/*
 * Copyright (c) 2011, the Dart project authors.
 * 
 * Licensed under the Eclipse Public License v1.0 (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.eclipse.org/legal/epl-v10.html
 * 
 * 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 com.google.dart.tools.ui.internal.text.functions;

import org.eclipse.core.runtime.Assert;

import java.text.CharacterIterator;

/**
 * A <code>CharSequence</code> based implementation of <code>CharacterIterator</code>.
 */
public class SequenceCharacterIterator implements CharacterIterator {

  private int fIndex = -1;
  private final CharSequence fSequence;
  private final int fFirst;
  private final int fLast;

  /**
   * Creates an iterator for the entire sequence.
   * 
   * @param sequence the sequence backing this iterator
   */
  public SequenceCharacterIterator(CharSequence sequence) {
    this(sequence, 0);
  }

  /**
   * Creates an iterator.
   * 
   * @param sequence the sequence backing this iterator
   * @param first the first character to consider
   * @throws IllegalArgumentException if the indices are out of bounds
   */
  public SequenceCharacterIterator(CharSequence sequence, int first)
      throws IllegalArgumentException {
    this(sequence, first, sequence.length());
  }

  /**
   * Creates an iterator.
   * 
   * @param sequence the sequence backing this iterator
   * @param first the first character to consider
   * @param last the last character index to consider
   * @throws IllegalArgumentException if the indices are out of bounds
   */
  public SequenceCharacterIterator(CharSequence sequence, int first, int last)
      throws IllegalArgumentException {
    if (sequence == null) {
      throw new NullPointerException();
    }
    if (first < 0 || first > last) {
      throw new IllegalArgumentException();
    }
    if (last > sequence.length()) {
      throw new IllegalArgumentException();
    }
    fSequence = sequence;
    fFirst = first;
    fLast = last;
    fIndex = first;
    invariant();
  }

  /*
   * @see java.text.CharacterIterator#clone()
   */
  @Override
  public Object clone() {
    try {
      return super.clone();
    } catch (CloneNotSupportedException e) {
      throw new InternalError();
    }
  }

  /*
   * @see java.text.CharacterIterator#current()
   */
  @Override
  public char current() {
    if (fIndex >= fFirst && fIndex < fLast) {
      return fSequence.charAt(fIndex);
    } else {
      return DONE;
    }
  }

  /*
   * @see java.text.CharacterIterator#first()
   */
  @Override
  public char first() {
    return setIndex(getBeginIndex());
  }

  /*
   * @see java.text.CharacterIterator#getBeginIndex()
   */
  @Override
  public int getBeginIndex() {
    return fFirst;
  }

  /*
   * @see java.text.CharacterIterator#getEndIndex()
   */
  @Override
  public int getEndIndex() {
    return fLast;
  }

  /*
   * @see java.text.CharacterIterator#getIndex()
   */
  @Override
  public int getIndex() {
    return fIndex;
  }

  /*
   * @see java.text.CharacterIterator#last()
   */
  @Override
  public char last() {
    if (fFirst == fLast) {
      return setIndex(getEndIndex());
    } else {
      return setIndex(getEndIndex() - 1);
    }
  }

  /*
   * @see java.text.CharacterIterator#next()
   */
  @Override
  public char next() {
    return setIndex(Math.min(fIndex + 1, getEndIndex()));
  }

  /*
   * @see java.text.CharacterIterator#previous()
   */
  @Override
  public char previous() {
    if (fIndex > getBeginIndex()) {
      return setIndex(fIndex - 1);
    } else {
      return DONE;
    }
  }

  /*
   * @see java.text.CharacterIterator#setIndex(int)
   */
  @Override
  public char setIndex(int position) {
    if (position >= getBeginIndex() && position <= getEndIndex()) {
      fIndex = position;
    } else {
      throw new IllegalArgumentException();
    }

    invariant();
    return current();
  }

  private void invariant() {
    Assert.isTrue(fIndex >= fFirst);
    Assert.isTrue(fIndex <= fLast);
  }
}