using System;
using System.IO;
using System.Net;

namespace CrawlerPDN
{
    class Core
    {
        class Cat
        {
            public String Name;
            public String url;
        }

        public void Go(String url)
        {
            String contents = Download(url);


            int indexCat = contents.LastIndexOf("<LI type=square>");

            Cat cat = new Cat();
            int indexUrlStart = contents.LastIndexOf("A href=\"", indexCat) + 1;
            int indexUrlLength = contents.IndexOf("\">") - indexUrlStart;
            int indexNameStart = contents.LastIndexOf("\">", indexUrlStart) + 1;
            int NameLength = contents.IndexOf("</A>") - indexNameStart;
            cat.url = contents.Substring(indexUrlStart, indexUrlLength);
            cat.Name = contents.Substring(indexNameStart, NameLength);
        }

        private static string Download(string url)
        {
            string r = null;
            StreamReader strResponse = null;
            HttpWebResponse webResponse = null;
            try
            {
                var webRequest = (HttpWebRequest)WebRequest.Create(url);
                webResponse = (HttpWebResponse)webRequest.GetResponse();
                strResponse = new StreamReader(webResponse.GetResponseStream());

                r = strResponse.ReadToEnd();
            }
            finally
            {
                if (strResponse != null) strResponse.Close();
                if (webResponse != null) webResponse.Close();
            }
            return r;
        }
    }
}