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// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.prelude.query;
import com.yahoo.search.Query;
import com.yahoo.search.query.QueryTree;
import java.util.*;
/**
* A class which canonicalizes and validates queries.
* This class is multithread safe.
*
* @author <a href="mailto:bratseth@yahoo-inc.com">Jon Bratseth</a>
*/
public class QueryCanonicalizer {
/** The name of the operation performed by this (for use in search chain ordering) */
public static final String queryCanonicalization = "queryCanonicalization";
/**
* Validates this query and carries out possible operations on this query
* which simplifies it without changing its semantics.
*
* @return null if the query is valid, an error message if it is invalid
*/
public static String canonicalize(Query query) {
Item root = query.getModel().getQueryTree().getRoot();
return canonicalize(query, root);
}
/**
* Validates this query and carries out possible operations on this query
* which simplifies it without changing its semantics.
*
* @return null if the query is valid, an error message if it is invalid
*/
public static String canonicalize(QueryTree query) {
QueryWrapper q = new QueryWrapper();
q.setRoot(query.getRoot()); // Could get rid of the wrapper...
treeCanonicalize(q, query.getRoot(), null);
query.setRoot(q.root);
return q.error;
}
/**
* Validates this query and
* carries out possible operations on this query which simplifies it
* without changing its semantics.
*
* @param item the item to canonicalize
* @return null if the query is valid, an error message if it is invalid
*/
private static String canonicalize(Query query, Item item) {
QueryWrapper q = new QueryWrapper();
q.setRoot(item);
treeCanonicalize(q, query.getModel().getQueryTree().getRoot(), null);
if (q.root == null)
q.root = new NullItem();
query.getModel().getQueryTree().setRoot(q.root);
return q.error;
}
/**
* @param bag wrapper for error message and query root
* @param item the item to canonicalize
* @param iterator iterator for the above item if pertinent
* @return whether the query could be canonicalized into something
*/
public static boolean treeCanonicalize(QueryWrapper bag, Item item, ListIterator<Item> iterator) {
if (iterator == null && (item == null || item instanceof NullItem)) {
bag.setError("No query");
return false;
}
if (item instanceof TermItem) {
return true;
}
if (item instanceof NullItem) {
iterator.remove();
}
if ( ! (item instanceof CompositeItem)) {
return true;
} // Impossible yet
CompositeItem composite = (CompositeItem) item;
for (ListIterator<Item> i = composite.getItemIterator(); i.hasNext();) {
Item child = i.next();
boolean subtreeOK = treeCanonicalize(bag, child, i);
if (!subtreeOK) {
return false;
}
}
if (composite instanceof EquivItem) {
removeDuplicates((EquivItem) composite);
}
else if (composite instanceof RankItem) {
makeDuplicatesCheap((RankItem)composite);
}
else if (composite instanceof NotItem) {
if (((NotItem) composite).getPositiveItem() == null) {
bag.setError("Can not search for only negative items");
return false;
}
}
if (composite.getItemCount() == 0) {
if (iterator == null) {
bag.setRoot(new NullItem());
bag.setError("No query: Contained an empty " + composite.getName() + " only");
return false;
} else {
iterator.remove();
}
}
if (composite.getItemCount() == 1 && ! (composite instanceof NonReducibleCompositeItem)) {
if (composite instanceof PhraseItem || composite instanceof PhraseSegmentItem) {
composite.getItem(0).setWeight(composite.getWeight());
}
if (iterator == null) {
bag.setRoot(composite.getItem(0));
} else {
iterator.set(composite.getItem(0));
}
}
return true;
}
private static void removeDuplicates(EquivItem composite) {
int origSize = composite.getItemCount();
for (int i = origSize - 1; i >= 1; --i) {
Item deleteCandidate = composite.getItem(i);
for (int j = 0; j < i; ++j) {
Item check = composite.getItem(j);
if (deleteCandidate.getClass() == check.getClass()) {
if (deleteCandidate instanceof PhraseItem) {
PhraseItem phraseDeletionCandidate = (PhraseItem) deleteCandidate;
PhraseItem phraseToCheck = (PhraseItem) check;
if (phraseDeletionCandidate.getIndexedString().equals(phraseToCheck.getIndexedString())) {
composite.removeItem(i);
break;
}
} else if (deleteCandidate instanceof PhraseSegmentItem) {
PhraseSegmentItem phraseSegmentDeletionCandidate = (PhraseSegmentItem) deleteCandidate;
PhraseSegmentItem phraseSegmentToCheck = (PhraseSegmentItem) check;
if (phraseSegmentDeletionCandidate.getIndexedString().equals(phraseSegmentToCheck.getIndexedString())) {
composite.removeItem(i);
break;
}
} else if (deleteCandidate instanceof BlockItem) {
BlockItem blockDeletionCandidate = (BlockItem) deleteCandidate;
BlockItem blockToCheck = (BlockItem) check;
if (blockDeletionCandidate.stringValue().equals(blockToCheck.stringValue())) {
composite.removeItem(i);
break;
}
}
}
}
}
}
/**
* If a term is present as both a rank term (i.e not the first child) and in
* the match condition (first child), then turn off any rank calculation for
* the term during matching, as it will be made available anyway for matches
* by the same term in the rank part.
*
* @param rankItem
* an item which will be simplified in place
*/
private static void makeDuplicatesCheap(RankItem rankItem) {
// Collect terms used for ranking
Set<TermItem> rankTerms = new HashSet<>();
for (int i = 1; i < rankItem.getItemCount(); i++) {
if (rankItem.getItem(i) instanceof TermItem)
rankTerms.add((TermItem)rankItem.getItem(i));
}
// Make terms used for matching cheap if they also are ranking terms
makeDuplicatesCheap(rankItem.getItem(0), rankTerms);
}
private static void makeDuplicatesCheap(Item item, Set<TermItem> rankTerms) {
if (item instanceof CompositeItem) {
for (ListIterator<Item> i = ((CompositeItem)item).getItemIterator(); i.hasNext();)
makeDuplicatesCheap(i.next(), rankTerms);
}
else if (rankTerms.contains(item)) {
item.setRanked(false);
item.setPositionData(false);
}
}
public static class QueryWrapper {
private Item root = null;
private String error = null;
public Item getRoot() { return root; }
public void setRoot(Item root) {
this.root = root;
}
public String getError() {
return error;
}
public void setError(String error) {
this.error = error;
}
}
}
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