using Fleet.Server;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace MoShiro.Backend.Gateway;

/// <summary>
/// 宿主开始停止时先关闭所有 Agent 的长连接（Close 握手，不发 revoked：Agent 会重连）。
/// 否则 Kestrel 的有序停止要等满 30 秒的超时，才会放弃这些永远不会自己结束的 WebSocket。
/// </summary>
public sealed class ConnectionShutdown : IHostedService
{
    private readonly IServiceProvider _services;
    private readonly IHostApplicationLifetime _lifetime;
    private Task? _closing;

    public ConnectionShutdown(IServiceProvider services, IHostApplicationLifetime lifetime)
    {
        _services = services;
        _lifetime = lifetime;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        // ApplicationStopping 在有序停止的最开始触发，早于 Kestrel 等待连接结束：这里不阻塞，关闭在后台进行，StopAsync 再等它做完
        _lifetime.ApplicationStopping.Register(() => _closing = CloseAsync());
        return Task.CompletedTask;
    }

    public async Task StopAsync(CancellationToken cancellationToken)
    {
        if (_closing is { } closing)
        {
            await closing.WaitAsync(TimeSpan.FromSeconds(5), cancellationToken);
        }
    }

    private async Task CloseAsync()
    {
        try
        {
            await _services.GetRequiredService<IFleetConnections>().CloseAllAsync("server shutting down");
        }
        catch (Exception ex) when (ex is ObjectDisposedException or InvalidOperationException)
        {
            // 停止过程中，服务已经在释放：Kestrel 的超时兜底
        }
    }
}