context: #region Copyright & License Information
  /*
   * Copyright 2007-2020 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.Collections.Generic;
  using System.Linq;
  using OpenRA.Activities;
  using OpenRA.Mods.Common.Traits;
  using OpenRA.Primitives;
  using OpenRA.Traits;
  
  namespace OpenRA.Mods.Common.Activities
  {
  	/* non-turreted attack */
  	public class Attack : Activity, IActivityNotifyStanceChanged
  	{
  		[Flags]
  		protected enum AttackStatus { UnableToAttack, NeedsToTurn, NeedsToMove, Attacking }
  
  		readonly IEnumerable<AttackFrontal> attackTraits;
  		readonly RevealsShroud[] revealsShroud;
  		readonly IMove move;
  		readonly IFacing facing;
  		readonly IPositionable positionable;
  		readonly bool forceAttack;
  		readonly Color? targetLineColor;
  
  		protected Target target;
  		Target lastVisibleTarget;
  		WDist lastVisibleMaximumRange;
  		BitSet<TargetableType> lastVisibleTargetTypes;
  		Player lastVisibleOwner;
  		bool useLastVisibleTarget;
  		bool wasMovingWithinRange;
  
  		WDist minRange;
  		WDist maxRange;
  		AttackStatus attackStatus = AttackStatus.UnableToAttack;
  
  		public Attack(Actor self, Target target, bool allowMovement, bool forceAttack, Color? targetLineColor = null)
  		{
  			this.target = target;
  			this.targetLineColor = targetLineColor;
  			this.forceAttack = forceAttack;
  
  			attackTraits = self.TraitsImplementing<AttackFrontal>().ToArray().Where(Exts.IsTraitEnabled);
  			revealsShroud = self.TraitsImplementing<RevealsShroud>().ToArray();
  			facing = self.Trait<IFacing>();
  			positionable = self.Trait<IPositionable>();
  
  			move = allowMovement ? self.TraitOrDefault<IMove>() : null;
  
  			// The target may become hidden between the initial order request and the first tick (e.g. if queued)
  			// Moving to any position (even if quite stale) is still better than immediately giving up
  			if ((target.Type == TargetType.Actor && target.Actor.CanBeViewedByPlayer(self.Owner))
  			    || target.Type == TargetType.FrozenActor || target.Type == TargetType.Terrain)
  			{
  				lastVisibleTarget = Target.FromPos(target.CenterPosition);
  				lastVisibleMaximumRange = attackTraits.Where(x => !x.IsTraitDisabled)
  					.Min(x => x.GetMaximumRangeVersusTarget(target));
  
  				if (target.Type == TargetType.Actor)
  				{
  					lastVisibleOwner = target.Actor.Owner;
  					lastVisibleTargetTypes = target.Actor.GetEnabledTargetTypes();
  				}
  				else if (target.Type == TargetType.FrozenActor)
  				{
  					lastVisibleOwner = target.FrozenActor.Owner;
  					lastVisibleTargetTypes = target.FrozenActor.TargetTypes;
  				}
  			}
  		}
  
  		protected virtual Target RecalculateTarget(Actor self, out bool targetIsHiddenActor)
  		{
  			return target.Recalculate(self.Owner, out targetIsHiddenActor);
  		}
  
  		public override bool Tick(Actor self)
  		{
  			if (IsCanceling)
  				return true;
  
  			if (!attackTraits.Any())
  			{
  				Cancel(self);
  				return false;
  			}
  
  			bool targetIsHiddenActor;
  			target = RecalculateTarget(self, out targetIsHiddenActor);
  
  			if (!targetIsHiddenActor && target.Type == TargetType.Actor)
  			{
  				lastVisibleTarget = Target.FromTargetPositions(target);
  				lastVisibleMaximumRange = attackTraits.Min(x => x.GetMaximumRangeVersusTarget(target));
  
  				lastVisibleOwner = target.Actor.Owner;
  				lastVisibleTargetTypes = target.Actor.GetEnabledTargetTypes();
  			}
  
  			useLastVisibleTarget = targetIsHiddenActor || !target.IsValidFor(self);
  
