// Copyright (C) 2009 The Android Open Source Project
//
// Licensed 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 com.google.gerrit.server.query;
import com.google.common.collect.Lists;
import com.google.inject.name.Named;
import java.lang.annotation.Annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
/**
* Rewrites a Predicate tree by applying rewrite rules.
* <p>
* Subclasses may document their rewrite rules by declaring public methods with
* {@link Rewrite} annotations, such as:
*
* <pre>
* @Rewrite("A=(owner:*) B=(status:*)")
* public Predicate r1_ownerStatus(@Named("A") OperatorPredicate owner,
* @Named("B") OperatorPredicate status) {
* }
* </pre>
* <p>
* Rewrite methods are applied in order by declared name, so naming methods with
* a numeric prefix to ensure a specific ordering (if required) is suggested.
*
* @param <T> type of object the predicate can evaluate in memory.
*/
public abstract class QueryRewriter<T> {
/**
* Defines the rewrite rules known by a QueryRewriter.
*
* This class is thread-safe and may be reused or cached.
*
* @param <T> type of object the predicates can evaluate in memory.
* @param <R> type of the rewriter subclass.
*/
public static class Definition<T, R extends QueryRewriter<T>> {
private final List<RewriteRule<T>> rewriteRules;
public Definition(Class<R> clazz, QueryBuilder<T> qb) {
rewriteRules = Lists.newArrayList();
Class<?> c = clazz;
while (c != QueryRewriter.class) {
Method[] declared = c.getDeclaredMethods();
for (Method m : declared) {
Rewrite rp = m.getAnnotation(Rewrite.class);
if ((m.getModifiers() & Modifier.ABSTRACT) != Modifier.ABSTRACT
&& (m.getModifiers() & Modifier.PUBLIC) == Modifier.PUBLIC
&& rp != null) {
rewriteRules.add(new MethodRewrite<>(qb, rp.value(), m));
}
}
c = c.getSuperclass();
}
Collections.sort(rewriteRules);
}
}
private final List<RewriteRule<T>> rewriteRules;
protected QueryRewriter(final Definition<T, ? extends QueryRewriter<T>> def) {
this.rewriteRules = def.rewriteRules;
}
/** Combine the passed predicates into a single AND node. */
public Predicate<T> and(Collection<? extends Predicate<T>> that) {
return Predicate.and(that);
}
/** Combine the passed predicates into a single AND node. */
public Predicate<T> and(@SuppressWarnings("unchecked") Predicate<T>... that) {
return and(Arrays.asList(that));
}
/** Combine the passed predicates into a single OR node. */
public Predicate<T> or(Collection<? extends Predicate<T>> that) {
return Predicate.or(that);
}
/** Combine the passed predicates into a single OR node. */
public Predicate<T> or(@SuppressWarnings("unchecked") Predicate<T>... that) {
return or(Arrays.asList(that));
}
/** Invert the passed node. */
public Predicate<T> not(Predicate<T> that) {
return Predicate.not(that);
}
protected Predicate<T> preRewrite(Predicate<T> in) {
return in;
}
/**
* Apply rewrites to a graph until it stops changing.
*
* @param in the graph to rewrite.
* @return the rewritten graph.
*/
public final Predicate<T> rewrite(Predicate<T> in) {
in = preRewrite(in);
return rewriteImpl(in);
}
private Predicate<T> rewriteImpl(Predicate<T> in) {
Predicate<T> old;
do {
old = in;
in = rewriteOne(in);
if (old.equals(in) && in.getChildCount() > 0) {
List<Predicate<T>> n = new ArrayList<>(in.getChildCount());
for (Predicate<T> p : in.getChildren()) {
n.add(rewriteImpl(p));
}
n = removeDuplicates(n);
if (n.size() == 1 && (isAND(in) || isOR(in))) {
in = n.get(0);
} else {
in = in.copy(n);
}
}
} while (!old.equals(in));
return replaceGenericNodes(in);
}
protected Predicate<T> replaceGenericNodes(final Predicate<T> in) {
if (in instanceof NotPredicate) {
return not(replaceGenericNodes(in.getChild(0)));
} else if (in instanceof AndPredicate) {
List<Predicate<T>> n = new ArrayList<>(in.getChildCount());
for (Predicate<T> c : in.getChildren()) {
n.add(replaceGenericNodes(c));
}
return and(n);
} else if (in instanceof OrPredicate) {
List<Predicate<T>> n = new ArrayList<>(in.getChildCount());
for (Predicate<T> c : in.getChildren()) {
n.add(replaceGenericNodes(c));
}
return or(n);
} else {
return in;
}
}
private Predicate<T> rewriteOne(Predicate<T> input) {
Predicate<T> best = null;
for (RewriteRule<T> r : rewriteRules) {
