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

namespace System.Web.UI {
    using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Reflection;
using System.Web.Configuration;
using System.Web.Script;

    // Caches Assembly APIs to improve performance
    internal static class AssemblyCache {
        // PERF: Cache reference to System.Web.Extensions assembly. Use ScriptManager since it's guaranteed to be in S.W.E
        public static readonly Assembly SystemWebExtensions = typeof(ScriptManager).Assembly;
        public static readonly Assembly SystemWeb = typeof(Page).Assembly;

        private static CompilationSection _compilationSection;
        internal static bool _useCompilationSection = true;

        // Maps string (assembly name) to Assembly
        private static readonly Hashtable _assemblyCache = Hashtable.Synchronized(new Hashtable());
        // Maps assembly to Version
        // internal so it can be manipulated by the unit test suite
        internal static readonly Hashtable _versionCache = Hashtable.Synchronized(new Hashtable());
        // Maps an assembly to its ajax framework assembly attribute. If it doesn't have one, it maps it to a null value
        private static readonly ConcurrentDictionary<Assembly, AjaxFrameworkAssemblyAttribute> _ajaxAssemblyAttributeCache =
            new ConcurrentDictionary<Assembly, AjaxFrameworkAssemblyAttribute>();

        private static CompilationSection CompilationSection {
            get {
                if (_compilationSection == null) {
                    _compilationSection = RuntimeConfig.GetAppConfig().Compilation;
                }
                return _compilationSection;
            }
        }

        public static Version GetVersion(Assembly assembly) {
            Debug.Assert(assembly != null);
            Version version = (Version)_versionCache[assembly];
            if (version == null) {
                // use new AssemblyName() instead of assembly.GetName() so it works in medium trust
                version = new AssemblyName(assembly.FullName).Version;
                _versionCache[assembly] = version;
            }
            return version;
        }

        public static Assembly Load(string assemblyName) {
            Debug.Assert(!String.IsNullOrEmpty(assemblyName));
            Assembly assembly = (Assembly)_assemblyCache[assemblyName];
            if (assembly == null) {
                // _useCompilationSection must be set to false in a unit test environment since there
                // is no http runtime, and therefore no trust level is set.
                if (_useCompilationSection) {
                    assembly = CompilationSection.LoadAssembly(assemblyName, true);
                }
                else {
                    assembly = Assembly.Load(assemblyName);
                }
                _assemblyCache[assemblyName] = assembly;
            }
            return assembly;
        }

        public static bool IsAjaxFrameworkAssembly(Assembly assembly) {
            return (GetAjaxFrameworkAssemblyAttribute(assembly) != null);
        }

        public static AjaxFrameworkAssemblyAttribute GetAjaxFrameworkAssemblyAttribute(Assembly assembly) {
            Debug.Assert(assembly != null);
            AjaxFrameworkAssemblyAttribute ajaxFrameworkAssemblyAttribute;
            if (!_ajaxAssemblyAttributeCache.TryGetValue(assembly, out ajaxFrameworkAssemblyAttribute)) {
                 ajaxFrameworkAssemblyAttribute = SafeGetAjaxFrameworkAssemblyAttribute(assembly);
                _ajaxAssemblyAttributeCache.TryAdd(assembly, ajaxFrameworkAssemblyAttribute);
            }
            return ajaxFrameworkAssemblyAttribute;
        }

        [SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes", Justification = "We do not want to throw from this method.")]
        internal static AjaxFrameworkAssemblyAttribute SafeGetAjaxFrameworkAssemblyAttribute(ICustomAttributeProvider attributeProvider) {
            try {
                foreach (Attribute attribute in attributeProvider.GetCustomAttributes(inherit: false)) {
                    AjaxFrameworkAssemblyAttribute ajaxFrameworkAttribute = attribute as AjaxFrameworkAssemblyAttribute;
                    if (ajaxFrameworkAttribute != null) {
                        return ajaxFrameworkAttribute;
                    }
                }
            }
            catch {
                // Bug 34311: If we are unable to load the attribute, don't throw. 
            }
            return null;
        }
    }
}