//------------------------------------------------------------------------------
// <copyright file="HttpCapabilitiesEvaluator.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
//------------------------------------------------------------------------------

namespace System.Web.Configuration {
    
    using System.Collections;
    using System.Collections.Specialized;
    using System.Diagnostics;
    using System.Globalization;
    using System.Reflection;
    using System.Security;
    using System.Text;
    using System.Text.RegularExpressions;
    using System.Threading;
    using System.Web.Caching;
    using System.Web.Compilation;
    using System.Web.Hosting;
    using System.Security.Permissions;

    public abstract class HttpCapabilitiesProvider {
        public abstract HttpBrowserCapabilities GetBrowserCapabilities(HttpRequest request);
    }

    //
    // CapabilitiesEvaluator encapabilitiesulates a set of rules for deducing
    // a capabilities object from an HttpRequest
    //
    public class HttpCapabilitiesDefaultProvider : HttpCapabilitiesProvider {

        internal CapabilitiesRule _rule;
        internal Hashtable _variables;
        internal Type _resultType;
        internal TimeSpan _cachetime;
        internal string _cacheKeyPrefix;

        private int _userAgentCacheKeyLength;
        private static int _idCounter;
        private const string _isMobileDeviceCapKey = "isMobileDevice";
        private static object _disableOptimisticCachingSingleton = new object();
        private const int _defaultUserAgentCacheKeyLength = 64;
        private string _browserCapabilitiesProviderType = null;
        private HttpCapabilitiesProvider _browserCapabilitiesProvider = null;

        public int UserAgentCacheKeyLength {
            get {
                return _userAgentCacheKeyLength;
            }
            set {
                _userAgentCacheKeyLength = value;
            }
        }

        public Type ResultType {
            get {
                return _resultType;
            }
            set {
                _resultType = value;
            }
        }

        public TimeSpan CacheTime {
            get {
                return _cachetime;
            }
            set {
                _cachetime = value;
            }
        }

        internal string BrowserCapabilitiesProviderType {
            get {
                return _browserCapabilitiesProviderType;
            }
            set {
                _browserCapabilitiesProviderType = value;
            }
        }

        internal HttpCapabilitiesProvider BrowserCapabilitiesProvider {
            get {
                if (_browserCapabilitiesProvider == null) {
                    if (BrowserCapabilitiesProviderType != null) {
                        Type t = System.Type.GetType(BrowserCapabilitiesProviderType, true, true);
                        _browserCapabilitiesProvider = (HttpCapabilitiesProvider)Activator.CreateInstance(t);
                    }
                }
                return _browserCapabilitiesProvider;
            }
            set {
                _browserCapabilitiesProvider = value;
            }
        }

        public HttpCapabilitiesDefaultProvider() : this(RuntimeConfig.GetAppConfig().BrowserCaps){
            if (RuntimeConfig.GetAppConfig().BrowserCaps != null) {
                _userAgentCacheKeyLength = RuntimeConfig.GetAppConfig().BrowserCaps.UserAgentCacheKeyLength;
            }
            if (_userAgentCacheKeyLength == 0) {
                _userAgentCacheKeyLength = _defaultUserAgentCacheKeyLength;
            }
        }

        //
        // internal constructor; inherit from parent
        //
        public HttpCapabilitiesDefaultProvider(HttpCapabilitiesDefaultProvider parent) {
            int id = Interlocked.Increment(ref _idCounter);
            // don't do id.ToString() on every request, do it here
            _cacheKeyPrefix = CacheInternal.PrefixHttpCapabilities + id.ToString(CultureInfo.InvariantCulture);

            if (parent == null) {
                ClearParent();
            }
            else {
                _rule = parent._rule;

                if (parent._variables == null)
                    _variables = null;
                else
                    _variables = new Hashtable(parent._variables);

                _cachetime = parent._cachetime;
                _resultType = parent._resultType;
            }
            //
            AddDependency(String.Empty);
        }

        internal BrowserCapabilitiesFactoryBase BrowserCapFactory {
            get {
                return BrowserCapabilitiesCompiler.BrowserCapabilitiesFactory;
            }
        }

        //
        // remove inheritance for <result inherit="false" />
        //
        internal void ClearParent() {
            _rule = null;
            _cachetime = TimeSpan.FromSeconds(60); // one minute default expiry
            _variables = new Hashtable();
            _resultType = typeof(HttpCapabilitiesBase);
        }

