using System;

using System.Collections.Concurrent;

using System.Diagnostics;

using System.Threading;

using System.Threading.Tasks;

namespace FastGithub.Http

{

/// <summary>

/// 表示LifetimeHttpHandler清理器

/// </summary>

sealed class LifetimeHttpHandlerCleaner

{

/// <summary>

/// 当前监视生命周期的记录的数量

/// </summary>

private int trackingEntryCount = 0;

/// <summary>

/// 监视生命周期的记录队列

/// </summary>

private readonly ConcurrentQueue<TrackingEntry> trackingEntries = new();

/// <summary>

/// 获取或设置清理的时间间隔

/// 默认10s

/// </summary>

public TimeSpan CleanupInterval { get; set; } = TimeSpan.FromSeconds(10d);

/// <summary>

/// 添加要清除的httpHandler

/// </summary>

/// <param name="handler">httpHandler</param>

public void Add(LifetimeHttpHandler handler)

{

var entry = new TrackingEntry(handler);

this.trackingEntries.Enqueue(entry);

// 从0变为1，要启动清理作业

if (Interlocked.Increment(ref this.trackingEntryCount) == 1)

{

this.StartCleanup();

}

}

/// <summary>

/// 启动清理作业

/// </summary>

private async void StartCleanup()

{

await Task.Yield();

while (this.Cleanup() == false)

{

await Task.Delay(this.CleanupInterval);

}

}

/// <summary>

/// 清理失效的拦截器

/// 返回是否完全清理

/// </summary>

/// <returns></returns>

private bool Cleanup()

{

var cleanCount = this.trackingEntries.Count;

for (var i = 0; i < cleanCount; i++)

{

this.trackingEntries.TryDequeue(out var entry);

Debug.Assert(entry != null);

if (entry.CanDispose == false)

{

this.trackingEntries.Enqueue(entry);

continue;

}

entry.Dispose();

if (Interlocked.Decrement(ref this.trackingEntryCount) == 0)

{

return true;

}

}

return false;

}

/// <summary>

/// 表示监视生命周期的记录

/// </summary>

private class TrackingEntry : IDisposable

{

/// <summary>

/// 用于释放资源的对象

/// </summary>

private readonly IDisposable disposable;

/// <summary>

/// 监视对象的弱引用

/// </summary>

private readonly WeakReference weakReference;

/// <summary>

/// 获取是否可以释放资源

/// </summary>

/// <returns></returns>

public bool CanDispose => this.weakReference.IsAlive == false;

/// <summary>

/// 监视生命周期的记录

/// </summary>

/// <param name="handler">激活状态的httpHandler</param>

public TrackingEntry(LifetimeHttpHandler handler)

{

this.disposable = handler.InnerHandler!;

this.weakReference = new WeakReference(handler);

}

/// <summary>

/// 释放资源

/// </summary>

public void Dispose()

{

try

{

this.disposable.Dispose();

}

catch (Exception)

{

}

}

}

}

}