com.stegosaurus.crypt.DefaultPermutationProvider.java Source code

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Here is the source code for com.stegosaurus.crypt.DefaultPermutationProvider.java

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/**
 * Stegosaurus: JPEG Steganography
 * Copyright (C) 2016 Jose Cortes-Varela
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.stegosaurus.crypt;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.inject.Singleton;

/**
 * Provides Permutation objects for given seeds and given lengths.
 * Permutations being immutable, this object actually keeps a reference to any
 * previously requested instances and returns them again on subsequent
 * requests
 */
@Singleton
public class DefaultPermutationProvider implements PermutationProvider {
    /**
     * The actual permutations to return, as a loading cache mapping from
     * permutation size, to the caches mapping from permutation seed to
     * the permutation itself.
     * This way, we can get rid of entire permutation sizes that haven't
     * seen use in a while.
     */
    private final LoadingCache<Integer, LoadingCache<Long, Permutation>> permutations;

    /**
     * CTOR.
     */
    public DefaultPermutationProvider() {
        /* TODO Every last thing about this is awful. */
        /* TODO Make this nicer on the eye... */
        /* TODO Externalize the damn parameters */
        permutations = CacheBuilder.newBuilder().maximumSize(5)
                .build(new CacheLoader<Integer, LoadingCache<Long, Permutation>>() {
                    public LoadingCache<Long, Permutation> load(final Integer size) {
                        return CacheBuilder.newBuilder().maximumSize(50)
                                .build(new CacheLoader<Long, Permutation>() {
                                    public Permutation load(Long seed) {
                                        Permutation retval = new Permutation(size, seed);
                                        retval.init();
                                        return retval;
                                    }
                                });
                    }
                });
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Permutation getPermutation(int size, long seed) {
        return permutations.getUnchecked(size).getUnchecked(seed);
    }
}