using System;
using System.Collections.Concurrent;
using System.Threading;
using UnityEngine;

namespace Kill.Video
{
    /// <summary>
    /// 把任意 Action 排到 Unity 主线程执行。
    /// 背景:IL2CPP 的自建后台线程 JVM attach 不可靠,AndroidJavaClass/AndroidJNI
    /// 在这些线程上 FindClass 会偶发返回空,导致"类未找到/偶尔成功偶尔失败"。
    /// 用它在主线程上跑所有 JNI 调用即可稳定。
    /// </summary>
    public static class MainThreadDispatcher
    {
        private static readonly ConcurrentQueue<Action> _pending = new ConcurrentQueue<Action>();
        private static int _mainThreadId = -1;
        private static bool _ensured;

        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterSceneLoad)]
        private static void Ensure()
        {
            if (_ensured) return;
            _mainThreadId = Thread.CurrentThread.ManagedThreadId;
            var go = new GameObject("MainThreadDispatcher");
            go.hideFlags = HideFlags.HideAndDontSave;
            UnityEngine.Object.DontDestroyOnLoad(go);
            go.AddComponent<DispatcherBehaviour>();
            _ensured = true;
        }

        public static bool IsMainThread =>
            !_ensured || Thread.CurrentThread.ManagedThreadId == _mainThreadId;

        /// <summary>在主线程执行 action;若调用方已是主线程则直接内联执行。</summary>
        public static void RunOnMainThread(Action action)
        {
            if (action == null) return;
            if (IsMainThread)
            {
                action();
                return;
            }
            using (var done = new ManualResetEventSlim(false))
            {
                _pending.Enqueue(() =>
                {
                    try { action(); }
                    finally { done.Set(); }
                });
                done.Wait();
            }
        }

        private class DispatcherBehaviour : MonoBehaviour
        {
            private void Update()
            {
                while (_pending.TryDequeue(out var a))
                {
                    try { a(); }
                    catch (Exception e) { Debug.LogException(e); }
                }
            }
        }
    }
}