com.flaptor.indextank.util.Intersection.java Source code

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Here is the source code for com.flaptor.indextank.util.Intersection.java

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/*
 * Copyright (c) 2011 LinkedIn, Inc
 * 
 * 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.flaptor.indextank.util;

import java.util.List;

import com.flaptor.util.CollectionsUtil.PeekingIterator;
import com.google.common.base.Function;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;

public abstract class Intersection<K, V extends Comparable<V>> extends AbstractSkippableIterable<V> {

    private Iterable<SkippableIterable<K>> cursors;

    public Intersection(Iterable<SkippableIterable<K>> cursors) {
        this.cursors = cursors;
    }

    protected abstract V transform(K k);

    protected boolean shouldUse(V v, List<K> ks) {
        return true;
    }

    @Override
    public SkippableIterator<V> iterator() {
        return new AbstractSkippableIterator<V>() {
            private List<PeekingSkippableIterator<K>> iterators = Lists
                    .newArrayList(Iterables.transform(cursors, Intersection.<K>peekingIteratorFunction()));

            @Override
            protected V computeNext() {
                V current = null;

                while (true) {
                    boolean found = true;
                    for (PeekingSkippableIterator<K> it : iterators) {
                        while (it.hasNext() && current != null && transform(it.peek()).compareTo(current) < 0) {
                            advanceTo(it, current);
                            it.next();
                        }
                        if (!it.hasNext()) {
                            return endOfData();
                        }
                        if (current != null && transform(it.peek()).equals(current)) {
                            continue;
                        } else {
                            found = false;
                            current = transform(it.peek());
                        }
                    }
                    if (found) {
                        V r = null;
                        if (shouldUse(current, peekedItems())) {
                            r = current;
                        }
                        for (PeekingIterator<K> it : iterators) {
                            it.next();
                        }
                        if (r != null)
                            return r;
                    }
                }
            }

            private List<K> peekedItems() {
                return Lists.transform(iterators, Intersection.<K>peekFunction());
            }

            @Override
            public void skipTo(int i) {
                for (PeekingSkippableIterator<K> it : iterators) {
                    it.skipTo(i);
                }
            }
        };
    }

    public static <T> Function<PeekingIterator<T>, T> peekFunction() {
        return new Function<PeekingIterator<T>, T>() {
            @Override
            public T apply(PeekingIterator<T> it) {
                return it.peek();
            }
        };
    }

    public static <T> Function<SkippableIterable<T>, PeekingSkippableIterator<T>> peekingIteratorFunction() {
        return new Function<SkippableIterable<T>, PeekingSkippableIterator<T>>() {
            @Override
            public PeekingSkippableIterator<T> apply(SkippableIterable<T> ts) {
                return new PeekingSkippableIterator<T>(ts.iterator());
            }
        };
    }

    protected void advanceTo(PeekingSkippableIterator<K> it, V current) {
    }

}