using System;
using System.Collections.Generic;
using JetBrains.Annotations;

namespace Robust.Shared.GameObjects
{
    /// <summary>
    ///     A subsystem that acts on all components of a type at once.
    ///     Entity systems are similar to TGstation13 subsystems.
    ///     They have a set of entities to run over and run every once in a while.
    ///     They get managed by an <see cref="IEntitySystemManager" />.
    /// </summary>
    [UsedImplicitly(ImplicitUseTargetFlags.WithInheritors)]
    [NotContentImplementable]
    public interface IEntitySystem : IEntityEventSubscriber
    {
        IEnumerable<Type> UpdatesAfter { get; }
        IEnumerable<Type> UpdatesBefore { get; }

        /// <summary>
        /// If prediction is disabled on the client, <see cref="Update"/> will not be ran unless this flag is set.
        /// </summary>
        bool UpdatesOutsidePrediction { get; }

        /// <summary>
        ///     Called once when the system is created to initialize its state.
        /// </summary>
        void Initialize();

        /// <summary>
        ///     Called once before the system is destroyed so that the system can clean up.
        /// </summary>
        void Shutdown();

        /// <summary>
        ///     Called once per frame/tick to update the system.
        /// </summary>
        /// <param name="frameTime">Delta time since Update() was last called.</param>
        void Update(float frameTime);
        void FrameUpdate(float frameTime);
    }
}