OpenRA/OpenRA.Mods.Common/Activities/Attack.cs

#region Copyright & License Information
/*
 * Copyright 2007-2017 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, either version 3 of
 * the License, or (at your option) any later version. For more
 * information, see COPYING.
 */
#endregion

using System;
using System.Linq;
using OpenRA.Activities;
using OpenRA.Mods.Common.Traits;
using OpenRA.Traits;

namespace OpenRA.Mods.Common.Activities
{
	/* non-turreted attack */
	public class Attack : Activity
	{
		[Flags]
		enum AttackStatus { UnableToAttack, NeedsToTurn, NeedsToMove, Attacking }

		protected readonly Target Target;
		readonly AttackBase[] attackTraits;
		readonly IMove move;
		readonly IFacing facing;
		readonly IPositionable positionable;
		readonly bool forceAttack;

		WDist minRange;
		WDist maxRange;
		Activity turnActivity;
		Activity moveActivity;
		AttackStatus attackStatus = AttackStatus.UnableToAttack;

		public Attack(Actor self, Target target, bool allowMovement, bool forceAttack)
		{
			Target = target;

			this.forceAttack = forceAttack;

			attackTraits = self.TraitsImplementing<AttackBase>().ToArray();
			facing = self.Trait<IFacing>();
			positionable = self.Trait<IPositionable>();

			move = allowMovement ? self.TraitOrDefault<IMove>() : null;
		}

		public override Activity Tick(Actor self)
		{
			turnActivity = moveActivity = null;
			attackStatus = AttackStatus.UnableToAttack;

			foreach (var attack in attackTraits.Where(x => !x.IsTraitDisabled))
			{
				var activity = InnerTick(self, attack);
				attack.IsAttacking = activity == this;
			}

			if (attackStatus.HasFlag(AttackStatus.Attacking))
				return this;

			if (attackStatus.HasFlag(AttackStatus.NeedsToTurn))
				return turnActivity;

			if (attackStatus.HasFlag(AttackStatus.NeedsToMove))
				return moveActivity;

			return NextActivity;
		}

		protected virtual Activity InnerTick(Actor self, AttackBase attack)
		{
			if (IsCanceled)
				return NextActivity;

			var type = Target.Type;
			if (!Target.IsValidFor(self) || type == TargetType.FrozenActor)
				return NextActivity;

			if (attack.Info.AttackRequiresEnteringCell && !positionable.CanEnterCell(Target.Actor.Location, null, false))
				return NextActivity;

			// Drop the target if it moves under the shroud / fog.
			// HACK: This would otherwise break targeting frozen actors
			// The problem is that Shroud.IsTargetable returns false (as it should) for
			// frozen actors, but we do want to explicitly target the underlying actor here.
			if (!attack.Info.IgnoresVisibility && type == TargetType.Actor && !Target.Actor.Info.HasTraitInfo<FrozenUnderFogInfo>() && !self.Owner.CanTargetActor(Target.Actor))
				return NextActivity;

			// Drop the target once none of the weapons are effective against it
			var armaments = attack.ChooseArmamentsForTarget(Target, forceAttack).ToList();
			if (armaments.Count == 0)
				return NextActivity;

			// Update ranges
			minRange = armaments.Max(a => a.Weapon.MinRange);
			maxRange = armaments.Min(a => a.MaxRange());

			var pos = self.CenterPosition;
			var mobile = move as Mobile;
			if (!Target.IsInRange(pos, maxRange) || Target.IsInRange(pos, minRange)
				|| (mobile != null && !mobile.CanInteractWithGroundLayer(self)))
			{
				// Try to move within range, drop the target otherwise
				if (move == null)
					return NextActivity;

				attackStatus |= AttackStatus.NeedsToMove;
				moveActivity = ActivityUtils.SequenceActivities(move.MoveWithinRange(Target, minRange, maxRange), this);
				return NextActivity;
			}

			var targetedPosition = attack.Info.AttackTargetCenter ? Target.CenterPosition : Target.Positions.PositionClosestTo(pos);
			var desiredFacing = (targetedPosition - pos).Yaw.Facing;
			if (facing.Facing != desiredFacing)
			{
				attackStatus |= AttackStatus.NeedsToTurn;
				turnActivity = ActivityUtils.SequenceActivities(new Turn(self, desiredFacing), this);
				return NextActivity;
			}

			attackStatus |= AttackStatus.Attacking;
			attack.DoAttack(self, Target, armaments);

			return this;
		}
	}
}