Calcium: A modular application toolset leveraging PRISM – Part 1

//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation.  All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious.  No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
using System.Security.Permissions;
using System.Security.Policy;
using System.Threading;
using Microsoft.Practices.Composite.Properties;

namespace Microsoft.Practices.Composite.Modularity
{
    /// <summary>
    /// Represets a catalog created from a directory on disk.
    /// </summary>
    /// <remarks>
    /// The directory catalog will scan the contents of a directory, locating classes that implement
    /// <see cref="IModule"/> and add them to the catalog based on contents in their associated <see cref="ModuleAttribute"/>.
    /// Assemblies are loaded into a new application domain with ReflectionOnlyLoad.  The application domain is destroyed
    /// once the assemblies have been discovered.
    /// 
    /// The diretory catalog does not continue to monitor the directory after it has created the initialze catalog.
    /// </remarks>
    [SecurityPermission(SecurityAction.LinkDemand)]
    [SecurityPermission(SecurityAction.InheritanceDemand)]
    public class DirectoryModuleCatalog : ModuleCatalog
    {
        /// <summary>
        /// Directory containing modules to search for.
        /// </summary>
        public string ModulePath { get; set; }

        /// <summary>
        /// Drives the main logic of building the child domain and searching for the assemblies.
        /// </summary>
        protected override void InnerLoad()
        {
            if (string.IsNullOrEmpty(this.ModulePath))
                throw new InvalidOperationException(Resources.ModulePathCannotBeNullOrEmpty);

            if (!Directory.Exists(this.ModulePath))
                throw new InvalidOperationException(
                    string.Format(CultureInfo.CurrentCulture, Resources.DirectoryNotFound, this.ModulePath));

            AppDomain childDomain = this.BuildChildDomain(AppDomain.CurrentDomain);

            try
            {
                List<string> loadedAssemblies = new List<string>();

                var assemblies = (
                                     from Assembly assembly in AppDomain.CurrentDomain.GetAssemblies()
                                     where !(assembly is System.Reflection.Emit.AssemblyBuilder)
                                           && !String.IsNullOrEmpty(assembly.Location)
                                     select assembly.Location
                                 );

                loadedAssemblies.AddRange(assemblies);

                Type loaderType = typeof (InnerModuleInfoLoader);

                if (loaderType.Assembly != null)
                {
                    var loader =
                        (InnerModuleInfoLoader)
                        childDomain.CreateInstanceFrom(loaderType.Assembly.Location, loaderType.FullName).Unwrap();
                    loader.LoadAssemblies(loadedAssemblies);
                    this.Items.AddRange(loader.GetModuleInfos(this.ModulePath));
                }
            }
            finally
            {
                AppDomain.Unload(childDomain);
            }
        }


        /// <summary>
        /// Creates a new child domain and copies the evidence from a parent domain.
        /// </summary>
        /// <param name="parentDomain">The parent domain.</param>
        /// <returns>The new child domain.</returns>
        /// <remarks>
        /// Grabs the <paramref name="parentDomain"/> evidence and uses it to construct the new
        /// <see cref="AppDomain"/> because in a ClickOnce execution environment, creating an
        /// <see cref="AppDomain"/> will by default pick up the partial trust environment of 
        /// the AppLaunch.exe, which was the root executable. The AppLaunch.exe does a 
        /// create domain and applies the evidence from the ClickOnce manifests to 
        /// create the domain that the application is actually executing in. This will 
        /// need to be Full Trust for Composite Application Library applications.
        /// </remarks>
        protected virtual AppDomain BuildChildDomain(AppDomain parentDomain)
        {
            Evidence evidence = new Evidence(parentDomain.Evidence);
            AppDomainSetup setup = parentDomain.SetupInformation;
            return AppDomain.CreateDomain("DiscoveryRegion", evidence, setup);
        }

        private class InnerModuleInfoLoader : MarshalByRefObject
        {
            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic")]
            internal ModuleInfo[] GetModuleInfos(string path)
            {
                DirectoryInfo directory = new DirectoryInfo(path);

                ResolveEventHandler resolveEventHandler =
                    delegate(object sender, ResolveEventArgs args) { return OnReflectionOnlyResolve(args, directory); };

                AppDomain.CurrentDomain.ReflectionOnlyAssemblyResolve += resolveEventHandler;

                Assembly moduleReflectionOnlyAssembly =
                    AppDomain.CurrentDomain.ReflectionOnlyGetAssemblies().First(
                        asm => asm.FullName == typeof (IModule).Assembly.FullName);
                Type IModuleType = moduleReflectionOnlyAssembly.GetType(typeof (IModule).FullName);

