using System;
using org.hwo.contracts;

using OpenTK;

namespace org.budnhead.core
{
	public static class Geometry
	{

		/**
		 * Intersect Plane and Ray: 
		 * 
		 * A 	+ i * (B-A) + j * (C-A) 			= P +	n * V
		 * A-P 	+ i * (B-A) + j * (C-A) 			= 		n * V
		 * 		  i * (B-A) + j * (C-A) - n * V		= P-A
		 * 
		 * =>
		 * 
		 * -n * V	+ i * (B-A)	+ j * (C-A)			= P-A
		 * 
		 * out p : receives the cooefficients of the solved equation (n,i,j)
		 * 
		 **/
		public static bool intersectPlainCoeff(Vector3 P,Vector3 V,Vector3 A,Vector3 B,Vector3 C,out Vector3 p){
			Vector3 BA,CA,PA;
			Vector3 coeff = new Vector3();
			p = coeff;

			BA = B-A;
			CA = C-A;
			PA = P-A;
/*
			Console.WriteLine("Interesction:");
			Console.WriteLine("Ray:           {0} + i * {1}",P,V);
			Console.WriteLine("A:             {0}",A);
			Console.WriteLine("B:             {0}",B);
			Console.WriteLine("C:             {0}",C);
*/
			return new BooleanConditional()
				.requires(Linear.Solve4x3(V,BA,CA,PA,out coeff))
				.does(delegate { coeff.X = -coeff.X;})
				.sets(ref p,coeff)
				.isSuccess();
		}

		public static bool intersectPlain(Vector3 P,Vector3 V,Vector3 A,Vector3 B,Vector3 C,out Vector3 p){
			Vector3 coeff = new Vector3();
			p = new Vector3();

			return new BooleanConditional()
				.requires(intersectPlainCoeff(P,V,A,B,C,out coeff))
				.assigns(ref p, delegate { return A + (coeff.Y * (B-A)) + (coeff.Z * (C-A)); })
				.isSuccess();
		}

		public static bool intersectPlainForward(Vector3 P,Vector3 V,Vector3 A,Vector3 B,Vector3 C,out Vector3 p){
			Vector3 coeff = new Vector3();
			p = new Vector3();

			return new BooleanConditional()
				.requires(intersectPlainCoeff(P,V,A,B,C,out coeff))
				.requires(coeff.X > 0)
				.assigns(ref p, delegate { return P + (coeff.X * V); })
				.isSuccess();
		}

		public static bool intersectPlainRect(Vector3 P,Vector3 V,Vector3 A,Vector3 B,Vector3 C,out Vector3 p){
			Vector3 coeff = new Vector3();
			p = new Vector3();

			return new BooleanConditional()
				.requires(intersectPlainCoeff(P,V,A,B,C,out coeff))
				.requires(coeff.Y >= 0)
				.requires(coeff.Z >= 0)
				.requires(coeff.Y <= 1)
				.requires(coeff.Z <= 1)
				.assigns(ref p, delegate { return P + (coeff.X * V); })
				.isSuccess();
		}

		public static bool intersectTriangle(Vector3 P,Vector3 V,Vector3 A,Vector3 B,Vector3 C,out Vector3 p){
			Vector3 coeff = new Vector3();
			p = new Vector3();

			Console.WriteLine("Check triangle intersection for {0} {1} {2}",A,B,C);

			return new BooleanConditional()
				.requires(intersectPlainCoeff(P,V,A,B,C,out coeff))
				.requires(coeff.Y >= 0)
				.requires(coeff.Z >= 0)
				.requires(coeff.Y <= 1)
				.requires(coeff.Z <= 1)
				.requires(coeff.Y + coeff.Z <= 1)
				.assigns(ref p, delegate { return A + (coeff.Y * (B-A)) + (coeff.Z * (C-A)); })
				.isSuccess();
		}

	}
}