#region Copyright & License Information
/*
 * Copyright 2007-2011 The OpenRA Developers (see AUTHORS)
 * This file is part of OpenRA, which is free software. It is made
 * available to you under the terms of the GNU General Public License
 * as published by the Free Software Foundation. For more information,
 * see COPYING.
 */
#endregion

using System.Collections.Generic;
using System.Linq;
using OpenRA.Traits;

namespace OpenRA.Traits
{
	public enum SubCell { FullCell, TopLeft, TopRight, Center, BottomLeft, BottomRight }

	class ActorMapInfo : ITraitInfo
	{
		public object Create(ActorInitializer init) { return new ActorMap(init.world); }
	}

	public class ActorMap
	{
		class InfluenceNode
		{
			public InfluenceNode next;
			public SubCell subCell;
			public Actor actor;
		}

		InfluenceNode[,] influence;
		Map map;

		public ActorMap(World world)
		{
			map = world.Map;
			influence = new InfluenceNode[world.Map.MapSize.X, world.Map.MapSize.Y];

			world.ActorAdded += a => Add(a, a.OccupiesSpace);
			world.ActorRemoved += a => Remove(a, a.OccupiesSpace);
		}

		public IEnumerable<Actor> GetUnitsAt(CPos a)
		{
			if (!map.IsInMap(a))
				yield break;

			for (var i = influence[a.X, a.Y]; i != null; i = i.next)
				if (!i.actor.Destroyed)
					yield return i.actor;
		}

		public IEnumerable<Actor> GetUnitsAt(CPos a, SubCell sub)
		{
			if (!map.IsInMap(a))
				yield break;

			for (var i = influence[a.X, a.Y]; i != null; i = i.next)
				if (!i.actor.Destroyed && (i.subCell == sub || i.subCell == SubCell.FullCell))
					yield return i.actor;
		}

		public bool HasFreeSubCell(CPos a)
		{
			if (!AnyUnitsAt(a))
				return true;

			return new[] { SubCell.TopLeft, SubCell.TopRight, SubCell.Center,
				SubCell.BottomLeft, SubCell.BottomRight }.Any(b => !AnyUnitsAt(a,b));
		}

		public SubCell? FreeSubCell(CPos a)
		{
			if (!HasFreeSubCell(a))
				return null;

			return new[] { SubCell.TopLeft, SubCell.TopRight, SubCell.Center,
				SubCell.BottomLeft, SubCell.BottomRight }.First(b => !AnyUnitsAt(a,b));
		}


		public bool AnyUnitsAt(CPos a)
		{
			return influence[a.X, a.Y] != null;
		}

		public bool AnyUnitsAt(CPos a, SubCell sub)
		{
			for (var i = influence[a.X, a.Y]; i != null; i = i.next)
				if (i.subCell == sub || i.subCell == SubCell.FullCell)
					return true;

			return false;
		}

		public void Add(Actor self, IOccupySpace unit)
		{
			if (unit != null)
				foreach (var c in unit.OccupiedCells())
					influence[c.First.X, c.First.Y] = new InfluenceNode { next = influence[c.First.X, c.First.Y], subCell = c.Second, actor = self };
		}

		public void Remove(Actor self, IOccupySpace unit)
		{
			if (unit != null)
				foreach (var c in unit.OccupiedCells())
					RemoveInner(ref influence[c.First.X, c.First.Y], self);
		}

		void RemoveInner(ref InfluenceNode influenceNode, Actor toRemove)
		{
			if (influenceNode == null)
				return;
			else if (influenceNode.actor == toRemove)
				influenceNode = influenceNode.next;

			if (influenceNode != null)
				RemoveInner(ref influenceNode.next, toRemove);
		}

		public void Update(Actor self, IOccupySpace unit)
		{
			Remove(self, unit);
			if (!self.IsDead())
				Add(self, unit);
		}
	}
}