namespace System.Web.Mvc {
    using System;
    using System.Collections.Generic;
    using System.Diagnostics.CodeAnalysis;
    using System.Globalization;
    using System.IO;
    using System.Linq;
    using System.Runtime.Caching;
    using System.Security.Cryptography;
    using System.Text;
    using System.Web;
    using System.Web.Mvc.Resources;
    using System.Web.UI;

    [SuppressMessage("Microsoft.Performance", "CA1813:AvoidUnsealedAttributes", Justification = "Unsealed so that subclassed types can set properties in the default constructor.")]
    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = false)]
    public class OutputCacheAttribute : ActionFilterAttribute, IExceptionFilter {

        private OutputCacheParameters _cacheSettings = new OutputCacheParameters { VaryByParam = "*" };
        private const string _cacheKeyPrefix = "_MvcChildActionCache_";
        private static ObjectCache _childActionCache;
        private Func<ObjectCache> _childActionCacheThunk = () => ChildActionCache;
        private static object _childActionFilterFinishCallbackKey = new object();
        private bool _locationWasSet;
        private bool _noStoreWasSet;

        public OutputCacheAttribute() {
        }

        internal OutputCacheAttribute(ObjectCache childActionCache) {
            _childActionCacheThunk = () => childActionCache;
        }

        public string CacheProfile {
            get {
                return _cacheSettings.CacheProfile ?? String.Empty;
            }
            set {
                _cacheSettings.CacheProfile = value;
            }
        }

        internal OutputCacheParameters CacheSettings {
            get {
                return _cacheSettings;
            }
        }

        public static ObjectCache ChildActionCache {
            get {
                return _childActionCache ?? MemoryCache.Default;
            }
            set {
                _childActionCache = value;
            }
        }

        private ObjectCache ChildActionCacheInternal {
            get {
                return _childActionCacheThunk();
            }
        }

        public int Duration {
            get {
                return _cacheSettings.Duration;
            }
            set {
                _cacheSettings.Duration = value;
            }
        }

        public OutputCacheLocation Location {
            get {
                return _cacheSettings.Location;
            }
            set {
                _cacheSettings.Location = value;
                _locationWasSet = true;
            }
        }

        public bool NoStore {
            get {
                return _cacheSettings.NoStore;
            }
            set {
                _cacheSettings.NoStore = value;
                _noStoreWasSet = true;
            }
        }

        public string SqlDependency {
            get {
                return _cacheSettings.SqlDependency ?? String.Empty;
            }
            set {
                _cacheSettings.SqlDependency = value;
            }
        }

        public string VaryByContentEncoding {
            get {
                return _cacheSettings.VaryByContentEncoding ?? String.Empty;
            }
            set {
                _cacheSettings.VaryByContentEncoding = value;
            }
        }

        public string VaryByCustom {
            get {
                return _cacheSettings.VaryByCustom ?? String.Empty;
            }
            set {
                _cacheSettings.VaryByCustom = value;
            }
        }

        public string VaryByHeader {
            get {
                return _cacheSettings.VaryByHeader ?? String.Empty;
            }
            set {
                _cacheSettings.VaryByHeader = value;
            }
        }

        [SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Param", Justification = "Matches the @ OutputCache page directive.")]
        public string VaryByParam {
            get {
                return _cacheSettings.VaryByParam ?? String.Empty;
            }
            set {
                _cacheSettings.VaryByParam = value;
            }
        }

        private static void ClearChildActionFilterFinishCallback(ControllerContext controllerContext) {
            controllerContext.HttpContext.Items.Remove(_childActionFilterFinishCallbackKey);
        }

        private static void CompleteChildAction(ControllerContext filterContext, bool wasException) {
            Action<bool> callback = GetChildActionFilterFinishCallback(filterContext);

            if (callback != null) {
                ClearChildActionFilterFinishCallback(filterContext);
                callback(wasException);
            }
        }

        private static Action<bool> GetChildActionFilterFinishCallback(ControllerContext controllerContext) {
            return controllerContext.HttpContext.Items[_childActionFilterFinishCallbackKey] as Action<bool>;
        }

        internal string GetChildActionUniqueId(ActionExecutingContext filterContext) {
            StringBuilder uniqueIdBuilder = new StringBuilder();

            // Start with a prefix, presuming that we share the cache with other users
            uniqueIdBuilder.Append(_cacheKeyPrefix);

            // Unique ID of the action description
            uniqueIdBuilder.Append(filterContext.ActionDescriptor.UniqueId);

            // Unique ID from the VaryByCustom settings, if any
            uniqueIdBuilder.Append(DescriptorUtil.CreateUniqueId(VaryByCustom));
            if (!String.IsNullOrEmpty(VaryByCustom)) {
                string varyByCustomResult = filterContext.HttpContext.ApplicationInstance.GetVaryByCustomString(HttpContext.Current, VaryByCustom);
                uniqueIdBuilder.Append(varyByCustomResult);
            }

            // Unique ID from the VaryByParam settings, if any
            uniqueIdBuilder.Append(GetUniqueIdFromActionParameters(filterContext, SplitVaryByParam(VaryByParam)));

