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

using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Diagnostics.Contracts;
using System.Net;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http.Controllers;
using System.Web.Http.Hosting;
using System.Web.Http.Properties;
using System.Web.Http.Routing;

namespace System.Web.Http.Dispatcher
{
    /// <summary>
    /// Dispatches an incoming <see cref="HttpRequestMessage"/> to an <see cref="IHttpController"/> implementation for processing.
    /// </summary>
    public class HttpControllerDispatcher : HttpMessageHandler
    {
        private const string ControllerKey = "controller";

        private IHttpControllerSelector _controllerSelector;
        private readonly HttpConfiguration _configuration;
        private bool _disposed;

        /// <summary>
        /// Initializes a new instance of the <see cref="HttpControllerDispatcher"/> class using default <see cref="HttpConfiguration"/>.
        /// </summary>
        [SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope",
            Justification = "The configuration object is disposed as part of this class.")]
        public HttpControllerDispatcher()
            : this(new HttpConfiguration())
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="HttpControllerDispatcher"/> class.
        /// </summary>
        public HttpControllerDispatcher(HttpConfiguration configuration)
        {
            if (configuration == null)
            {
                throw Error.ArgumentNull("configuration");
            }

            _configuration = configuration;
        }

        /// <summary>
        /// Gets the <see cref="HttpConfiguration"/>.
        /// </summary>
        public HttpConfiguration Configuration
        {
            get { return _configuration; }
        }

        private IHttpControllerSelector ControllerSelector
        {
            get
            {
                if (_controllerSelector == null)
                {
                    _controllerSelector = _configuration.Services.GetHttpControllerSelector();
                }

                return _controllerSelector;
            }
        }

        /// <summary>
        /// Releases unmanaged and - optionally - managed resources
        /// </summary>
        /// <param name="disposing"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged SRResources.</param>
        protected override void Dispose(bool disposing)
        {
            if (!_disposed)
            {
                _disposed = true;
                if (disposing)
                {
                    _configuration.Dispose();
                }
            }

            base.Dispose(disposing);
        }

        /// <summary>
        /// Dispatches an incoming <see cref="HttpRequestMessage"/> to an <see cref="IHttpController"/>.
        /// </summary>
        /// <param name="request">The request to dispatch</param>
        /// <param name="cancellationToken">The cancellation token.</param>
        /// <returns>A <see cref="Task{HttpResponseMessage}"/> representing the ongoing operation.</returns>
        [SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes", Justification = "We report the error in the HTTP response.")]
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            // Runs Content Negotiation and Error Handling on the result of SendAsyncInternal
            try
            {
                return SendAsyncInternal(request, cancellationToken)
                      .Catch(info => info.Handled(HandleException(request, info.Exception, _configuration)));
            }
            catch (Exception exception)
            {
                return TaskHelpers.FromResult(HandleException(request, exception, _configuration));
            }
        }

        [SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope", Justification = "Caller becomes owner.")]
        private Task<HttpResponseMessage> SendAsyncInternal(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            if (request == null)
            {
                throw Error.ArgumentNull("request");
            }

            if (_disposed)
            {
                throw Error.ObjectDisposed(SRResources.HttpMessageHandlerDisposed, typeof(HttpControllerDispatcher).Name);
            }

            // Lookup route data, or if not found as a request property then we look it up in the route table
            IHttpRouteData routeData;
            if (!request.Properties.TryGetValue(HttpPropertyKeys.HttpRouteDataKey, out routeData))
            {
                routeData = _configuration.Routes.GetRouteData(request);
                if (routeData != null)
                {
                    request.Properties.Add(HttpPropertyKeys.HttpRouteDataKey, routeData);
                }
                else
                {
                    // TODO, 328927, add an error message in the response body
                    return TaskHelpers.FromResult(request.CreateResponse(HttpStatusCode.NotFound));
                }
            }

            RemoveOptionalRoutingParameters(routeData.Values);

            HttpControllerDescriptor httpControllerDescriptor = ControllerSelector.SelectController(request);
            if (httpControllerDescriptor == null)
            {
                // TODO, 328927, add an error message in the response body
                return TaskHelpers.FromResult(request.CreateResponse(HttpStatusCode.NotFound));
            }

            IHttpController httpController = httpControllerDescriptor.CreateController(request);

            if (httpController == null)
            {
                // TODO, 328927, add an error message in the response body
                return TaskHelpers.FromResult(request.CreateResponse(HttpStatusCode.NotFound));
            }

            // Create context
            HttpControllerContext controllerContext = new HttpControllerContext(_configuration, routeData, request);
            controllerContext.Controller = httpController;
            controllerContext.ControllerDescriptor = httpControllerDescriptor;

            return httpController.ExecuteAsync(controllerContext, cancellationToken);
        }

        [SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope", Justification = "Caller owns HttpResponseMessage instance.")]
        private static HttpResponseMessage HandleException(HttpRequestMessage request, Exception exception, HttpConfiguration configuration)
        {
            Exception unwrappedException = exception.GetBaseException();
            HttpResponseException httpResponseException = unwrappedException as HttpResponseException;

            if (httpResponseException != null)
            {
                return httpResponseException.Response;
            }

            if (configuration.ShouldIncludeErrorDetail(request))
            {
                return request.CreateResponse<ExceptionSurrogate>(HttpStatusCode.InternalServerError, new ExceptionSurrogate(unwrappedException));
            }

            return new HttpResponseMessage(HttpStatusCode.InternalServerError);
        }

        private static void RemoveOptionalRoutingParameters(IDictionary<string, object> routeValueDictionary)
        {
            Contract.Assert(routeValueDictionary != null);

            // Get all keys for which the corresponding value is 'Optional'.
            // Having a separate array is necessary so that we don't manipulate the dictionary while enumerating.
            // This is on a hot-path and linq expressions are showing up on the profile, so do array manipulation.
            int max = routeValueDictionary.Count;
            int i = 0;
            string[] matching = new string[max];
            foreach (KeyValuePair<string, object> kv in routeValueDictionary)
            {
                if (kv.Value == RouteParameter.Optional)
                {
                    matching[i] = kv.Key;
                    i++;
                }
            }
            for (int j = 0; j < i; j++)
            {
                string key = matching[j];
                routeValueDictionary.Remove(key);
            }
        }
    }
}