Predicate<T> n = r.rewrite(this, input);
if (n == null) {
continue;
}
if (!r.useBestCost()) {
return n;
}
if (best == null || n.getCost() < best.getCost()) {
best = n;
continue;
}
}
return best != null ? best : input;
}
private static class MatchResult<T> {
private static final MatchResult<?> FAIL = new MatchResult<>(null);
private static final MatchResult<?> OK = new MatchResult<>(null);
@SuppressWarnings("unchecked")
static <T> MatchResult<T> fail() {
return (MatchResult<T>) FAIL;
}
@SuppressWarnings("unchecked")
static <T> MatchResult<T> ok() {
return (MatchResult<T>) OK;
}
final Predicate<T> extra;
MatchResult(Predicate<T> extra) {
this.extra = extra;
}
boolean success() {
return this != FAIL;
}
}
private MatchResult<T> match(final Map<String, Predicate<T>> outVars,
final Predicate<T> pattern, final Predicate<T> actual) {
if (pattern instanceof VariablePredicate) {
final VariablePredicate<T> v = (VariablePredicate<T>) pattern;
final MatchResult<T> r = match(outVars, v.getChild(0), actual);
if (r.success()) {
Predicate<T> old = outVars.get(v.getName());
if (old == null) {
outVars.put(v.getName(), actual);
return r;
} else if (old.equals(actual)) {
return r;
} else {
return MatchResult.fail();
}
} else {
return MatchResult.fail();
}
}
if ((isAND(pattern) && isAND(actual)) //
|| (isOR(pattern) && isOR(actual)) //
|| (isNOT(pattern) && isNOT(actual)) //
) {
// Order doesn't actually matter here. That does make our logic quite
// a bit more complex as we need to consult each child at most once,
// but in any order.
//
final LinkedList<Predicate<T>> have = dup(actual);
final LinkedList<Predicate<T>> extra = new LinkedList<>();
for (final Predicate<T> pat : pattern.getChildren()) {
boolean found = false;
for (final Iterator<Predicate<T>> i = have.iterator(); i.hasNext();) {
final MatchResult<T> r = match(outVars, pat, i.next());
if (r.success()) {
found = true;
i.remove();
if (r.extra != null) {
extra.add(r.extra);
}
break;
}
}
if (!found) {
return MatchResult.fail();
}
}
have.addAll(extra);
switch (have.size()) {
case 0:
return MatchResult.ok();
case 1:
if (isNOT(actual)) {
return new MatchResult<>(actual.copy(have));
}
return new MatchResult<>(have.get(0));
default:
return new MatchResult<>(actual.copy(have));
}
} else if (pattern.equals(actual)) {
return MatchResult.ok();
} else if (pattern instanceof WildPatternPredicate
&& actual instanceof OperatorPredicate
&& ((OperatorPredicate<T>) pattern).getOperator().equals(
((OperatorPredicate<T>) actual).getOperator())) {
return MatchResult.ok();
} else {
return MatchResult.fail();
}
}
private static <T> LinkedList<Predicate<T>> dup(final Predicate<T> actual) {
return new LinkedList<>(actual.getChildren());
}
/**
* Denotes a method which wants to replace a predicate expression.
* <p>
* This annotation must be applied to a public method which returns
* {@link Predicate}. The arguments of the method should {@link Predicate}, or
* any subclass of it. The annotation value is a query language string which
* describes the subtree this rewrite applies to. Method arguments should be
* named with a {@link Named} annotation, and the same names should be used in
* the query.
* <p>
* For example:
*
* <pre>
* @Rewrite("A=(owner:*) B=(status:*)")
* public Predicate ownerStatus(@Named("A") OperatorPredicate owner,
* @Named("B") OperatorPredicate status) {
* }
* </pre>
*
* matches an AND Predicate with at least two children, one being an operator
* predicate called "owner" and the other being an operator predicate called
* "status". The variables in the query are matched by name against the
* parameters.
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
protected @interface Rewrite {
String value();
}
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
protected @interface NoCostComputation {
}
/** Applies a rewrite rule to a Predicate. */
protected interface RewriteRule<T> extends Comparable<RewriteRule<T>> {
/**
* Apply a rewrite rule to the Predicate.
*
* @param input the input predicate to be tested, and possibly rewritten.
* @return a rewritten form of the predicate if this rule matches with the
* tree {@code input} and has a rewrite for it; {@code null} if this
* rule does not want this predicate.
