/*
   Quaternion math helper class.
   (C)2018 Marisa Kirisame, UnSX Team.
   Released under the GNU Lesser General Public License version 3 (or later).
   See https://www.gnu.org/licenses/lgpl-3.0.txt for its terms.
*/

Class Quat
{
	protected double W, X, Y, Z;

	Quat init( double w, double x, double y, double z )
	{
		self.W = w;
		self.X = x;
		self.Y = y;
		self.Z = z;
		return self;
	}

	void copy( Quat q )
	{
		W = q.W;
		X = q.X;
		Y = q.Y;
		Z = q.Z;
	}

	static Quat create( double w, double x, double y, double z )
	{
		return new("Quat").init(w,x,y,z);
	}

	static Quat create_axis( Vector3 axis, double theta )
	{
		double scale = axis dot axis;
		if ( scale < double.epsilon ) return Quat.create(1,0,0,0);
		theta *= 0.5;
		double f = sin(theta)/sqrt(scale);
		return Quat.create(cos(theta),axis.x*f,axis.y*f,axis.z*f);
	}

	static Quat create_euler( double pitch, double yaw, double roll )
	{
		Quat zrot = Quat.create_axis((0,0,1),yaw);
		Quat yrot = Quat.create_axis((0,1,0),pitch);
		Quat xrot = Quat.create_axis((1,0,0),roll);
		Quat sum = zrot.qmul(yrot);
		sum = sum.qmul(xrot);
		return sum;
	}

	// copied here since Actor.Normalize180 is not (yet) clearscope
	static double Normalize180( double ang )
	{
		ang = ang%360;
		ang = (ang+360)%360;
		if ( ang > 180 ) ang -= 360;
		return ang;
	}

	double, double, double to_euler()
	{
		double stest = z*x-w*y;
		double yawY = 2*(w*z+x*y);
		double yawX = 1-2*(y*y+z*z);
		double st = 0.4999995;
		double pitch = 0;
		double yaw = 0;
		double roll = 0;
		if ( stest <= -st )
		{
			pitch = 90;
			yaw = atan2(yawY,yawX);
			roll = Normalize180(yaw+(2*atan2(x,w)));
		}
		else if ( stest > st )
		{
			pitch = -90;
			yaw = atan2(yawY,yawX);
			roll = Normalize180(yaw+(2*atan2(x,w)));
		}
		else
		{
			pitch = -asin(2*stest);
			yaw = atan2(yawY,yawX);
			roll = atan2(2*(w*x+y*z),(1-2*(x*x+y*y)));
		}
		return pitch, yaw, roll;
	}

	Quat qmul( Quat q )
	{
		return Quat.create(w*q.w-x*q.x-y*q.y-z*q.z,w*q.x+x*q.w+y*q.z-z
			*q.y,w*q.y+y*q.w+z*q.x-x*q.z,w*q.z+z*q.w+x*q.y-y*q.x);
	}
}