TechbloxModdingAPI/TechbloxModdingAPI/Common/EcsObjectBase.cs

using System;
using System.Collections.Generic;
using Svelto.DataStructures;
using Svelto.ECS;
using Svelto.ECS.Hybrid;
using Svelto.ECS.Internal;
using TechbloxModdingAPI.Common.Engines;
using TechbloxModdingAPI.Common.Utils;
using TechbloxModdingAPI.Utility;

namespace TechbloxModdingAPI.Common;

public abstract class EcsObjectBase<TDescriptor> : EcsObjectBase where TDescriptor : IEntityDescriptor, new()
{
    protected EcsObjectBase(EGID id) : base(id, typeof(TDescriptor))
    {
    }

    protected EcsObjectBase(EntityReference reference) : base(reference, typeof(TDescriptor))
    {
    }

    protected bool RemoveEntity()
    {
        if (!Exists) return false;
        _engine.Functions.RemoveEntity<TDescriptor>(Id);
        return true;
    }
}

public abstract class EcsObjectBase {
    public EGID Id => _engine.GetEgid(Reference);
    /// <summary>
    /// A reference to a specific entity that persists through group swaps and such.
    /// May be an invalid reference, in that case operations do not have any effect.
    /// </summary>
    public EntityReference Reference { get; }

    /// <summary>
    /// Whether the entity reference is still valid. Returns false if this object no longer exists.
    /// </summary>
    public bool Exists => Id != default; // TODO: Might need extra code to support IDs during init

    public readonly Type EntityDescriptorType;
    public readonly Type[] AllowedEntityComponents;
        
    private static readonly Dictionary<Type, WeakDictionary<EntityReference, EcsObjectBase>> _instances = new();
    internal static readonly EcsObjectBaseEngine _engine = new();

    private static WeakDictionary<EntityReference, EcsObjectBase> GetInstances(Type type)
    {
        return _instances.TryGetValue(type, out var dict) ? dict : null;
    }

    /// <summary>
    /// Returns a cached instance if there's an actively used instance of the object already.
    /// Objects still get garbage collected and then they will be removed from the cache.<br />
    /// <b>Only use for existing entities!</b> Use the other overload for newly created entities.
    /// </summary>
    /// <param name="egid">The EGID of the entity</param>
    /// <param name="constructor">The constructor to construct the object</param>
    /// <typeparam name="T">The object type</typeparam>
    /// <returns></returns>
    internal static T GetInstanceExisting<T>(EGID egid, Func<EGID, T> constructor, Type type = null) where T : EcsObjectBase
    {
        var instances = GetInstances(type ?? typeof(T));
        if (instances == null || !instances.TryGetValue(_engine.GetEntityReference(egid), out var instance))
            return constructor(egid); // It will be added by the constructor
        return (T)instance;
    }

    /// <summary>
    /// Returns a cached instance if there's an actively used instance of the object already.
    /// Objects still get garbage collected and then they will be removed from the cache.<br />
    /// <b>Only use for newly created entities!</b> Use the other overload for existing entities.
    /// </summary>
    /// <param name="egid">The EGID of the entity</param>
    /// <param name="constructor">The constructor to construct the object</param>
    /// <typeparam name="T">The object type</typeparam>
    /// <returns></returns>
    internal static T GetInstanceNew<T>(EcsInitData initData, Func<EGID, T> constructor, Type type = null) where T : EcsObjectBase
    {
        var instances = GetInstances(type ?? typeof(T));
        if (instances == null || !instances.TryGetValue(initData.Reference, out var instance))
        {
            var ret = constructor(initData.EGID);
            ret.InitData = initData;
            return ret; // It will be added by the constructor
        }

        return (T)instance;
    }

    protected static V CreateEntity<U, V>(EGID egid, Func<EGID, V> constructor, Type type = null) where U : IEntityDescriptor, new() where V : EcsObjectBase<U>
    {
        return GetInstanceNew(_engine.Factory.BuildEntity<U>(egid), constructor, type);
    }

    protected EcsObjectBase(EGID id, Type entityDescriptorType) : this(_engine.GetEntityReference(id), entityDescriptorType)
    {
    }

    protected EcsObjectBase(EntityReference reference, Type entityDescriptorType)
    {
        if (!_instances.TryGetValue(GetType(), out var dict))
        {
            dict = new();
            _instances.Add(GetType(), dict);
        }
        if (!dict.ContainsKey(reference)) // Multiple instances may be created
            dict.Add(reference, this);
        Reference = reference;
        EntityDescriptorType = entityDescriptorType;
        AllowedEntityComponents = EcsUtils.GetValidEntityComponents(entityDescriptorType);
        // Remove init data once the entity gets submitted so that it won't be used again once the entity is removed
        if (InitData != default) _engine.TrackNewEntity(this, obj => obj.InitData = default);
    }

    protected internal OptionalRef<T> GetComponentOptional<T>() where T : unmanaged, IEntityComponent
    {
        return _engine.GetComponentOptional<T>(this);
    }

    protected internal ref T GetComponent<T>() where T : unmanaged, IEntityComponent
    {
        return ref _engine.GetComponent<T>(this);
    }

    protected internal ref T GetViewComponent<T>() where T : struct, IEntityViewComponent
    {
        return ref _engine.GetViewComponent<T>(this);
    }

    protected internal object GetComponent(Type type, string name)
    {
        return _engine.GetComponent(this, type, name);
    }

    protected internal void SetComponent(Type type, string name, object value)
    {
        _engine.SetComponent(this, type, name, value);
    }

    #region ECS initializer stuff

    internal EcsInitData InitData { get; private set; }

    /// <summary>
    /// Holds information needed to construct a component initializer.
    /// Necessary because the initializer is a ref struct which cannot be assigned to a field.
    /// </summary>
    protected internal readonly record struct EcsInitData(FasterDictionary<RefWrapperType, ITypeSafeDictionary> group, EntityReference Reference, EGID EGID)
    {
        public static implicit operator EcsInitData(EntityInitializer initializer) => new(GetInitGroup(initializer), initializer.reference, initializer.EGID);

        private readonly FasterDictionary<RefWrapperType, ITypeSafeDictionary> group = group;
        public readonly EntityReference Reference = Reference;
        public readonly EGID EGID = EGID;
        public EntityInitializer Initializer(EGID id = default) => new(id == default ? EGID : id, group, Reference);
        public bool Valid => group != null;
    }

    private delegate FasterDictionary<RefWrapperType, ITypeSafeDictionary> GetInitGroupFunc(
        EntityInitializer initializer);

    /// <summary>
    /// Accesses the group field of the initializer
    /// </summary>
    private static readonly GetInitGroupFunc GetInitGroup = Reflections.CreateAccessor<GetInitGroupFunc>("_group");

    #endregion

    public static void Init()
    {
        EngineManager.AddEngine(_engine, ApiEngineType.Build, ApiEngineType.Menu, ApiEngineType.PlayClient, ApiEngineType.PlayServer);
    }
}