/*******************************************************************************
* Copyright (c) 2012-2015 Codenvy, S.A.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Codenvy, S.A. - initial API and implementation
*******************************************************************************/
package org.eclipse.che.ide.ext.java.jdt.text;
import org.eclipse.che.ide.runtime.Assert;
/**
* Implements a gap managing text store. The gap text store relies on the assumption that consecutive changes to a document are
* co-located. The start of the gap is always moved to the location of the last change.
* <p>
* <strong>Performance:</strong> Typing-style changes perform in constant time unless re-allocation becomes necessary. Generally,
* a change that does not cause re-allocation will cause at most one {@linkplain System#arraycopy(Object, int, Object, int, int)
* arraycopy} operation of a length of about <var>d</var>, where <var>d</var> is the distance from the previous change. Let
* <var>a(x)</var> be the algorithmic performance of an <code>arraycopy</code> operation of the length <var>x</var>, then such a
* change then performs in <i>O(a(x))</i>, {@linkplain #get(int, int) get(int, <var>length</var>)} performs in
* <i>O(a(length))</i>, {@link #get(int)} in <i>O(1)</i>.
* <p>
* How frequently the array needs re-allocation is controlled by the constructor parameters.
* </p>
* <p>
* This class is not intended to be subclassed.
* </p>
*
* @noextend This class is not intended to be subclassed by clients.
* @see CopyOnWriteTextStore for a copy-on-write text store wrapper
*/
public class GapTextStore implements TextStore {
/**
* The minimum gap size allocated when re-allocation occurs.
*
* @since 3.3
*/
private final int fMinGapSize;
/**
* The maximum gap size allocated when re-allocation occurs.
*
* @since 3.3
*/
private final int fMaxGapSize;
/**
* The multiplier to compute the array size from the content length (1 <= fSizeMultiplier <= 2).
*
* @since 3.3
*/
private final float fSizeMultiplier;
/** The store's content */
private char[] fContent = new char[0];
/** Starting index of the gap */
private int fGapStart = 0;
/** End index of the gap */
private int fGapEnd = 0;
/**
* The current high water mark. If a change would cause the gap to grow larger than this, the array is re-allocated.
*
* @since 3.3
*/
private int fThreshold = 0;
/**
* Creates a new empty text store using the specified low and high watermarks.
*
* @param lowWatermark
* unused - at the lower bound, the array is only resized when the content does not fit
* @param highWatermark
* if the gap is ever larger than this, it will automatically be shrunken (>= 0)
* @deprecated use {@link GapTextStore#GapTextStore(int, int, float)} instead
*/
public GapTextStore(int lowWatermark, int highWatermark) {
/*
* Legacy constructor. The API contract states that highWatermark is the upper bound for the gap size. Albeit this contract
* was not previously adhered to, it is now: The allocated gap size is fixed at half the highWatermark. Since the threshold
* is always twice the allocated gap size, the gap will never grow larger than highWatermark. Previously, the gap size was
* initialized to highWatermark, causing re-allocation if the content length shrunk right after allocation. The fixed gap
* size is now only half of the previous value, circumventing that problem (there was no API contract specifying the initial
* gap size). The previous implementation did not allow the gap size to become smaller than lowWatermark, which doesn't make
* any sense: that area of the gap was simply never ever used.
*/
this(highWatermark / 2, highWatermark / 2, 0f);
}
/**
* Equivalent to {@linkplain GapTextStore#GapTextStore(int, int, float) new GapTextStore(256, 4096, 0.1f)}.
*
* @since 3.3
*/
public GapTextStore() {
this(256, 4096, 0.1f);
}
/**
* Creates an empty text store that uses re-allocation thresholds relative to the content length. Re-allocation is controlled
* by the <em>gap factor</em> , which is the quotient of the gap size and the array size. Re-allocation occurs if a change
* causes the gap factor to go outside <code>[0, maxGapFactor]</code>. When re-allocation occurs, the array is sized such
* that the gap factor is <code>0.5 * maxGapFactor</code>. The gap size computed in this manner is bounded by the
* <code>minSize</code> and <code>maxSize</code> parameters.
* <p>
* A <code>maxGapFactor</code> of <code>0</code> creates a text store that never has a gap at all (if <code>minSize</code> is
* 0); a <code>maxGapFactor</code> of <code>1</code> creates a text store that doubles its size with every re-allocation and
* that never shrinks.
