/************************************************************************
    * Copyright (c) 1999-2006 The Apache Software Foundation.             *
    * All rights reserved.                                                *
    * ------------------------------------------------------------------- *
    * Licensed under the Apache License, Version 2.0 (the "License"); you *
    * may not use this file except in compliance with the License. You    *
    * may obtain a copy of the License at:                                *
    *                                                                     *
    *     http://www.apache.org/licenses/LICENSE-2.0                      *
   *                                                                     *
   * Unless required by applicable law or agreed to in writing, software *
   * distributed under the License is distributed on an "AS IS" BASIS,   *
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or     *
   * implied.  See the License for the specific language governing       *
   * permissions and limitations under the License.                      *
   ***********************************************************************/
  
  package org.apache.james.util;
  
  import java.io.IOException;
  import java.io.InputStream;
  
  /***
   * An InputStream class that terminates the stream when it encounters a
   * particular byte sequence.
   *
   * @version 1.0.0, 24/04/1999
   */
  public class CharTerminatedInputStream
      extends InputStream {
  
      /***
       * The wrapped input stream
       */
      private InputStream in;
  
      /***
       * The terminating character array
       */
      private int match[];
  
      /***
       * An array containing the last N characters read from the stream, where
       * N is the length of the terminating character array
       */
      private int buffer[];
  
      /***
       * The number of bytes that have been read that have not been placed
       * in the internal buffer.
       */
      private int pos = 0;
  
      /***
       * Whether the terminating sequence has been read from the stream
       */
      private boolean endFound = false;
  
      /***
       * A constructor for this object that takes a stream to be wrapped
       * and a terminating character sequence.
       *
       * @param in the <code>InputStream</code> to be wrapped
       * @param terminator the array of characters that will terminate the stream.
       *
       * @throws IllegalArgumentException if the terminator array is null or empty
       */
      public CharTerminatedInputStream(InputStream in, char[] terminator) {
          if (terminator == null) {
              throw new IllegalArgumentException("The terminating character array cannot be null.");
          }
          if (terminator.length == 0) {
              throw new IllegalArgumentException("The terminating character array cannot be of zero length.");
          }
          match = new int[terminator.length];
          buffer = new int[terminator.length];
          for (int i = 0; i < terminator.length; i++) {
              match[i] = (int)terminator[i];
              buffer[i] = (int)terminator[i];
          }
          this.in = in;
      }
  
      /***
       * Read a byte off this stream.
       *
       * @return the byte read off the stream
       * @throws IOException if an IOException is encountered while reading off the stream
       * @throws ProtocolException if the underlying stream returns -1 before the terminator is seen.
       */
      public int read() throws IOException {
          if (endFound) {
              //We've found the match to the terminator
              return -1;
          }
          if (pos == 0) {
              //We have no data... read in a record
              int b = in.read();
              if (b == -1) {
                 //End of stream reached without seeing the terminator
                 throw new java.net.ProtocolException("pre-mature end of data");
             }
             if (b != match[0]) {
                 //this char is not the first char of the match
                 return b;
             }
             //this is a match...put this in the first byte of the buffer,
             // and fall through to matching logic
             buffer[0] = b;
             pos++;
         } else {
             if (buffer[0] != match[0]) {
                 //Maybe from a previous scan, there is existing data,
                 // and the first available char does not match the
                 // beginning of the terminating string.
                 return topChar();
             }
             //we have a match... fall through to matching logic.
         }
         //MATCHING LOGIC
 
         //The first character is a match... scan for complete match,
         // reading extra chars as needed, until complete match is found
         for (int i = 0; i < match.length; i++) {
             if (i >= pos) {
                 int b = in.read();
                 if (b == -1) {
                     //end of stream found, so match cannot be fulfilled.
                     // note we don't set endFound, because otherwise
                     // remaining part of buffer won't be returned.
                     return topChar();
                 }
                 //put the read char in the buffer
                 buffer[pos] = b;
                 pos++;
             }
             if (buffer[i] != match[i]) {
                 //we did not find a match... return the top char
                 return topChar();
             }
         }
         //A complete match was made...
         endFound = true;
         return -1;
     }
 
     /***
      * Private helper method to update the internal buffer of last read characters
      *
      * @return the byte that was previously at the front of the internal buffer
      */
     private int topChar() {
         int b = buffer[0];
         if (pos > 1) {
             //copy down the buffer to keep the fresh data at top
             System.arraycopy(buffer, 1, buffer, 0, pos - 1);
         }
         pos--;
         return b;
     }
 }