/*
    * Licensed to The Apereo Foundation under one or more contributor license
    * agreements. See the NOTICE file distributed with this work for additional
    * information regarding copyright ownership.
    *
    *
    * The Apereo Foundation licenses this file to you under the Educational
    * Community 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://opensource.org/licenses/ecl2.txt
   *
   * 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.opencastproject.util.data.functions;
  
  import static org.opencastproject.util.data.Monadics.mlist;
  import static org.opencastproject.util.data.Option.some;
  
  import org.opencastproject.util.data.Effect;
  import org.opencastproject.util.data.Function;
  import org.opencastproject.util.data.Function2;
  import org.opencastproject.util.data.Option;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /** {@link Option} related functions. */
  public final class Options {
    private Options() {
    }
  
    /** m (m a) -> m a */
    public static <A> Option<A> join(Option<Option<A>> a) {
      return a.bind(Functions.<Option<A>> identity());
    }
  
    public static <A> Function<Option<A>, List<A>> asList() {
      return new Function<Option<A>, List<A>>() {
        @Override
        public List<A> apply(Option<A> a) {
          return a.list();
        }
      };
    }
  
    /** Returns some(message) if predicate is false, none otherwise. */
    public static Option<String> toOption(boolean predicate, String message) {
      return predicate ? Option.<String> none() : some(message);
    }
  
    /** Sequence a list of options. [Option a] -&gt; Option [a] */
    public static <A> Option<List<A>> sequenceOpt(List<Option<A>> as) {
      final List<A> seq = mlist(as).foldl(new ArrayList<A>(), new Function2<List<A>, Option<A>, List<A>>() {
        @Override
        public List<A> apply(List<A> sum, Option<A> o) {
          for (A a : o) {
            sum.add(a);
            return sum;
          }
          return sum;
        }
      });
      return some(seq);
    }
  
    /** Apply effect <code>e</code> to the result of <code>f</code> which is then returned. */
    public static <A, B> Function<A, Option<B>> foreach(final Function<? super A, ? extends Option<? extends B>> f,
            final Effect<? super B> e) {
      return new Function<A, Option<B>>() {
        @Override
        public Option<B> apply(A a) {
          return (Option<B>) f.apply(a).foreach(e);
        }
      };
    }
  
  }