* </p>
* <p>
* The <code>minSize</code> and <code>maxSize</code> parameters are absolute bounds to the allocated gap size. Use
* <code>minSize</code> to avoid frequent re-allocation for small documents. Use <code>maxSize</code> to avoid a huge gap being
* allocated for large documents.
* </p>
*
* @param minSize
* the minimum gap size to allocate (>= 0; use 0 for no minimum)
* @param maxSize
* the maximum gap size to allocate (>= minSize; use {@link Integer#MAX_VALUE} for no maximum)
* @param maxGapFactor
* is the maximum fraction of the array that is occupied by the gap (
* <code>0 <= maxGapFactor <= 1</code> )
* @since 3.3
*/
public GapTextStore(int minSize, int maxSize, float maxGapFactor) {
Assert.isLegal(0f <= maxGapFactor && maxGapFactor <= 1f);
Assert.isLegal(0 <= minSize && minSize <= maxSize);
fMinGapSize = minSize;
fMaxGapSize = maxSize;
fSizeMultiplier = 1 / (1 - maxGapFactor / 2);
}
/* @see org.eclipse.jface.text.ITextStore#get(int) */
public final char get(int offset) {
if (offset < fGapStart)
return fContent[offset];
return fContent[offset + gapSize()];
}
/* @see org.eclipse.jface.text.ITextStore#get(int, int) */
public final String get(int offset, int length) {
if (fGapStart <= offset)
return new String(fContent, offset + gapSize(), length);
final int end = offset + length;
if (end <= fGapStart)
return new String(fContent, offset, length);
StringBuffer buf = new StringBuffer(length);
buf.append(fContent, offset, fGapStart - offset);
buf.append(fContent, fGapEnd, end - fGapStart);
return buf.toString();
}
/* @see org.eclipse.jface.text.ITextStore#getLength() */
public final int getLength() {
return fContent.length - gapSize();
}
/* @see org.eclipse.jface.text.ITextStore#set(java.lang.String) */
public final void set(String text) {
/*
* Moves the gap to the end of the content. There is no sensible prediction of where the next change will occur, but at
* least the next change will not trigger re-allocation. This is especially important when using the GapTextStore within a
* CopyOnWriteTextStore, where the GTS is only initialized right before a modification.
*/
replace(0, getLength(), text);
}
/* @see org.eclipse.jface.text.ITextStore#replace(int, int, java.lang.String) */
public final void replace(int offset, int length, String text) {
if (text == null) {
adjustGap(offset, length, 0);
} else {
int textLength = text.length();
adjustGap(offset, length, textLength);
if (textLength != 0)
text.getChars(0, textLength, fContent, offset);
}
}
/**
* Moves the gap to <code>offset + add</code>, moving any content after <code>offset + remove</code> behind the gap. The gap
* size is kept between 0 and {@link #fThreshold}, leading to re-allocation if needed. The content between <code>offset</code>
* and <code>offset + add</code> is undefined after this operation.
*
* @param offset
* the offset at which a change happens
* @param remove
* the number of character which are removed or overwritten at <code>offset</code>
* @param add
* the number of character which are inserted or overwriting at <code>offset</code>
*/
private void adjustGap(int offset, int remove, int add) {
final int oldGapSize = gapSize();
final int newGapSize = oldGapSize - add + remove;
final boolean reuseArray = 0 <= newGapSize && newGapSize <= fThreshold;
final int newGapStart = offset + add;
final int newGapEnd;
if (reuseArray)
newGapEnd = moveGap(offset, remove, oldGapSize, newGapSize, newGapStart);
else
newGapEnd = reallocate(offset, remove, oldGapSize, newGapSize, newGapStart);
fGapStart = newGapStart;
fGapEnd = newGapEnd;
}
/**
* Moves the gap to <code>newGapStart</code>.
*
* @param offset
* the change offset
* @param remove
* the number of removed / overwritten characters
* @param oldGapSize
* the old gap size
* @param newGapSize
* the gap size after the change
* @param newGapStart
* the offset in the array to move the gap to
* @return the new gap end
* @since 3.3
*/
private int moveGap(int offset, int remove, int oldGapSize, int newGapSize, int newGapStart) {
/*
* No re-allocation necessary. The area between the change offset and gap can be copied in at most one operation. Don't copy
* parts that will be overwritten anyway.
