using Microsoft.Extensions.Primitives;
using Yarp.ReverseProxy.Configuration;
using YarpGateway.Config;

namespace YarpGateway.DynamicProxy;

public class DynamicProxyConfigProvider : IProxyConfigProvider
{
    private volatile IProxyConfig _config;
    private readonly DatabaseRouteConfigProvider _routeProvider;
    private readonly DatabaseClusterConfigProvider _clusterProvider;
    private readonly object _lock = new();
    private CancellationTokenSource? _cts;

    public DynamicProxyConfigProvider(
        DatabaseRouteConfigProvider routeProvider,
        DatabaseClusterConfigProvider clusterProvider)
    {
        _routeProvider = routeProvider;
        _clusterProvider = clusterProvider;
        _cts = new CancellationTokenSource();
        UpdateConfig();
    }

    public IProxyConfig GetConfig()
    {
        return _config;
    }

    public void UpdateConfig()
    {
        lock (_lock)
        {
            _cts?.Cancel();
            _cts = new CancellationTokenSource();
            
            var routes = _routeProvider.GetRoutes();
            var clusters = _clusterProvider.GetClusters();

            _config = new InMemoryProxyConfig(
                routes,
                clusters,
                Array.Empty<IReadOnlyDictionary<string, string>>(),
                _cts.Token
            );
        }
    }

    public async Task ReloadAsync()
    {
        await _routeProvider.ReloadAsync();
        await _clusterProvider.ReloadAsync();
        UpdateConfig();
    }

    private class InMemoryProxyConfig : IProxyConfig
    {
        private readonly CancellationChangeToken _changeToken;

        public InMemoryProxyConfig(
            IReadOnlyList<RouteConfig> routes,
            IReadOnlyList<ClusterConfig> clusters,
            IReadOnlyList<IReadOnlyDictionary<string, string>> transforms,
            CancellationToken token)
        {
            Routes = routes;
            Clusters = clusters;
            Transforms = transforms;
            _changeToken = new CancellationChangeToken(token);
        }

        public IReadOnlyList<RouteConfig> Routes { get; }
        public IReadOnlyList<ClusterConfig> Clusters { get; }
        public IReadOnlyList<IReadOnlyDictionary<string, string>> Transforms { get; }
        public IChangeToken ChangeToken => _changeToken;
    }
}