src/main/java/org/apache/sling/query/impl/selector/SelectorFunction.java

/*-
 * 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.
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package org.apache.sling.query.impl.selector;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.function.Function;
import java.util.function.Predicate;

import org.apache.sling.query.api.SearchStrategy;
import org.apache.sling.query.api.internal.IteratorToIteratorFunction;
import org.apache.sling.query.api.internal.Option;
import org.apache.sling.query.api.internal.TreeProvider;
import org.apache.sling.query.impl.function.CompositeFunction;
import org.apache.sling.query.impl.function.FilterFunction;
import org.apache.sling.query.impl.iterator.AlternativeIterator;
import org.apache.sling.query.impl.iterator.EmptyElementFilter;
import org.apache.sling.query.impl.iterator.SuppIterator;
import org.apache.sling.query.impl.selector.parser.Modifier;
import org.apache.sling.query.impl.selector.parser.Selector;
import org.apache.sling.query.impl.selector.parser.SelectorParser;
import org.apache.sling.query.impl.selector.parser.SelectorSegment;
import org.apache.sling.query.impl.util.IteratorUtils;
import org.apache.sling.query.impl.util.LazyList;

public class SelectorFunction<T> implements IteratorToIteratorFunction<T>, Predicate<T> {

    private final List<IteratorToIteratorFunction<T>> selectorFunctions;

    private final TreeProvider<T> provider;

    private final SearchStrategy strategy;

    public SelectorFunction(String selector, TreeProvider<T> provider, SearchStrategy strategy) {
        this.provider = provider;
        this.strategy = strategy;
        List<Selector> selectors = SelectorParser.parse(selector);
        selectorFunctions = new ArrayList<>();
        for (Selector s : selectors) {
            selectorFunctions.add(createSelectorFunction(s.getSegments()));
        }
    }

    @Override
    public Iterator<Option<T>> apply(Iterator<Option<T>> input) {
        LazyList<Option<T>> list = new LazyList<Option<T>>(input);
        List<Iterator<Option<T>>> iterators = new ArrayList<>();
        for (IteratorToIteratorFunction<T> function : selectorFunctions) {
            iterators.add(new SuppIterator<T>(list, function));
        }
        return new AlternativeIterator<T>(iterators);
    }

    @Override
    public boolean test(T resource) {
        Iterator<Option<T>> result = apply(IteratorUtils.singleElementIterator(Option.of(resource, 0)));
        return new EmptyElementFilter<T>(result).hasNext();
    }

    private IteratorToIteratorFunction<T> createSelectorFunction(List<SelectorSegment> segments) {
        List<Function<?, ?>> segmentFunctions = new ArrayList<>();
        for (SelectorSegment segment : segments) {
            segmentFunctions.addAll(createSegmentFunction(segment));
        }
        return new CompositeFunction<T>(segmentFunctions);
    }

    private List<Function<?, ?>> createSegmentFunction(SelectorSegment segment) {
        List<Function<?, ?>> functions = new ArrayList<>();
        HierarchyOperator operator = HierarchyOperator.findByCharacter(segment.getHierarchyOperator());
        functions.add(operator.getFunction(segment, strategy, provider));
        Predicate<T> predicate = provider.getPredicate(segment.getType(), segment.getName(), segment.getAttributes());
        functions.add(new FilterFunction<T>(predicate));
        for (Modifier modifiers : segment.getModifiers()) {
            FunctionType type = FunctionType.valueOf(modifiers.getName().toUpperCase());
            Function<?, ?> f = type.getFunction(modifiers.getArgument(), strategy, provider);
            functions.add(f);
        }
        return functions;
    }

}