using System;
using System.Collections.Generic;
using Cysharp.Threading.Tasks;
using UnityEngine;

/// <summary>
/// 异步懒加载：保证 factory 只执行一次，支持多个并发 await（每个调用者独立 TCS）
/// 非泛型设计，避免热更 AOT 泛型问题
/// </summary>
public class AsyncLazy
{
    public delegate UniTask AsyncFactory();

    private readonly AsyncFactory factory;
    private List<UniTaskCompletionSource> waiters;
    private bool hasCompleted;
    private bool isRunning;

    public AsyncLazy(AsyncFactory factory, string debugName = "")
    {
        this.factory = factory;
    }

    public UniTask Task
    {
        get
        {
            if (hasCompleted)
            {
                return UniTask.CompletedTask;
            }

            var tcs = new UniTaskCompletionSource();
            if (waiters == null) waiters = new List<UniTaskCompletionSource>();
            waiters.Add(tcs);

            if (!isRunning)
            {
                isRunning = true;
                Run().Forget();
            }

            return tcs.Task;
        }
    }

    private async UniTaskVoid Run()
    {
        try
        {
            await factory();
            hasCompleted = true;
            if (waiters != null)
            {
                for (int i = 0; i < waiters.Count; i++)
                    waiters[i].TrySetResult();
                waiters.Clear();
            }
        }
        catch (Exception ex)
        {
            if (waiters != null)
            {
                for (int i = 0; i < waiters.Count; i++)
                    waiters[i].TrySetException(ex);
                waiters.Clear();
            }
        }
    }

    public void Reset()
    {
        hasCompleted = false;
        isRunning = false;
        waiters = null;
    }
}