gcc/libjava/classpath/javax/swing/text/GapContent.java

/* GapContent.java --
   Copyright (C) 2002, 2004, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package javax.swing.text;

import java.io.Serializable;
import java.util.Collections;
import java.util.LinkedList;
import java.util.ListIterator;

import javax.swing.undo.UndoableEdit;

/**
 * This implementation of {@link AbstractDocument.Content} uses a gapped buffer.
 * This takes advantage of the fact that text area content is mostly inserted
 * sequentially. The buffer is a char array that maintains a gap at the current
 * insertion point. If characters a inserted at gap boundaries, the cost is
 * minimal (simple array access). The array only has to be shifted around when
 * the insertion point moves (then the gap also moves and one array copy is
 * necessary) or when the gap is filled up and the buffer has to be enlarged.
 * 
 * TODO: Implement UndoableEdit support stuff
 */
public class GapContent
    implements AbstractDocument.Content, Serializable
{

  /**
   * A {@link Position} implementation for <code>GapContent</code>.
   */
  class GapContentPosition
      implements Position, Comparable
  {

    /** The index within the buffer array. */
    int mark;

    /**
     * Creates a new GapContentPosition object.
     * 
     * @param mark the mark of this Position
     */
    GapContentPosition(int mark)
    {
      this.mark = mark;
    }

    /**
     * Comparable interface implementation. This is used to store all
     * positions in an ordered fashion.
     * 
     * @param o the object to be compared to this
     * 
     * @return a negative integer if this is less than <code>o</code>, zero
     *         if both are equal or a positive integer if this is greater than
     *         <code>o</code>
     * 
     * @throws ClassCastException if <code>o</code> is not a
     *         GapContentPosition or Integer object
     */
    public int compareTo(Object o)
    {
      if (o instanceof Integer)
      {
        int otherMark = ((Integer) o).intValue();
        return mark - otherMark;
      }
      else
      {
        GapContentPosition other = (GapContentPosition) o;
        return mark - other.mark;
      }
    }

    /**
     * Returns the current offset of this Position within the content.
     * 
     * @return the current offset of this Position within the content.
     */
    public int getOffset()
    {
      if (mark <= gapStart)
        return mark;
      else
        return mark - (gapEnd - gapStart);
    }
  }

  private static final long serialVersionUID = 8374645204155842629L;

  /**
   * This is the default buffer size and the amount of bytes that a buffer is
   * extended if it is full.
   */
  static final int DEFAULT_BUFSIZE = 64;

  /**
   * The text buffer.
   */
  char[] buffer;

  /**
   * The index of the first character of the gap.
   */
  int gapStart;

  /**
   * The index of the character after the last character of the gap.
   */
  int gapEnd;

  /**
   * The positions generated by this GapContent. They are kept in an ordered
   * fashion, so they can be looked up easily.
   */
  LinkedList positions;

  /**
   * Creates a new GapContent object.
   */
  public GapContent()
  {
    this(DEFAULT_BUFSIZE);
  }

  /**
   * Creates a new GapContent object with a specified initial size.
   * 
   * @param size the initial size of the buffer
   */
  public GapContent(int size)
  {
    buffer = (char[]) allocateArray(size);
    gapStart = 0;
    gapEnd = size - 1;
    buffer[size - 1] = '\n';
    positions = new LinkedList();
  }

  /**
   * Allocates an array of the specified length that can then be used as
   * buffer.
   * 
   * @param size the size of the array to be allocated
   * 
   * @return the allocated array
   */
  protected Object allocateArray(int size)
  {
    return new char[size];
  }

  /**
   * Returns the length of the allocated buffer array.
   * 
   * @return the length of the allocated buffer array
   */
  protected int getArrayLength()
  {
    return buffer.length;
  }

  /**
   * Returns the length of the content.
   * 
   * @return the length of the content
   */
  public int length()
  {
    return buffer.length - (gapEnd - gapStart);
  }

