#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.Collections.Generic;
using OpenRA.Support;
using OpenRA.Traits;

namespace OpenRA.Mods.Common.Traits
{
	/// <summary>Use as base class for *Info to subclass of ConditionalTrait. (See ConditionalTrait.)</summary>
	public abstract class ConditionalTraitInfo : IObservesVariablesInfo, IRulesetLoaded
	{
		[ConsumedConditionReference]
		[Desc("Boolean expression defining the condition to enable this trait.")]
		public readonly BooleanExpression RequiresCondition = null;

		public abstract object Create(ActorInitializer init);

		// HACK: A shim for all the ActorPreview code that used to query UpgradeMinEnabledLevel directly
		// This can go away after we introduce an InitialConditions ActorInit and have the traits query the
		// condition directly
		public bool EnabledByDefault { get; private set; }

		public virtual void RulesetLoaded(Ruleset rules, ActorInfo ai)
		{
			EnabledByDefault = RequiresCondition == null || RequiresCondition.Evaluate(VariableExpression.NoVariables);
		}
	}

	/// <summary>
	/// Abstract base for enabling and disabling trait using conditions.
	/// Requires basing *Info on ConditionalTraitInfo and using base(info) constructor.
	/// TraitEnabled will be called at creation if the trait starts enabled or does not use conditions.
	/// </summary>
	public abstract class ConditionalTrait<InfoType> : IObservesVariables, IDisabledTrait, INotifyCreated, ISync where InfoType : ConditionalTraitInfo
	{
		public readonly InfoType Info;

		// Overrides must call `base.GetVariableObservers()` to avoid breaking RequiresCondition.
		public virtual IEnumerable<VariableObserver> GetVariableObservers()
		{
			if (Info.RequiresCondition != null)
				yield return new VariableObserver(RequiredConditionsChanged, Info.RequiresCondition.Variables);
		}

		[Sync]
		public bool IsTraitDisabled { get; private set; }

		public ConditionalTrait(InfoType info)
		{
			Info = info;

			// Conditional traits will be enabled (if appropriate) by the ConditionManager
			// calling ConditionConsumers at the end of INotifyCreated.
			IsTraitDisabled = Info.RequiresCondition != null;
		}

		protected virtual void Created(Actor self)
		{
			if (Info.RequiresCondition == null)
				TraitEnabled(self);
		}

		void INotifyCreated.Created(Actor self) { Created(self); }

		void RequiredConditionsChanged(Actor self, IReadOnlyDictionary<string, int> conditions)
		{
			if (Info.RequiresCondition == null)
				return;

			var wasDisabled = IsTraitDisabled;
			IsTraitDisabled = !Info.RequiresCondition.Evaluate(conditions);

			if (IsTraitDisabled != wasDisabled)
			{
				if (wasDisabled)
					TraitEnabled(self);
				else
					TraitDisabled(self);
			}
		}

		// Subclasses can add condition support by querying IsTraitDisabled and/or overriding these methods.
		protected virtual void TraitEnabled(Actor self) { }
		protected virtual void TraitDisabled(Actor self) { }
	}
}