*/
final int newGapEnd = newGapStart + newGapSize;
if (offset < fGapStart) {
int afterRemove = offset + remove;
if (afterRemove < fGapStart) {
final int betweenSize = fGapStart - afterRemove;
arrayCopy(afterRemove, fContent, newGapEnd, betweenSize);
}
// otherwise, only the gap gets enlarged
} else {
final int offsetShifted = offset + oldGapSize;
final int betweenSize = offsetShifted - fGapEnd; // in the typing case, betweenSize is 0
arrayCopy(fGapEnd, fContent, fGapStart, betweenSize);
}
return newGapEnd;
}
/**
* Reallocates a new array and copies the data from the previous one.
*
* @param offset
* the change offset
* @param remove
* the number of removed / overwritten characters
* @param oldGapSize
* the old gap size
* @param newGapSize
* the gap size after the change if no re-allocation would occur (can be negative)
* @param newGapStart
* the offset in the array to move the gap to
* @return the new gap end
* @since 3.3
*/
private int reallocate(int offset, int remove, final int oldGapSize, int newGapSize, final int newGapStart) {
// the new content length (without any gap)
final int newLength = fContent.length - newGapSize;
// the new array size based on the gap factor
int newArraySize = (int)(newLength * fSizeMultiplier);
newGapSize = newArraySize - newLength;
// bound the gap size within min/max
if (newGapSize < fMinGapSize) {
newGapSize = fMinGapSize;
newArraySize = newLength + newGapSize;
} else if (newGapSize > fMaxGapSize) {
newGapSize = fMaxGapSize;
newArraySize = newLength + newGapSize;
}
// the upper threshold is always twice the gapsize
fThreshold = newGapSize * 2;
final char[] newContent = allocate(newArraySize);
final int newGapEnd = newGapStart + newGapSize;
/*
* Re-allocation: The old content can be copied in at most 3 operations to the newly allocated array. Either one of change
* offset and the gap may come first. - unchanged area before the change offset / gap - area between the change offset and
* the gap (either one may be first) - rest area after the change offset / after the gap
*/
if (offset < fGapStart) {
// change comes before gap
arrayCopy(0, newContent, 0, offset);
int afterRemove = offset + remove;
if (afterRemove < fGapStart) {
// removal is completely before the gap
final int betweenSize = fGapStart - afterRemove;
arrayCopy(afterRemove, newContent, newGapEnd, betweenSize);
final int restSize = fContent.length - fGapEnd;
arrayCopy(fGapEnd, newContent, newGapEnd + betweenSize, restSize);
} else {
// removal encompasses the gap
afterRemove += oldGapSize;
final int restSize = fContent.length - afterRemove;
arrayCopy(afterRemove, newContent, newGapEnd, restSize);
}
} else {
// gap comes before change
arrayCopy(0, newContent, 0, fGapStart);
final int offsetShifted = offset + oldGapSize;
final int betweenSize = offsetShifted - fGapEnd;
arrayCopy(fGapEnd, newContent, fGapStart, betweenSize);
final int afterRemove = offsetShifted + remove;
final int restSize = fContent.length - afterRemove;
arrayCopy(afterRemove, newContent, newGapEnd, restSize);
}
fContent = newContent;
return newGapEnd;
}
/**
* Allocates a new <code>char[size]</code>.
*
* @param size
* the length of the new array.
* @return a newly allocated char array
* @since 3.3
*/
private char[] allocate(int size) {
return new char[size];
}
/*
* Executes System.arraycopy if length != 0. A length < 0 cannot happen -> don't hide coding errors by checking for negative
* lengths.
* @since 3.3
*/
private void arrayCopy(int srcPos, char[] dest, int destPos, int length) {
if (length != 0) {
System.arraycopy(fContent, srcPos, dest, destPos, length);
}
}
/**
* Returns the gap size.
*
* @return the gap size
* @since 3.3
*/
private int gapSize() {
return fGapEnd - fGapStart;
}
/**
* Returns a copy of the content of this text store. For internal use only.
*
* @return a copy of the content of this text store
*/
protected String getContentAsString() {
return new String(fContent);
}
/**
* Returns the start index of the gap managed by this text store. For internal use only.
*
* @return the start index of the gap managed by this text store
*/
protected int getGapStartIndex() {
return fGapStart;
}
/**
* Returns the end index of the gap managed by this text store. For internal use only.
*
* @return the end index of the gap managed by this text store
*/
protected int getGapEndIndex() {
return fGapEnd;
}
}