/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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.commons.net.io;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PushbackInputStream;
  
  /***
   * This class wraps an input stream, replacing all occurrences
   * of <CR><LF> (carriage return followed by a linefeed),
   * which is the NETASCII standard for representing a newline, with the
   * local line separator representation.  You would use this class to
   * implement ASCII file transfers requiring conversion from NETASCII.
   * <p>
   * <p>
   ***/
  
  public final class FromNetASCIIInputStream extends PushbackInputStream
  {
      static final boolean _noConversionRequired;
      static final String _lineSeparator;
      static final byte[] _lineSeparatorBytes;
  
      static {
          _lineSeparator = System.getProperty("line.separator");
          _noConversionRequired = _lineSeparator.equals("\r\n");
          _lineSeparatorBytes = _lineSeparator.getBytes();
      }
  
      private int __length = 0;
  
      /***
       * Returns true if the NetASCII line separator differs from the system
       * line separator, false if they are the same.  This method is useful
       * to determine whether or not you need to instantiate a
       * FromNetASCIIInputStream object.
       * <p>
       * @return True if the NETASCII line separator differs from the local
       *   system line separator, false if they are the same.
       ***/
      public static final boolean isConversionRequired()
      {
          return !_noConversionRequired;
      }
  
      /***
       * Creates a FromNetASCIIInputStream instance that wraps an existing
       * InputStream.
       ***/
      public FromNetASCIIInputStream(InputStream input)
      {
          super(input, _lineSeparatorBytes.length + 1);
      }
  
  
      private int __read() throws IOException
      {
          int ch;
  
          ch = super.read();
  
          if (ch == '\r')
          {
              ch = super.read();
              if (ch == '\n')
              {
                  unread(_lineSeparatorBytes);
                  ch = super.read();
                  // This is a kluge for read(byte[], ...) to read the right amount
                  --__length;
              }
              else
              {
                  if (ch != -1) {
                      unread(ch);
                  }
                  return '\r';
              }
          }
  
          return ch;
      }
  
 
     /***
      * Reads and returns the next byte in the stream.  If the end of the
      * message has been reached, returns -1.  Note that a call to this method
      * may result in multiple reads from the underlying input stream in order
      * to convert NETASCII line separators to the local line separator format.
      * This is transparent to the programmer and is only mentioned for
      * completeness.
      * <p>
      * @return The next character in the stream. Returns -1 if the end of the
      *          stream has been reached.
      * @exception IOException If an error occurs while reading the underlying
      *            stream.
      ***/
     @Override
     public int read() throws IOException
     {
         if (_noConversionRequired) {
             return super.read();
         }
 
         return __read();
     }
 
 
     /***
      * Reads the next number of bytes from the stream into an array and
      * returns the number of bytes read.  Returns -1 if the end of the
      * stream has been reached.
      * <p>
      * @param buffer  The byte array in which to store the data.
      * @return The number of bytes read. Returns -1 if the
      *          end of the message has been reached.
      * @exception IOException If an error occurs in reading the underlying
      *            stream.
      ***/
     @Override
     public int read(byte buffer[]) throws IOException
     {
         return read(buffer, 0, buffer.length);
     }
 
 
     /***
      * Reads the next number of bytes from the stream into an array and returns
      * the number of bytes read.  Returns -1 if the end of the
      * message has been reached.  The characters are stored in the array
      * starting from the given offset and up to the length specified.
      * <p>
      * @param buffer The byte array in which to store the data.
      * @param offset  The offset into the array at which to start storing data.
      * @param length   The number of bytes to read.
      * @return The number of bytes read. Returns -1 if the
      *          end of the stream has been reached.
      * @exception IOException If an error occurs while reading the underlying
      *            stream.
      ***/
     @Override
     public int read(byte buffer[], int offset, int length) throws IOException
     {
         if (_noConversionRequired) {
             return super.read(buffer, offset, length);
         }
 
         if (length < 1) {
             return 0;
         }
 
         int ch, off;
 
         ch = available();
 
         __length = (length > ch ? ch : length);
 
         // If nothing is available, block to read only one character
         if (__length < 1) {
             __length = 1;
         }
 
 
         if ((ch = __read()) == -1) {
             return -1;
         }
 
         off = offset;
 
         do
         {
             buffer[offset++] = (byte)ch;
         }
         while (--__length > 0 && (ch = __read()) != -1);
 
 
         return (offset - off);
     }
 
 
     // PushbackInputStream in JDK 1.1.3 returns the wrong thing
     // TODO - can we delete this override now?
     /***
      * Returns the number of bytes that can be read without blocking EXCEPT
      * when newline conversions have to be made somewhere within the
      * available block of bytes.  In other words, you really should not
      * rely on the value returned by this method if you are trying to avoid
      * blocking.
      ***/
     @Override
     public int available() throws IOException
     {
         if (in == null) {
             throw new IOException("Stream closed");
         }
         return (buf.length - pos) + in.available();
     }
 
 }