// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

using System.Diagnostics.Contracts;
using System.Net.Http;
using System.Runtime.ExceptionServices;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http.ExceptionHandling;

namespace System.Web.Http.WebHost.Routing
{
    /// <summary>Represents a handler that asynchronously handles an unhandled exception from routing.</summary>
    internal class HttpRouteExceptionHandler : HttpTaskAsyncHandler
    {
        private readonly ExceptionDispatchInfo _exceptionInfo;
        private readonly IExceptionLogger _exceptionLogger;
        private readonly IExceptionHandler _exceptionHandler;

        public HttpRouteExceptionHandler(ExceptionDispatchInfo exceptionInfo)
            : this(exceptionInfo, ExceptionServices.GetLogger(GlobalConfiguration.Configuration),
            ExceptionServices.GetHandler(GlobalConfiguration.Configuration))
        {
        }

        internal HttpRouteExceptionHandler(ExceptionDispatchInfo exceptionInfo,
            IExceptionLogger exceptionLogger, IExceptionHandler exceptionHandler)
        {
            Contract.Assert(exceptionInfo != null);
            Contract.Assert(exceptionLogger != null);
            Contract.Assert(exceptionHandler != null);

            _exceptionInfo = exceptionInfo;
            _exceptionLogger = exceptionLogger;
            _exceptionHandler = exceptionHandler;
        }

        internal ExceptionDispatchInfo ExceptionInfo
        {
            get { return _exceptionInfo; }
        }

        internal IExceptionLogger ExceptionLogger
        {
            get { return _exceptionLogger; }
        }

        internal IExceptionHandler ExceptionHandler
        {
            get { return _exceptionHandler; }
        }

        public override Task ProcessRequestAsync(HttpContext context)
        {
            return ProcessRequestAsync(new HttpContextWrapper(context));
        }

        internal async Task ProcessRequestAsync(HttpContextBase context)
        {
            Exception exception = _exceptionInfo.SourceException;
            Contract.Assert(exception != null);

            OperationCanceledException canceledException = exception as OperationCanceledException;
            if (canceledException != null)
            {
                // If the route throws a cancelation exception, then we'll abort the request instead of
                // reporting an 'error'. We don't expect this to happen, but aborting the request is 
                // consistent with our behavior in other hosts.
                context.Request.Abort();
                return;
            }

            HttpRequestMessage request = context.GetOrCreateHttpRequestMessage();
            HttpResponseMessage response = null;
            CancellationToken cancellationToken = context.Response.GetClientDisconnectedTokenWhenFixed();

            HttpResponseException responseException = exception as HttpResponseException;

            try
            {
                if (responseException != null)
                {
                    response = responseException.Response;
                    Contract.Assert(response != null);

                    // This method call is hardened and designed not to throw exceptions (since they won't be caught
                    // and handled further by its callers).
                    await HttpControllerHandler.CopyResponseAsync(context, request, response, _exceptionLogger,
                        _exceptionHandler, cancellationToken);
                }
                else
                {
                    // This method call is hardened and designed not to throw exceptions (since they won't be caught and
                    // handled further by its callers).
                    bool handled = await HttpControllerHandler.CopyErrorResponseAsync(
                        WebHostExceptionCatchBlocks.HttpWebRoute, context, request, null,
                        _exceptionInfo.SourceException, _exceptionLogger, _exceptionHandler, cancellationToken);

                    if (!handled)
                    {
                        _exceptionInfo.Throw();
                    }
                }
            }
            catch (OperationCanceledException)
            {
                // This block handles cancellations that might occur while we're writing an 'error' response.
                //
                // HttpTaskAsyncHandler treats a canceled task as an unhandled exception (logged to Application event
                // log). Instead of returning a canceled task, abort the request and return a completed task.
                context.Request.Abort();
            }
            finally
            {
                // The other HttpTaskAsyncHandler is HttpControllerHandler; it has similar cleanup logic.
                request.DisposeRequestResources();
                request.Dispose();

                if (response != null)
                {
                    response.Dispose();
                }
            }
        }
    }
}
