namespace System.Web.Mvc {
    using System;
    using System.Globalization;
    using System.Linq;
    using System.Reflection;
    using System.Threading;
    using System.Web;
    using System.Web.Mvc.Async;
    using System.Web.Mvc.Resources;
    using System.Web.Routing;
    using System.Web.SessionState;
    using Microsoft.Web.Infrastructure.DynamicValidationHelper;

    public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState {
        private static readonly object _processRequestTag = new object();
        private ControllerBuilder _controllerBuilder;

        internal static readonly string MvcVersion = GetMvcVersionString();
        public static readonly string MvcVersionHeaderName = "X-AspNetMvc-Version";

        public MvcHandler(RequestContext requestContext) {
            if (requestContext == null) {
                throw new ArgumentNullException("requestContext");
            }

            RequestContext = requestContext;
        }

        internal ControllerBuilder ControllerBuilder {
            get {
                if (_controllerBuilder == null) {
                    _controllerBuilder = ControllerBuilder.Current;
                }
                return _controllerBuilder;
            }
            set {
                _controllerBuilder = value;
            }
        }

        public static bool DisableMvcResponseHeader {
            get;
            set;
        }

        protected virtual bool IsReusable {
            get {
                return false;
            }
        }

        public RequestContext RequestContext {
            get;
            private set;
        }

        protected internal virtual void AddVersionHeader(HttpContextBase httpContext) {
            if (!DisableMvcResponseHeader) {
                httpContext.Response.AppendHeader(MvcVersionHeaderName, MvcVersion);
            }
        }

        protected virtual IAsyncResult BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, object state) {
            HttpContextBase iHttpContext = new HttpContextWrapper(httpContext);
            return BeginProcessRequest(iHttpContext, callback, state);
        }

        protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state) {
            return SecurityUtil.ProcessInApplicationTrust(() => {
                IController controller;
                IControllerFactory factory;
                ProcessRequestInit(httpContext, out controller, out factory);

                IAsyncController asyncController = controller as IAsyncController;
                if (asyncController != null) {
                    // asynchronous controller
                    BeginInvokeDelegate beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState) {
                        try {
                            return asyncController.BeginExecute(RequestContext, asyncCallback, asyncState);
                        }
                        catch {
                            factory.ReleaseController(asyncController);
                            throw;
                        }
                    };

                    EndInvokeDelegate endDelegate = delegate(IAsyncResult asyncResult) {
                        try {
                            asyncController.EndExecute(asyncResult);
                        }
                        finally {
                            factory.ReleaseController(asyncController);
                        }
                    };

                    SynchronizationContext syncContext = SynchronizationContextUtil.GetSynchronizationContext();
                    AsyncCallback newCallback = AsyncUtil.WrapCallbackForSynchronizedExecution(callback, syncContext);
                    return AsyncResultWrapper.Begin(newCallback, state, beginDelegate, endDelegate, _processRequestTag);
                }
                else {
                    // synchronous controller
                    Action action = delegate {
                        try {
                            controller.Execute(RequestContext);
                        }
                        finally {
                            factory.ReleaseController(controller);
                        }
                    };

                    return AsyncResultWrapper.BeginSynchronous(callback, state, action, _processRequestTag);
                }
            });
        }

        protected internal virtual void EndProcessRequest(IAsyncResult asyncResult) {
            SecurityUtil.ProcessInApplicationTrust(() => {
                AsyncResultWrapper.End(asyncResult, _processRequestTag);
            });
        }

        private static string GetMvcVersionString() {
            // DevDiv 216459:
            // This code originally used Assembly.GetName(), but that requires FileIOPermission, which isn't granted in
            // medium trust. However, Assembly.FullName *is* accessible in medium trust.
            return new AssemblyName(typeof(MvcHandler).Assembly.FullName).Version.ToString(2);
        }

        protected virtual void ProcessRequest(HttpContext httpContext) {
            HttpContextBase iHttpContext = new HttpContextWrapper(httpContext);
            ProcessRequest(iHttpContext);
        }

        protected internal virtual void ProcessRequest(HttpContextBase httpContext) {
            SecurityUtil.ProcessInApplicationTrust(() => {
                IController controller;
                IControllerFactory factory;
                ProcessRequestInit(httpContext, out controller, out factory);

                try {
                    controller.Execute(RequestContext);
                }
                finally {
                    factory.ReleaseController(controller);
                }
            });
        }

        private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory) {
            // If request validation has already been enabled, make it lazy. This allows attributes like [HttpPost] (which looks
            // at Request.Form) to work correctly without triggering full validation.
            bool? isRequestValidationEnabled = ValidationUtility.IsValidationEnabled(HttpContext.Current);
            if (isRequestValidationEnabled == true) {
                ValidationUtility.EnableDynamicValidation(HttpContext.Current);
            }

            AddVersionHeader(httpContext);
            RemoveOptionalRoutingParameters();

            // Get the controller type
            string controllerName = RequestContext.RouteData.GetRequiredString("controller");

            // Instantiate the controller and call Execute
            factory = ControllerBuilder.GetControllerFactory();
            controller = factory.CreateController(RequestContext, controllerName);
            if (controller == null) {
                throw new InvalidOperationException(
                    String.Format(
                        CultureInfo.CurrentCulture,
                        MvcResources.ControllerBuilder_FactoryReturnedNull,
                        factory.GetType(),
                        controllerName));
            }
        }

        private void RemoveOptionalRoutingParameters() {
            RouteValueDictionary rvd = RequestContext.RouteData.Values;

            // Get all keys for which the corresponding value is 'Optional'.
            // ToArray() necessary so that we don't manipulate the dictionary while enumerating.
            string[] matchingKeys = (from entry in rvd
                                     where entry.Value == UrlParameter.Optional
                                     select entry.Key).ToArray();

            foreach (string key in matchingKeys) {
                rvd.Remove(key);
            }
        }

        #region IHttpHandler Members
        bool IHttpHandler.IsReusable {
            get {
                return IsReusable;
            }
        }

        void IHttpHandler.ProcessRequest(HttpContext httpContext) {
            ProcessRequest(httpContext);
        }
        #endregion

        #region IHttpAsyncHandler Members
        IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData) {
            return BeginProcessRequest(context, cb, extraData);
        }

        void IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) {
            EndProcessRequest(result);
        }
        #endregion
    }
}