using System;
using System.Collections.Generic;
using System.Net;
using System.Threading.Tasks;
using System.Web;

namespace Sony.Filtr.API
{
    public class ProxyAsyncHandler : HttpTaskAsyncHandler
    {
        public override async Task ProcessRequestAsync(HttpContext context)
        {
            string url = context.Request.QueryString["url"];
            if (string.IsNullOrWhiteSpace(url))
            {
                context.Response.StatusCode = (int) HttpStatusCode.NotFound;
                return;
            }
                

            var uri = new Uri(url);
            if (uri.Host != "userserve-ak.last.fm" && uri.Host != "img2-ak.lst.fm")
                throw new Exception("Proxy only enabled for http://userserve-ak.last.fm or http://img2-ak.lst.fm");

            var webRequest = (HttpWebRequest)WebRequest.Create(url);
            webRequest.UserAgent = context.Request.UserAgent;
            webRequest.AllowAutoRedirect = true;
            if (context.Request.AcceptTypes != null) 
                webRequest.Accept = context.Request.AcceptTypes.ToString();

            DateTime ifModifiedSince;
            if (DateTime.TryParse(context.Request.Headers["If-Modified-Since"], out ifModifiedSince))
                webRequest.IfModifiedSince = ifModifiedSince;

            foreach (string headerKey in context.Request.Headers)
            {
                if (!_restrictedHeaders.Contains(headerKey.ToLowerInvariant()))
                    webRequest.Headers[headerKey] = context.Request.Headers[headerKey];
            }

            webRequest.ContentType = context.Request.ContentType;
            webRequest.Method = context.Request.HttpMethod;

            HttpWebResponse webResponse;
            try
            {
                webResponse = await webRequest.GetResponseAsync() as HttpWebResponse;
                if (webResponse != null)
                { 
                    var responseStream = webResponse.GetResponseStream();
                    if (responseStream != null)
                        await responseStream.CopyToAsync(context.Response.OutputStream);
                }
            }
            catch (WebException ex)
            {
                webResponse = ex.Response as HttpWebResponse;
                if (webResponse == null || ex.Status != WebExceptionStatus.ProtocolError)
                    throw;
            }

            if (webResponse != null)
            {
                context.Response.ContentType = webResponse.ContentType;
                context.Response.StatusCode = (int)webResponse.StatusCode;
                context.Response.StatusDescription = webResponse.StatusDescription;
                foreach (string responseHeader in webResponse.Headers)
                {
                    context.Response.Headers[responseHeader] = webResponse.Headers[responseHeader];
                }
                
            }
        }

        private readonly List<string> _restrictedHeaders = new List<string>()
        {
            "accept",
            "connection",
            "content-length",
            "Content-type",
            "date",
            "expect",
            "host",
            "if-modified-since",
            "range",
            "referer",
            "transfer-encoding",
            "user-agent",
            "proxy-connection",
        };

    }
}