namespace Microsoft.AspNetCore.Hosting

{

    public static class WebHostBuilderIISExtensions

    {

        // These are defined as ASPNETCORE_ environment variables by IIS's AspNetCoreModule.

        private static readonly string ServerPort = "PORT";

        private static readonly string ServerPath = "APPL_PATH";

        private static readonly string PairingToken = "TOKEN";

        private static readonly string IISAuth = "IIS_HTTPAUTH";

        private static readonly string IISWebSockets = "IIS_WEBSOCKETS_SUPPORTED";

        /// <summary>

        /// Configures the port and base path the server should listen on when running behind AspNetCoreModule.

        /// The app will also be configured to capture startup errors.

        public static IWebHostBuilder UseIISIntegration(this IWebHostBuilder hostBuilder)

        {

            var port = hostBuilder.GetSetting(ServerPort) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{ServerPort}");

            var path = hostBuilder.GetSetting(ServerPath) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{ServerPath}");

            var pairingToken = hostBuilder.GetSetting(PairingToken) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{PairingToken}");

            var iisAuth = hostBuilder.GetSetting(IISAuth) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{IISAuth}");

            var websocketsSupported = hostBuilder.GetSetting(IISWebSockets) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{IISWebSockets}");

            bool isWebSocketsSupported;

            if (!bool.TryParse(websocketsSupported, out isWebSocketsSupported))

            {

                // If the websocket support variable is not set, we will always fallback to assuming websockets are enabled.

                isWebSocketsSupported = (Environment.OSVersion.Version >= new Version(, ));

            }

            if (!string.IsNullOrEmpty(port) && !string.IsNullOrEmpty(path) && !string.IsNullOrEmpty(pairingToken))

            {

                // Set flag to prevent double service configuration

                hostBuilder.UseSetting(nameof(UseIISIntegration), true.ToString());

                var enableAuth = false;

                if (string.IsNullOrEmpty(iisAuth))

                {

                    // back compat with older ANCM versions

                    enableAuth = true;

                }

                else

                {

                    // Lightup a new ANCM variable that tells us if auth is enabled.

                    foreach (var authType in iisAuth.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries))

                    {

                        if (!string.Equals(authType, "anonymous", StringComparison.OrdinalIgnoreCase))

                        {

                            enableAuth = true;

                            break;

                        }

                    }

                }

                var address = "http://127.0.0.1:" + port;

                hostBuilder.CaptureStartupErrors(true);

                hostBuilder.ConfigureServices(services =>

                {

                    // Delay register the url so users don't accidentally overwrite it.

                    hostBuilder.UseSetting(WebHostDefaults.ServerUrlsKey, address);

                    hostBuilder.PreferHostingUrls(true);

                    services.AddSingleton<IServerIntegratedAuth>(_ => new ServerIntegratedAuth()

                    {

                        IsEnabled = enableAuth,

                        AuthenticationScheme = IISDefaults.AuthenticationScheme

                    });

                    services.AddSingleton<IStartupFilter>(new IISSetupFilter(pairingToken, new PathString(path), isWebSocketsSupported));

                    services.Configure<ForwardedHeadersOptions>(options =>

                    {

                        options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto;

                    });

                    services.Configure<IISOptions>(options =>

                    {

                        options.ForwardWindowsAuthentication = enableAuth;

                    });

                    services.AddAuthenticationCore();

                });

            }

            return hostBuilder;

        }

    }

}