using System;
using System.Collections.Concurrent;
using System.Threading;
using Microsoft.Extensions.Hosting;
using Umbraco.Core;
using Umbraco.Core.Hosting;

namespace Umbraco.Web.Common.AspNetCore
{
    public class AspNetCoreApplicationShutdownRegistry : IApplicationShutdownRegistry
    {
        private readonly IHostApplicationLifetime _hostApplicationLifetime;
        private readonly ConcurrentDictionary<IRegisteredObject, RegisteredObjectWrapper> _registeredObjects =
            new ConcurrentDictionary<IRegisteredObject, RegisteredObjectWrapper>();

        public AspNetCoreApplicationShutdownRegistry(IHostApplicationLifetime hostApplicationLifetime)
        {
            _hostApplicationLifetime = hostApplicationLifetime;
        }

        public void RegisterObject(IRegisteredObject registeredObject)
        {
            var wrapped = new RegisteredObjectWrapper(registeredObject);
            if (!_registeredObjects.TryAdd(registeredObject, wrapped))
            {
                throw new InvalidOperationException("Could not register object");
            }

            var cancellationTokenRegistration = _hostApplicationLifetime.ApplicationStopping.Register(() => wrapped.Stop(true));
            wrapped.CancellationTokenRegistration = cancellationTokenRegistration;
        }

        public void UnregisterObject(IRegisteredObject registeredObject)
        {
            if (_registeredObjects.TryGetValue(registeredObject, out var wrapped))
            {
                wrapped.CancellationTokenRegistration.Unregister();
            }
        }


        private class RegisteredObjectWrapper
        {
            private readonly IRegisteredObject _inner;

            public RegisteredObjectWrapper(IRegisteredObject inner)
            {
                _inner = inner;
            }

            public CancellationTokenRegistration CancellationTokenRegistration { get; set; }

            public void Stop(bool immediate)
            {
                _inner.Stop(immediate);
            }
        }
    }
}