/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.lucene.index;
import java.io.IOException;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;
import org.apache.lucene.util.IntsRefBuilder;
import org.apache.lucene.util.StringHelper;
import org.apache.lucene.util.automaton.Automaton;
import org.apache.lucene.util.automaton.ByteRunAutomaton;
import org.apache.lucene.util.automaton.CompiledAutomaton;
import org.apache.lucene.util.automaton.Transition;
/**
* A FilteredTermsEnum that enumerates terms based upon what is accepted by a
* DFA.
* <p>
* The algorithm is such:
* <ol>
* <li>As long as matches are successful, keep reading sequentially.
* <li>When a match fails, skip to the next string in lexicographic order that
* does not enter a reject state.
* </ol>
* <p>
* The algorithm does not attempt to actually skip to the next string that is
* completely accepted. This is not possible when the language accepted by the
* FSM is not finite (i.e. * operator).
* </p>
* @lucene.internal
*/
public class AutomatonTermsEnum extends FilteredTermsEnum {
// a tableized array-based form of the DFA
private final ByteRunAutomaton runAutomaton;
// common suffix of the automaton
private final BytesRef commonSuffixRef;
// true if the automaton accepts a finite language
private final boolean finite;
// array of sorted transitions for each state, indexed by state number
private final Automaton automaton;
// for path tracking: each long records gen when we last
// visited the state; we use gens to avoid having to clear
private final long[] visited;
private long curGen;
// the reference used for seeking forwards through the term dictionary
private final BytesRefBuilder seekBytesRef = new BytesRefBuilder();
// true if we are enumerating an infinite portion of the DFA.
// in this case it is faster to drive the query based on the terms dictionary.
// when this is true, linearUpperBound indicate the end of range
// of terms where we should simply do sequential reads instead.
private boolean linear = false;
private final BytesRef linearUpperBound = new BytesRef(10);
/**
* Construct an enumerator based upon an automaton, enumerating the specified
* field, working on a supplied TermsEnum
*
* @lucene.experimental
* @param compiled CompiledAutomaton
*/
public AutomatonTermsEnum(TermsEnum tenum, CompiledAutomaton compiled) {
super(tenum);
if (compiled.type != CompiledAutomaton.AUTOMATON_TYPE.NORMAL) {
throw new IllegalArgumentException("please use CompiledAutomaton.getTermsEnum instead");
}
this.finite = compiled.finite;
this.runAutomaton = compiled.runAutomaton;
assert this.runAutomaton != null;
this.commonSuffixRef = compiled.commonSuffixRef;
this.automaton = compiled.automaton;
// used for path tracking, where each bit is a numbered state.
visited = new long[runAutomaton.getSize()];
}
/**
* Returns true if the term matches the automaton. Also stashes away the term
* to assist with smart enumeration.
*/
@Override
protected AcceptStatus accept(final BytesRef term) {
if (commonSuffixRef == null || StringHelper.endsWith(term, commonSuffixRef)) {
if (runAutomaton.run(term.bytes, term.offset, term.length))
return linear ? AcceptStatus.YES : AcceptStatus.YES_AND_SEEK;
else
return (linear && term.compareTo(linearUpperBound) < 0) ?
AcceptStatus.NO : AcceptStatus.NO_AND_SEEK;
} else {
return (linear && term.compareTo(linearUpperBound) < 0) ?
AcceptStatus.NO : AcceptStatus.NO_AND_SEEK;
}
}
@Override
protected BytesRef nextSeekTerm(final BytesRef term) throws IOException {
//System.out.println("ATE.nextSeekTerm term=" + term);
if (term == null) {
assert seekBytesRef.length() == 0;
// return the empty term, as it's valid
if (runAutomaton.isAccept(0)) {
return seekBytesRef.get();
}
} else {
seekBytesRef.copyBytes(term);
}
// seek to the next possible string;
if (nextString()) {
return seekBytesRef.get(); // reposition
} else {
return null; // no more possible strings can match
}
}
private Transition transition = new Transition();
/**
* Sets the enum to operate in linear fashion, as we have found
* a looping transition at position: we set an upper bound and
* act like a TermRangeQuery for this portion of the term space.
*/
private void setLinear(int position) {
assert linear == false;
int state = 0;
assert state == 0;
int maxInterval = 0xff;
//System.out.println("setLinear pos=" + position + " seekbytesRef=" + seekBytesRef);
for (int i = 0; i < position; i++) {
state = runAutomaton.step(state, seekBytesRef.byteAt(i) & 0xff);
assert state >= 0: "state=" + state;
}
final int numTransitions = automaton.getNumTransitions(state);
automaton.initTransition(state, transition);
for (int i = 0; i < numTransitions; i++) {
automaton.getNextTransition(transition);
if (transition.min <= (seekBytesRef.byteAt(position) & 0xff) &&
(seekBytesRef.byteAt(position) & 0xff) <= transition.max) {
maxInterval = transition.max;
break;
}
}
// 0xff terms don't get the optimization... not worth the trouble.
if (maxInterval != 0xff)
maxInterval++;
int length = position + 1; /* position + maxTransition */
if (linearUpperBound.bytes.length < length)
linearUpperBound.bytes = new byte[length];
System.arraycopy(seekBytesRef.bytes(), 0, linearUpperBound.bytes, 0, position);
linearUpperBound.bytes[position] = (byte) maxInterval;
linearUpperBound.length = length;
linear = true;
}
private final IntsRefBuilder savedStates = new IntsRefBuilder();
/**
* Increments the byte buffer to the next String in binary order after s that will not put
* the machine into a reject state. If such a string does not exist, returns
* false.
