text: /*
   * 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.snapshots;
  
  import org.elasticsearch.action.support.IndicesOptions;
  import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
  import org.elasticsearch.common.regex.Regex;
  import org.elasticsearch.index.IndexNotFoundException;
  
  import java.util.Arrays;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  
  /**
   * Snapshot utilities
   */
  public class SnapshotUtils {
  
      /**
       * Filters out list of available indices based on the list of selected indices.
       *
       * @param availableIndices list of available indices
       * @param selectedIndices  list of selected indices
       * @param indicesOptions    ignore indices flag
       * @return filtered out indices
       */
      public static List<String> filterIndices(List<String> availableIndices, String[] selectedIndices, IndicesOptions indicesOptions) {
          if (IndexNameExpressionResolver.isAllIndices(Arrays.asList(selectedIndices))) {
              return availableIndices;
          }
          Set<String> result = null;
          for (int i = 0; i < selectedIndices.length; i++) {
              String indexOrPattern = selectedIndices[i];
              boolean add = true;
              if (!indexOrPattern.isEmpty()) {
                  if (availableIndices.contains(indexOrPattern)) {
                      if (result == null) {
                          result = new HashSet<>();
                      }
                      result.add(indexOrPattern);
                      continue;
                  }
                  if (indexOrPattern.charAt(0) == '+') {
                      add = true;
                      indexOrPattern = indexOrPattern.substring(1);
                      // if its the first, add empty set
                      if (i == 0) {
                          result = new HashSet<>();
                      }
                  } else if (indexOrPattern.charAt(0) == '-') {
                      // if its the first, fill it with all the indices...
                      if (i == 0) {
                          result = new HashSet<>(availableIndices);
                      }
                      add = false;
                      indexOrPattern = indexOrPattern.substring(1);
                  }
              }
              if (indexOrPattern.isEmpty() || !Regex.isSimpleMatchPattern(indexOrPattern)) {
                  if (!availableIndices.contains(indexOrPattern)) {
                      if (!indicesOptions.ignoreUnavailable()) {
                          throw new IndexNotFoundException(indexOrPattern);
                      } else {
                          if (result == null) {
                              // add all the previous ones...
                              result = new HashSet<>(availableIndices.subList(0, i));
                          }
                      }
                  } else {
                      if (result != null) {
                          if (add) {
                              result.add(indexOrPattern);
                          } else {
                              result.remove(indexOrPattern);
                          }
                      }
                  }
                  continue;
              }
              if (result == null) {
                  // add all the previous ones...
                  result = new HashSet<>(availableIndices.subList(0, i));
              }
              boolean found = false;
              for (String index : availableIndices) {
                  if (Regex.simpleMatch(indexOrPattern, index)) {
                      found = true;
                      if (add) {
                          result.add(index);
                      } else {
                          result.remove(index);
                      }
                  }
              }
              if (!found && !indicesOptions.allowNoIndices()) {
                  throw new IndexNotFoundException(indexOrPattern);
              }
          }
          if (result == null) {
              return List.of(selectedIndices);
          }
          return List.copyOf(result);
      }
  }
  