/*
 * VisualGrid.cs
 * Authors: Mike Dapiran
 * Copyright (c) 2007-2008 Cornell University

 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 as published by the Free Software Foundation; either version 2
 of the License, or (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
*/

using System;
using Microsoft.Xna.Framework;
using tAC_Engine.Graphics.Cameras;
using Util;

namespace ColonySim
{
	class VisualGrid : DrawableGameScreenComponent
	{
		private readonly Perspective3DCamera mPlayerCam;
		private BoundingFrustum mFrustum;
		private readonly Plane mZeroPlane = new Plane(Vector3.Left, Vector3.Forward, Vector3.Zero);

		public VisualGrid(Perspective3DCamera pCamera)
		{
			mPlayerCam = pCamera;
		}

		public override void Update(GameTime gameTime)
		{
			mFrustum = new BoundingFrustum(mPlayerCam.View * mPlayerCam.Projection);
			if (mFrustum.Intersects(mZeroPlane) == PlaneIntersectionType.Intersecting)
			{
				Vector3[] corners = mFrustum.GetCorners();

				Vector3[] areaOfGridViewable = new Vector3[4];
				int curAreaIndex = 0;

				for(int i = 0; i < 4; i++)
				{
					if(i != 3)
					{
						float? distanceToPlane = Intersects(new Ray(corners[i], corners[i] - corners[i + 1]), mZeroPlane);

						if(distanceToPlane != null)
						{
							areaOfGridViewable[curAreaIndex] = corners[i] + ((corners[i] - corners[i+1]) * distanceToPlane.Value);
							curAreaIndex++;
						}
					}
					else
					{
						float? distanceToPlane = Intersects(new Ray(corners[i], corners[i] - corners[0]), mZeroPlane);

						if(distanceToPlane != null)
						{
							areaOfGridViewable[curAreaIndex] = corners[i] + ((corners[i] - corners[0]) * distanceToPlane.Value);
							curAreaIndex++;
						}
					}
				}

				for(int i = 4; i < 8; i++)
				{
					if(i != 7)
					{
						float? distanceToPlane = Intersects(new Ray(corners[i], corners[i] - corners[i + 1]), mZeroPlane);

						if(distanceToPlane != null)
						{
							areaOfGridViewable[curAreaIndex] = corners[i] + ((corners[i] - corners[i+1]) * distanceToPlane.Value);
							curAreaIndex++;
						}
					}
					else
					{
						float? distanceToPlane = Intersects(new Ray(corners[i], corners[i] - corners[4]), mZeroPlane);

						if(distanceToPlane != null)
						{
							areaOfGridViewable[curAreaIndex] = corners[i] + ((corners[i] - corners[4]) * distanceToPlane.Value);
							curAreaIndex++;
						}
					}
				}

				Vector2[] areaToDrawGrid = new Vector2[4];
				areaToDrawGrid[0] = new Vector2(areaOfGridViewable[0].X, areaOfGridViewable[0].Z);
				areaToDrawGrid[1] = new Vector2(areaOfGridViewable[1].X, areaOfGridViewable[1].Z);
				areaToDrawGrid[2] = new Vector2(areaOfGridViewable[2].X, areaOfGridViewable[2].Z);
				areaToDrawGrid[3] = new Vector2(areaOfGridViewable[3].X, areaOfGridViewable[3].Z);

				for (int i = 0; i < 4; i++)
				{ 
					areaToDrawGrid[0].X = areaToDrawGrid[3].X = Math.Min(areaToDrawGrid[0].X, areaOfGridViewable[i].X);
					areaToDrawGrid[0].Y = areaToDrawGrid[1].Y = Math.Min(areaToDrawGrid[0].Y, areaOfGridViewable[i].Z);
					areaToDrawGrid[1].X = areaToDrawGrid[2].X = Math.Max(areaToDrawGrid[1].X, areaOfGridViewable[i].X);
					areaToDrawGrid[2].Y = areaToDrawGrid[3].Y = Math.Max(areaToDrawGrid[2].Y, areaOfGridViewable[i].Y);
				}

						
			}
		}

		private static float? Intersects(Ray ray, Plane plane)
		{
			float denom = Vector3.Dot(plane.Normal, ray.Direction);
			if (Math.Abs(denom) >= float.Epsilon)
			{
				float nom = Vector3.Dot(plane.Normal, ray.Position) + plane.D;
				float t = -(nom / denom);

				if (t >= 0)
				{
					return t;
				}
			}
			return null;
		}
	}
}