using UnityEngine;

namespace PhxhSDK
{
    public class SingletonMono<T> : MonoBehaviour where T : MonoBehaviour
    {
        // Check to see if we're about to be destroyed.
        private static bool m_ShuttingDown;
        private static readonly object m_Lock = new();
        private static T m_Instance;

        /// <summary>
        ///     Access singleton instance through this propriety.
        /// </summary>
        public static T Instance
        {
            get
            {
                if (!Application.isPlaying)
                {
                    Debug.LogError("[Singleton] Instance '" + typeof(T) + "' not found. (非运行状态下调用Instance)");
                    return null;
                }
#if UNITY_EDITOR
                if (m_ShuttingDown)
                {
                    DebugUtil.LogWarning("[Singleton] Instance '" + typeof(T) + "' already destroyed. Returning null.");
                    return null;
                }
#endif
                lock (m_Lock)
                {
                    if (m_Instance == null)
                    {
                        // Search for existing instance.
                        m_Instance = (T)FindObjectOfType(typeof(T));

                        // Create new instance if one doesn't already exist.
                        if (m_Instance == null)
                        {
                            // Need to create a new GameObject to attach the singleton to.
                            var singletonObject = new GameObject();
                            m_Instance = singletonObject.AddComponent<T>();
                            singletonObject.name = typeof(T) + " (Singleton)";
                            singletonObject.hideFlags = HideFlags.HideInHierarchy;
                            // Make instance persistent.
                            if (Application.isPlaying)
                            {
                                // 有人在非运行状态下调用Instance，不要设置DontDestroyOnLoad
                                DontDestroyOnLoad(singletonObject);
                            }
                            (m_Instance as SingletonMono<T>)?.InitImmediately();
                        }
                    }

                    return m_Instance;
                }
            }
        }

        private void OnApplicationQuit()
        {
            m_ShuttingDown = true;
        }

        // 这个方法如果override，会在Instance创建完立刻调用, 派生类可以用来默认初始化一些东西
        protected virtual void InitImmediately()
        {
        }
    }
}