/*
* SonarQube
* Copyright (C) 2009-2017 SonarSource SA
* mailto:info AT sonarsource DOT com
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or (at your option) any later version.
*
* This program 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
package org.sonar.duplications.detector.original;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.sonar.duplications.block.Block;
import org.sonar.duplications.block.ByteArray;
import org.sonar.duplications.index.CloneGroup;
import org.sonar.duplications.index.CloneIndex;
import org.sonar.duplications.index.ClonePart;
/**
* Implementation of algorithm described in paper
* <a href="http://www4.in.tum.de/~juergens/publications/icsm2010_crc.pdf">Index-Based Code Clone Detection: Incremental, Distributed, Scalable</a>
* by Benjamin Hummel, Elmar Juergens, Michael Conradt and Lars Heinemann.
*/
public final class OriginalCloneDetectionAlgorithm {
private final CloneIndex cloneIndex;
private final Filter filter = new Filter();
private String originResourceId;
private OriginalCloneDetectionAlgorithm(CloneIndex cloneIndex) {
this.cloneIndex = cloneIndex;
}
private BlocksGroup[] createGroups(Collection<Block> fileBlocks) {
// 2: let f be the list of tuples corresponding to filename sorted by statement index
// either read from the index or calculated on the fly
int size = fileBlocks.size();
// Godin: create one group per unique hash
// TODO Godin: can we create map with expected size?
Map<ByteArray, BlocksGroup> groupsByHash = new HashMap<>();
for (Block fileBlock : fileBlocks) {
ByteArray hash = fileBlock.getBlockHash();
BlocksGroup sameHash = groupsByHash.get(hash);
if (sameHash == null) {
sameHash = BlocksGroup.empty();
groupsByHash.put(hash, sameHash);
}
sameHash.blocks.add(fileBlock);
}
// Godin: retrieve blocks from index
for (Map.Entry<ByteArray, BlocksGroup> entry : groupsByHash.entrySet()) {
ByteArray hash = entry.getKey();
BlocksGroup group = entry.getValue();
for (Block blockFromIndex : cloneIndex.getBySequenceHash(hash)) {
// Godin: skip blocks for this file if they come from index
if (!originResourceId.equals(blockFromIndex.getResourceId())) {
group.blocks.add(blockFromIndex);
}
}
Collections.sort(group.blocks, BlocksGroup.BlockComparator.INSTANCE);
}
// 3: let c be a list with c(0) = empty
BlocksGroup[] sameHashBlocksGroups = new BlocksGroup[size + 2];
sameHashBlocksGroups[0] = BlocksGroup.empty();
// 4: for i := 1 to length(f) do
for (Block fileBlock : fileBlocks) {
ByteArray hash = fileBlock.getBlockHash();
int i = fileBlock.getIndexInFile() + 1;
// 5: retrieve tuples with same sequence hash as f(i)
// 6: store this set as c(i)
sameHashBlocksGroups[i] = groupsByHash.get(hash);
}
// Godin: allows to report clones at the end of file, because condition at line 13 would be evaluated as true
sameHashBlocksGroups[size + 1] = BlocksGroup.empty();
return sameHashBlocksGroups;
}
private void findClones(Collection<Block> fileBlocks) {
originResourceId = fileBlocks.iterator().next().getResourceId();
BlocksGroup[] sameHashBlocksGroups = createGroups(fileBlocks);
// 7: for i := 1 to length(c) do
for (int i = 1; i < sameHashBlocksGroups.length; i++) {
// In the main loop (starting from Line 7), we first check
// whether any new clones might start at this position. If there
// is only a single tuple with this hash (which has to belong
// to the inspected file at the current location) we skip this loop
// iteration. The same holds if all tuples at position i have already
// been present at position i − 1, as in this case any clone group
// found at position i would be included in a clone group starting
// at position i − 1.
// Although we use the subset operator in the
// algorithm description, this is not really a subset operation,
// as of course the statement index of the tuples in c(i) will be
// increased by 1 compared to the corresponding ones in c(i − 1)
// and the hash and info fields will differ.
