org.eclipse.m2e.refactoring/src/org/eclipse/m2e/refactoring/ChangeCreator.java

/*******************************************************************************
 * Copyright (c) 2008-2010 Sonatype, Inc.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *      Sonatype, Inc. - initial API and implementation
 *******************************************************************************/

package org.eclipse.m2e.refactoring;

import java.util.ArrayList;
import java.util.Arrays;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.eclipse.compare.rangedifferencer.IRangeComparator;
import org.eclipse.compare.rangedifferencer.RangeDifference;
import org.eclipse.compare.rangedifferencer.RangeDifferencer;
import org.eclipse.core.resources.IFile;
import org.eclipse.jface.text.BadLocationException;
import org.eclipse.jface.text.IDocument;
import org.eclipse.jface.text.IRegion;
import org.eclipse.ltk.core.refactoring.TextFileChange;
import org.eclipse.text.edits.DeleteEdit;
import org.eclipse.text.edits.InsertEdit;
import org.eclipse.text.edits.MultiTextEdit;
import org.eclipse.text.edits.ReplaceEdit;
import org.eclipse.text.edits.TextEdit;
import org.eclipse.text.edits.TextEditGroup;


/**
 * This class creates an org.eclipse.ltk.core.refactoring.DocumentChange instance based on old and new text values
 * 
 * @author Anton Kraev
 */
public class ChangeCreator {
  private static final Logger log = LoggerFactory.getLogger(ChangeCreator.class);

  private String label;

  private IDocument oldDocument;

  private IDocument newDocument;

  private IFile oldFile;

  public ChangeCreator(IFile oldFile, IDocument oldDocument, IDocument newDocument, String label) {
    this.newDocument = newDocument;
    this.oldDocument = oldDocument;
    this.oldFile = oldFile;
    this.label = label;
  }

  public TextFileChange createChange() throws Exception {
    TextFileChange change = new TextFileChange(label, oldFile);
    // change.setSaveMode(TextFileChange.FORCE_SAVE);
    change.setEdit(new MultiTextEdit());
    Object leftSide = new LineComparator(oldDocument);
    Object rightSide = new LineComparator(newDocument);

    RangeDifference[] differences = RangeDifferencer.findDifferences((IRangeComparator) leftSide,
        (IRangeComparator) rightSide);
    int insertOffset = 0;
    for(int i = 0; i < differences.length; i++ ) {
      RangeDifference curr = differences[i];
      int startLine = 0;
      // when comparing 2 files, only RangeDifference.CHANGE is possible, no need to test
      if(curr.rightLength() == curr.leftLength()) {
        // replace
        startLine = curr.rightStart();
        int endLine = curr.rightEnd() - 1;
        for(int j = startLine; j <= endLine; j++ ) {
          int newPos = curr.leftStart() - startLine + j;
          String newText = newDocument.get(newDocument.getLineOffset(newPos), newDocument.getLineLength(newPos));
          addEdit(change, startLine,
              new ReplaceEdit(oldDocument.getLineOffset(j), oldDocument.getLineLength(j), newText));
        }
      } else if(curr.rightLength() > 0 && curr.leftLength() == 0) {
        // insert
        startLine = curr.rightStart();
        int endLine = curr.rightEnd() - 1;
        int posInsert = oldDocument.getLineOffset(curr.leftStart());
        String newText = ""; //$NON-NLS-1$
        for(int j = startLine; j <= endLine; j++ ) {
          int newPos = curr.leftStart() - startLine + j + insertOffset;
          newText += newDocument.get(newDocument.getLineOffset(newPos), newDocument.getLineLength(newPos));
        }
        if(newText.length() > 0) {
          addEdit(change, startLine, new InsertEdit(posInsert, newText));
        }
        insertOffset += curr.rightEnd() - curr.rightStart();
      } else if(curr.leftLength() > 0 && curr.rightLength() == 0) {
        // delete
        startLine = curr.leftStart();
        int endLine = curr.leftEnd() - 1;
        int startOffset = oldDocument.getLineOffset(startLine);
        int endOffset = 0;
        for(int j = startLine; j <= endLine; j++ ) {
          endOffset += oldDocument.getLineLength(j);
        }
        addEdit(change, startLine, new DeleteEdit(startOffset, endOffset));
        insertOffset -= (curr.leftEnd() - curr.leftStart());
      } else {
        // unhandled
      }
    }
    return change;
  }

  private void addEdit(TextFileChange change, int startLine, TextEdit edit) {
    change.addTextEditGroup(new TextEditGroup("Line " + (startLine + 1), edit));
    change.addEdit(edit);
  }

  public static class LineComparator implements IRangeComparator {
    private final IDocument document;

    private final ArrayList<Integer> hashes;

    /**
     * Create a line comparator for the given document.
     * 
     * @param document
     */
    public LineComparator(IDocument document) {
      this.document = document;
      this.hashes = new ArrayList<>(Arrays.asList(new Integer[document.getNumberOfLines()]));
    }

    @Override
    public int getRangeCount() {
      return document.getNumberOfLines();
    }

    @Override
    public boolean rangesEqual(int thisIndex, IRangeComparator other, int otherIndex) {
      try {
        return getHash(thisIndex).equals(((LineComparator) other).getHash(otherIndex));
      } catch(BadLocationException e) {
        log.error("Problem comparing", e);
        return false;
      }
    }

    @Override
    public boolean skipRangeComparison(int length, int maxLength, IRangeComparator other) {
      return false;
    }

    /**
     * @param line the number of the line in the document to get the hash for
     * @return the hash of the line
     * @throws BadLocationException if the line number is invalid
     */
    private Integer getHash(int line) throws BadLocationException {
      Integer hash = hashes.get(line);
      if(hash == null) {
        IRegion lineRegion;
        lineRegion = document.getLineInformation(line);
        String lineContents = document.get(lineRegion.getOffset(), lineRegion.getLength());
        hash = Integer.valueOf(computeDJBHash(lineContents));
        hashes.set(line, hash);
      }
      return hash;
    }

    /**
     * Compute a hash using the DJB hash algorithm
     * 
     * @param string the string for which to compute a hash
     * @return the DJB hash value of the string
     */
    private int computeDJBHash(String string) {
      int hash = 5381;
      int len = string.length();
      for(int i = 0; i < len; i++ ) {
        hash = (hash << 5) + hash + string.charAt(i);
      }
      return hash;
    }
  }

}