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#ifndef VIGRA_CONTOURCIRCULATOR_HXX
#define VIGRA_CONTOURCIRCULATOR_HXX

#include "pixelneighborhood.hxx"

namespace vigra
{

/** \addtogroup ImageIteratorAdapters
 */
//@{

/********************************************************/
/*                                                      */
/*                CrackContourCirculator                */
/*                                                      */
/********************************************************/

/** \brief Circulator that walks around a given region.

    The circulator follows the <em>crack contour</em> of a given region.
    Here, a region is an 8-connected component of pixels with the same
    value, such as the regions in a label image.
    The crack contour is located between the inside and outside
    pixels, that is "on the crack" between the region and the background.
    Thus, the circulator moves from pixel corner to pixel corner. By definition,
    the first corner (where the circulator was initialized) gets the
    coordinate (0,0), and calls to <tt>*circulator</tt> return the distance
    of the current corner to the initial one.

    The circulator can be used to calculate the area of a region (in pixels):

    \code
    // start with a pixel within the region, whose left neighbor is outside
    // (see CrackContourCirculator constructor)
    ImageIterator region_anchor = ...;
    int area = 0;

    // calculate area from following the crack contour of the region
    CrackContourCirculator<ImageIterator> crack(region_anchor);
    CrackContourCirculator<ImageIterator> crackend(crack);
    do
    {
        area += crack.diff().x * crack.pos().y -
                crack.diff().y * crack.pos().x;
    }
    while(++crack != crackend);

    area /= 2;
    std::cout << "Area of region " << *region_anchor << ": " << area << std::endl;
    \endcode

    <b>\#include</b> \<vigra/contourcirculator.hxx\><br>
    Namespace: vigra
*/
template <class IMAGEITERATOR>
class CrackContourCirculator
{
    typedef NeighborhoodCirculator<IMAGEITERATOR, EightNeighborCode>
            NEIGHBORHOODCIRCULATOR;
    typedef typename IMAGEITERATOR::value_type label_type;

protected:
    NEIGHBORHOODCIRCULATOR neighborCirc_;
    label_type label_;
    Point2D pos_;

    CrackContourCirculator(NEIGHBORHOODCIRCULATOR const & circ)
        : neighborCirc_(circ),
          label_(*(circ.center())),
          pos_(0, 0)
    {}

public:
        /** the circulator's value type
        */
    typedef Point2D value_type;

        /** the circulator's reference type (return type of <TT>*circ</TT>)
        */
    typedef Point2D const & reference;

        /** the circulator's pointer type (return type of <TT>operator-></TT>)
        */
    typedef Point2D const * pointer;

        /** the circulator tag
        */
    typedef forward_circulator_tag iterator_category;

        /** Initialize the circulator for a given region.

            The image iterator <tt>in_the_region</tt> must refer
            to a boundary pixel of the region to be analysed. The
            direction code <tt>dir</tt> must point to a pixel outside the
            region (the default assumes that the pixel left of the
            given region pixel belongs to the background).
            The first corner of the crack contour is the corner to the
            right of this direction (i.e. the north west corner of
            the region pixel, if the direction was West).
        */
    CrackContourCirculator(IMAGEITERATOR const & in_the_region,
                           vigra::FourNeighborCode::Direction dir = vigra::FourNeighborCode::West)
        : neighborCirc_(in_the_region, EightNeighborCode::code(dir)),
          label_(*in_the_region),
          pos_(0, 0)
    {
        neighborCirc_.turnLeft();
    }

        /** Move to the next crack corner of the contour (pre-increment).
        */
    CrackContourCirculator & operator++()
    {
        pos_ += neighborCirc_.diff();

        neighborCirc_--;

        if(*neighborCirc_ == label_)
        {
            neighborCirc_.moveCenterToNeighbor(); // TODO: simplify moveCenterToNeighbor()s
            --neighborCirc_;
        }
        else
        {
            neighborCirc_.moveCenterToNeighbor(); // jump out
            neighborCirc_ += 3;
            if(*neighborCirc_ == label_)
            {
                neighborCirc_.moveCenterToNeighbor();
                neighborCirc_.turnRight();
            }
            else
            {
                neighborCirc_.moveCenterToNeighbor();
                neighborCirc_.turnLeft();
                neighborCirc_.moveCenterToNeighbor();
                neighborCirc_.turnRight();
            }
        }

        return *this;
    }

        /** Move to the next crack corner of the contour (post-increment).
        */
    CrackContourCirculator operator++(int)
    {
        CrackContourCirculator ret(*this);
        ++(*this);
        return ret;
    }

        /** equality
        */
    bool operator==(CrackContourCirculator const & o) const
    {
        return neighborCirc_ == o.neighborCirc_;
    }

        /** inequality
        */
    bool operator!=(CrackContourCirculator const & o) const
    {
        return neighborCirc_ != o.neighborCirc_;
    }

        /** Get the coordinate of the current corner
            (relative to the first corner).
        */
    reference pos() const
        { return pos_; }

        /** Equivalent to pos()
        */
    reference operator*() const
        { return pos_; }

        /** Access member of the current coordinate.
        */
    pointer operator->() const
        { return &pos_; }

        /** Access pixel to the right of the crack edge (outside of
         * the region bounded by the crack contour we walk on). Note
         * that after operator++, the iterator can still point to the
         * same pixel (looking from another direction now).
         */
    IMAGEITERATOR outerPixel() const
        { return NEIGHBORHOODCIRCULATOR(neighborCirc_).turnRight().base(); }

        /** Get the offset from the current corner of the contour
            to the next one.
        */
    Diff2D const & diff() const
        { return neighborCirc_.diff(); }
};

//@}

} // namespace vigra

#endif /* VIGRA_CONTOURCIRCULATOR_HXX */