  			// If we are ticking again after previously sequencing a MoveWithRange then that move must have completed
  			// Either we are in range and can see the target, or we've lost track of it and should give up
  			if (wasMovingWithinRange && targetIsHiddenActor)
  				return true;
  
  			// Target is hidden or dead, and we don't have a fallback position to move towards
  			if (useLastVisibleTarget && !lastVisibleTarget.IsValidFor(self))
  				return true;
  
  			wasMovingWithinRange = false;
  			var pos = self.CenterPosition;
  			var checkTarget = useLastVisibleTarget ? lastVisibleTarget : target;
  
  			// We don't know where the target actually is, so move to where we last saw it
  			if (useLastVisibleTarget)
  			{
  				// We've reached the assumed position but it is not there or we can't move any further - give up
  				if (checkTarget.IsInRange(pos, lastVisibleMaximumRange) || move == null || lastVisibleMaximumRange == WDist.Zero)
  					return true;
  
  				// Move towards the last known position
  				wasMovingWithinRange = true;
  				QueueChild(move.MoveWithinRange(target, WDist.Zero, lastVisibleMaximumRange, checkTarget.CenterPosition, Color.Red));
  				return false;
  			}
  
  			attackStatus = AttackStatus.UnableToAttack;
  
  			foreach (var attack in attackTraits)
  			{
  				var status = TickAttack(self, attack);
  				attack.IsAiming = status == AttackStatus.Attacking || status == AttackStatus.NeedsToTurn;
  			}
  
  			if (attackStatus.HasFlag(AttackStatus.NeedsToMove))
  				wasMovingWithinRange = true;
  
  			if (attackStatus >= AttackStatus.NeedsToTurn)
  				return false;
  
  			return true;
  		}
  
  		protected virtual AttackStatus TickAttack(Actor self, AttackFrontal attack)
  		{
  			if (!target.IsValidFor(self))
  				return AttackStatus.UnableToAttack;
  
  			if (attack.Info.AttackRequiresEnteringCell && !positionable.CanEnterCell(target.Actor.Location, null, BlockedByActor.None))
  				return AttackStatus.UnableToAttack;
  
  			if (!attack.Info.TargetFrozenActors && !forceAttack && target.Type == TargetType.FrozenActor)
  			{
  				// Try to move within range, drop the target otherwise
  				if (move == null)
  					return AttackStatus.UnableToAttack;
  
  				var rs = revealsShroud
  					.Where(Exts.IsTraitEnabled)
  					.MaxByOrDefault(s => s.Range);
  
  				// Default to 2 cells if there are no active traits
  				var sightRange = rs != null ? rs.Range : WDist.FromCells(2);
  
  				attackStatus |= AttackStatus.NeedsToMove;
  				QueueChild(move.MoveWithinRange(target, sightRange, target.CenterPosition, Color.Red));
  				return AttackStatus.NeedsToMove;
  			}
  
  			// Drop the target once none of the weapons are effective against it
  			var armaments = attack.ChooseArmamentsForTarget(target, forceAttack).ToList();
  			if (armaments.Count == 0)
  				return AttackStatus.UnableToAttack;
  
  			// 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)
  				|| (minRange.Length != 0 && target.IsInRange(pos, minRange))
  				|| (mobile != null && !mobile.CanInteractWithGroundLayer(self)))
  			{
  				// Try to move within range, drop the target otherwise
  				if (move == null)
  					return AttackStatus.UnableToAttack;
  
  				attackStatus |= AttackStatus.NeedsToMove;
  				var checkTarget = useLastVisibleTarget ? lastVisibleTarget : target;
  				QueueChild(move.MoveWithinRange(target, minRange, maxRange, checkTarget.CenterPosition, Color.Red));
  				return AttackStatus.NeedsToMove;
  			}
  
  			if (!attack.TargetInFiringArc(self, target, 4 * attack.Info.FacingTolerance))
  			{
  				var desiredFacing = (attack.GetTargetPosition(pos, target) - pos).Yaw;
  
gt: 				attackStatus |= AttackStatus.NeedsToTurn;