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.arrow.driver.jdbc.client.utils;
  
  import java.util.ArrayDeque;
  import java.util.Deque;
  import java.util.Iterator;
  import java.util.List;
  import java.util.NoSuchElementException;
  import org.apache.arrow.flight.Location;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * A queue of Flight locations to connect to for an endpoint.
   *
   * <p>This helper class is intended to encapsulate the retry logic in a testable manner.
   */
  public final class FlightLocationQueue implements Iterator<Location> {
    private final Deque<Location> locations;
    private final Deque<Location> badLocations;
  
    /**
     * Create a new queue.
     *
     * @param flightClientCache An optional cache used to sort previously unreachable locations to the
     *     end.
     * @param locations The locations to try.
     */
    public FlightLocationQueue(
        @Nullable FlightClientCache flightClientCache, List<Location> locations) {
      this.locations = new ArrayDeque<>();
      this.badLocations = new ArrayDeque<>();
  
      for (Location location : locations) {
        if (flightClientCache != null && flightClientCache.isDud(location.toString())) {
          this.badLocations.add(location);
        } else {
          this.locations.add(location);
        }
      }
    }
  
    @Override
    public boolean hasNext() {
      return !locations.isEmpty() || !badLocations.isEmpty();
    }
  
    @Override
    public Location next() {
      if (!locations.isEmpty()) {
        return locations.pop();
      } else if (!badLocations.isEmpty()) {
        return badLocations.pop();
      }
      throw new NoSuchElementException();
    }
  }
  