package org.apache.blur.utils;

/**
 * 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.
 */
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;

import org.apache.blur.log.Log;
import org.apache.blur.log.LogFactory;
import org.apache.blur.thrift.generated.BlurException;
import org.apache.blur.utils.BlurExecutorCompletionService.Cancel;


public class ForkJoin {

  private static Log LOG = LogFactory.getLog(ForkJoin.class);

  public static interface ParallelCall<INPUT, OUTPUT> {
    OUTPUT call(INPUT input) throws Exception;
  }

  public static interface ParallelReturn<OUTPUT> {
    OUTPUT merge(Merger<OUTPUT> merger) throws BlurException;
  }

  public static interface Merger<OUTPUT> {
    OUTPUT merge(BlurExecutorCompletionService<OUTPUT> service) throws BlurException;
  }

  public static Cancel CANCEL = new Cancel() {
    @Override
    public void cancel() {
      // do nothing
    }
  };

  public static <INPUT, OUTPUT> ParallelReturn<OUTPUT> execute(ExecutorService executor, Iterable<INPUT> it, final ParallelCall<INPUT, OUTPUT> parallelCall) {
    return execute(executor, it, parallelCall, CANCEL);
  }

  public static <INPUT, OUTPUT> ParallelReturn<OUTPUT> execute(ExecutorService executor, Iterable<INPUT> it, final ParallelCall<INPUT, OUTPUT> parallelCall, Cancel cancel) {
    final BlurExecutorCompletionService<OUTPUT> service = new BlurExecutorCompletionService<OUTPUT>(executor, cancel);
    for (final INPUT input : it) {
      service.submit(new Callable<OUTPUT>() {
        @Override
        public OUTPUT call() throws Exception {
          return parallelCall.call(input);
        }
      });
    }
    return new ParallelReturn<OUTPUT>() {
      @Override
      public OUTPUT merge(Merger<OUTPUT> merger) throws BlurException {
        boolean exception = true;
        try {
          OUTPUT merge = merger.merge(service);
          exception = false;
          return merge;
        } finally {
          if (exception) {
            service.cancelAll();
          }
        }
      }
    };
  }

  public static <T> T ignoreExecutionException(Future<T> future, T defaultValue) throws InterruptedException {
    try {
      return future.get();
    } catch (ExecutionException e) {
      LOG.error("Error while trying to execute task [{0}]", e, e.getMessage());
      return defaultValue;
    }
  }
}