/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch 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.elasticsearch.index.analysis;

import com.ibm.icu.text.FilteredNormalizer2;
import com.ibm.icu.text.Normalizer2;
import com.ibm.icu.text.UnicodeSet;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.icu.ICUFoldingFilter;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.env.Environment;
import org.elasticsearch.index.IndexSettings;


/**
 * Uses the {@link org.apache.lucene.analysis.icu.ICUFoldingFilter}.
 * Applies foldings from UTR#30 Character Foldings.
 * <p>
 * Can be filtered to handle certain characters in a specified way (see http://icu-project.org/apiref/icu4j/com/ibm/icu/text/UnicodeSet.html)
 * E.g national chars that should be retained (filter : "[^åäöÅÄÖ]").
 *
 * <p>The <tt>unicodeSetFilter</tt> attribute can be used to provide the UniCodeSet for filtering.
 *
 * @author kimchy (shay.banon)
 */
public class IcuFoldingTokenFilterFactory extends AbstractTokenFilterFactory implements MultiTermAwareComponent {
    private final String unicodeSetFilter;

    public IcuFoldingTokenFilterFactory(IndexSettings indexSettings, Environment environment, String name, Settings settings) {
        super(indexSettings, name, settings);
        this.unicodeSetFilter = settings.get("unicodeSetFilter");
    }

    @Override
    public TokenStream create(TokenStream tokenStream) {

        // The ICUFoldingFilter is in fact implemented as a ICUNormalizer2Filter.
        // ICUFoldingFilter lacks a constructor for adding filtering so we implemement it here
        if (unicodeSetFilter != null) {
            Normalizer2 base = Normalizer2.getInstance(
                    ICUFoldingFilter.class.getResourceAsStream("utr30.nrm"),
                    "utr30", Normalizer2.Mode.COMPOSE);
            UnicodeSet unicodeSet = new UnicodeSet(unicodeSetFilter);

            unicodeSet.freeze();
            Normalizer2 filtered = new FilteredNormalizer2(base, unicodeSet);
            return new org.apache.lucene.analysis.icu.ICUNormalizer2Filter(tokenStream, filtered);
        }
        else {
            return new ICUFoldingFilter(tokenStream);
        }
    }

    @Override
    public Object getMultiTermComponent() {
        return this;
    }
}