/******************************************************************/
/* This file is part of the homework assignments for CSCI-427/527 */
/* at The College of William & Mary and authored by Pieter Peers. */
/* No part of this file, whether altered or in original form, can */
/* be distributed or used outside the context of CSCI-427/527     */
/* without consent of either the College of William & Mary or     */
/* Pieter Peers.                                                  */
/******************************************************************/
#include <cassert>
#include "constants.h"
#include "areaLightsource.h"

//////////////////
// Constructors //
//////////////////
areaLightsource::areaLightsource(const color& power, const std::shared_ptr<const boundedPrimitive>& geometry, const vec3d& attenuation)
{
  _power = power;
  _geometry = geometry;
  _attenuation = attenuation;

  if(_geometry)
  {
    _center = _geometry->sample(0.5f, 0.5).position();
    _area = _geometry->area();
  }
}


/////////////
// Methods //
/////////////
lightSample areaLightsource::intensityAt(const vec3d& point) const
{
  // use the 'center position' and emulate a point light source
  vec3d direction = point - _center;
  float distance = direction.length();
  float attenuation = ((_attenuation[2]*distance + _attenuation[1])*distance + _attenuation[0]);

  // Done.
  return lightSample(direction, _power / attenuation, distance - 2.0f * EPSILON);  // reduce distance to avoid self-intersection
}


lightSample areaLightsource::emittanceAt(const vec3d& point, float r1, float r2) const
{
  if(!_geometry) return lightSample();

  // sample surface
  surfaceSample sample = _geometry->sample(r1, r2);

  // direction
  vec3d direction = point - sample.position();
  float distance = direction.length();

  // handle backside case
  if(direction.dot(sample.normal()) < 0.0f) return lightSample();

  // Done.
  return lightSample(direction,
		     _power / (2.0f * PI * _area),
		     distance - 2.0f * EPSILON,     // reduce distance to avoid self-intersection
		     sample.pdf(),
		     direction.dot( sample.normal() ) / distance);
}


color areaLightsource::_emittance(const intersectionPoint& ip) const
{
  // check if back hit
  // Note: ip.direction toward the intersection point
  if(ip.normal().dot(ip.direction()) > 0.0f) return color();

  // evaluate emittance (assume point lies on light source)
  return _power / (2.0f * PI * _area);
}

/////////////////////
// Private Methods //
/////////////////////
void areaLightsource::_print(std::ostream& s) const
{
  if(_geometry)
    s << "Area Lightsource: power=" << _power << ", attenuation=" << _attenuation << ", area=" << _area << " centered at: " << _center;
  else s << "Invalid Area Lightsource";
}