Syntriax.Engine/Engine.Core/Universe.cs

using System;
using System.Collections;
using System.Collections.Generic;

namespace Engine.Core;

[System.Diagnostics.DebuggerDisplay("UniverseObject Count: {_universeObjects.Count}")]
public class Universe : BaseEntity, IUniverse
{
    public Event<IUniverse, IUniverse.UpdateArguments> OnPreUpdate { get; } = new();
    public Event<IUniverse, IUniverse.UpdateArguments> OnUpdate { get; } = new();
    public Event<IUniverse, IUniverse.UpdateArguments> OnPostUpdate { get; } = new();
    public Event<IUniverse> OnPreDraw { get; } = new();
    public Event<IUniverse> OnDraw { get; } = new();
    public Event<IUniverse> OnPostDraw { get; } = new();
    public Event<IUniverse, IUniverse.UniverseObjectRegisteredArguments> OnPreUniverseObjectRegistered { get; } = new();
    public Event<IUniverse, IUniverse.UniverseObjectRegisteredArguments> OnUniverseObjectRegistered { get; } = new();
    public Event<IUniverse, IUniverse.UniverseObjectUnRegisteredArguments> OnPreUniverseObjectUnRegistered { get; } = new();
    public Event<IUniverse, IUniverse.UniverseObjectUnRegisteredArguments> OnUniverseObjectUnRegistered { get; } = new();
    public Event<IUniverse, IUniverse.TimeScaleChangedArguments> OnTimeScaleChanged { get; } = new();

    private readonly Event<IInitializable>.EventHandler delegateOnUniverseObjectFinalize = null!;
    private readonly Event<IUniverseObject, IUniverseObject.ExitedUniverseArguments>.EventHandler delegateOnUniverseObjectExitedUniverse = null!;

    private readonly FastList<IUniverseObject> _universeObjects = new(Constants.UNIVERSE_OBJECTS_SIZE_INITIAL);
    private float _timeScale = 1f;

    public Universe()
    {
        delegateOnUniverseObjectFinalize = OnUniverseObjectFinalize;
        delegateOnUniverseObjectExitedUniverse = OnUniverseObjectExitedUniverse;
    }

    public IUniverseObject Root { get; private set; } = Factory.UniverseObjectFactory.Instantiate().SetUniverseObject("Root");

    public UniverseTime Time { get; private set; } = new();
    public UniverseTime UnscaledTime { get; private set; } = new();
    public float TimeScale
    {
        get => _timeScale;
        set
        {
            value = value.Max(0f);
            if (value == _timeScale)
                return;

            float previousTimeScale = _timeScale;
            _timeScale = value;
            OnTimeScaleChanged?.Invoke(this, new(previousTimeScale));
        }
    }

    public void Register(IUniverseObject universeObject)
    {
        if (_universeObjects.Contains(universeObject))
            throw new Exception($"{nameof(IUniverseObject)} named {universeObject.Name} is already registered to the {nameof(Universe)}.");

        OnPreUniverseObjectRegistered?.Invoke(this, new(universeObject));

        universeObject.OnFinalized.AddListener(delegateOnUniverseObjectFinalize);
        universeObject.OnExitedUniverse.AddListener(delegateOnUniverseObjectExitedUniverse);

        if (!universeObject.Initialize())
            throw new Exception($"{universeObject.Name} can't be initialized");

        if (universeObject.Parent == null)
            universeObject.Parent = Root;

        _universeObjects.Add(universeObject);

        if (!universeObject.EnterUniverse(this))
            throw new Exception($"{universeObject.Name} can't enter the universe");

        for (int i = 0; i < universeObject.Children.Count; i++)
            Register(universeObject.Children[i]);

        OnUniverseObjectRegistered?.Invoke(this, new(universeObject));
    }

    public T InstantiateUniverseObject<T>(params object?[]? args) where T : class, IUniverseObject
    {
        T universeObject = Factory.UniverseObjectFactory.Instantiate<T>(args);
        Register(universeObject);
        return universeObject;
    }

    public void Remove(IUniverseObject universeObject)
    {
        universeObject.Parent = null;
        RemoveIncursive(universeObject);
    }

    private void RemoveIncursive(IUniverseObject universeObject)
    {
        if (!_universeObjects.Contains(universeObject))
            throw new Exception($"{nameof(IUniverseObject)} named {universeObject.Name} is not registered to the {nameof(Universe)}.");

        OnPreUniverseObjectUnRegistered?.Invoke(this, new(universeObject));

        universeObject.OnFinalized.RemoveListener(delegateOnUniverseObjectFinalize);
        universeObject.OnExitedUniverse.RemoveListener(delegateOnUniverseObjectExitedUniverse);

        for (int i = universeObject.Children.Count - 1; i >= 0; i--)
            Remove(universeObject.Children[i]);

        _universeObjects.Remove(universeObject);

        if (!universeObject.ExitUniverse())
            throw new Exception($"{universeObject.Name} can't exit the universe");

        if (!universeObject.Finalize())
            throw new Exception($"{universeObject.Name} can't be finalized");

        OnUniverseObjectUnRegistered?.Invoke(this, new(universeObject));
    }

    protected override void InitializeInternal()
    {
        foreach (IUniverseObject universeObject in _universeObjects)
            universeObject.Initialize();
    }

    protected override void FinalizeInternal()
    {
        base.FinalizeInternal();
        for (int i = _universeObjects.Count - 1; i >= 0; i--)
            Remove(_universeObjects[i]);
    }

    public void Update(UniverseTime engineTime)
    {
        Debug.Assert.AssertInitialized(this);

        UnscaledTime = engineTime;
        Time = new(TimeSpan.FromTicks((long)(Time.TimeSinceStart.Ticks + engineTime.DeltaSpan.Ticks * TimeScale)), TimeSpan.FromTicks((long)(engineTime.DeltaSpan.Ticks * TimeScale)));

        IUniverse.UpdateArguments args = new(Time);
        OnPreUpdate?.Invoke(this, args);
        OnUpdate?.Invoke(this, args);
        OnPostUpdate?.Invoke(this, args);
    }

    public void Draw()
    {
        Debug.Assert.AssertInitialized(this);

        OnPreDraw?.Invoke(this);
        OnDraw?.Invoke(this);
        OnPostDraw?.Invoke(this);
    }

    private void OnUniverseObjectFinalize(IInitializable initializable)
    {
        if (initializable is IUniverseObject universeObject)
            Remove(universeObject);
    }

    private void OnUniverseObjectExitedUniverse(IUniverseObject sender, IUniverseObject.ExitedUniverseArguments args)
    {
        if (sender is IUniverseObject universeObject)
            Remove(universeObject);
    }

    public IEnumerator<IUniverseObject> GetEnumerator() => Root.TraverseChildren();
    IEnumerator IEnumerable.GetEnumerator() => Root.TraverseChildren();
}