                IEnumerable<ModuleInfo> modules = GetNotAllreadyLoadedModuleInfos(directory, IModuleType);

                var array = modules.ToArray();
                AppDomain.CurrentDomain.ReflectionOnlyAssemblyResolve -= resolveEventHandler;
                return array;
            }

            private IEnumerable<ModuleInfo> GetNotAllreadyLoadedModuleInfos(DirectoryInfo directory, Type IModuleType)
            {
                Assembly[] alreadyLoadedAssemblies = AppDomain.CurrentDomain.ReflectionOnlyGetAssemblies();
                return directory.GetFiles("*.dll")
                    .Where(file => alreadyLoadedAssemblies
                                       .FirstOrDefault(
                                       assembly =>
                                       String.Compare(Path.GetFileName(assembly.Location), file.Name,
                                                      StringComparison.OrdinalIgnoreCase) == 0) == null)
                    .SelectMany(file => Assembly.ReflectionOnlyLoadFrom(file.FullName)
                                            .GetExportedTypes()
                                            .Where(IModuleType.IsAssignableFrom)
                                            .Where(t => t != IModuleType)
                                            .Where(t => !t.IsAbstract)
                                            .Select(type => CreateModuleInfo(type)));
            }

            private Assembly OnReflectionOnlyResolve(ResolveEventArgs args, DirectoryInfo directory)
            {
                Assembly loadedAssembly = AppDomain.CurrentDomain.ReflectionOnlyGetAssemblies().FirstOrDefault(
                    asm => string.Equals(asm.FullName, args.Name, StringComparison.OrdinalIgnoreCase));
                if (loadedAssembly != null)
                {
                    return loadedAssembly;
                }
                AssemblyName assemblyName = new AssemblyName(args.Name);
                string dependentAssemblyFilename = Path.Combine(directory.FullName, assemblyName.Name + ".dll");
                if (File.Exists(dependentAssemblyFilename))
                {
                    return Assembly.ReflectionOnlyLoadFrom(dependentAssemblyFilename);
                }
                return Assembly.ReflectionOnlyLoad(args.Name);
            }

            [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic")]
            internal void LoadAssemblies(IEnumerable<string> assemblies)
            {
                foreach (string assemblyPath in assemblies)
                {
                    try
                    {
                        Assembly.ReflectionOnlyLoadFrom(assemblyPath);
                    }
                    catch (FileNotFoundException)
                    {
                        // Continue loading assemblies even if an assembly can not be loaded in the new AppDomain
                    }
                }
            }

            private static ModuleInfo CreateModuleInfo(Type type)
            {
                string moduleName = type.Name;
                List<string> dependsOn = new List<string>();
                bool onDemand = false;
                var moduleAttribute =
                    CustomAttributeData.GetCustomAttributes(type).FirstOrDefault(
                        cad => cad.Constructor.DeclaringType.FullName == typeof (ModuleAttribute).FullName);

                if (moduleAttribute != null)
                {
                    foreach (CustomAttributeNamedArgument argument in moduleAttribute.NamedArguments)
                    {
                        string argumentName = argument.MemberInfo.Name;
                        switch (argumentName)
                        {
                            case "ModuleName":
                                moduleName = (string) argument.TypedValue.Value;
                                break;

                            case "OnDemand":
                                onDemand = (bool) argument.TypedValue.Value;
                                break;

                            case "StartupLoaded":
                                onDemand = !((bool) argument.TypedValue.Value);
                                break;
                        }                           
                    }
                }

                var moduleDependencyAttributes =
                    CustomAttributeData.GetCustomAttributes(type).Where(
                        cad => cad.Constructor.DeclaringType.FullName == typeof (ModuleDependencyAttribute).FullName);

                foreach (CustomAttributeData cad in moduleDependencyAttributes)
                {
                    dependsOn.Add((string) cad.ConstructorArguments[0].Value);
                }

                ModuleInfo moduleInfo = new ModuleInfo(moduleName, type.AssemblyQualifiedName)
                                            {
                                                InitializationMode =
                                                    onDemand
                                                        ? InitializationMode.OnDemand
                                                        : InitializationMode.WhenAvailable,
                                                Ref = type.Assembly.CodeBase,
                                            };
                moduleInfo.DependsOn.AddRange(dependsOn);
                return moduleInfo;
            }
        }
    }
}