content: /*
   * Copyright (c) OSGi Alliance 2015. All Rights Reserved.
   *
   * 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.osgi.util.promise;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.List;
  
  /**
   * Static helper methods for Promises.
   */
  public class Promises {
      /**
       * Create a new Promise that has been resolved with the specified value.
       *
       * @param value The value of the resolved Promise.
       * @param <T>   The value type associated with the returned Promise.
       * @return A new Promise that has been resolved with the specified value.
       */
      public static <T> Promise<T> resolved(T value) {
          Deferred<T> def = new Deferred<T>();
          def.resolve(value);
          return def.getPromise();
      }
  
      /**
       * Create a new Promise that has been resolved with the specified failure.
       *
       * @param failure The failure of the resolved Promise. Must not be null.
       * @param <T>     The value type associated with the returned Promise.
       * @return A new Promise that has been resolved with the specified failure.
       */
      public static <T> Promise<T> failed(Throwable failure) {
          if (failure == null)
              throw new NullPointerException();
          Deferred<T> def = new Deferred<T>();
          def.fail(failure);
          return def.getPromise();
      }
  
      /**
       * Create a new Promise that is a latch on the resolution of the specified Promises.
       * <p/>
       * The new Promise acts as a gate and must be resolved after all of the specified Promises are resolved.
       *
       * @param promises The Promises which must be resolved before the returned Promise must be resolved. Must not be
       *                 null.
       * @param <T>      The value type of the List value associated with the returned Promise.
       * @param <S>      A subtype of the value type of the List value associated with the returned Promise.
       * @return A Promise that is resolved only when all the specified Promises are resolved. The returned Promise will
       * be successfully resolved, with a List of the values in the order of the specified Promises, if all the specified
       * Promises are successfully resolved. The List in the returned Promise is the property of the caller and is
       * modifiable. The returned Promise will be resolved with a failure of FailedPromisesException if any of the
       * specified Promises are resolved with a failure. The failure FailedPromisesException must contain all of the
       * specified Promises which resolved with a failure.
       */
      public static <T, S> Promise<List<T>> all(final Collection<Promise<S>> promises) {
          if (promises == null)
              throw new NullPointerException();
          final Deferred<List<T>> result = new Deferred<List<T>>();
          final Collection<Promise<?>> failedPromises = new ArrayList<Promise<?>>();
          final List<T> resolvedValues = new ArrayList<T>();
  
          if (promises.size() == 0) {
              result.resolve(resolvedValues);
          }
          for (final Promise<S> promise : promises) {
              promise.then(new Success<S, T>() {
                  @Override
                  public Promise<T> call(Promise<S> resolved) throws Exception {
                      // "S is subtype of the value type of the List"
                      @SuppressWarnings("unchecked")
                      T value = (T) resolved.getValue();
                      resolvedValues.add(value);
  
                      if (resolvedValues.size() == promises.size()) {
                          result.resolve(resolvedValues);
                      } else if (failedPromises.size() + resolvedValues.size() == promises.size()) {
                          result.fail(new FailedPromisesException(failedPromises));
                      }
                      return null;
                  }
              }, new Failure() {
                  @Override
                  public void fail(Promise<?> resolved) throws Exception {
                      failedPromises.add(resolved);
                      if (failedPromises.size() + resolvedValues.size() == promises.size()) {
                          result.fail(new FailedPromisesException(failedPromises));
                      }
                  }
              });
  
          }
  
          return result.getPromise();
      }
  
      /**
       * Create a new Promise that is a latch on the resolution of the specified Promises.
       * <p/>
       * The new Promise acts as a gate and must be resolved after all of the specified Promises are resolved.
       *
       * @param promises The Promises which must be resolved before the returned Promise must be resolved. Must not be
       *                 null.
       * @param <T>      The value type associated with the specified Promises.
       * @return A Promise that is resolved only when all the specified Promises are resolved. The returned Promise will
       * be successfully resolved, with a List of the values in the order of the specified Promises, if all the specified
       * Promises are successfully resolved. The List in the returned Promise is the property of the caller and is
       * modifiable. The returned Promise will be resolved with a failure of FailedPromisesException if any of the
       * specified Promises are resolved with a failure. The failure FailedPromisesException must contain all of the
       * specified Promises which resolved with a failure.
       */
      public static <T> Promise<List<T>> all(final Promise<? extends T>... promises) {
          if (promises == null)
              throw new NullPointerException();
          List<Promise<T>> list = new ArrayList<Promise<T>>();
          for (Promise<? extends T> promise : promises) {
              @SuppressWarnings("unchecked")
              Promise<T> pt = (Promise<T>) promise;
              list.add(pt);
          }
          return all(list);
      }
  }
  