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package it.unimi.dsi.big.mg4j.search;
/*
* MG4J: Managing Gigabytes for Java (big)
*
* Copyright (C) 2005-2011 Sebastiano Vigna
*
* This library 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 library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITfNESS 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, see Often, scores exhaust the intervals produced by a document iterator to compute their
* result. However, often you also need those intervals for other purposes (maybe just
* because you are aggregating several interval-based scorers). Decorating a document
* iterator with an instance of this class you get again a document iterator, but its intervals can
* be retrieved several times by calling {@link #intervalIterator(Index)}, {@link #intervalIterator()} and
* {@link #intervalIterators()}.
*
* Important: calls are not nestable: when you require again an iterator,
* the one previously returned is no longer valid, and when the current document changes (e.g.,
* because of a call to {@link #nextDocument()}) the previously returned interval iterators are invalidated.
*
* @author Sebastiano Vigna
* @since 0.9.1
*/
public class CachingDocumentIterator implements DocumentIterator {
/** The underlying document iterator. */
private final DocumentIterator documentIterator;
/** If not null, the sole index involved in this iterator. */
final private Index soleIndex;
/** A map from indices to caching iterators. We reuse iterators, and we create
* them on demand, so we must keep track of them separately from the set of current
* iterators (which will be returned to the user). */
final private Reference2ReferenceArrayMap cachingIterators;
/** A map from indices to the iterators already returned for the current document. The key set may
* not contain an index because the related iterator has never been requested. */
final private Reference2ReferenceArrayMap currentIterators;
/** An unmodifiable wrapper around {@link #currentIterators}. */
final private Reference2ReferenceMap unmodifiableCurrentIterators;
public CachingDocumentIterator( final DocumentIterator documentIterator ) {
this.documentIterator = documentIterator;
final int n = documentIterator.indices().size();
soleIndex = n == 1 ? indices().iterator().next() : null;
this.currentIterators = new Reference2ReferenceArrayMap( new Index[ n ], new IntervalIterator[ n ] );
this.cachingIterators = new Reference2ReferenceArrayMap( new Index[ n ], new CachingIntervalIterator[ n ] );
this.unmodifiableCurrentIterators = Reference2ReferenceMaps.unmodifiable( currentIterators );
}
public long document() {
return documentIterator.document();
}
public ReferenceSet indices() {
return documentIterator.indices();
}
/** An instance of this class caches lazily the intervals returning by the underlying interval iterator, and can
* return them from the start after a call to {@link #restart()}. */
private final static class CachingIntervalIterator extends AbstractObjectIterator implements IntervalIterator {
/** The list of cached intervals (must be emitted before the ones returned by the iterator). */
private final ObjectArrayList cachedIntervals = new ObjectArrayList();
/** The actual iterator (might be partially exhausted). */
private IntervalIterator intervalIterator;
/** The current position in the cached intervals array. */
private int pos = 0;
/** Sets the underlying iterator.
*
* Most MG4J classes reuse interval iterators, but in principle a document
* iterator might return a different interval iterator at each call. This
* method is used to set it.
*
* @param intervalIterator the new underlying iterator.
*/
public void wrap( final IntervalIterator intervalIterator ) {
this.intervalIterator = intervalIterator;
}
public int extent() {
return intervalIterator.extent();
}
public boolean hasNext() {
return pos < cachedIntervals.size() || intervalIterator.hasNext();
}
@Deprecated
public Interval next() {
if ( ! hasNext() ) throw new NoSuchElementException();
if ( pos < cachedIntervals.size() ) return cachedIntervals.get( pos++ );
else {
final Interval next = intervalIterator.next();
cachedIntervals.add( next );
pos++;
return next;
}
}
public Interval nextInterval() throws IOException {
if ( pos < cachedIntervals.size() ) return cachedIntervals.get( pos++ );
else {
final Interval next = intervalIterator.nextInterval();
if ( next == null ) return null;
cachedIntervals.add( next );
pos++;
return next;
}
}
public void reset() {
cachedIntervals.clear();
restart();
}
public void restart() {
pos = 0;
}
public void intervalTerms( final LongSet terms ) {
intervalIterator.intervalTerms( terms );
}
};
public IntervalIterator intervalIterator( final Index index ) throws IOException {
if ( ! documentIterator.indices().contains( index ) ) return IntervalIterators.FALSE;
CachingIntervalIterator result = cachingIterators.get( index );
if ( currentIterators.containsKey( index ) ) {
// the interval iterator for index is result
result.restart();
return result;
}
final IntervalIterator intervalIterator = documentIterator.intervalIterator( index );
if ( intervalIterator == IntervalIterators.TRUE || intervalIterator == IntervalIterators.FALSE ) return intervalIterator;
// We instantiate caching iterators on demand
if ( result == null ) cachingIterators.put( index, result = new CachingIntervalIterator() );
result.wrap( intervalIterator );
result.reset();
currentIterators.put( index, result );
return result;
}
public IntervalIterator intervalIterator() throws IOException {
if ( soleIndex == null ) throw new IllegalStateException();
return intervalIterator( soleIndex );
}
public Reference2ReferenceMap intervalIterators() throws IOException {
for( Index i : indices() ) intervalIterator( i );
return unmodifiableCurrentIterators;
}
public long nextDocument() throws IOException {
currentIterators.clear();
return documentIterator.nextDocument();
}
public boolean mayHaveNext() {
return documentIterator.mayHaveNext();
}
public long skipTo( final long n ) throws IOException {
currentIterators.clear();
return documentIterator.skipTo( n );
}
public void dispose() throws IOException {
documentIterator.dispose();
}
public T accept( DocumentIteratorVisitor visitor ) throws IOException {
return documentIterator.accept( visitor );
}
public T acceptOnTruePaths( DocumentIteratorVisitor visitor ) throws IOException {
return documentIterator.acceptOnTruePaths( visitor );
}
public IntervalIterator iterator() {
try {
return intervalIterator();
}
catch ( IOException e ) {
throw new RuntimeException( e );
}
}
public double weight() {
return documentIterator.weight();
}
public DocumentIterator weight( final double weight ) {
return documentIterator.weight( weight );
}
}