/******************************************************************/
/* 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);
}