        //
        // add a dependency when we encounter a <use var="HTTP_ACCEPT_LANGUAGE" as="lang" />
        //
        public void AddDependency(String variable) {
            if (variable.Equals("HTTP_USER_AGENT"))
                variable = String.Empty;

            _variables[variable] = true;
        }

        //
        // sets the set of rules
        //
        public virtual void AddRuleList(ArrayList ruleList) {
            if (ruleList.Count == 0)
                return;

            if (_rule != null)
                ruleList.Insert(0, _rule);

            _rule = new CapabilitiesSection(CapabilitiesRule.Filter, null, null, ruleList);
        }

        internal static string GetUserAgent(HttpRequest request) {
            string userAgent;

            if (request.ClientTarget.Length > 0) {
                userAgent = GetUserAgentFromClientTarget(
                    request.Context.ConfigurationPath, request.ClientTarget);
            }
            else {
                userAgent = request.UserAgent;
            }

            // Protect against attacks with long User-Agent headers
            if (userAgent != null && userAgent.Length > 512) {
                userAgent = userAgent.Substring(0, 512);
            }

            return userAgent;
        }

        internal static string GetUserAgentFromClientTarget(VirtualPath configPath, string clientTarget) {

            // Lookup ClientTarget section in config.
            ClientTargetSection clientTargetConfig = RuntimeConfig.GetConfig(configPath).ClientTarget;

            string userAgent = null;

            if ( clientTargetConfig.ClientTargets[ clientTarget ] != null )
            {
                userAgent = clientTargetConfig.ClientTargets[ clientTarget ].UserAgent;
            }

            if ( userAgent == null )
            {
                throw new HttpException(SR.GetString(SR.Invalid_client_target, clientTarget));
            }

            return userAgent;
        }

        private void CacheBrowserCapResult(ref HttpCapabilitiesBase result) {
            // Use the previously cached browserCap object if an identical
            // browserCap is found.
            CacheStoreProvider cacheInternal = System.Web.HttpRuntime.Cache.InternalCache;

            if (result.Capabilities == null) {
                return;
            }

            string hashKey = CacheInternal.PrefixBrowserCapsHash;
            StringBuilder builder = new StringBuilder();
            foreach (string attribute in result.Capabilities.Keys) {
                // Ignore useragent that is stored with empty key.
                if (String.IsNullOrEmpty(attribute)) {
                    continue;
                }

                string value = (String)result.Capabilities[attribute];
                if (value != null) {
                    builder.Append(attribute);
                    builder.Append("$");
                    builder.Append(value);
                    builder.Append("$");
                }
            }
            hashKey += builder.ToString().GetHashCode().ToString(CultureInfo.InvariantCulture);

            HttpCapabilitiesBase newResult = cacheInternal.Get(hashKey) as HttpCapabilitiesBase;
            if (newResult != null) {
                result = newResult;
            }
            else {
                // cache it and respect cachetime
                cacheInternal.Insert(hashKey, result, new CacheInsertOptions() { SlidingExpiration = _cachetime });
            }
        }

        public override HttpBrowserCapabilities GetBrowserCapabilities(HttpRequest request) {
            return (HttpBrowserCapabilities)Evaluate(request);
        }

        //
        // Actually computes the browser capabilities
        //
        internal HttpCapabilitiesBase Evaluate(HttpRequest request) {

            HttpCapabilitiesBase result;
            CacheStoreProvider cacheInternal = System.Web.HttpRuntime.Cache.InternalCache;

            //
            // 1) grab UA and do optimistic cache lookup (if UA is in dependency list) 
            //
            string userAgent = GetUserAgent(request);
            string userAgentCacheKey = userAgent;

            // Use the shorten userAgent as the cache key.
            Debug.Assert(UserAgentCacheKeyLength != 0);
            // Trim the useragent string based on <browserCaps> config
            if (userAgentCacheKey != null && userAgentCacheKey.Length > UserAgentCacheKeyLength) {
                userAgentCacheKey = userAgentCacheKey.Substring(0, UserAgentCacheKeyLength);
            }

            bool doFullCacheKeyLookup = false;
            string optimisticCacheKey = _cacheKeyPrefix + userAgentCacheKey;
            object optimisticCacheResult = cacheInternal.Get(optimisticCacheKey);