*/
Predicate<T> rewrite(QueryRewriter<T> rewriter, Predicate<T> input);
/** @return true if the best cost should be selected. */
boolean useBestCost();
}
/** Implements the magic behind {@link Rewrite} annotations. */
private static class MethodRewrite<T> implements RewriteRule<T> {
private final Method method;
private final Predicate<T> pattern;
private final String[] argNames;
private final Class<? extends Predicate<T>>[] argTypes;
private final boolean useBestCost;
@SuppressWarnings("unchecked")
MethodRewrite(QueryBuilder<T> queryBuilder, String patternText, Method m) {
method = m;
useBestCost = m.getAnnotation(NoCostComputation.class) == null;
Predicate<T> p;
try {
p = queryBuilder.parse(patternText);
} catch (QueryParseException e) {
throw new RuntimeException("Bad @Rewrite(\"" + patternText + "\")"
+ " on " + m.toGenericString() + " in " + m.getDeclaringClass()
+ ": " + e.getMessage(), e);
}
if (!Predicate.class.isAssignableFrom(m.getReturnType())) {
throw new RuntimeException(m.toGenericString() + " in "
+ m.getDeclaringClass() + " must return " + Predicate.class);
}
pattern = p;
argNames = new String[method.getParameterTypes().length];
argTypes = new Class[argNames.length];
for (int i = 0; i < argNames.length; i++) {
Named name = null;
for (Annotation a : method.getParameterAnnotations()[i]) {
if (a instanceof Named) {
name = (Named) a;
break;
}
}
if (name == null) {
throw new RuntimeException("Argument " + (i + 1) + " of "
+ m.toGenericString() + " in " + m.getDeclaringClass()
+ " has no @Named annotation");
}
if (!Predicate.class.isAssignableFrom(method.getParameterTypes()[i])) {
throw new RuntimeException("Argument " + (i + 1) + " of "
+ m.toGenericString() + " in " + m.getDeclaringClass()
+ " must be of type " + Predicate.class);
}
argNames[i] = name.value();
argTypes[i] = (Class<Predicate<T>>) method.getParameterTypes()[i];
}
}
@Override
public boolean useBestCost() {
return useBestCost;
}
@SuppressWarnings("unchecked")
@Override
public Predicate<T> rewrite(QueryRewriter<T> rewriter,
final Predicate<T> input) {
final HashMap<String, Predicate<T>> args = new HashMap<>();
final MatchResult<T> res = rewriter.match(args, pattern, input);
if (!res.success()) {
return null;
}
final Predicate<T>[] argList = new Predicate[argNames.length];
for (int i = 0; i < argList.length; i++) {
argList[i] = args.get(argNames[i]);
if (argList[i] == null) {
final String a = "@Named(\"" + argNames[i] + "\")";
throw error(new IllegalStateException("No value bound for " + a));
}
if (!argTypes[i].isInstance(argList[i])) {
return null;
}
}
final Predicate<T> rep;
try {
rep = (Predicate<T>) method.invoke(rewriter, (Object[]) argList);
} catch (IllegalArgumentException e) {
throw error(e);
} catch (IllegalAccessException e) {
throw error(e);
} catch (InvocationTargetException e) {
throw error(e.getCause());
}
if (rep instanceof RewritePredicate) {
((RewritePredicate<T>) rep).init(method.getName(), argList);
}
if (res.extra == null) {
return rep;
}
Predicate<T> extra = removeDuplicates(res.extra);
Predicate<T>[] newArgs = new Predicate[] {extra, rep};
return input.copy(Arrays.asList(newArgs));
}
private IllegalArgumentException error(Throwable e) {
final String msg = "Cannot apply " + method.getName();
return new IllegalArgumentException(msg, e);
}
@Override
public int compareTo(RewriteRule<T> in) {
if (in instanceof MethodRewrite) {
return method.getName().compareTo(
((MethodRewrite<T>) in).method.getName());
}
return 1;
}
}
private static <T> Predicate<T> removeDuplicates(Predicate<T> in) {
if (in.getChildCount() > 0) {
List<Predicate<T>> n = removeDuplicates(in.getChildren());
if (n.size() == 1 && (isAND(in) || isOR(in))) {
in = n.get(0);
} else {
in = in.copy(n);
}
}
return in;
}
private static <T> List<Predicate<T>> removeDuplicates(List<Predicate<T>> n) {
List<Predicate<T>> r = new ArrayList<>();
for (Predicate<T> p : n) {
if (!r.contains(p)) {
r.add(p);
}
}
return r;
}
private static <T> boolean isAND(final Predicate<T> p) {
return p instanceof AndPredicate;
}
private static <T> boolean isOR(final Predicate<T> p) {
return p instanceof OrPredicate;
}
private static <T> boolean isNOT(final Predicate<T> p) {
return p instanceof NotPredicate;
}
}