//------------------------------------------------------------------------------
// <copyright file="XmlUrlResolver.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
// <owner current="true" primary="true">[....]</owner>
//------------------------------------------------------------------------------

using System.Threading;
using System.Security.Permissions;
using System.Net;
using System.Net.Cache;
using System.Runtime.Versioning;

namespace System.Xml {

    // Resolves external XML resources named by a Uniform Resource Identifier (URI).
    public partial class XmlUrlResolver : XmlResolver {
        private static object s_DownloadManager;
        private ICredentials _credentials;
        private IWebProxy _proxy;
        private RequestCachePolicy _cachePolicy;

        static XmlDownloadManager DownloadManager {
            get {
                if ( s_DownloadManager == null ) {
                    object dm = new XmlDownloadManager();
                    Interlocked.CompareExchange<object>( ref s_DownloadManager, dm, null );
                }
                return (XmlDownloadManager)s_DownloadManager;
            }
        }

        // Construction

        // Creates a new instance of the XmlUrlResolver class.
        public XmlUrlResolver() {
        }

        public override ICredentials Credentials {
            set { _credentials = value; }
        }

        public IWebProxy Proxy {
            set { _proxy = value; }
        }

        public RequestCachePolicy CachePolicy {
            set { _cachePolicy = value; }
        }

        // Resource resolution

        // Maps a URI to an Object containing the actual resource.
        [ResourceConsumption(ResourceScope.Machine)]
        [ResourceExposure(ResourceScope.Machine)]
        public override Object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn) {
            if (ofObjectToReturn == null || ofObjectToReturn == typeof(System.IO.Stream) || ofObjectToReturn == typeof(System.Object)) {
                return DownloadManager.GetStream(absoluteUri, _credentials, _proxy, _cachePolicy);
            }
            else {
                throw new XmlException(Res.Xml_UnsupportedClass, string.Empty);
            }
        }

        [PermissionSetAttribute(SecurityAction.InheritanceDemand, Name = "FullTrust")]
        [ResourceConsumption(ResourceScope.Machine)]
        [ResourceExposure(ResourceScope.Machine)]
        public override Uri ResolveUri(Uri baseUri, string relativeUri){
            return base.ResolveUri(baseUri, relativeUri);
        }
    }
}