path: root/libjava/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
the Free Software Foundation; either version 2, or (at your option)
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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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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package javax.swing.text;

import java.io.Serializable;

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
{
  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;

  /**
   * 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';
  }

  /**
   * 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);

    // check if the gap is big enough to hold the string
    if ((gapEnd - gapStart) < strLen)
      // make room for this string and some more
      shiftEnd(strLen + DEFAULT_BUFSIZE);

    // are we at the gap boundary?
    if (where != gapStart)
      shiftGap(where);

    // now we can simple copy the string into the gap and adjust the
    // gap boundaries
    System.arraycopy(str.toCharArray(), 0, buffer, gapStart, strLen);
    gapStart += strLen;
    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);

    // check if we are at the gap boundary
    if (where != gapStart)
      shiftGap(where);

    // now we simply have to enlarge the gap
    gapEnd += nitems;
    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();
    getChars(where, len, seg);
    return new String(seg.array, seg.offset, seg.count);
  }

  /**
   * 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
  {
    return new Position()
      {
	int off = offset;

	public int getOffset()
	{
	  return off;
	}
      };
  }

  /**
   * 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)
  {
    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;
  }

  /**
   * 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);

    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;
  }
}