#ifndef __JVERSOR2D__
#define __JVERSOR2D__

#include <limits>
#include <cmath>


/**
 * \author mdejong
 */

namespace JGEOMETRY2D {}
namespace JPP { using namespace JGEOMETRY2D; }

namespace JGEOMETRY2D {

  /**
   * Data structure for normalised vector in two dimensions.
   */
  class JVersor2D
  {
  public:
    /**
     * Default constructor.
     * This constructor yields a unit y-vector.  
     */
    JVersor2D() :
      __dx(0.0),
      __dy(1.0)
    {}


    /**
     * Constructor.
     *
     * \param  dx            dx value
     * \param  dy            dy value
     */
    JVersor2D(const double dx,
              const double dy) :
      __dx(dx),
      __dy(dy)
    {
      normalise();
    }


    /**
     * Get x direction.
     *
     * \return               x direction
     */
    double getDX() const
    {
      return __dx;
    }


    /**
     * Get y direction.
     *
     * \return               y direction
     */
    double getDY() const
    {
      return __dy;
    }


    /**
     * Get phi angle.
     *
     * \return          phi angle [rad]
     */
    double getPhi() const 
    { 
      return atan2(__dy, __dx);
    }


    /**
     * Negate versor.
     *
     * \return               this versor
     */
    JVersor2D& negate()
    {
      __dx = -__dx;
      __dy = -__dy;

      return *this;
    }
    

    /**
     * Check equality.
     *
     * \param  versor        versor
     * \param  precision     precision
     * \return               true if versors are equal; else false
     */
    bool equals(const JVersor2D& versor,
                const double     precision = std::numeric_limits<double>::min()) const
    {
      return (fabs(getDX() - versor.getDX()) <= precision &&
              fabs(getDY() - versor.getDY()) <= precision);
    }


    /**
     * Get dot product.
     *
     * \param  versor        versor
     * \return               dot product
     */
    double getDot(const JVersor2D& versor) const
    {
      return
	getDX() * versor.getDX() + 
	getDY() * versor.getDY();
    }


    /**
     * Get perpendicular dot product.
     *
     * \param  versor        versor
     * \return               perpendicular dot product
     */
    double getPerpDot(const JVersor2D& versor) const
    {
      return
	getDX() * versor.getDY() - 
	getDY() * versor.getDX();
    }


    /**
     * Normalise versor.
     * This operation may set the result to the unit y-vector.
     *
     * \return               this versor
     */
    JVersor2D& normalise()
    {
      const double v = sqrt(getDX()*getDX() + getDY()*getDY());

      if (v != 0.0) {
        __dx /= v;
        __dy /= v;
      } else {
	__dx = 0.0;
	__dy = 1.0;
      }

      return *this;
    }

  protected:
    double __dx;
    double __dy;
  };


  static const JVersor2D JVersor2X_t(1,0);   //!< unit x-vector
  static const JVersor2D JVersor2Y_t(0,1);   //!< unit y-vector
}

#endif