Syntriax.Engine/Engine.Core/GameManager.cs

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

using Syntriax.Engine.Core.Abstract;
using Syntriax.Engine.Core.Exceptions;
using Syntriax.Engine.Core.Factory;

namespace Syntriax.Engine.Core;

[System.Diagnostics.DebuggerDisplay("GameObject Count: {_gameObjects.Count}")]
public class GameManager : BaseEntity, IGameManager
{
    public event IGameManager.OnUpdateDelegate? OnUpdate = null;
    public event IGameManager.OnPreDawDelegate? OnPreDraw = null;

    public event IGameManager.OnGameObjectRegisteredDelegate? OnGameObjectRegistered = null;
    public event IGameManager.OnGameObjectUnRegisteredDelegate? OnGameObjectUnRegistered = null;
    public event IGameManager.OnHierarchyObjectRegisteredDelegate? OnHierarchyObjectRegistered = null;
    public event IGameManager.OnHierarchyObjectUnRegisteredDelegate? OnHierarchyObjectUnRegistered = null;

    private readonly List<IGameObject> _gameObjects = new(Constants.GAME_OBJECTS_SIZE_INITIAL);
    private readonly List<IHierarchyObject> _hierarchyObjects = new(Constants.GAME_OBJECTS_SIZE_INITIAL);

    private GameObjectFactory _gameObjectFactory = null!;

    private GameObjectFactory GameObjectFactory
    {
        get
        {
            if (_gameObjectFactory is null)
                _gameObjectFactory = new GameObjectFactory();
            return _gameObjectFactory;
        }
    }

    public IReadOnlyList<IGameObject> GameObjects => _gameObjects;
    public IReadOnlyList<IHierarchyObject> HierarchyObjects => _hierarchyObjects;

    public override IStateEnable StateEnable
    {
        get
        {
            if (base.StateEnable is null)
            {
                Assign(new StateEnableFactory().Instantiate(this));
                if (base.StateEnable is null)
                    throw NotAssignedException.From(this, base.StateEnable);
            }

            return base.StateEnable;
        }
    }

    public void Register(IHierarchyObject hierarchyObject)
    {
        if (_hierarchyObjects.Contains(hierarchyObject))
            throw new Exception($"{nameof(IHierarchyObject)} named {hierarchyObject.Name} is already registered to the {nameof(GameManager)}.");

        if (hierarchyObject is IGameObject gameObject)
            Register(gameObject);
        else
        {
            if (!hierarchyObject.Initialize())
                throw new Exception($"{nameof(hierarchyObject)} can't be initialized");

            _hierarchyObjects.Add(hierarchyObject);
            hierarchyObject.EnterHierarchy(this);

            OnHierarchyObjectRegistered?.Invoke(this, hierarchyObject);
        }
    }

    public T InstantiateGameObject<T>(params object?[]? args) where T : class, IGameObject
    {
        T gameObject = GameObjectFactory.Instantiate<T>(args);
        Register(gameObject);
        return gameObject;
    }

    public void Remove(IHierarchyObject hierarchyObject)
    {
        if (!_hierarchyObjects.Contains(hierarchyObject))
            throw new Exception($"{nameof(IHierarchyObject)} named {hierarchyObject.Name} is not registered to the {nameof(GameManager)}.");

        if (hierarchyObject is IGameObject gameObject)
            Unregister(gameObject);
        else
        {
            _hierarchyObjects.Remove(hierarchyObject);
            hierarchyObject.ExitHierarchy();

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

            OnHierarchyObjectUnRegistered?.Invoke(this, hierarchyObject);
        }
    }

    protected override void InitializeInternal()
    {
        base.InitializeInternal();
        NotAssignedException.Check(this, StateEnable);

        foreach (var gameObject in GameObjects)
            gameObject.Initialize();
    }

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

    public void Update(EngineTime time)
    {
        Time.SetTime(time);
        for (int i = 0; i < GameObjects.Count; i++)
            GameObjects[i].BehaviourController.Update();

        OnUpdate?.Invoke(this, time);
    }

    public void PreDraw()
    {
        for (int i = 0; i < GameObjects.Count; i++)
            GameObjects[i].BehaviourController.UpdatePreDraw();

        OnPreDraw?.Invoke(this);
    }

    /////////////////////////////////////////////////////////////////

    private void Register(IGameObject gameObject)
    {
        if (_gameObjects.Contains(gameObject))
            throw new Exception($"{nameof(IGameObject)} named {gameObject.Name} is already registered to the {nameof(GameManager)}.");

        gameObject.OnFinalized += OnGameObjectFinalize;
        gameObject.OnExitedHierarchy += OnGameObjectExitedHierarchy;

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

        foreach (ITransform child in gameObject.Transform.Children)
            Register(child.GameObject);

        _gameObjects.Add(gameObject);
        _hierarchyObjects.Add(gameObject);

        if (!gameObject.EnterHierarchy(this))
            throw new Exception($"{nameof(gameObject)} can't enter the hierarchy");

        OnHierarchyObjectRegistered?.Invoke(this, gameObject);
        OnGameObjectRegistered?.Invoke(this, gameObject);
    }

    private void Unregister(IGameObject gameObject)
    {
        if (!_gameObjects.Contains(gameObject))
            throw new Exception($"{nameof(IGameObject)} named {gameObject.Name} is not registered to the {nameof(GameManager)}.");

        gameObject.OnFinalized -= OnGameObjectFinalize;
        gameObject.OnExitedHierarchy -= OnGameObjectExitedHierarchy;

        foreach (ITransform child in gameObject.Transform.Children)
            Unregister(child.GameObject);

        _gameObjects.Remove(gameObject);
        _hierarchyObjects.Remove(gameObject);

        if (!gameObject.ExitHierarchy())
            throw new Exception($"{nameof(gameObject)} can't exit the hierarchy");

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

        OnHierarchyObjectUnRegistered?.Invoke(this, gameObject);
        OnGameObjectUnRegistered?.Invoke(this, gameObject);
    }

    private void OnGameObjectFinalize(IInitialize initialize)
    {
        if (initialize is IGameObject gameObject)
            Unregister(gameObject);
    }

    private void OnGameObjectExitedHierarchy(IHierarchyObject sender, IGameManager gameManager)
    {
        if (sender is IGameObject gameObject)
            Unregister(gameObject);
    }

    /////////////////////////////////////////////////////////////////

    public IEnumerator<IGameObject> GetEnumerator() => _gameObjects.GetEnumerator();
    IEnumerator IEnumerable.GetEnumerator() => _gameObjects.GetEnumerator();
}