#region Copyright & License Information
/*
 * Copyright 2007,2009,2010 Chris Forbes, Robert Pepperell, Matthew Bowra-Dean, Paul Chote, Alli Witheford.
 * This file is part of OpenRA.
 * 
 *  OpenRA 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 3 of the License, or
 *  (at your option) any later version.
 * 
 *  OpenRA 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 OpenRA.  If not, see <http://www.gnu.org/licenses/>.
 */
#endregion

using System;
using System.Linq;
using OpenRA.Effects;
using OpenRA.GameRules;
using OpenRA.Traits;
using OpenRA.FileFormats;

namespace OpenRA
{
	public static class Combat			/* some utility bits that are shared between various things */
	{
		static string GetImpactSound(WarheadInfo warhead, bool isWater)
		{
			if (isWater && warhead.WaterImpactSound != null)
				return warhead.WaterImpactSound + ".aud";

			if (warhead.ImpactSound != null)
				return warhead.ImpactSound + ".aud";

			return null;
		}

		public static void DoImpact(WarheadInfo warhead, ProjectileArgs args)
		{
			var world = args.firedBy.World;
			var targetTile = Util.CellContaining(args.dest);

			if (!world.Map.IsInMap(targetTile))
				return;

			// Todo: Unhardcode "Water" terraintype reference
			var isWater = world.GetTerrainType(targetTile) == "Water";

			if (warhead.Explosion != 0)
				world.AddFrameEndTask(
					w => w.Add(new Explosion(w, args.dest, warhead.Explosion, isWater)));

			Sound.Play(GetImpactSound(warhead, isWater), args.dest);
			
			if (warhead.SmudgeType != null)
			{
				var smudgeLayer = world.WorldActor.traits.WithInterface<SmudgeLayer>()
					.FirstOrDefault(x => x.Info.Type == warhead.SmudgeType);
				if (smudgeLayer == null)
					throw new NotImplementedException("Unknown smudge type `{0}`".F(warhead.SmudgeType));

				if (warhead.Size[0] > 0)
				{
					var smudgeCells = world.FindTilesInCircle(targetTile, warhead.Size[0])
						.Except(world.FindTilesInCircle(targetTile, warhead.Size[1]));

					foreach (var sc in smudgeCells)
						smudgeLayer.AddSmudge(sc);
				}
				else
					smudgeLayer.AddSmudge(targetTile);
			}
			
			if (warhead.Ore)
				world.WorldActor.traits.Get<ResourceLayer>().Destroy(targetTile);

			var firepowerModifier = args.firedBy.traits
				.WithInterface<IFirepowerModifier>()
				.Select(a => a.GetFirepowerModifier())
				.Product();

			switch (warhead.DamageModel)
			{
				case DamageModel.Normal:
					{
						var maxSpread = warhead.Spread * (float)Math.Log(Math.Abs(warhead.Damage), 2);
						var hitActors = world.FindUnitsInCircle(args.dest, maxSpread);

						foreach (var victim in hitActors)
						{
							var damage = (int)GetDamageToInflict(victim, args, warhead, firepowerModifier);
							victim.InflictDamage(args.firedBy, damage, warhead);
						}
					} break;

				case DamageModel.PerCell:
					{
						foreach (var t in world.FindTilesInCircle(targetTile, warhead.Size[0]))
							foreach (var unit in world.FindUnits(Game.CellSize * t, Game.CellSize * (t + new float2(1,1))))
								unit.InflictDamage(args.firedBy,
									(int)(warhead.Damage * warhead.EffectivenessAgainst(
									unit.Info.Traits.Get<OwnedActorInfo>().Armor)), warhead);
					} break;
			}
		}

		public static void DoImpacts(ProjectileArgs args)
		{
			foreach (var warhead in args.weapon.Warheads)
			{
				Action a = () => DoImpact(warhead, args);
				if (warhead.Delay > 0)
					args.firedBy.World.AddFrameEndTask(
						w => w.Add(new DelayedAction(warhead.Delay, a)));
				else
					a();
			}
		}

		public static void DoExplosion(Actor attacker, string weapontype, int2 location, int altitude)
		{
			var args = new ProjectileArgs
			{
				src = location,
				dest = location,
				srcAltitude = altitude,
				destAltitude = altitude,
				firedBy = attacker,
				target = null,
				weapon = Rules.Weapons[ weapontype.ToLowerInvariant() ],
				facing = 0
			};

			DoImpacts(args);
		}

		static readonly float[] falloff = 
		{
			1f, 0.3678795f, 0.1353353f, 0.04978707f, 
			0.01831564f, 0.006737947f, 0.002478752f, 0.000911882f
		};

		static float GetDamageFalloff(float x)
		{
			var u = (int)x;
			if (u >= falloff.Length - 1) return 0;
			var t = x - u;
			return (falloff[u] * (1 - t)) + (falloff[u + 1] * t);
		}

		static float GetDamageToInflict(Actor target, ProjectileArgs args, WarheadInfo warhead, float modifier)
		{
			// don't hit air units with splash from ground explosions, etc
			if (!WeaponValidForTarget(args.weapon, target)) return 0f;

			var selectable = target.Info.Traits.GetOrDefault<SelectableInfo>();
			var radius = selectable != null ? selectable.Radius : 0;
			var distance = (int)Math.Max(0, (target.CenterLocation - args.dest).Length - radius);
			var falloff = (float)GetDamageFalloff(distance / warhead.Spread);
			var rawDamage = (float)(warhead.Damage * modifier * falloff);
			var multiplier = (float)warhead.EffectivenessAgainst(target.Info.Traits.Get<OwnedActorInfo>().Armor);

			return (float)(rawDamage * multiplier);
		}

		public static bool WeaponValidForTarget(WeaponInfo weapon, Actor target)
		{
			var ownedInfo = target.Info.Traits.GetOrDefault<OwnedActorInfo>();

			if (!weapon.ValidTargets.Contains(ownedInfo.TargetType))
				return false;

			if (weapon.Warheads.All( w => w.EffectivenessAgainst(ownedInfo.Armor) <= 0))
				return false;

			if (weapon.Underwater && !ownedInfo.WaterBound)
				return false;

			return true;
		}

		public static bool HasAnyValidWeapons(Actor self, Actor target)
		{
			var info = self.Info.Traits.Get<AttackBaseInfo>();
			if (info.PrimaryWeapon != null &&
				WeaponValidForTarget(self.GetPrimaryWeapon(), target)) return true;
			if (info.SecondaryWeapon != null &&
				WeaponValidForTarget(self.GetSecondaryWeapon(), target)) return true;

			return false;
		}
	}
}