#pragma once
#include "light.hpp"

class SquareLight :
	public Light
{
	Vector edge1;
	Vector edge2;
public:
	Vector polyNodes[4];
	unsigned int nPolyNodes;

	SquareLight(Vector* nodes, int nNodes, const Vector& radiance)
	{
		if(nNodes < 3) exit(-1);
		nPolyNodes = nNodes;
		for(int i=0; i<nPolyNodes; i++)
			polyNodes[i] = nodes[i];
		Vector a; a.setDifference(nodes[0], nodes[1]);
		Vector b; b.setDifference(nodes[0], nodes[2]);
		edge1 = a;
		edge2.setDifference(nodes[0], nodes[nNodes-1]);
		this->direction.setCrossProduct(b, a);
		this->direction.normalize();
		this->radiance = radiance;
		luminance = radiance.r + radiance.g + radiance.b;
		this->position.clear();
		for(int c=0; c<nNodes; c++)
			this->position += nodes[c];
		this->position *= 1.0f / (float)nNodes;

		area = sqrt(edge1.norm2() * edge2.norm2());
		power = radiance;
		power *= area;
	}
	float getFormFactor(const Vector& lookpoint, const Vector& normal) const
	{
		Vector ffxcd, dif[4], cutRemains[5];
		ffxcd.clear();
		float acc = 0.0f;

		bool in[4];
		for(int iCutter=0; iCutter<4; iCutter++)
		{
			dif[iCutter].setDifference(polyNodes[iCutter], lookpoint);
			dif[iCutter].normalize();
			in[iCutter] = (dif[iCutter] * normal > 0.0f);
		}
		int nRemain = 0;
		for(int iGutter=0;iGutter<4;iGutter++)
		{
			int ta = iGutter & 3;
			int tb = (iGutter + 1) & 3;
			if(in[ta])
			{
				cutRemains[nRemain++] = dif[ta];
				if(!in[tb])
				{
					Vector cutEdgePlaneNormal;
					cutEdgePlaneNormal.setCrossProduct(dif[ta],dif[tb]);
					cutEdgePlaneNormal.normalize();
					cutRemains[nRemain].setCrossProduct(cutEdgePlaneNormal, normal);
					cutRemains[nRemain++].normalize();
				}
			}
			else
				if(in[tb])
				{
					Vector cutEdgePlaneNormal;
					cutEdgePlaneNormal.setCrossProduct(dif[ta],dif[tb]);
					cutEdgePlaneNormal.normalize();
					cutRemains[nRemain].setCrossProduct(normal, cutEdgePlaneNormal);
					cutRemains[nRemain++].normalize();
				}
		}

		if(nRemain == 0) return 0.0f;

		for(int pir = 0; pir < nRemain; pir++)
		{
			Vector rxr; rxr.setCrossProduct(cutRemains[pir], cutRemains[(pir + 1)%nRemain]);
			float sinb = rxr.norm();
			rxr *= 1.0f / sinb;
			float alfa = asinf(sinb);
			if(cutRemains[pir] * cutRemains[(pir + 1)%nRemain] < 0.0f)
				alfa = 3.14f - alfa;
			rxr *= alfa;
//			ffxcd += rxr;
			acc += rxr * normal;
		}
		return acc * 0.5f;
//		return ffxcd * normal * 0.5f;
	}
	Vector getSample() const
	{
		Vector ret = polyNodes[0];
		ret.addScaled(-(float)rand() / RAND_MAX, edge1 );
		ret.addScaled(-(float)rand() / RAND_MAX, edge2 );
		return ret;
	}
	bool isPossiblyVisible(const Vector& point) const
	{
		Vector diff; diff.setDifference(point, position);
		return diff * direction > 0;
	}
};