#region Copyright & License Information
/*
 * Copyright 2007-2014 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.Mods.RA.Move;
using OpenRA.Traits;

namespace OpenRA.Mods.RA.Activities
{
	public class MoveAdjacentTo : Activity
	{
		readonly Target target;
		readonly Mobile mobile;
		readonly PathFinder pathFinder;

		Activity inner;
		CPos cachedTargetPosition;
		CPos[] adjacentCells;
		bool repath;

		public MoveAdjacentTo(Actor self, Target target)
		{
			this.target = target;

			mobile = self.Trait<Mobile>();
			pathFinder = self.World.WorldActor.Trait<PathFinder>();

			repath = true;
		}

		public override Activity Tick(Actor self)
		{
			if (IsCanceled || !target.IsValidFor(self))
				return NextActivity;

			var targetPosition = target.CenterPosition.ToCPos();

			// Calculate path to target
			if (inner == null && repath)
			{
				cachedTargetPosition = targetPosition;
				adjacentCells = Util.AdjacentCells(target).ToArray();
				repath = false;

				var ps1 = new PathSearch(self.World, mobile.Info, self)
				{
					checkForBlocked = true,
					heuristic = location => 0,
					inReverse = true
				};

				foreach (var cell in adjacentCells)
				{
					if (cell == self.Location)
						return NextActivity;
					else
						ps1.AddInitialCell(cell);
				}

				ps1.heuristic = PathSearch.DefaultEstimator(mobile.toCell);
				var ps2 = PathSearch.FromPoint(self.World, mobile.Info, self, mobile.toCell, target.CenterPosition.ToCPos(), true);
				var ret = pathFinder.FindBidiPath(ps1, ps2);

				inner = mobile.MoveTo(() => ret);
			}

			// Force a repath once the actor reaches the next cell
			if (!repath && cachedTargetPosition != targetPosition)
			{
				if (inner != null)
					inner.Cancel(self);

				repath = true;
			}

			inner = Util.RunActivity(self, inner);

			// Move completed
			if (inner == null && adjacentCells.Contains(self.Location))
				return NextActivity;

			return this;
		}

		public override IEnumerable<Target> GetTargets(Actor self)
		{
			if (inner != null)
				return inner.GetTargets(self);

			return Target.None;
		}
	}
}