Implementation of interface CharStream from Antlr4 to be integrated into the Netbeans IDE

AntlrCharStream.java

/**
 * AntlrCharStream
 * 
 * Code based on Daniel's implementation of Antlr4 CharStream interface found on
 * http://stackoverflow.com/questions/16152666/netbeans-platform-language-and-antlr-lexer 
 * 
 * I've modified the proposed implementation to deal with the tracking of index position in a different way and to
 * implement the function getText
 */
package org.antlr;

import org.antlr.v4.runtime.CharStream;
import org.antlr.v4.runtime.misc.Interval;
import org.netbeans.spi.lexer.LexerInput;

public class AntlrCharStream implements CharStream {

  private final LexerInput input;
  private final String name;
  private int index = 0;
  private int markDepth = 0;

  public AntlrCharStream(LexerInput input, String name) {
    this.input = input;
    this.name = name;
  }

  @Override
  public String getText(Interval interval) {
    int start = interval.a;
    int stop = interval.b;
    
    if (start < 0 || stop < start) {
      return "";
    }

    final int pos = this.index;
    final int length = interval.length();
    final char[] data = new char[length];

    seek(interval.a);
    int r = 0;
    while (r < length) {
      final int character = read();
      if (character == EOF) {
        break;
      }

      data[r] = (char) character;
      r++;
    }
    seek(pos);

    if (r > 0) {
      return new String(data, 0, r);
    } else {
      return "";
    }
  }

  @Override
  public void consume() {
    int character = read();
    if (character == EOF) {
      backup(1);
      throw new IllegalStateException("Attempting to consume EOF");
    }
  }

  @Override
  public int LA(int lookaheadAmount) {
    if (lookaheadAmount < 0) {
      return lookBack(-lookaheadAmount);
    } else if (lookaheadAmount > 0) {
      return lookAhead(lookaheadAmount);
    } else {
      return 0; //Behaviour is undefined when lookaheadAmount == 0
    }
  }

  private int lookBack(int amount) {
    backup(amount);
    int character = read();
    for (int i = 1; i < amount; i++) {
      read();
    }
    return character;
  }

  private int lookAhead(int amount) {
    int character = 0;
    for (int i = 0; i < amount; i++) {
      character = read();
    }
    backup(amount);
    return character;
  }

  @Override
  public int mark() {
    return ++markDepth;
  }

  @Override
  public void release(int marker) {
    // unwind any other markers made after m and release m
    markDepth = marker;
    // release this marker
    markDepth--;
  }

  @Override
  public void seek(int index) {
    if (index < 0) {
      throw new IllegalArgumentException(String.format("Invalid index (%s < 0)", index));
    }

    if (index < this.index) {
      backup(this.index - index);
      return;
    }

    // seek forward, consume until p hits index
    while (this.index < index) {
      consume();
    }
  }

  @Override
  public int index() {
    return index;
  }

  @Override
  public int size() {
    return -1; //unknown...
  }

  @Override
  public String getSourceName() {
    return name;
  }

  private int read() {
    int result = input.read();
    index++;
    
    if (result == LexerInput.EOF) {
      return EOF;
    } else {
      return result;
    }
  }

  private void backup(int count) {
    input.backup(count);
    index -= count;
  }
}