/* ======================================================================
   Parts Copyright 2006 University of Leeds, Oxford University, University of the Highlands and Islands.

   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.bodington.servlet.template;

/**
 * This interface describes a character stream that maintains line and
 * column number positions of the characters.  It also has the capability
 * to backup the stream to some extent.  An implementation of this
 * interface is used in the TokenManager implementation generated by
 * JavaCCParser.
 *
 * All the methods except backup can be implemented in any fashion. backup
 * needs to be implemented correctly for the correct operation of the lexer.
 * Rest of the methods are all used to get information like line number,
 * column number and the String that constitutes a token and are not used
 * by the lexer. Hence their implementation won't affect the generated lexer's
 * operation.
 */

abstract public interface CharStream {

  /**
   * Returns the next character from the selected input.  The method
   * of selecting the input is the responsibility of the class
   * implementing this interface.  Can throw any java.io.IOException.
   */
  abstract public char readChar() throws java.io.IOException;

  /**
   * Returns the column position of the character last read.
   * @deprecated 
   * @see #getEndColumn
   */
  abstract public int getColumn();

  /**
   * Returns the line number of the character last read.
   * @deprecated 
   * @see #getEndLine
   */
  abstract public int getLine();

  /**
   * Returns the column number of the last character for current token (being
   * matched after the last call to BeginTOken).
   */
  abstract public int getEndColumn();

  /**
   * Returns the line number of the last character for current token (being
   * matched after the last call to BeginTOken).
   */
  abstract public int getEndLine();

  /**
   * Returns the column number of the first character for current token (being
   * matched after the last call to BeginTOken).
   */
  abstract public int getBeginColumn();

  /**
   * Returns the line number of the first character for current token (being
   * matched after the last call to BeginTOken).
   */
  abstract public int getBeginLine();

  /**
   * Backs up the input stream by amount steps. Lexer calls this method if it
   * had already read some characters, but could not use them to match a
   * (longer) token. So, they will be used again as the prefix of the next
   * token and it is the implemetation's responsibility to do this right.
   */
  abstract public void backup(int amount);

  /**
   * Returns the next character that marks the beginning of the next token.
   * All characters must remain in the buffer between two successive calls
   * to this method to implement backup correctly.
   */
  abstract public char BeginToken() throws java.io.IOException;

  /**
   * Returns a string made up of characters from the marked token beginning 
   * to the current buffer position. Implementations have the choice of returning
   * anything that they want to. For example, for efficiency, one might decide
   * to just return null, which is a valid implementation.
   */
  abstract public String GetImage();

  /**
   * Returns an array of characters that make up the suffix of length 'len' for
   * the currently matched token. This is used to build up the matched string
   * for use in actions in the case of MORE. A simple and inefficient
   * implementation of this is as follows :
   *
   *   {
   *      String t = GetImage();
   *      return t.substring(t.length() - len, t.length()).toCharArray();
   *   }
   */
  abstract public char[] GetSuffix(int len);

  /**
   * The lexer calls this function to indicate that it is done with the stream
   * and hence implementations can free any resources held by this class.
   * Again, the body of this function can be just empty and it will not
   * affect the lexer's operation.
   */
  abstract public void Done();

}
