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API for web agent persistence support

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// Copyright 2015-2024 Nstream, inc.
//
// 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 nstream.persist.api.cache;

import swim.structure.Value;
import swim.util.OrderedMap;

/**
 * Interface for stores that provide persistence for map lanes.
 */
public interface MapBackingStore extends BackingStore, OrderedMap {

  /**
   * Drop a prefix of the map.
   *
   * @param lower The number of elements to drop.
   */
  void dropPrefix(int lower);

  /**
   * Retain only a prefix of the map.
   *
   * @param keep The number of elements to retain.
   */
  void takePrefix(int keep);

  /**
   * Futures changes to the backing store must not be reflected by this map.
   * @return An instantaneous snapshot of the map.
   */
  OrderedMap snapshot();

}