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

using System;
using System.Collections.Generic;

public class LevelManager : Singleton<LevelManager>
{
    public event System.Action<ILevelObject> Added;
    public event System.Action<ILevelObject> Removed;

    private List<ILevelObject> levelObjects;
    public LevelManager()
    {
        levelObjects = new List<ILevelObject>();
    }

    public void Add(ILevelObject levelObject)
    {
        if (levelObjects.Contains(levelObject)) return;
        levelObjects.Add(levelObject);
        Added?.Invoke(levelObject);
    }
    public void Remove(ILevelObject levelObject)
    {
        if (!levelObjects.Contains(levelObject)) return;
        levelObjects.Remove(levelObject);
        Removed?.Invoke(levelObject);
    }
    public void Clear()
    {
        levelObjects.RemoveAll(obj =>
        {
            Removed?.Invoke(obj);
            return true;
        });
    }
    public T Get<T>(System.Func<T, bool> predicate = default) where T : ILevelObject
    {
        if (predicate == default) predicate = (t) => true;
        return (T)levelObjects.Find(t => t is T t1 && predicate(t1));
    }
    public List<T> GetAll<T>(System.Func<T, bool> predicate = default) where T : ILevelObject
    {
        if (predicate == default) predicate = (t) => true;
        List<T> ret = new List<T>();
        foreach (var t in levelObjects) if (t is T t1 && predicate(t1)) ret.Add(t1);
        return ret;
    }

    public int Count<T>(Func<T, bool> predicate = default) where T : ILevelObject
    {
        return GetAll(predicate).Count;
    }

    public bool Has<T>(System.Func<T, bool> predicate = default)
    {
        if (predicate == default) predicate = (t) => true;
        return levelObjects.Exists(t => t is T && predicate((T)t));
    }
}