content: /**
   * 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 org.apache.aurora.scheduler.storage.durability;
  
  import java.util.Objects;
  import java.util.stream.Stream;
  
  import javax.annotation.Nullable;
  
  import org.apache.aurora.gen.storage.Op;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Persistence layer for storage operations.
   */
  public interface Persistence {
  
    /**
     * Prepares the persistence layer.  The implementation may use this, for example, to advertise as
     * a replica to cohort schedulers, or begin syncing state for warm standby.
     */
    void prepare();
  
    /**
     * Recovers previously-persisted records.
     *
     * @return All edits to apply.
     * @throws PersistenceException If recovery failed.
     */
    Stream<Edit> recover() throws PersistenceException;
  
    /**
     * Saves new records.  No records may be considered durably saved until this method returns
     * successfully.
     *
     * @param records Records to save.
     * @throws PersistenceException If the records could not be saved.
     */
    void persist(Stream<Op> records) throws PersistenceException;
  
    /**
     * An edit to apply when recovering from persistence.
     */
    class Edit {
      @Nullable private final Op op;
  
      private Edit(@Nullable Op op) {
        this.op = op;
      }
  
      public static Edit op(Op op) {
        return new Edit(requireNonNull(op));
      }
  
      public static Edit deleteAll() {
        return new Edit(null);
      }
  
      public boolean isDeleteAll() {
        return op == null;
      }
  
      public Op getOp() {
        return requireNonNull(op);
      }
  
      @Override
      public boolean equals(Object obj) {
        if (!(obj instanceof Edit)) {
          return false;
        }
  
        Edit other = (Edit) obj;
        return Objects.equals(op, other.op);
      }
  
      @Override
      public int hashCode() {
        return Objects.hashCode(op);
      }
  
      @Override
      public String toString() {
        return Objects.toString(op);
      }
    }
  
    /**
     * Thrown when a persistence operation fails.
     */
    class PersistenceException extends Exception {
      public PersistenceException(String msg) {
        super(msg);
      }
  
      public PersistenceException(Throwable cause) {
        super(cause);
      }
  
      public PersistenceException(String msg, Throwable cause) {
        super(msg, cause);
      }
    }
  }
  