                const rectangle& r,
                point& p
            ) const
            {
                p.x() += 1;
                if (p.x() > r.right())
                {
                    p.x() = r.left();
                    p.y() += 1;
                }

                return r.contains(p);
            }

            point p;
            rectangle rect;
            rectangle inner_rect;  // the non-border regions of rect

            enum emode
            {
                atleft,
                atright,
                atbottom,
                attop
            };

            emode mode;

            rectangle btop, bleft, bright, bbottom;
        };

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_BORDER_EnUMERATOR_H_