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/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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 ai.platon.pulsar.skeleton.common.domain;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.InputStream;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * A Top-Level Domain is the suffix tied to a website, such as com, net, or org.
 * 

 * A top-level domain (TLD) is the suffix or extension tied to a website.
 * Around half of all websites use the top-level domain com, commonly called “dot” com.
 * 
 * There is no algorithmic way of knowing whether a suffix is a public domain suffix, or not.
 */
public class DomainSuffixes {
    private static final Logger LOG = LoggerFactory.getLogger(DomainSuffixes.class);

    public static String DOMAIN_SUFFIXES_FILE = "domain-suffixes.xml";
    private static DomainSuffixes instance;
    private Map domains = new ConcurrentHashMap<>();

    private DomainSuffixes() {
    }

    /**
     * Singleton instance, lazy instantination
     *
     * @return DomainSuffixes
     */
    public static DomainSuffixes getInstance() {
        if (instance == null) {
            synchronized (DomainSuffixes.class) {
                if (instance == null) {
                    instance = load(DOMAIN_SUFFIXES_FILE);
                }
            }
        }

        return instance;
    }

    private static DomainSuffixes load(String resource) {
        DomainSuffixes suffixes = null;

        LOG.info("Loading domain suffixes from resource " + resource);
        try (InputStream input = DomainSuffixes.class.getClassLoader().getResourceAsStream(resource)) {
            if (input == null) {
                LOG.error("Failed to load resource " + resource);
            } else {
                suffixes = new DomainSuffixesReader().read(new DomainSuffixes(), input);
                LOG.info("Total {} known domains", suffixes.domains.size());
            }
        } catch (Exception e) {
            LOG.warn(e.getMessage());
        }

        return suffixes;
    }

    void addDomainSuffix(DomainSuffix tld) {
        domains.put(tld.getDomain(), tld);
    }

    /**
     * return whether the extension is a registered domain entry
     */
    public boolean isDomainSuffix(String extension) {
        return domains.containsKey(extension);
    }

    /**
     * Return the {@link DomainSuffix} object for the extension, if extension is a
     * top level domain returned object will be an instance of
     * {@link TopLevelDomain}
     *
     * @param extension of the domain
     */
    public DomainSuffix get(String extension) {
        return domains.get(extension);
    }
}