package ian.torrent;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

// http://wiki.theory.org/BitTorrentSpecification
public class Bdecode {
   private static Map<String, Object> convertToMap(final List<Object> list) {
      final Map<String, Object> m = new HashMap<String, Object>();
      final int length = list.size();
      for (int i = 0; i < length; i += 2) {
         final String key = (String) list.get(i);
         Object value = null;
         if (i + 1 < length) {
            value = list.get(i + 1);
         }
         m.put(key, value);
      }
      return m;
   }
   private static List<Object> readList(final byte ba[], final int pos[])
         throws Exception {
      final List<Object> list = new ArrayList<Object>();
      char ch = (char) ba[pos[0]];
      while (ch != 'e') {
         if ((ch >= '0') && (ch <= '9')) {
            int end = pos[0];
            ++end;
            while (ba[end] != ':') {
               ++end;
            }
            final int len = Integer.parseInt(new String(ba, pos[0], end
                  - pos[0]));
            final String str = new String(ba, end + 1, len);
            list.add(str);
            pos[0] = end + len;
         }
         else if (ch == 'l') {
            ++pos[0];
            list.add(readList(ba, pos));
         }
         else if (ch == 'd') {
            ++pos[0];
            list.add(convertToMap(readList(ba, pos)));
         }
         else if (ch == 'i') {
            ++pos[0];
            int end = pos[0];
            while (ba[end] != 'e') {
               ++end;
            }
            list.add(Long.parseLong(new String(ba, pos[0], end - pos[0])));
            pos[0] = end;
         }
         else {
            System.out.println("unrecognized " + ch);
            break;
         }
         ++pos[0];
         if (pos[0] < ba.length) {
            ch = (char) ba[pos[0]];
         }
         else {
            break;
         }
      }
      return list;
   }
   public static Map<String, Object> bdecode(final byte ba[]) throws Exception {
      return convertToMap(readList(ba, new int[] { 1 }));
   }
}