/*
 * Copyright (c) 2014 Spotify AB.
 *
 * 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 com.spotify.docker;

import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

import static java.lang.System.nanoTime;

public class Polling {

  public static <T> T await(final long timeout, final TimeUnit timeUnit, final Callable<T> callable)
      throws Exception {
    final long deadline = nanoTime() + timeUnit.toNanos(timeout);
    while (nanoTime() < deadline) {
      final T value = callable.call();
      if (value != null) {
        return value;
      }
      Thread.sleep(500);
    }

    final String msg = String.format(
        "The callable %s defined in %s failed to return anything after %d ms",
        callable.getClass().getName(),
        // since this is just test code, include the class/method/line number that called this
        // method  to help diagnose where the failure was since most Callables will just be
        // anonymous classes.
        // The class that called this method will be the 3rd element in the array - the first is the
        // getStackTrace method and the second is Polling.await
        Thread.currentThread().getStackTrace()[2],
        timeUnit.toMillis(timeout)
    );
    throw new TimeoutException(msg);
  }
}
