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/*
 * LensKit, an open source recommender systems toolkit.
 * Copyright 2010-2014 LensKit Contributors.  See CONTRIBUTORS.md.
 * Work on LensKit has been funded by the National Science Foundation under
 * grants IIS 05-34939, 08-08692, 08-12148, and 10-17697.
 *
 * This program 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 2.1 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */
package org.lenskit.knn.item.model;

import com.google.common.base.MoreObjects;
import com.google.common.base.Stopwatch;
import com.google.common.collect.Lists;
import it.unimi.dsi.fastutil.longs.LongIterator;
import it.unimi.dsi.fastutil.longs.LongSortedSet;
import org.lenskit.inject.Transient;
import org.lenskit.knn.item.ItemSimilarity;
import org.grouplens.lenskit.transform.normalize.ItemVectorNormalizer;
import org.grouplens.lenskit.transform.truncate.VectorTruncator;
import org.grouplens.lenskit.vectors.ImmutableSparseVector;
import org.grouplens.lenskit.vectors.MutableSparseVector;
import org.grouplens.lenskit.vectors.SparseVector;
import org.lenskit.util.keys.SortedKeyIndex;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.inject.Inject;
import javax.inject.Provider;
import java.util.List;

/**
 * Build an item-item CF model from rating data.
 * This builder is more advanced than the standard builder. It allows arbitrary
 * vector truncation and normalization.
 */
public class NormalizingItemItemModelBuilder implements Provider {
    private static final Logger logger = LoggerFactory.getLogger(NormalizingItemItemModelBuilder.class);

    private final ItemSimilarity similarity;
    private final ItemItemBuildContext buildContext;
    private final ItemVectorNormalizer rowNormalizer;
    private final VectorTruncator truncator;
    private final NeighborIterationStrategy iterationStrategy;

    /**
     * Construct a normalizing item-item model builder.
     *
     * @param sim     The item similarity function.
     * @param context The item-item build context.
     * @param rowNorm The normalizer for item neighborhood vectors.
     * @param trunc   The truncator for truncating neighborhood vectors.  Bind this to the provider
     *                {@link StandardVectorTruncatorProvider} to get the same threshold and model
     *                size configuration behavior as {@link ItemItemModelBuilder}.
     * @param iterStrat The neighbor iteration strategy.
     */
    @Inject
    public NormalizingItemItemModelBuilder(@Transient ItemSimilarity sim,
                                           @Transient ItemItemBuildContext context,
                                           @Transient ItemVectorNormalizer rowNorm,
                                           @Transient VectorTruncator trunc,
                                           @Transient NeighborIterationStrategy iterStrat) {
        similarity = sim;
        buildContext = context;
        rowNormalizer = rowNorm;
        truncator = trunc;
        iterationStrategy = iterStrat;
    }


    @SuppressWarnings("deprecation")
    @Override
    public SimilarityMatrixModel get() {
        logger.debug("building item-item model");

        LongSortedSet itemUniverse = buildContext.getItems();

        final int nitems = itemUniverse.size();

        SortedKeyIndex itemDomain = SortedKeyIndex.fromCollection(itemUniverse);
        assert itemDomain.size() == nitems;
        List matrix = Lists.newArrayListWithCapacity(itemDomain.size());

        // working space for accumulating each row (reuse between rows)
        MutableSparseVector currentRow = MutableSparseVector.create(itemUniverse);
        Stopwatch timer = Stopwatch.createStarted();

        for (int i = 0; i < nitems; i++) {
            assert matrix.size() == i;
            final long rowItem = itemDomain.getKey(i);
            final SparseVector vec1 = buildContext.itemVector(rowItem);

            // Take advantage of sparsity if we can
            LongIterator neighbors = iterationStrategy.neighborIterator(buildContext, rowItem, false);
            currentRow.fill(0);

            // Compute similarities and populate the vector
            while (neighbors.hasNext()) {
                final long colItem = neighbors.nextLong();
                final SparseVector vec2 = buildContext.itemVector(colItem);
                assert currentRow.containsKey(colItem);
                currentRow.set(colItem, similarity.similarity(rowItem, vec1, colItem, vec2));
            }

            // Remove the current item (it is not its own neighbor)
            currentRow.unset(rowItem);

            // Normalize and truncate the row
            MutableSparseVector normalized = rowNormalizer.normalize(rowItem, currentRow, null);
            truncator.truncate(normalized);

            matrix.add(normalized.immutable());
        }

        timer.stop();
        logger.info("built model for {} items in {}", nitems, timer);

        return new SimilarityMatrixModel(itemDomain, matrix);
    }

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(NormalizingItemItemModelBuilder.class)
                          .add("similarity", similarity)
                          .add("normalizer", rowNormalizer)
                          .add("truncator", truncator)
                          .toString();
    }
}