            // The key is typically too long to be useful, so we use a cryptographic hash
            // as the actual key (better randomization and key distribution, so small vary
            // values will generate dramtically different keys).
            using (SHA256 sha = SHA256.Create()) {
                return Convert.ToBase64String(sha.ComputeHash(Encoding.UTF8.GetBytes(uniqueIdBuilder.ToString())));
            }
        }

        private static string GetUniqueIdFromActionParameters(ActionExecutingContext filterContext, IEnumerable<string> keys) {
            // Generate a unique ID of normalized key names + key values
            var keyValues = new Dictionary<string, object>(filterContext.ActionParameters, StringComparer.OrdinalIgnoreCase);
            keys = (keys ?? keyValues.Keys).Select(key => key.ToUpperInvariant())
                                           .OrderBy(key => key, StringComparer.Ordinal);

            return DescriptorUtil.CreateUniqueId(keys.Concat(keys.Select(key => keyValues.ContainsKey(key) ? keyValues[key] : null)));
        }

        public static bool IsChildActionCacheActive(ControllerContext controllerContext) {
            return GetChildActionFilterFinishCallback(controllerContext) != null;
        }

        public override void OnActionExecuted(ActionExecutedContext filterContext) {
            if (filterContext == null) {
                throw new ArgumentNullException("filterContext");
            }

            // Complete the request if the child action threw an exception
            if (filterContext.IsChildAction && filterContext.Exception != null) {
                CompleteChildAction(filterContext, wasException: true);
            }
        }

        public override void OnActionExecuting(ActionExecutingContext filterContext) {
            if (filterContext == null) {
                throw new ArgumentNullException("filterContext");
            }

            if (filterContext.IsChildAction) {
                ValidateChildActionConfiguration();

                // Already actively being captured? (i.e., cached child action inside of cached child action)
                // Realistically, this needs write substitution to do properly (including things like authentication)
                if (GetChildActionFilterFinishCallback(filterContext) != null) {
                    throw new InvalidOperationException(MvcResources.OutputCacheAttribute_CannotNestChildCache);
                }

                // Already cached?
                string uniqueId = GetChildActionUniqueId(filterContext);
                string cachedValue = ChildActionCacheInternal.Get(uniqueId) as string;
                if (cachedValue != null) {
                    filterContext.Result = new ContentResult() { Content = cachedValue };
                    return;
                }

                // Swap in a new TextWriter so we can capture the output
                StringWriter cachingWriter = new StringWriter(CultureInfo.InvariantCulture);
                TextWriter originalWriter = filterContext.HttpContext.Response.Output;
                filterContext.HttpContext.Response.Output = cachingWriter;

                // Set a finish callback to clean up
                SetChildActionFilterFinishCallback(filterContext, wasException => {
                    // Restore original writer
                    filterContext.HttpContext.Response.Output = originalWriter;

                    // Grab output and write it
                    string capturedText = cachingWriter.ToString();
                    filterContext.HttpContext.Response.Write(capturedText);

                    // Only cache output if this wasn't an error
                    if (!wasException) {
                        ChildActionCacheInternal.Add(uniqueId, capturedText, DateTimeOffset.UtcNow.AddSeconds(Duration));
                    }
                });
            }
        }

        public void OnException(ExceptionContext filterContext) {
            if (filterContext == null) {
                throw new ArgumentNullException("filterContext");
            }

            if (filterContext.IsChildAction) {
                CompleteChildAction(filterContext, wasException: true);
            }
        }

        public override void OnResultExecuting(ResultExecutingContext filterContext) {
            if (filterContext == null) {
                throw new ArgumentNullException("filterContext");
            }

            if (!filterContext.IsChildAction) {
                // we need to call ProcessRequest() since there's no other way to set the Page.Response intrinsic
                using (OutputCachedPage page = new OutputCachedPage(_cacheSettings)) {
                    page.ProcessRequest(HttpContext.Current);
                }
            }
        }

        public override void OnResultExecuted(ResultExecutedContext filterContext) {
            if (filterContext == null) {
                throw new ArgumentNullException("filterContext");
            }

            if (filterContext.IsChildAction) {
                CompleteChildAction(filterContext, wasException: filterContext.Exception != null);
            }
        }

        private static void SetChildActionFilterFinishCallback(ControllerContext controllerContext, Action<bool> callback) {
            controllerContext.HttpContext.Items[_childActionFilterFinishCallbackKey] = callback;
        }

        private static IEnumerable<string> SplitVaryByParam(string varyByParam) {
            if (String.Equals(varyByParam, "none", StringComparison.OrdinalIgnoreCase)) {  // Vary by nothing
                return Enumerable.Empty<string>();
            }

            if (String.Equals(varyByParam, "*", StringComparison.OrdinalIgnoreCase)) {  // Vary by everything
                return null;
            }

            return from part in varyByParam.Split(';')  // Vary by specific parameters
                   let trimmed = part.Trim()
                   where !String.IsNullOrEmpty(trimmed)
                   select trimmed;
        }

        private void ValidateChildActionConfiguration() {
            if (Duration <= 0) {
                throw new InvalidOperationException(MvcResources.OutputCacheAttribute_InvalidDuration);
            }

            if (String.IsNullOrWhiteSpace(VaryByParam)) {
                throw new InvalidOperationException(MvcResources.OutputCacheAttribute_InvalidVaryByParam);
            }

            if (!String.IsNullOrWhiteSpace(CacheProfile) ||
                !String.IsNullOrWhiteSpace(SqlDependency) ||
                !String.IsNullOrWhiteSpace(VaryByContentEncoding) ||
                !String.IsNullOrWhiteSpace(VaryByHeader) ||
                _locationWasSet || _noStoreWasSet) {
                throw new InvalidOperationException(MvcResources.OutputCacheAttribute_ChildAction_UnsupportedSetting);
            }
        }

        private sealed class OutputCachedPage : Page {
            private OutputCacheParameters _cacheSettings;

            public OutputCachedPage(OutputCacheParameters cacheSettings) {
                // Tracing requires Page IDs to be unique.
                ID = Guid.NewGuid().ToString();
                _cacheSettings = cacheSettings;
            }

            protected override void FrameworkInitialize() {
                // when you put the <%@ OutputCache %> directive on a page, the generated code calls InitOutputCache() from here
                base.FrameworkInitialize();
                InitOutputCache(_cacheSettings);
            }
        }
    }
}