// 8: if |c(i)| < 2 or c(i) subsumed by c(i - 1) then
if (sameHashBlocksGroups[i].size() < 2 || sameHashBlocksGroups[i].subsumedBy(sameHashBlocksGroups[i - 1], 1)) {
// 9: continue with next loop iteration
continue;
}
// The set a introduced in Line 10 is called the active set and
// contains all tuples corresponding to clones which have not yet
// been reported. At each iteration of the inner loop the set a
// is reduced to tuples which are also present in c(j); again the
// intersection operator has to account for the increased statement
// index and different hash and info fields. The new value is
// stored in a0. Clones are only reported, if tuples are lost in
// Line 12, as otherwise all current clones could be prolonged
// by one statement. Clone reporting matches tuples that, after
// correction of the statement index, appear in both c(i) and a,
// each matched pair corresponds to a single clone. Its location
// can be extracted from the filename and info fields.
// 10: let a := c(i)
BlocksGroup currentBlocksGroup = sameHashBlocksGroups[i];
// 11: for j := i + 1 to length(c) do
for (int j = i + 1; j < sameHashBlocksGroups.length; j++) {
// 12: let a0 := a intersect c(j)
BlocksGroup intersectedBlocksGroup = currentBlocksGroup.intersect(sameHashBlocksGroups[j]);
// 13: if |a0| < |a| then
if (intersectedBlocksGroup.size() < currentBlocksGroup.size()) {
// 14: report clones from c(i) to a (see text)
// One problem of this algorithm is that clone classes with
// multiple instances in the same file are encountered and
// reported multiple times. Furthermore, when calculating the clone
// groups for all files in a system, clone groups will be reported
// more than once as well. Both cases can be avoided, by
// checking whether the first element of a0 (with respect to a
// fixed order) is equal to f(j) and only report in this case.
Block first = currentBlocksGroup.first(originResourceId);
if (first != null && first.getIndexInFile() == j - 2) {
// Godin: We report clones, which start in i-1 and end in j-2, so length is j-2-(i-1)+1=j-i
reportClones(sameHashBlocksGroups[i], currentBlocksGroup, j - i);
}
}
// 15: a := a0
currentBlocksGroup = intersectedBlocksGroup;
// Line 16 early exits the inner loop if either no more clones are starting
// from position i (i.e., a is too small), or if all tuples from a
// have already been in c(i − 1), corrected for statement index.
// In this case they have already been reported in the previous
// iteration of the outer loop.
// IMPORTANT Godin: note that difference in indexes between "a" and "c(i-1)" greater than one,
// so method subsumedBy should take this into account
// 16: if |a| < 2 or a subsumed by c(i-1) then
if (currentBlocksGroup.size() < 2 || currentBlocksGroup.subsumedBy(sameHashBlocksGroups[i - 1], j - i + 1)) {
// 17: break inner loop
break;
}
}
}
}
private void reportClones(BlocksGroup beginGroup, BlocksGroup endGroup, int cloneLength) {
List<Block[]> pairs = beginGroup.pairs(endGroup, cloneLength);
ClonePart origin = null;
List<ClonePart> parts = new ArrayList<>();
for (int i = 0; i < pairs.size(); i++) {
Block[] pair = pairs.get(i);
Block firstBlock = pair[0];
Block lastBlock = pair[1];
ClonePart part = new ClonePart(firstBlock.getResourceId(),
firstBlock.getIndexInFile(),
firstBlock.getStartLine(),
lastBlock.getEndLine());
if (originResourceId.equals(part.getResourceId())) {
if (origin == null || part.getUnitStart() < origin.getUnitStart()) {
origin = part;
}
}
parts.add(part);
}
filter.add(CloneGroup.builder().setLength(cloneLength).setOrigin(origin).setParts(parts).build());
}
/**
* Performs detection and returns list of clone groups between file (which represented as a collection of blocks) and index.
* Note that this method ignores blocks for this file, that will be retrieved from index.
*/
public static List<CloneGroup> detect(CloneIndex cloneIndex, Collection<Block> fileBlocks) {
if (fileBlocks.isEmpty()) {
return Collections.emptyList();
}
OriginalCloneDetectionAlgorithm reporter = new OriginalCloneDetectionAlgorithm(cloneIndex);
reporter.findClones(fileBlocks);
return reporter.filter.getResult();
}
}