/*

 * kdtree.cc: KdTree class

 *

 * This file is part of Pyrit Ray Tracer.

 *

 * Copyright 2006, 2007  Radek Brich

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

 * THE SOFTWARE.

 */

#include <algorithm>

#include <stack>

#include "common.h"

#include "kdtree.h"

class ShapeBound

{

public:

	Shape *shape;

	Float pos;

	bool end;

	ShapeBound(Shape *ashape, const Float apos, const bool aend):

		shape(ashape), pos(apos), end(aend) {};

	friend bool operator<(const ShapeBound& a, const ShapeBound& b)

	{

		if (a.pos == b.pos)

			return a.shape < b.shape;

		else

			return a.pos < b.pos;

	};

};

// stack element for kd-tree traversal

class StackElem

{

public:

	KdNode* node; /* pointer to far child */

	Float t; /* the entry/exit signed distance */

	Vector3 pb; /* the coordinates of entry/exit point */

	StackElem(KdNode *anode, const Float &at, const Vector3 &apb):

		node(anode), t(at), pb(apb) {};

};

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

KdNode::~KdNode()

{

	if (isLeaf())

		delete shapes;

	else

		delete[] children;

}

// kd-tree recursive build algorithm, inspired by PBRT (www.pbrt.org)

void KdNode::subdivide(BBox bounds, int maxdepth)

{

	if (maxdepth <= 0 || shapes->size() <= 2)

	{

		setLeaf();

		return;

	}

	// choose split axis

	/*axis = 0;

	if (bounds.h() > bounds.w() && bounds.h() > bounds.d())

		axis = 1;

	if (bounds.d() > bounds.w() && bounds.d() > bounds.h())

		axis = 2;

*/

	// create sorted list of shape bounds (= find all posible splits)

	vector<ShapeBound> edges[3];

	ShapeList::iterator shape;

	for (shape = shapes->begin(); shape != shapes->end(); shape++)

	{

		BBox shapebounds = (*shape)->get_bbox();

		for (int ax = 0; ax < 3; ax++)

		{

			edges[ax].push_back(ShapeBound(*shape, shapebounds.L[ax], 0));

			edges[ax].push_back(ShapeBound(*shape, shapebounds.H[ax], 1));

		}

	}

	for (int ax = 0; ax < 3; ax++)

		sort(edges[ax].begin(), edges[ax].end());

	// choose best split pos

	const Float K = 1.4; // constant, K = cost of traversal / cost of ray-triangle intersection

	Float SAV = (bounds.w()*bounds.h() +  // surface area of node

		bounds.w()*bounds.d() + bounds.h()*bounds.d());

	Float cost = SAV * (K + shapes->size()); // initial cost = non-split cost

	vector<ShapeBound>::iterator edge, splitedge = edges[2].end();

	for (int ax = 0; ax < 3; ax++)

	{

		int lnum = 0, rnum = shapes->size();

		BBox lbb = bounds;

		BBox rbb = bounds;

		for (edge = edges[ax].begin(); edge != edges[ax].end(); edge++)

		{

			if (edge->end)

				rnum--;

			// calculate SAH cost of this split

			lbb.H.cell[ax] = edge->pos;

			rbb.L.cell[ax] = edge->pos;

			Float SAL = (lbb.w()*lbb.h() + lbb.w()*lbb.d() + lbb.h()*lbb.d());

			Float SAR = (rbb.w()*rbb.h() + rbb.w()*rbb.d() + rbb.h()*rbb.d());

			Float splitcost = K*SAV + SAL*(K + lnum) + SAR*(K + rnum);

			if (splitcost < cost)

			{

				axis = ax;

				splitedge = edge;

				cost = splitcost;

				split = edge->pos;

			}

			if (!edge->end)

				lnum++;

		}

	}

	if (splitedge == edges[2].end())

	{

		setLeaf();

		return;

	}

#if 0

// export kd-tree as .obj for visualization

// this would be hard to reconstruct later

	static ofstream F("kdtree.obj");

	Vector3 v;

	static int f=0;

	v.cell[axis] = split;

	v.cell[(axis+1)%3] = bounds.L.cell[(axis+1)%3];

	v.cell[(axis+2)%3] = bounds.L.cell[(axis+2)%3];

	F << "v " << v.x << " " << v.y << " " << v.z << endl;

	v.cell[(axis+1)%3] = bounds.L.cell[(axis+1)%3];

	v.cell[(axis+2)%3] = bounds.H.cell[(axis+2)%3];

	F << "v " << v.x << " " << v.y << " " << v.z << endl;

	v.cell[(axis+1)%3] = bounds.H.cell[(axis+1)%3];

	v.cell[(axis+2)%3] = bounds.H.cell[(axis+2)%3];

	F << "v " << v.x << " " << v.y << " " << v.z << endl;

	v.cell[(axis+1)%3] = bounds.H.cell[(axis+1)%3];

	v.cell[(axis+2)%3] = bounds.L.cell[(axis+2)%3];

	F << "v " << v.x << " " << v.y << " " << v.z << endl;

	F << "f " << f+1 << " " << f+2 << " " << f+3 << " " << f+4 << endl;

	f += 4;

#endif

	// split this node

	delete shapes;

	BBox lbb = bounds;

