// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Concurrent;
using Microsoft.Extensions.Primitives;
 
namespace HtmlGenerationWebSite;
 
public class SignalTokenProviderService<TKey> : ISignalTokenProviderService<TKey>
{
    private readonly ConcurrentDictionary<object, ChangeTokenInfo> _changeTokens
        = new ConcurrentDictionary<object, ChangeTokenInfo>();
 
    public IChangeToken GetToken(object key)
    {
        return _changeTokens.GetOrAdd(
            key,
            _ =>
            {
                var cancellationTokenSource = new CancellationTokenSource();
                var changeToken = new CancellationChangeToken(cancellationTokenSource.Token);
                return new ChangeTokenInfo(changeToken, cancellationTokenSource);
            }).ChangeToken;
    }
 
    public void SignalToken(object key)
    {
        ChangeTokenInfo changeTokenInfo;
        if (_changeTokens.TryRemove(key, out changeTokenInfo))
        {
            changeTokenInfo.TokenSource.Cancel();
        }
    }
 
    private class ChangeTokenInfo
    {
        public ChangeTokenInfo(IChangeToken changeToken, CancellationTokenSource tokenSource)
        {
            ChangeToken = changeToken;
            TokenSource = tokenSource;
        }
 
        public IChangeToken ChangeToken { get; }
 
        public CancellationTokenSource TokenSource { get; }
    }
}