using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using UnityEngine;

public class Loom : MonoBehaviour
{
    public const int maxThreads = 8;

    private static int numThreads;

    private static bool initialized;

    private static Loom current;

    private readonly List<Action> actions = new List<Action>();

    private readonly List<DelayedQueueItem> delayed = new List<DelayedQueueItem>();

    private readonly List<DelayedQueueItem> currentDelayed = new List<DelayedQueueItem>();

    private readonly List<Action> currentActions = new List<Action>();

    public static Loom Current
    {
        get
        {
            Initialize();
            return current;
        }
    }

    void Start()
    {

    }

    void Update()
    {
        lock (actions)
        {
            currentActions.Clear();
            currentActions.AddRange(actions);
            actions.Clear();
        }
        foreach (var a in currentActions)
        {
            a();
        }

        lock (delayed)
        {
            currentDelayed.Clear();
            currentDelayed.AddRange(delayed.Where(d => d.time <= Time.time));
            foreach (var item in currentDelayed)
                delayed.Remove(item);
        }
        foreach (var delayed in currentDelayed)
        {
            delayed.action();
        }
    }

    /// <summary>
    /// 初始化
    /// </summary>
    public static void Initialize()
    {
        if (!initialized)
        {
            if (!Application.isPlaying)
                return;

            initialized = true;
            GameObject g = new GameObject("Loom");
            // 永不销毁
            DontDestroyOnLoad(g);
            current = g.AddComponent<Loom>();
        }

    }

    public static void QueueOnMainThread(Action action)
    {
        QueueOnMainThread(action, 0f);
    }

    public static void QueueOnMainThread(Action action, float time)
    {
        if (time != 0)
        {
            if (Current != null)
            {
                lock (Current.delayed)
                {
                    Current.delayed.Add(new DelayedQueueItem { time = Time.time + time, action = action });
                }
            }
        }
        else
        {
            if (Current != null)
            {
                lock (Current.actions)
                {
                    Current.actions.Add(action);
                }
            }
        }
    }

    public static Thread RunAsync(Action a)
    {
        Initialize();
        while (numThreads >= maxThreads)
        {
            Thread.Sleep(1);
        }
        Interlocked.Increment(ref numThreads);
        ThreadPool.QueueUserWorkItem(RunAction, a);
        return null;
    }

    private static void RunAction(object action)
    {
        try
        {
            ((Action)action)();
        }
        catch
        {
        }
        finally
        {
            Interlocked.Decrement(ref numThreads);
        }

    }

    void OnDisable()
    {
        if (current == this)
        {
            current = null;
        }
    }

    public struct DelayedQueueItem
    {
        public float time;
        public Action action;
    }
}