using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
using System.ComponentModel.Composition.ReflectionModel;
using System.Linq;

publicclass LoadCatalog : IResult
{
    staticreadonly Dictionary<string, DeploymentCatalog> Catalogs = new Dictionary<string, DeploymentCatalog>();
    readonlystring uri;

    [Import]
    public AggregateCatalog Catalog { get; set; }

    public LoadCatalog(string relativeUri)
    {
        uri = relativeUri;
    }

    publicvoid Execute(ActionExecutionContext context)
    {
        DeploymentCatalog catalog;

        if(Catalogs.TryGetValue(uri, out catalog))
            Completed(this, new ResultCompletionEventArgs());
        else
        {
            catalog = new DeploymentCatalog(uri);
            catalog.DownloadCompleted += (s, e) =>{
                if(e.Error == null)
                {
                    Catalogs[uri] = catalog;
                    Catalog.Catalogs.Add(catalog);
                    catalog.Parts
                        .Select(part => ReflectionModelServices.GetPartType(part).Value.Assembly)
                        .Where(assembly => !AssemblySource.Instance.Contains(assembly))
                        .Apply(x => AssemblySource.Instance.Add(x));
                }

                Completed(this, new ResultCompletionEventArgs {
                    Error = e.Error,
                    WasCancelled = false
                });
            };

            catalog.DownloadAsync();
        }
    }

    publicevent EventHandler<ResultCompletionEventArgs> Completed = delegate { };
}

public IEnumerable<IResult> LoadCatalogs()
{
    yieldreturnnew LoadCatalog("TestCatalog1.xap");
    yieldreturnnew LoadCatalog("TestCatalog2.xap");
    yieldreturnnew LoadCatalog("TestCatalog3.xap");
    yieldreturnnew LoadCatalog("TestCatalog4.xap");
}