content: /*
   *
   * 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 org.apache.bookkeeper.util;
  
  
  import java.io.File;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  import org.apache.commons.lang3.tuple.Pair;
  
  public class LedgerDirUtil {
  
      public static final Pattern FILE_PATTERN = Pattern.compile("^([0-9a-fA-F]+)\\.log$");
      public static final Pattern COMPACTED_FILE_PATTERN =
              Pattern.compile("^([0-9a-fA-F]+)\\.log\\.([0-9a-fA-F]+)\\.compacted$");
  
      public static List<Integer> logIdsInDirectory(File directory) {
          List<Integer> ids = new ArrayList<>();
          if (directory.exists() && directory.isDirectory()) {
              File[] files = directory.listFiles();
              if (files != null && files.length > 0) {
                  for (File f : files) {
                      Matcher m = FILE_PATTERN.matcher(f.getName());
                      if (m.matches()) {
                          int logId = Integer.parseUnsignedInt(m.group(1), 16);
                          ids.add(logId);
                      }
                  }
              }
          }
          return ids;
      }
  
      public static List<Integer> compactedLogIdsInDirectory(File directory) {
          List<Integer> ids = new ArrayList<>();
          if (directory.exists() && directory.isDirectory()) {
              File[] files = directory.listFiles();
              if (files != null && files.length > 0) {
                  for (File f : files) {
                      Matcher m = COMPACTED_FILE_PATTERN.matcher(f.getName());
                      if (m.matches()) {
                          int logId = Integer.parseUnsignedInt(m.group(1), 16);
                          ids.add(logId);
                      }
                  }
              }
          }
          return ids;
      }
  
      /**
       * O(nlogn) algorithm to find largest contiguous gap between
       * integers in a passed list. n should be relatively small.
       * Entry logs should be about 1GB in size, so even if the node
       * stores a PB, there should be only 1000000 entry logs.
       */
      public static Pair<Integer, Integer> findLargestGap(List<Integer> currentIds) {
          if (currentIds.isEmpty()) {
              return Pair.of(0, Integer.MAX_VALUE);
          }
  
          Collections.sort(currentIds);
  
          int nextIdCandidate = 0;
          int maxIdCandidate = currentIds.get(0);
          int maxGap = maxIdCandidate - nextIdCandidate;
          for (int i = 0; i < currentIds.size(); i++) {
              int gapStart = currentIds.get(i) + 1;
              int j = i + 1;
              int gapEnd = Integer.MAX_VALUE;
              if (j < currentIds.size()) {
                  gapEnd = currentIds.get(j);
              }
              int gapSize = gapEnd - gapStart;
              if (gapSize > maxGap) {
                  maxGap = gapSize;
                  nextIdCandidate = gapStart;
                  maxIdCandidate = gapEnd;
              }
          }
          return Pair.of(nextIdCandidate, maxIdCandidate);
      }
  }
  