#pragma region CPL License
/*
Nuclex Native Framework
Copyright (C) 2002-2015 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#pragma endregion // CPL License

#ifndef NUCLEX_GEOMETRY_AREAS_TRACERS_TRIANGLE2TRACER_H
#define NUCLEX_GEOMETRY_AREAS_TRACERS_TRIANGLE2TRACER_H

#include "Nuclex/Geometry/Config.h"
#include "Nuclex/Geometry/Areas/Triangle2.h"
#include "Nuclex/Geometry/Lines/Line2.h"
#include "Nuclex/Geometry/LineContacts.h"

namespace Nuclex { namespace Geometry { namespace Areas { namespace Tracers {

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

  /// <summary>Determines contacts between lines and 2D triangles</summary>
  template <typename TScalar>
  class Triangle2Tracer {

    /// <summary>Determines where a line enters and where it exits a triangle</summary>
    /// <param name="line">
    ///   Line whose entry and exit through the triangle will be determined
    /// </param>
    /// <param name="triangle">Triangle the line will be checked against</param>
    /// <returns>The times at which the line enters and leaves the triangle</returns>
    public: static LineContacts<TScalar> FindLineContacts(
      const Lines::Line2<TScalar> &line, const Triangle2<TScalar> &triangle
    ) {
      // Careful, line could start inside triangle - but it's a line, so negative
      // entry time is okay?
      TScalar abContact = findLineContact(line, triangle.A, triangle.B);
      TScalar bcContact = findLineContact(line, triangle.B, triangle.C);
      TScalar caContact = findLineContact(line, triangle.C, triangle.A);

      // A line can either cross none of the triangle's edges or two of them.
      // We consider any other number of crossed edges impossible (exactly hitting
      // a corner or such things are simply considered misses)
      if(Math<TScalar>::IsNan(abContact)) {
        if(Math<TScalar>::IsNan(bcContact)) {
          return LineContacts<TScalar>(caContact, caContact);
        } else if(Math<TScalar>::IsNan(caContact)) {
          return LineContacts<TScalar>(bcContact, bcContact);
        } else if(bcContact < caContact) {
          return LineContacts<TScalar>(bcContact, caContact);
        } else {
          return LineContacts<TScalar>(caContact, bcContact);
        }
      } else if(Math<TScalar>::IsNan(bcContact)) {
        if(Math<TScalar>::IsNan(caContact)) {
          return LineContacts<TScalar>(abContact, abContact);
        } else if(abContact < caContact) {
          return LineContacts<TScalar>(abContact, caContact);
        } else {
          return LineContacts<TScalar>(caContact, abContact);
        }
      } else {
        if(abContact < bcContact) {
          return LineContacts<TScalar>(abContact, bcContact);
        } else {
          return LineContacts<TScalar>(bcContact, abContact);
        }
      }
    }
                        
    /// <summary>Determines where a line crosses a line segment</summary>
    /// <param name="line">Line whose time of crossing will be determined</param>
    /// <param name="start">Point at which the line segment begins</param>
    /// <param name="end">Point at which the line segment ends</param>
    /// <returns>The time at which the line crosses the line segment</returns>
    private: static TScalar findLineContact(
      const Lines::Line2<TScalar> &line,
      const Point2<TScalar> &start, const Point2<TScalar> &end
    ) {
      Vector2<TScalar> segmentDirection = (end - start);

      // Time of intersection of the segment with the traced line. This allows us to see
      // if the segment hits the traced line inside its length.
      TScalar s = (
        line.Direction.X * (line.Origin.Y - start.Y) -
        line.Direction.Y * (line.Origin.X - start.X)
      ) / (line.Direction.X * segmentDirection.Y - segmentDirection.X * line.Direction.Y);
      
      if((s >= 0) && (s < 1)) {
        TScalar t = (
          segmentDirection.X * (line.Origin.Y - start.Y) -
          segmentDirection.Y * (line.Origin.X - start.X)
        ) / (line.Direction.X * segmentDirection.Y - segmentDirection.X * line.Direction.Y);

        return t;
      } else {
        return std::numeric_limits<TScalar>::signaling_NaN();
      }
    }

  };

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

}}}} // namespace Nuclex::Geometry::Areas::Tracers

#endif // NUCLEX_GEOMETRY_AREAS_TRACERS_TRIANGLE2TRACER_H