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 : IGameManager
{
    public Action<IGameManager, IGameObject>? OnGameObjectRegistered { get; set; } = null;
    public Action<IGameManager, IGameObject>? OnGameObjectUnRegistered { get; set; } = null;

    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 readonly List<IGameObject> _gameObjects = new(Constants.GAME_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 IReadOnlyList<IGameObject> GameObjects => _gameObjects;

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

            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();

        _initialized = true;
        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);
        _initialized = false;
        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(EngineTime time)
    {
        Time.SetTime(time);
        foreach (var gameObject in GameObjects)
            gameObject.BehaviourController.Update();
    }

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

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

    private void Register(IGameObject gameObject)
    {
        gameObject.Assign(this);

        gameObject.OnFinalized += OnGameObjectFinalize;

        _gameObjects.Add(gameObject);
        OnGameObjectRegistered?.Invoke(this, gameObject);
    }

    private void Unregister(IGameObject gameObject)
    {
        gameObject.OnFinalized -= OnGameObjectFinalize;

        _gameObjects.Remove(gameObject);
        OnGameObjectUnRegistered?.Invoke(this, gameObject);
    }

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

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

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