// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
 
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Runtime;
 
namespace System.ServiceModel.Channels
{
    internal static class HttpResponseMessageExtensionMethods
    {
        internal static HashSet<string> s_wellKnownContentHeaders = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
                { "Content-Disposition", "Content-Encoding", "Content-Language", "Content-Length", "Content-Location",
                  "Content-MD5", "Content-Range", "Content-Type", "Expires", "Last-Modified" };
 
        // It is possible to receive an HttpResponseMessage without Content set from HttpClient. We presume that we have an HttpContent
        // in many places so this ensures we have one and removes the need for special casing in many places.
        internal static bool CreateContentIfNull(this HttpResponseMessage httpResponseMessage)
        {
            Fx.Assert(httpResponseMessage != null, "The 'httpResponseMessage' parameter should never be null.");
 
            if (httpResponseMessage.Content == null)
            {
                httpResponseMessage.Content = new ByteArrayContent(Array.Empty<byte>());
                return true;
            }
 
            return false;
        }
 
        internal static void MergeWebHeaderCollection(this HttpResponseMessage responseMessage, WebHeaderCollection headersToMerge)
        {
            responseMessage.CreateContentIfNull();
            MergeWebHeaderCollectionWithHttpHeaders(headersToMerge, responseMessage.Headers, responseMessage.Content.Headers);
        }
 
        internal static WebHeaderCollection ToWebHeaderCollection(this HttpResponseMessage httpResponse)
        {
            IEnumerable<KeyValuePair<string, IEnumerable<string>>> headers = httpResponse.Headers;
            if (httpResponse.Content != null)
            {
                headers = headers.Concat(httpResponse.Content.Headers);
            }
            return headers.ToWebHeaderCollection();
        }
 
        internal static void MergeWebHeaderCollectionWithHttpHeaders(WebHeaderCollection headersToMerge, HttpHeaders mainHeaders, HttpHeaders contentHeaders)
        {
            foreach (string headerKey in headersToMerge.AllKeys)
            {
                if (s_wellKnownContentHeaders.Contains(headerKey))
                {
                    contentHeaders.TryAddWithoutValidation(headerKey, headersToMerge[headerKey]);
                }
                else
                {
                    mainHeaders.TryAddWithoutValidation(headerKey, headersToMerge[headerKey]);
                }
            }
        }
 
        internal static WebHeaderCollection ToWebHeaderCollection(this IEnumerable<KeyValuePair<string, IEnumerable<string>>> headers)
        {
            var webHeaders = new WebHeaderCollection();
            foreach (var header in headers)
            {
                webHeaders[header.Key] = String.Join(",", header.Value);
            }
            return webHeaders;
        }
    }
}