/******************************************************************/
/* 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 <algorithm>

#include "boundedVolumeNode.h"
#include "random_number.h"

boundedVolumeNode::boundedVolumeNode(const std::vector<std::shared_ptr<const boundedPrimitive>>::iterator& start, const std::vector<std::shared_ptr<const boundedPrimitive>>::iterator& end)

  : _left(nullptr), _right(nullptr), boundedPrimitive()
{
  assert(std::distance(start, end) > 1);

  // compute the bounding box
  for_each(start, end, [&](const std::shared_ptr<const boundedPrimitive>& prim)
  {
    _bb += prim->boundingbox();
  });

  // select random splitting dimension & pivot
  unsigned int split = random_int(2);
  float pivot  = _bb.center()[split];

  // partition
  auto middle = std::partition(start, end, [&](const std::shared_ptr<const boundedPrimitive>& prim)
  {
    return prim->boundingbox().center()[split] < pivot;
  });

  // special case: all centers are the same.
  if(start == middle) middle++;

  // create _left (recurse if more than one primitive)
  if(std::distance(start, middle) == 1)
    _left = *start;
  else 
    _left = std::shared_ptr<const boundedPrimitive>(new boundedVolumeNode(start, middle));

  // create _right (recurse if more than one primitive)
  if(std::distance(middle, end) == 1)
    _right = *middle;
  else 
    _right = std::shared_ptr<const boundedPrimitive>(new boundedVolumeNode(middle, end));

  // Done.
}

intersectionPoint boundedVolumeNode::intersect(const ray& r) const
{
  intersectionPoint leftIp, rightIp;

  // check left child
  if(_left && _left->hitBoundingBox(r))
    leftIp = _left->intersect(r);

  // check right child
  if(_right && _right->hitBoundingBox(r))
    rightIp = _right->intersect(r);

  // return closest
  return std::min(leftIp, rightIp);
}


float boundedVolumeNode::area(void) const
{
  float total_area = 0.0f;
  if(_left) total_area += _left->area();
  if(_right) total_area += _right->area();
  return total_area;
}


surfaceSample boundedVolumeNode::sample(float r1, float r2) const
{
  if(_left && !_right) return _left->sample(r1, r2);
  else if(_right && !_left) return _right->sample(r1, r2);
  else
  {
    float area_left = _left->area();
    float area_right = _right->area();
    float prob_left = area_left / (area_left + area_right);
    float prob_right = 1.0f - prob_left;

    if(r1 <= prob_left)
      return _left->sample(r1 / prob_left, r2) * prob_left;
    else
      return _right->sample((r1 - prob_left) / prob_right, r2) * prob_right;
  }
}