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

namespace OpenRA.GameRules
{
	public class SpreadDamageWarhead : DamageWarhead
	{
		[Desc("For Normal DamageModel: Distance from the explosion center at which damage is 1/2.")]
		public readonly WRange Spread = new WRange(43);

		public override void DoImpact(Target target, Actor firedBy, float firepowerModifier)
		{
			// Used by traits that damage a single actor, rather than a position
			if (target.Type == TargetType.Actor)
				DoImpact(target.Actor, firedBy, firepowerModifier);
			else
				DoImpact(target.CenterPosition, firedBy, firepowerModifier);
		}

		public void DoImpact(WPos pos, Actor firedBy, float firepowerModifier)
		{
			var world = firedBy.World;
			var maxSpread = new WRange((int)(Spread.Range * (float)Math.Log(Math.Abs(Damage), 2)));
			var hitActors = world.FindActorsInCircle(pos, maxSpread);

			foreach (var victim in hitActors)
				if (IsValidAgainst(victim, firedBy))
				{
					var damage = (int)GetDamageToInflict(pos, victim, firedBy, firepowerModifier);
					victim.InflictDamage(firedBy, damage, this);
				}
		}

		public void DoImpact(Actor victim, Actor firedBy, float firepowerModifier)
		{
			if (IsValidAgainst(victim, firedBy))
			{
				var damage = GetDamageToInflict(victim.CenterPosition, victim, firedBy, firepowerModifier);
				victim.InflictDamage(firedBy, damage, this);
			}
		}

		public int GetDamageToInflict(WPos pos, Actor target, Actor firedBy, float modifier)
		{
			var healthInfo = target.Info.Traits.GetOrDefault<HealthInfo>();
			if (healthInfo == null)
				return 0;

			var distance = Math.Max(0, (target.CenterPosition - pos).Length - healthInfo.Radius.Range);
			var falloff = (float)GetDamageFalloff(distance * 1f / Spread.Range);
			var rawDamage = (float)(falloff * Damage);

			return (int)(rawDamage * modifier * EffectivenessAgainst(target.Info));
		}

		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);
		}
	}
}