            // optimize for common case (desktop browser)
            result = optimisticCacheResult as HttpCapabilitiesBase;
            if (result != null) {
                return result;
            }

            //
            // 1.1) optimistic cache entry could tell us to do full cache lookup
            // 
            if (optimisticCacheResult == _disableOptimisticCachingSingleton) {
                doFullCacheKeyLookup = true;
            }
            else {
                // cache it and respect _cachetime
                result = EvaluateFinal(request, true);

                // Optimized cache key is disabled if the request matches any headers defined within identifications.
                if (result.UseOptimizedCacheKey) {

                    // Use the same browserCap result if one with the same capabilities can be found in the cache.
                    // This is to reduce the number of identical browserCap instances being cached.
                    CacheBrowserCapResult(ref result);

                    // Cache the result using the optimisicCacheKey
                    cacheInternal.Insert(optimisticCacheKey, result, new CacheInsertOptions() { SlidingExpiration = _cachetime });

                    return result;
                }
            }

            //
            // 2) either:
            //
            //      We've never seen the UA before (parse all headers to 
            //          determine if the new UA also carries modile device
            //          httpheaders).
            //
            //      It's a mobile UA (so parse all headers) and do full 
            //          cache lookup
            //
            //      UA isn't in dependency list (customer custom caps section)
            //

            IDictionaryEnumerator de = _variables.GetEnumerator();
            StringBuilder sb = new StringBuilder(_cacheKeyPrefix);

            InternalSecurityPermissions.AspNetHostingPermissionLevelLow.Assert();

            while (de.MoveNext()) {
                string key = (string)de.Key;
                string value;

                if (key.Length == 0) {
                    value = userAgent;
                }
                else {
                    value = request.ServerVariables[key];
                }

                if (value != null) {
                    sb.Append(value);
                }    
            }

            CodeAccessPermission.RevertAssert();

            sb.Append(BrowserCapabilitiesFactoryBase.GetBrowserCapKey(BrowserCapFactory.InternalGetMatchedHeaders(), request));
            string fullCacheKey = sb.ToString();

            //
            // Only do full cache lookup if the optimistic cache 
            // result was _disableOptimisticCachingSingleton or 
            // if UserAgent wasn't in the cap var list.
            //
            if (userAgent == null || doFullCacheKeyLookup) {

                result = cacheInternal.Get(fullCacheKey) as HttpCapabilitiesBase;

                if (result != null)
                    return result;
            }

            result = EvaluateFinal(request, false);

            // Use the same browserCap result if one with the same matched nodes can be found in the cache.
            // This is to reduce the number of identical browserCap instances being cached.
            CacheBrowserCapResult(ref result);

             // cache it and respect _cachetime
            cacheInternal.Insert(fullCacheKey, result, new CacheInsertOptions() { SlidingExpiration = _cachetime });
            if(optimisticCacheKey != null) {
                cacheInternal.Insert(optimisticCacheKey, _disableOptimisticCachingSingleton, new CacheInsertOptions() { SlidingExpiration = _cachetime });
            }

            return result;
        }

        internal HttpCapabilitiesBase EvaluateFinal(HttpRequest request, bool onlyEvaluateUserAgent) {
            HttpBrowserCapabilities browserCaps = BrowserCapFactory.GetHttpBrowserCapabilities(request);
            CapabilitiesState state = new CapabilitiesState(request, browserCaps.Capabilities);
            if (onlyEvaluateUserAgent) {
                state.EvaluateOnlyUserAgent = true;
            }

            if(_rule != null) {
                string oldIsMobileDevice = browserCaps[_isMobileDeviceCapKey];
                browserCaps.Capabilities[_isMobileDeviceCapKey] = null;

                _rule.Evaluate(state);

                string newIsMobileDevice = browserCaps[_isMobileDeviceCapKey];
                if (newIsMobileDevice == null) {
                    browserCaps.Capabilities[_isMobileDeviceCapKey] = oldIsMobileDevice;
                }
                else if (newIsMobileDevice.Equals("true")) {
                    browserCaps.DisableOptimizedCacheKey();
                }
            }

            // create the new type
            // 
            HttpCapabilitiesBase result = (HttpCapabilitiesBase)HttpRuntime.CreateNonPublicInstance(_resultType);
            result.InitInternal(browserCaps);
            
            return result;
        }

    }
}