  /**
   * Inserts a string at the specified position.
   * 
   * @param where the position where the string is inserted
   * @param str the string that is to be inserted
   * 
   * @return an UndoableEdit object (currently not supported, so
   *         <code>null</code> is returned)
   * 
   * @throws BadLocationException if <code>where</code> is not a valid
   *         location in the buffer
   */
  public UndoableEdit insertString(int where, String str)
      throws BadLocationException
  {
    // check arguments
    int length = length();
    int strLen = str.length();

    if (where >= length)
      throw new BadLocationException("the where argument cannot be greater"
          + " than the content length", where);

    replace(where, 0, str.toCharArray(), str.length());

    return null;
  }

  /**
   * Removes a piece of content at th specified position.
   * 
   * @param where the position where the content is to be removed
   * @param nitems number of characters to be removed
   * 
   * @return an UndoableEdit object (currently not supported, so
   *         <code>null</code> is returned)
   * 
   * @throws BadLocationException if <code>where</code> is not a valid
   *         location in the buffer
   */
  public UndoableEdit remove(int where, int nitems) throws BadLocationException
  {
    // check arguments
    int length = length();

    if (where >= length)
      throw new BadLocationException("the where argument cannot be greater"
          + " than the content length", where);
    if ((where + nitems) > length)
      throw new BadLocationException("where + nitems cannot be greater"
          + " than the content length", where + nitems);

    replace(where, nitems, null, 0);

    return null;
  }

  /**
   * Returns a piece of content as String.
   * 
   * @param where the start location of the fragment
   * @param len the length of the fragment
   * 
   * @throws BadLocationException if <code>where</code> or
   *         <code>where + len</code> are no valid locations in the buffer
   */
  public String getString(int where, int len) throws BadLocationException
  {
    Segment seg = new Segment();
    try
      {
        getChars(where, len, seg);
        return new String(seg.array, seg.offset, seg.count);
      }
    catch (StringIndexOutOfBoundsException ex)
      {
        int invalid = 0;
        if (seg.offset < 0 || seg.offset >= seg.array.length)
          invalid = seg.offset;
        else
          invalid = seg.offset + seg.count;
        throw new BadLocationException("Illegal location: array.length = "
                                       + seg.array.length + ", offset = "
                                       + seg.offset + ", count = "
                                       + seg.count, invalid);
      }
  }

  /**
   * Fetches a piece of content and stores it in a {@link Segment} object.
   * 
   * If the requested piece of text spans the gap, the content is copied into a
   * new array. If it doesn't then it is contiguous and the actual content
   * store is returned.
   * 
   * @param where the start location of the fragment
   * @param len the length of the fragment
   * @param txt the Segment object to store the fragment in
   * 
   * @throws BadLocationException if <code>where</code> or
   *         <code>where + len</code> are no valid locations in the buffer
   */
  public void getChars(int where, int len, Segment txt)
      throws BadLocationException
  {
    // check arguments
    int length = length();
    if (where >= length)
      throw new BadLocationException("the where argument cannot be greater"
          + " than the content length", where);
    if ((where + len) > length)
      throw new BadLocationException("len plus where cannot be greater"
          + " than the content length", len + where);

    // check if requested segment is contiguous
    if ((where < gapStart) && ((gapStart - where) < len))
    {
      // requested segment is not contiguous -> copy the pieces together
      char[] copy = new char[len];
      int lenFirst = gapStart - where; // the length of the first segment
      System.arraycopy(buffer, where, copy, 0, lenFirst);
      System.arraycopy(buffer, gapEnd, copy, lenFirst, len - lenFirst);
      txt.array = copy;
      txt.offset = 0;
      txt.count = len;
    }
    else
    {
      // requested segment is contiguous -> we can simply return the
      // actual content
      txt.array = buffer;
      if (where < gapStart)
        txt.offset = where;
      else
        txt.offset = where + (gapEnd - gapStart);
      txt.count = len;
    }
  }

  /**
   * Creates and returns a mark at the specified position.
   * 
   * @param offset the position at which to create the mark
   * 
   * @return the create Position object for the mark
   * 
   * @throws BadLocationException if the offset is not a valid position in the
   *         buffer
   */
  public Position createPosition(final int offset) throws BadLocationException
  {
    if (offset < 0 || offset > length())
      throw new BadLocationException("The offset was out of the bounds of this"
          + " buffer", offset);

