Syntriax.Engine/Engine.Core/GameManager.cs

using System;
using System.Collections.Generic;

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

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

namespace Syntriax.Engine.Core;

public class GameManager : IEntity
{
    public Action<IInitialize>? OnInitialized { get; set; } = null;
    public Action<IInitialize>? OnFinalized { get; set; } = null;
    public Action<IAssignable>? OnUnassigned { get; set; } = null;
    public Action<IAssignableStateEnable>? OnStateEnableAssigned { get; set; } = null;


    private IList<IGameObject> _gameObjects = new List<IGameObject>(Constants.GAME_OBJECTS_SIZE_INITIAL);
    private IList<IDisplayable> _drawables = new List<IDisplayable>(Constants.DRAWABLE_OBJECTS_SIZE_INITIAL);

    private IStateEnable _stateEnable = null!;
    private GameObjectFactory _gameObjectFactory = null!;
    private bool _initialized = false;

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

    public bool Initialized => _initialized;
    public IList<IGameObject> GameObjects => _gameObjects;
    public IStateEnable StateEnable { get { if (_stateEnable is null) Assign(new StateEnableFactory().Instantiate(this)); return _stateEnable; } }

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

        Register(gameObject);
    }

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

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

        Unregister(gameObject);
        return gameObject;
    }

    public bool Initialize()
    {
        if (Initialized)
            return false;

        NotAssignedException.Check(this, StateEnable);

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

        OnInitialized?.Invoke(this);
        return true;
    }

    public bool Finalize()
    {
        if (!Initialized)
            return false;

        for (int i = GameObjects.Count; i >= 0; i--)
            GameObjects[i].Finalize();

        OnFinalized?.Invoke(this);
        return true;
    }

    public bool Assign(IStateEnable stateEnable)
    {
        if (Initialized)
            return false;

        _stateEnable = stateEnable;
        OnStateEnableAssigned?.Invoke(this);
        return true;
    }

    public bool Unassign()
    {
        if (Initialized)
            return false;

        _stateEnable = null!;
        OnUnassigned?.Invoke(this);
        return true;
    }

    public void Update(GameTime time)
    {
        foreach (var gameObject in GameObjects)
            gameObject.BehaviourController.Update(time);
    }

    public void PreDraw(GameTime time)
    {
        foreach (var gameObject in GameObjects)
            gameObject.BehaviourController.UpdatePreDraw(time);
    }

    public void Draw(SpriteBatch spriteBatch)
    {
        spriteBatch.Begin();

        foreach (var drawable in _drawables)
            drawable.Draw(spriteBatch);

        spriteBatch.End();
    }

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

    private void Unregister(IGameObject gameObject)
    {
        gameObject.BehaviourController.OnBehaviourAdded -= OnBehaviourAdd;
        gameObject.BehaviourController.OnBehaviourRemoved -= OnBehaviourRemove;
        gameObject.OnFinalized -= OnGameObjectFinalize;

        if (gameObject.BehaviourController.TryGetBehaviour<IDisplayable>(out var drawable))
            _drawables.Remove(drawable);

        _gameObjects.Remove(gameObject);
    }

    private void Register(IGameObject gameObject)
    {
        gameObject.BehaviourController.OnBehaviourAdded += OnBehaviourAdd;
        gameObject.BehaviourController.OnBehaviourRemoved += OnBehaviourRemove;
        gameObject.OnFinalized += OnGameObjectFinalize;

        if (gameObject.BehaviourController.TryGetBehaviour<IDisplayable>(out var drawable))
            _drawables.Add(drawable);

        _gameObjects.Add(gameObject);
    }

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

    private void OnBehaviourAdd(IBehaviourController controller, IBehaviour behaviour)
    {
        if (behaviour is IDisplayable drawable)
            _drawables.Add(drawable);
    }

    private void OnBehaviourRemove(IBehaviourController controller, IBehaviour behaviour)
    {
        if (behaviour is IDisplayable drawable)
            _drawables.Remove(drawable);
    }
}