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/**
 * Copyright 2017 Goldman Sachs.
 * Licensed 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 com.gs.obevo.util.vfs;

import java.nio.charset.Charset;

import org.mozilla.universalchardet.UniversalDetector;

/**
 * Detect the charset of some input bytes, or returns null if unable to detect.
 * Leverages the Mozilla universalchardet library: https://code.google.com/archive/p/juniversalchardet/
 */
class DetectCharsetStrategy implements CharsetStrategy {
    private static final ThreadLocal charsetDetector = new ThreadLocal() {
        @Override
        protected UniversalDetector initialValue() {
            return new UniversalDetector(null);
        }
    };

    @Override
    public Charset determineCharset(byte[] bytes) {
        UniversalDetector detector = charsetDetector.get();
        try {
            detector.handleData(bytes, 0, bytes.length);
            detector.dataEnd();

            String encoding = detector.getDetectedCharset();
            if (encoding != null) {
                return Charset.forName(encoding);
            }

            return null;
        } finally {
            detector.reset();
        }
    }
}