io.telicent.smart.cache.sources.file.NumericFilenameComparator Maven / Gradle / Ivy

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/**
 * Copyright (C) Telicent Ltd
 *
 * 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 io.telicent.smart.cache.sources.file;

import org.apache.commons.lang3.StringUtils;

import java.io.File;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;

/**
 * A comparator for filenames which extracts the numeric portion of the filename, parses it to a long integer and
 * compares based on that resulting in sorting files into numeric order
 */
public class NumericFilenameComparator implements Comparator {

    private final Map fileToNumberCache = new HashMap<>();

    @Override
    public int compare(File x, File y) {
        if (x == y) {
            return 0;
        } else if (x == null) {
            return -1;
        } else if (y == null) {
            return 1;
        }

        Long xNum = fileToNumberCache.computeIfAbsent(x, NumericFilenameComparator::fileToNumber);
        Long yNum = fileToNumberCache.computeIfAbsent(y, NumericFilenameComparator::fileToNumber);

        int c = xNum.compareTo(yNum);
        if (c == 0) {
            c = x.getAbsolutePath().compareTo(y.getAbsolutePath());
        }

        return c;
    }

    /**
     * Converts a file into a number, or if not possible returns {@link Long#MIN_VALUE}
     *
     * @param f File, MUST not be {@code null}
     * @return Number
     */
    private static Long fileToNumber(File f) {
        String name = f.getName();
        if (StringUtils.contains(name, ".")) {
            name = name.substring(0, name.indexOf("."));
        }
        name = StringUtils.getDigits(name);
        if (StringUtils.isBlank(name)) {
            return Long.MIN_VALUE;
        }
        try {
            return Long.parseLong(name);
        } catch (NumberFormatException e) {
            return Long.MIN_VALUE;
        }
    }
}