content: /*
   * Copyright (C) 2020 ActiveJ LLC.
   *
   * 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 io.activej.ot.reducers;
  
  import io.activej.ot.OTCommit;
  import io.activej.promise.Promise;
  
  import java.util.Collection;
  
  public interface GraphReducer<K, D, R> {
  	default void onStart(Collection<OTCommit<K, D>> queue) {
  	}
  
  	@SuppressWarnings("WeakerAccess")
  	final class Result<R> {
  		private final boolean resume;
  		private final boolean skip;
  		private final R value;
  
  		public Result(boolean resume, boolean skip, R value) {
  			this.resume = resume;
  			this.skip = skip;
  			this.value = value;
  		}
  
  		public static <T> Result<T> resume() {
  			return new Result<>(true, false, null);
  		}
  
  		public static <T> Result<T> skip() {
  			return new Result<>(false, true, null);
  		}
  
  		public static <T> Result<T> complete(T value) {
  			return new Result<>(false, false, value);
  		}
  
  		public static <T> Promise<Result<T>> resumePromise() {
  			return Promise.of(resume());
  		}
  
  		public static <T> Promise<Result<T>> skipPromise() {
  			return Promise.of(skip());
  		}
  
  		public static <T> Promise<Result<T>> completePromise(T value) {
  			return Promise.of(complete(value));
  		}
  
  		public boolean isResume() {
  			return resume;
  		}
  
  		public boolean isSkip() {
  			return skip;
  		}
  
  		public boolean isComplete() {
  			return !resume && !skip;
  		}
  
  		public R get() {
  			if (isComplete()) {
  				return value;
  			}
  			throw new IllegalStateException();
  		}
  	}
  
  	Promise<Result<R>> onCommit(OTCommit<K, D> commit);
  }
  