UnityPackages/Assets/Common/Infrastructure/Runtime/ScriptableObjectSingleton.cs

using UnityEngine;

namespace JoeSiu.Common.Infrastructure.Runtime
{
    /// <summary>
    /// <see href="https://youtu.be/6kWUGEQiMUI"/>
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public abstract class ScriptableObjectSingleton<T> : ScriptableObject where T : ScriptableObjectSingleton<T>
    {
        private static T _instance;
        public static T Instance
        {
            get
            {
                if (_instance != null) return _instance;

                var assets = Resources.LoadAll<T>("");

                if (assets.Length > 0)
                {
                    AssignInstance(assets[0]);
                }

                if (assets.Length > 1)
                {
                    Debug.LogError(
                        $"[ScriptableObjectSingleton] More than 1 instance of Singleton Scriptable Object of type: {typeof(T)} found");
                }

                if (!_instance)
                {
                    Debug.LogWarning(
                        $"[ScriptableObjectSingleton] No instance of type '{typeof(T).Name}' is found, make sure to add it to the Resources folder!");
                }

                return _instance;
            }
        }

        public static T GetInstance() => _instance;

        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
        public static void RemoveInstance()
        {
            _instance = null;
            Debug.Log($"[ScriptableObjectSingleton] Removed instance of type '{typeof(T).Name}'");
        }

        private static void AssignInstance(T instance)
        {
            if (!instance) return;
            _instance = instance;
            Debug.Log($"[ScriptableObjectSingleton] Assigned instance of type '{typeof(T).Name}' to object '{instance.name}'", instance);
        }
    }
}