// FastCharStream.java
package org.apache.commons.jrcs.rcs;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * 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.
 */

import java.io.*;

/** An efficient implementation of JavaCC's CharStream interface.  <p>Note that
 * this does not do line-number counting, but instead keeps track of the
 * character position of the token in the input, as required by Lucene's {@link
 * org.apache.lucene.analysis.Token} API. */
public final class FastCharStream implements CharStream {
  byte[] buffer = null;

  int bufferLength = 0;				  // end of valid chars
  int bufferPosition = 0;			  // next char to read
  
  int tokenStart = 0;				  // offset in buffer
  int bufferStart = 0;				  // position in file of buffer

  InputStream input;					  // source of chars

  /** Constructs from a Reader. */
  public FastCharStream(InputStream in) {
    input = in;
  }

  public final char readChar() throws IOException {
    if (bufferPosition >= bufferLength)
      refill();
    return (char) buffer[bufferPosition++];
  }

  private final void refill() throws IOException {
    int newPosition = bufferLength - tokenStart;

    if (tokenStart == 0) {			  // token won't fit in buffer
      if (buffer == null) {			  // first time: alloc buffer
	buffer = new byte[2048];		  
      } else if (bufferLength == buffer.length) { // grow buffer
	byte[] newBuffer = new byte[buffer.length*2];
	System.arraycopy(buffer, 0, newBuffer, 0, bufferLength);
	buffer = newBuffer;
      }
    } else {					  // shift token to front
      System.arraycopy(buffer, tokenStart, buffer, 0, newPosition);
    }

    bufferLength = newPosition;			  // update state
    bufferPosition = newPosition;
    bufferStart += tokenStart;
    tokenStart = 0;

    int charsRead =				  // fill space in buffer
      input.read(buffer, newPosition, buffer.length-newPosition);
    if (charsRead == -1)
      throw new IOException("read past eof");
    else
      bufferLength += charsRead;
  }

  public final char BeginToken() throws IOException {
    tokenStart = bufferPosition;
    return readChar();
  }

  public final void backup(int amount) {
    bufferPosition -= amount;
  }

  public final String GetImage() {
  	int len = bufferPosition - tokenStart;
  	StringBuilder sb = new StringBuilder(len);
	for(int i = 0; i < len ; i++) {
		sb.append((char) buffer[tokenStart + i]);
	}
  	return sb.toString();
  }

  public final char[] GetSuffix(int len) {
    char[] value = new char[len];
    System.arraycopy(buffer, bufferPosition - len, value, 0, len);
    return value;
  }

  public final void Done() {
    try {
      input.close();
    } catch (IOException e) {
      System.err.println("Caught: " + e + "; ignoring.");
    }
  }

  public final int getEndColumn() {
    return bufferStart + bufferPosition;
  }
  public final int getEndLine() {
    return 1;
  }
  public final int getBeginColumn() {
    return bufferStart + tokenStart;
  }
  public final int getBeginLine() {
    return 1;
  }
}