gather-and-defend/Assets/Scripts/LevelManager/LevelManagerScript.cs

using System.Collections.Generic;
using System.Linq;
using Unity.Plastic.Newtonsoft.Json;
using UnityEngine;

public class LevelManager : Singleton<LevelManager>
{
    public delegate void LevelAction(ILevelObject levelObject);
    public delegate bool LevelPredicate<T>(T levelObject) where T : ILevelObject;
    public event LevelAction Added;
    public event LevelAction Removed;

    private readonly List<ILevelObject> toAdd;
    private readonly List<ILevelObject> toRemove;
    private readonly List<ILevelObject> levelObjects;

    public Transform LevelTransform
    {
        get;private set;
    }
    public LevelManager()
{
        toAdd = new List<ILevelObject>();
        toRemove = new List<ILevelObject>();
        levelObjects = new List<ILevelObject>();

        var mgrScript = Object.FindObjectOfType<LevelManagerScript>();
        if (!mgrScript) mgrScript = new GameObject(nameof(LevelManager)).AddComponent<LevelManagerScript>();
        LevelTransform = mgrScript.transform;
    }

    public void Add(ILevelObject levelObject)
    {
        toAdd.Add(levelObject);
    }
    public void Remove(ILevelObject levelObject)
    {
        toRemove.Add(levelObject);
    }
    public void Clear()
    {
        toAdd.Clear();
        toRemove.Clear();
        levelObjects.Clear();
    }
    public T Get<T>(LevelPredicate<T> predicate = null) where T : ILevelObject
    {
        if (predicate == null) predicate = (generic) => true;
        return (T)levelObjects.Find(levelObject => levelObject is T generic && predicate(generic));
    }
    public List<T> GetAll<T>(LevelPredicate<T> predicate = null) where T : ILevelObject
    {
        if (predicate == null) predicate = (generic) => true;
        List<T> ret = new();
        foreach (var levelObject in levelObjects) if (levelObject is T generic && predicate(generic)) ret.Add(generic);
        return ret;
    }

    public int Count<T>(LevelPredicate<T> predicate = null) where T : ILevelObject
    {
        return GetAll(predicate).Count;
    }

    public bool Has<T>(LevelPredicate<T> predicate = null) where T : ILevelObject
    {
        if (predicate == null) predicate = (generic) => true;
        return levelObjects.Exists(levelObject => levelObject is T generic && predicate(generic));
    }

    public void UpdateLevel()
    {
        levelObjects.ForEach(levelObject => levelObject.LevelUpdate());

        var toAdd = new List<ILevelObject>(this.toAdd);
        toAdd.ForEach(addedObject =>
        {
            this.toAdd.Remove(addedObject);
            levelObjects.Add(addedObject);
            Added?.Invoke(addedObject);
            addedObject.LevelStart();
        });

        var toRemove = new List<ILevelObject>(this.toRemove);
        toRemove.ForEach(removedObject =>
        {
            this.toRemove.Remove(removedObject);
            levelObjects.Remove(removedObject);
            Removed?.Invoke(removedObject);
            removedObject.LevelDestroy();
        });
        toRemove.Clear();
    }
    void SaveLevel()
    {
        var list = levelObjects.Select(obj => obj.ToDictionary()).ToList();
        Debug.Log(JsonConvert.SerializeObject(list));
    }
    void LoadLevel()
    {

    }
}
public class LevelManagerScript : MonoBehaviour
{
    private static LevelManagerScript _instance;
    void Awake()
    {
        if (!_instance) _instance = this;
        else Destroy(gameObject);

        DontDestroyOnLoad(gameObject);
    }
    void Update()
    {
        LevelManager.Instance.UpdateLevel();
    }
}