*
* The correctness of this method depends upon the automaton being deterministic,
* and having no transitions to dead states.
*
* @return true if more possible solutions exist for the DFA
*/
private boolean nextString() {
int state;
int pos = 0;
savedStates.grow(seekBytesRef.length()+1);
savedStates.setIntAt(0, 0);
while (true) {
curGen++;
linear = false;
// walk the automaton until a character is rejected.
for (state = savedStates.intAt(pos); pos < seekBytesRef.length(); pos++) {
visited[state] = curGen;
int nextState = runAutomaton.step(state, seekBytesRef.byteAt(pos) & 0xff);
if (nextState == -1)
break;
savedStates.setIntAt(pos+1, nextState);
// we found a loop, record it for faster enumeration
if (!finite && !linear && visited[nextState] == curGen) {
setLinear(pos);
}
state = nextState;
}
// take the useful portion, and the last non-reject state, and attempt to
// append characters that will match.
if (nextString(state, pos)) {
return true;
} else { /* no more solutions exist from this useful portion, backtrack */
if ((pos = backtrack(pos)) < 0) /* no more solutions at all */
return false;
final int newState = runAutomaton.step(savedStates.intAt(pos), seekBytesRef.byteAt(pos) & 0xff);
if (newState >= 0 && runAutomaton.isAccept(newState))
/* String is good to go as-is */
return true;
/* else advance further */
// TODO: paranoia? if we backtrack thru an infinite DFA, the loop detection is important!
// for now, restart from scratch for all infinite DFAs
if (!finite) pos = 0;
}
}
}
/**
* Returns the next String in lexicographic order that will not put
* the machine into a reject state.
*
* This method traverses the DFA from the given position in the String,
* starting at the given state.
*
* If this cannot satisfy the machine, returns false. This method will
* walk the minimal path, in lexicographic order, as long as possible.
*
* If this method returns false, then there might still be more solutions,
* it is necessary to backtrack to find out.
*
* @param state current non-reject state
* @param position useful portion of the string
* @return true if more possible solutions exist for the DFA from this
* position
*/
private boolean nextString(int state, int position) {
/*
* the next lexicographic character must be greater than the existing
* character, if it exists.
*/
int c = 0;
if (position < seekBytesRef.length()) {
c = seekBytesRef.byteAt(position) & 0xff;
// if the next byte is 0xff and is not part of the useful portion,
// then by definition it puts us in a reject state, and therefore this
// path is dead. there cannot be any higher transitions. backtrack.
if (c++ == 0xff)
return false;
}
seekBytesRef.setLength(position);
visited[state] = curGen;
final int numTransitions = automaton.getNumTransitions(state);
automaton.initTransition(state, transition);
// find the minimal path (lexicographic order) that is >= c
for (int i = 0; i < numTransitions; i++) {
automaton.getNextTransition(transition);
if (transition.max >= c) {
int nextChar = Math.max(c, transition.min);
// append either the next sequential char, or the minimum transition
seekBytesRef.grow(seekBytesRef.length() + 1);
seekBytesRef.append((byte) nextChar);
state = transition.dest;
/*
* as long as is possible, continue down the minimal path in
* lexicographic order. if a loop or accept state is encountered, stop.
*/
while (visited[state] != curGen && !runAutomaton.isAccept(state)) {
visited[state] = curGen;
/*
* Note: we work with a DFA with no transitions to dead states.
* so the below is ok, if it is not an accept state,
* then there MUST be at least one transition.
*/
automaton.initTransition(state, transition);
automaton.getNextTransition(transition);
state = transition.dest;
// append the minimum transition
seekBytesRef.grow(seekBytesRef.length() + 1);
seekBytesRef.append((byte) transition.min);
// we found a loop, record it for faster enumeration
if (!finite && !linear && visited[state] == curGen) {
setLinear(seekBytesRef.length()-1);
}
}
return true;
}
}
return false;
}
/**
* Attempts to backtrack thru the string after encountering a dead end
* at some given position. Returns false if no more possible strings
* can match.
*
* @param position current position in the input String
* @return {@code position >= 0} if more possible solutions exist for the DFA
*/
private int backtrack(int position) {
while (position-- > 0) {
int nextChar = seekBytesRef.byteAt(position) & 0xff;
// if a character is 0xff it's a dead-end too,
// because there is no higher character in binary sort order.
if (nextChar++ != 0xff) {
seekBytesRef.setByteAt(position, (byte) nextChar);
seekBytesRef.setLength(position+1);
return position;
}
}
return -1; /* all solutions exhausted */
}
}