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This project contains some of the configurable modules used within the Heritrix application to crawl the web. The modules in this project can be used in applications other than Heritrix, however.

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/*
 *  This file is part of the Heritrix web crawler (crawler.archive.org).
 *
 *  Licensed to the Internet Archive (IA) by one or more individual 
 *  contributors. 
 *
 *  The IA 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.
 */
package org.archive.modules.recrawl;

import org.archive.modules.CrawlURI;

/**
 * Represents a store of information, presumably persistent, keyed by content
 * digest.
 * 
 * @author nlevitt
 */
public abstract class AbstractContentDigestHistory {
    /**
     * Looks up the history by key {@code persistKeyFor(curi)} and loads it into
     * {@code curi.getContentDigestHistory()}.
     * 
     * @param curi
     */
    public abstract void load(CrawlURI curi);
    
    /**
     * Stores {@code curi.getContentDigestHistory()} for the key
     * {@code persistKeyFor(curi)}.
     * 
     * @param curi
     */
    public abstract void store(CrawlURI curi);

    /**
     * 
     * @param curi
     * @return {@code curi.getContentDigestSchemeString()}
     * @throws IllegalStateException if {@code curi.getContentDigestSchemeString()} is null
     */
    protected String persistKeyFor(CrawlURI curi) {
        String key = curi.getContentDigestSchemeString();
        if (key == null) {
            throw new IllegalStateException("cannot load content digest history, CrawlURI does not have content digest value for " + curi);
        }
        return key;
    }
}