com.calclab.emite.base.util.KeySequencer.java Source code

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Here is the source code for com.calclab.emite.base.util.KeySequencer.java

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/*
 * ((e)) emite: A pure Google Web Toolkit XMPP library
 * Copyright (c) 2008-2011 The Emite development team
 * 
 * This file is part of Emite.
 *
 * Emite 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 3
 * of the License, or (at your option) any later version.
 *
 * Emite 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 Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with Emite.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.calclab.emite.base.util;

import java.util.LinkedList;
import java.util.Random;

import javax.annotation.Nullable;

import com.calclab.emite.base.crypto.Digest;
import com.calclab.emite.base.crypto.SHA1Digest;
import com.google.common.collect.Lists;

public final class KeySequencer {

    private static final Random random = new Random();
    private static final Digest digest = new SHA1Digest();

    private final LinkedList<String> keyList;

    public KeySequencer() {
        keyList = Lists.newLinkedList();
    }

    private static final String seed() {
        final byte[] seed = new byte[50];
        random.nextBytes(seed);
        return Hex.encodeHexString(digest.doHash(seed));
    }

    private static final String nextDigest(final String current) {
        return Hex.encodeHexString(digest.doHash(current.getBytes()));
    }

    public final void reset() {
        final int size = 10 + random.nextInt(40);

        keyList.clear();
        String current = seed();
        for (int i = 0; i < size; i++) {
            current = nextDigest(current);
            keyList.addLast(current);
        }
    }

    public final boolean hasNext() {
        return !keyList.isEmpty();
    }

    @Nullable
    public final String next() {
        if (keyList.isEmpty())
            return null;

        return keyList.removeLast();
    }

}