struct pos2d
{
	double X;
	double Y;
};

// Two variable linear equation class

class lin_equation2
{
public:
	double A;
	double B;
	double C;
	lin_equation2();
};

lin_equation2::lin_equation2()
{
	A = 0;
	B = 0;
	C = 0;
}

class circle
{
	
public:
	// Creates a circle using the center coordinates and the radius
	circle(double Cx,double Cy,double Cradius);

	double X;
	double Y;
	double radius;
	
	// Get boundaries
	double GetLeftBound() { return (X - radius); };
	double GetRightBound(){ return (X + radius); };
	double GetUpperBound(){ return (Y + radius); };
	double GetLowerBound(){ return (Y - radius); };
	
	// Useful for debugging
	void DisplayEquation();

};

circle::circle(double Cx,double Cy,double Cradius)
{
	X = Cx;
	Y = Cy;
	radius = Cradius;
}

void circle::DisplayEquation()
{
	cout << "Center: " << X << " , "  << Y << endl;
	cout << "Radius: " << radius << endl;
	cout << "Xbound[0]: " << GetLeftBound() << endl;
	cout << "Xbound[1]: " << GetRightBound() << endl;
	cout << "Ybound[0]: " << GetLowerBound() << endl;
	cout << "Ybound[1]: " << GetUpperBound() << endl << endl;

}

class line_segment
{
	pos2d GetIntersectionPoint(const line_segment &ls1);
	lin_equation2 eq;
	double Xbound[2];
	double Ybound[2];
public:
	
	line_segment();
	// Creates a line segment using its extremity points
	line_segment(double X1,double Y1,double X2,double Y2);
	// Checks for collision with another line_segment
	bool CheckCollision(const line_segment &ls1);
	// Checks for collision with a circle
	bool CheckCollision( circle &cc1);
	// Useful for debugging
	void DisplayEquation();
		
};

line_segment::line_segment()
{
	Xbound[0] = 0;
	Xbound[1] = 0;
	Ybound[0] = 0;
	Ybound[1] = 0;

}

line_segment::line_segment(double X1,double Y1,double X2,double Y2)
{
	
	// Uses 0 for left/down and 1 for right/up
	if(X1 < X2)
	{
		Xbound[0] = X1;
		Xbound[1] = X2;
	}
	else
	{
		Xbound[0] = X2;
		Xbound[1] = X1;
	}
	
	if(Y1 < Y2)
	{
		Ybound[0] = Y1;
		Ybound[1] = Y2;
	}
	else
	{
		Ybound[0] = Y2;
		Ybound[1] = Y1;
	}

	eq.A = Y1 - Y2;
	eq.B = X2 - X1;
	eq.C = -X1*Y2 + X2*Y1;
	
	// make eq.A always positive to simplify calculations
	if(eq.A < 0)
	{
		eq.A = -eq.A;
		eq.B = -eq.B;
		eq.C = -eq.C;
	}


	
}

bool line_segment::CheckCollision(const line_segment &ls1)
{
	
	// check if the segment has points in common within the boxes created by their extremities
	if((Xbound[1] < ls1.Xbound[0]) || (Xbound[0] > ls1.Xbound[1]) 
|| (Ybound[1] < ls1.Ybound[0]) || (Ybound[0] > ls1.Ybound[1]) ) return false; 
	
	// calculate the intersection point if it existed and check if they belong to both line segments
	pos2d inp = GetIntersectionPoint(ls1);

	if( (eq.A * inp.X + eq.B * inp.Y == eq.C) 
&& (ls1.eq.A * inp.X + ls1.eq.B * inp.Y == ls1.eq.C) )
	{
		// displays intersection point on the screen if enabled
		if(DEBUG_OPTIONS) 
		{
			cout << "refpoint added\n";
			refpoints.push_back(inp);
		}
		return true;
	}
	
	return false;
	
}

bool line_segment::CheckCollision( circle &cc1)
{
	// first of all, check boundaries cause we're dealing with a line segment here not an infinite line
	if((Xbound[1] < cc1.GetLeftBound()) 
|| (Xbound[0] > cc1.GetRightBound()) || (Ybound[1] < cc1.GetLowerBound()) 
|| (Ybound[0] > cc1.GetUpperBound()) ) return false; 
	
	// uses distance from circle's center to the line segment(equation to calculate distance from line to point)
	// using -eq.C since we're passing it to the first member

	double e1 = ( abs(eq.A * cc1.X + eq.B * cc1.Y - eq.C) ) / sqrt(eq.A*eq.A + eq.B*eq.B);
	
	if(e1 > cc1.radius )
	{
		return false;
	}
		
	return true;
	
}

pos2d line_segment::GetIntersectionPoint(const line_segment &ls1)
{
	
	// Intersection points
	pos2d interpoint;
	interpoint.X = (eq.B * ls1.eq.C - eq.C * ls1.eq.B) / 
(eq.B * ls1.eq.A - eq.A * ls1.eq.B);
	interpoint.Y = (eq.A * ls1.eq.C - eq.C * ls1.eq.A) / 
(eq.A * ls1.eq.B - eq.B * ls1.eq.A);
	
	return interpoint;
	
}

void line_segment::DisplayEquation()
{
	if(eq.A != 0) cout << eq.A << "x" ;
	if(eq.B != 0) cout << eq.B << "y" ;
	cout << " = " << eq.C << "\n\n";
	
	cout << "Xbound left: " << Xbound[0] << endl;
	cout << "Xbound right: " << Xbound[1] << endl;
	cout << "Ybound down: " << Ybound[0] << endl;
	cout << "Ybound up: " << Ybound[1] << "\n\n";
}