# AsyncAction.java

    /*
    ** Module   : AsyncAction.java
    ** Abstract : AsyncAction is an abstract asynchronous call back action that can chain
    **            the next dependent asynchronous call back or consumer.
    **
    ** Copyright (c) 2017, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- ----------------Description----------------------
    ** 001 SBI 20170601 Created initial version.
    */
    /*
    ** This program is free software: you can redistribute it and/or modify
    ** it under the terms of the GNU Affero General Public License as
    ** published by the Free Software Foundation, either version 3 of the
    ** License, or (at your option) any later version.
    **
    ** This program is distributed in the hope that it will be useful,
    ** but WITHOUT ANY WARRANTY; without even the implied warranty of
    ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    ** GNU Affero General Public License for more details.
    **
    ** You may find a copy of the GNU Affero GPL version 3 at the following
    ** location: https://www.gnu.org/licenses/agpl-3.0.en.html
    **
    ** Additional terms under GNU Affero GPL version 3 section 7:
    **
    **   Under Section 7 of the GNU Affero GPL version 3, the following additional
    **   terms apply to the works covered under the License.  These additional terms
    **   are non-permissive additional terms allowed under Section 7 of the GNU
    **   Affero GPL version 3 and may not be removed by you.
    **
    **   0. Attribution Requirement.
    **
    **     You must preserve all legal notices or author attributions in the covered
    **     work or Appropriate Legal Notices displayed by works containing the covered
    **     work.  You may not remove from the covered work any author or developer
    **     credit already included within the covered work.
    **
    **   1. No License To Use Trademarks.
    **
    **     This license does not grant any license or rights to use the trademarks
    **     Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
    **     of Golden Code Development Corporation. You are not authorized to use the
    **     name Golden Code, FWD, or the names of any author or contributor, for
    **     publicity purposes without written authorization.
    **
    **   2. No Misrepresentation of Affiliation.
    **
    **     You may not represent yourself as Golden Code Development Corporation or FWD.
    **
    **     You may not represent yourself for publicity purposes as associated with
    **     Golden Code Development Corporation, FWD, or any author or contributor to
    **     the covered work, without written authorization.
    **
    **   3. No Misrepresentation of Source or Origin.
    **
    **     You may not represent the covered work as solely your work.  All modified
    **     versions of the covered work must be marked in a reasonable way to make it
    **     clear that the modified work is not originating from Golden Code Development
    **     Corporation or FWD.  All modified versions must contain the notices of
    **     attribution required in this license.
    */

    package com.goldencode.p2j.admin.client.application.home;

    import java.util.function.Consumer;

    import com.google.common.base.Function;
    import com.google.gwt.user.client.rpc.AsyncCallback;

    /**
     * AsyncAction is an abstract asynchronous call back action that can chain the next dependent
     * asynchronous call back or consumer.
     *
     * @param    <I>
     *           An input type
     * @param    <R>
     *           A result type
     */
    public abstract class AsyncAction<I, R> implements AsyncCallback<R>, Consumer<I>
    {
       /** The main asynchronous task */
       protected final AsyncCallback<R> first;

       /** The chained asynchronous task */
       protected Consumer<R> next;

       /** The exposed callback used by subclasses of this asynchronous task */
       protected final DefaultAsyncCallback delegate;

       /**
        * Setups the base functionality.
        */
       public AsyncAction()
       {
          delegate = new DefaultAsyncCallback();
          first = this;
       }

       /**
        * The default asynchronous callback.
        */
       private class DefaultAsyncCallback
       implements AsyncCallback<R>
       {

          @Override
          public void onFailure(Throwable caught)
          {
             first.onFailure(caught);
          }

          @Override
          public void onSuccess(R result)
          {
             first.onSuccess(result);
             if (next != null)
             {
                next.accept(result);
             }
          }

       }

       /**
        * Makes the given action to be executed after the main asynchronous action.
        *
        * @param    <I2>
        *           An input type
        * @param    <R2>
        *           A result type
        * @param    action
        *           The chained asynchronous action
        * @param    mapper
        *           Maps the output of the main asynchronous action to the input of the next action
        */
       public <I2, R2> void then(AsyncAction<I2, R2> action, Function<R, I2> mapper)
       {
          next = new Consumer<R>()
          {
             @Override
             public void accept(R result)
             {
                action.accept(mapper.apply(result));
             }
          };
       }

       /**
        * Makes the given action to be executed after the main asynchronous action. The output of
        * the main asynchronous action is the input of the given chained asynchronous action.
        *
        * @param    <R2>
        *           A result type
        * @param    action
        *           The chained asynchronous action
        */
       public <R2> void then(AsyncAction<R, R2> action)
       {
          then(action, r -> r);
       }

       /**
        * Adds a consumer of the output of the main asynchronous action.
        *
        * @param    consumer
        *           The consumer of the output of the main asynchronous action
        */
       public void then(Consumer<R> consumer)
       {
          next = consumer;
       }

       /**
        * The default on error callback method.
        *
        * @param    caught
        *           The exception thrown by the main asynchronous action
        */
       @Override
       public void onFailure(Throwable caught)
       {
       }

       /**
        * The default on success callback method.
        *
        * @param    result
        *           The output of the main asynchronous action
        */
       @Override
       public void onSuccess(R result)
       {
       }
    }