# TransparentWrapper.java

    /*
    ** Module   : TransparentWrapper.java
    ** Abstract : simple container that implements WrappedResource for any object
    **
    ** Copyright (c) 2007-2020, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- --JPRM-- --------------------------Description---------------------------
    ** 001 GES 20070221   @32199 Created initial version which represents a
    **                           simple container that implements
    **                           WrappedResource for any object.
    ** 002 CA  20090227   @41382 Added WrappedResources.isUnknown method; this
    **                           implementation returns false, if referent is
    **                           not an instance of WrappedResource; else,
    **                           it returns referent.isUnknown() value.
    ** 003 CA  20130112          Made the referent field protected. Fixed equals.
    ** 004 OM  20130304          Refactored isValid and isUnknown of WrappedResource to valid
    **                           and unknown.
    ** 005 CA  20150502          The resource ID needs to be kept at the resource, so it can be
    **                           accessed after the resource is deleted.
    ** 006 CA  20200514          Fixed equals() and hashCode() when there is no referent.
    */
    /*
    ** 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.util;

    /**
     * Simple container that stores an object instance and implements the
     * {@link WrappedResource} interface. Since {@link #hashCode} and
     * {@link #equals} are redirected to the contained reference, this is as
     * suitable for use in a collection as the contained reference.
     */
    public class TransparentWrapper
    implements WrappedResource
    {
       /** The object being contained. */
       protected Object referent = null;

       /**
        * The resource's ID.  Remains <code>null</code> until the ID is requested via
        * {@link handle#resourceId}
        */
       private Long id = null;

       /**
        * Construct an instance given the object reference to contain.
        *
        * @param    referent
        *           The object to contain.
        */
       public TransparentWrapper(Object referent)
       {
          this.referent = referent;
       }

       /**
        * Get this resource's ID, if is already set.
        *
        * @return   The resource's ID or <code>null</code> if not set.
        */
       @Override
       public Long id()
       {
          return id;
       }

       /**
        * Set this resource's ID.
        *
        * @param    id
        *           The resource's ID.
        */
       @Override
       public void id(long id)
       {
          this.id = id;
       }

       /**
        * Returns the referent of this instance as an <code>Object</code>.
        *
        * @return   The value as an <code>Object</code> or <code>null</code> if
        *           there is no contained object.
        */
       public Object get()
       {
          return referent;
       }

       /**
        * Set the referent of this instance.
        *
        * @param    referent
        *           The value to be represented in this instance.
        */
       public void set(Object referent)
       {
          this.referent = referent;
       }

       /**
        * Reports if this object is valid for use.  If the contained object
        * reference itself implements {@link WrappedResource}, then this
        * call will be redirected to the contained object.  Otherwise, if
        * the contained object is <code>null</code>, then it is considered
        * invalid and not <code>null</code> is valid.
        *
        * @return   <code>true</code> if we are valid (can be used).
        */
       public boolean valid()
       {
          if (referent != null && referent instanceof WrappedResource)
          {
             // pass through the validity check
             WrappedResource res = (WrappedResource) referent;
             return res.valid();
          }

          // otherwise non-null means valid
          return (referent != null);
       }

       /**
        * Reports if this object is unknown.<p>
        * If {@link #referent} is not an instance of {@link WrappedResource}, it
        * returns false. Else, it returns {@link WrappedResource#unknown()}
        * result.
        *
        * @return   <code>true</code> if object is unknown.
        */
       public boolean unknown()
       {
          if (referent != null && referent instanceof WrappedResource)
          {
             WrappedResource res = (WrappedResource) referent;
             return res.unknown();
          }

          return false;
       }

       /**
        * Hash code implementation which is redirected to that of the
        * contained object so long as that object is not <code>null</code>.
        *
        * @return   Hash code value for this object instance.
        */
       public int hashCode()
       {
          return referent == null ? super.hashCode() : referent.hashCode();
       }

       /**
        * Determines if this instance and the passed-in instance are equivalent.
        *
        * @param    obj
        *           The instance to compare against.
        *
        * @return   <code>true</code> if the objects are the same.
        */
       public boolean equals(Object obj)
       {
          if (obj != null && obj instanceof TransparentWrapper)
          {
             obj = ((TransparentWrapper) obj).referent;
          }

          return (referent == null) ? super.equals(obj) : referent.equals(obj);
       }
    }