	BBox rbb = bounds;

	lbb.H.cell[axis] = split;

	rbb.L.cell[axis] = split;

	children = new KdNode[2];

	for (edge = edges[axis].begin(); edge != splitedge; edge++)

		if (!edge->end && edge->shape->intersect_bbox(lbb))

			children[0].addShape(edge->shape);

	for (edge = splitedge; edge < edges[axis].end(); edge++)

		if (edge->end && edge->shape->intersect_bbox(rbb))

			children[1].addShape(edge->shape);

	children[0].subdivide(lbb, maxdepth-1);

	children[1].subdivide(rbb, maxdepth-1);

}

void KdTree::build()

{

	dbgmsg(1, "* building kd-tree\n");

	root = new KdNode();

	ShapeList::iterator shape;

	for (shape = shapes.begin(); shape != shapes.end(); shape++)

		root->addShape(*shape);

	root->subdivide(bbox, max_depth);

	built = true;

}

/* algorithm by Vlastimil Havran, Heuristic Ray Shooting Algorithms, appendix C */

Shape *KdTree::nearest_intersection(const Shape *origin_shape, const Ray &ray,

	Float &nearest_distance)

{

	Float a, b; /* entry/exit signed distance */

	Float t;    /* signed distance to the splitting plane */

	/* if we have no tree, fall back to naive test */

	if (!built)

		return Container::nearest_intersection(origin_shape, ray, nearest_distance);

	if (!bbox.intersect(ray, a, b))

		return NULL;

	/* pointers to the far child node and current node */

	KdNode *farchild, *node;

	node = root; /* start from the kd-tree root node */

	/* std vector is much faster than stack */

	vector<StackElem*> st;

	StackElem *enPt = new StackElem(NULL, a,

		/* distinguish between internal and external origin of a ray*/

		a >= 0.0 ?

			ray.o + ray.dir * a : /* external */

			ray.o);               /* internal */

	/* setup initial exit point in the stack */

	StackElem *exPt = new StackElem(NULL, b, ray.o + ray.dir * b);

	st.push_back(exPt);

	/* loop, traverse through the whole kd-tree, until an object is intersected or ray leaves the scene */

	while (node)

	{

		exPt = st.back();

		/* loop until a leaf is found */

		while (!node->isLeaf())

		{

			/* retrieve position of splitting plane */

			Float splitVal = node->getSplit();

			short axis = node->getAxis();

			if (enPt->pb[axis] <= splitVal)

			{

				if (exPt->pb[axis] <= splitVal)

				{ /* case N1, N2, N3, P5, Z2, and Z3 */

					node = node->getLeftChild();

					continue;

				}

				if (exPt->pb[axis] == splitVal)

				{ /* case Z1 */

					node = node->getRightChild();

					continue;

				}

				/* case N4 */

				farchild = node->getRightChild();

				node = node->getLeftChild();

			}

			else

			{ /* (enPt->pb[axis] > splitVal) */

				if (splitVal < exPt->pb[axis])

				{

					/* case P1, P2, P3, and N5 */

					node = node->getRightChild();

					continue;

				}

				/* case P4*/

				farchild = node->getLeftChild();

				node = node->getRightChild();

			}

			/* case P4 or N4 . . . traverse both children */

			/* signed distance to the splitting plane */

			t = (splitVal - ray.o.cell[axis]) / ray.dir.cell[axis];

			/* setup the new exit point and push it onto stack */

			exPt = new StackElem(farchild, t, Vector3());

			exPt->pb.cell[axis] = splitVal;

			exPt->pb.cell[(axis+1)%3] = ray.o.cell[(axis+1)%3] + t * ray.dir.cell[(axis+1)%3];

			exPt->pb.cell[(axis+2)%3] = ray.o.cell[(axis+2)%3] + t * ray.dir.cell[(axis+2)%3];

			st.push_back(exPt);

		} /* while */

		/* current node is the leaf . . . empty or full */

		/* "intersect ray with each object in the object list, discarding "

		"those lying before stack[enPt].t or farther than stack[exPt].t" */

		Shape *nearest_shape = NULL;

		Float dist = exPt->t;

		ShapeList::iterator shape;

		for (shape = node->shapes->begin(); shape != node->shapes->end(); shape++)

			if (*shape != origin_shape && (*shape)->intersect(ray, dist)

			&& dist >= enPt->t)

			{

				nearest_shape = *shape;

				nearest_distance = dist;

			}

		delete enPt;

		if (nearest_shape)

		{

			while (!st.empty())

			{

				delete st.back();

				st.pop_back();

			}

			return nearest_shape;

		}

		enPt = exPt;

		/* retrieve the pointer to the next node, it is possible that ray traversal terminates */

		node = enPt->node;

		st.pop_back();

	} /* while */

	delete enPt;

	/* ray leaves the scene */

	return NULL;

}

// this should save whole kd-tree with triangles distributed into leaves

void KdTree::save(ostream &str, KdNode *node)

{

	if (!built)

		return;

	if (node == NULL)

		node = root;

	if (node->isLeaf())

		str << "(leaf: " << node->shapes->size() << " shapes)";

	else

	{

		str << "(split " << (char)('x'+node->getAxis()) << " at " << node->getSplit() << "; L=";

		save(str, node->getLeftChild());

		str << "; R=";

		save(str, node->getRightChild());

		str << ";)";

	}

}

// load kd-tree from file/stream

void KdTree::load(istream &str, KdNode *node)

{

}