    // We store the actual array index in the GapContentPosition. The real
    // offset is then calculated in the GapContentPosition.
    int mark = offset;
    if (offset > gapStart)
      mark += gapEnd - gapStart;
    GapContentPosition pos = new GapContentPosition(mark);

    // Add this into our list in a sorted fashion.
    int index = Collections.binarySearch(positions, pos);
    if (index < 0)
      index = -(index + 1);
    positions.add(index, pos);

    return pos;
  }

  /**
   * Enlarges the gap. This allocates a new bigger buffer array, copy the
   * segment before the gap as it is and the segment after the gap at the end
   * of the new buffer array. This does change the gapEnd mark but not the
   * gapStart mark.
   * 
   * @param newSize the new size of the gap
   */
  protected void shiftEnd(int newSize)
  {
    int delta = (gapEnd - gapStart) - newSize;
    char[] newBuf = (char[]) allocateArray(length() + newSize);
    System.arraycopy(buffer, 0, newBuf, 0, gapStart);
    System.arraycopy(buffer, gapEnd, newBuf, gapStart + newSize, buffer.length
        - gapEnd);
    gapEnd = gapStart + newSize;
    buffer = newBuf;

    // Update the marks after the gapEnd.
    int index = Collections.binarySearch(positions, new GapContentPosition(
        gapEnd));
    if (index < 0)
    {
      index = -(index + 1);
    }
    for (ListIterator i = positions.listIterator(index); i.hasNext();)
    {
      GapContentPosition p = (GapContentPosition) i.next();
      p.mark += delta;
    }
  }

  /**
   * Shifts the gap to the specified position.
   * 
   * @param newGapStart the new start position of the gap
   */
  protected void shiftGap(int newGapStart)
  {
    int newGapEnd = newGapStart + (gapEnd - gapStart);

    // Update the positions between newGapEnd and (old) gapEnd. The marks
    // must be shifted by (gapEnd - newGapEnd).
    int index1 = Collections.binarySearch(positions,
                                          new GapContentPosition(gapEnd));
    int index2 = Collections.binarySearch(positions,
                                          new GapContentPosition(newGapEnd));
    if (index1 > 0 && index2 > 0)
      {
        int i1 = Math.min(index1, index2);
        int i2 = Math.max(index1, index2);
        for (ListIterator i = positions.listIterator(i1); i.hasNext();)
          {
            if (i.nextIndex() > i2)
              break;
            
            GapContentPosition p = (GapContentPosition) i.next();
            p.mark += gapEnd - newGapEnd;
          }
      }

    if (newGapStart == gapStart)
      return;
    else if (newGapStart < gapStart)
      {
        System.arraycopy(buffer, newGapStart, buffer, newGapEnd, gapStart
                         - newGapStart);
        gapStart = newGapStart;
        gapEnd = newGapEnd;
      }
    else
      {
        System.arraycopy(buffer, gapEnd, buffer, gapStart, newGapStart
                         - gapStart);
        gapStart = newGapStart;
        gapEnd = newGapEnd;
      }
  }

  /**
   * Returns the allocated buffer array.
   * 
   * @return the allocated buffer array
   */
  protected Object getArray()
  {
    return buffer;
  }

  /**
   * Replaces a portion of the storage with the specified items.
   * 
   * @param position the position at which to remove items
   * @param rmSize the number of items to remove
   * @param addItems the items to add at location
   * @param addSize the number of items to add
   */
  protected void replace(int position, int rmSize, Object addItems,
                         int addSize)
  {
    // Remove content
    shiftGap(position);
    gapEnd += rmSize;

    // If gap is too small, enlarge the gap.
    if ((gapEnd - gapStart) < addSize)
      shiftEnd(addSize);

    // Add new items to the buffer.
    if (addItems != null)
      {
        System.arraycopy(addItems, 0, buffer, gapStart, addSize);
        gapStart += addSize;
      }
  }
}