/*

  * #%L

  * DocumentReference.java - mongodb-async-driver - Allanbank Consulting, Inc.

  * %%

  * Copyright (C) 2011 - 2014 Allanbank Consulting, Inc.

  * %%

  * 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.

  * #L%

  */

 package com.allanbank.mongodb.bson;

 import static com.allanbank.mongodb.util.Assertions.assertNotNull;

 import java.io.Serializable;

 import com.allanbank.mongodb.bson.builder.BuilderFactory;

 import com.allanbank.mongodb.bson.builder.DocumentBuilder;

 /**

  * DocumentReference provides a standard MongoDB reference to a document within

  * a collection. This is commonly referred to as a DBRef.

  * <p>

  * A DocumentReference contains:

  * <ol>

  * <li>The name of the collection where the referenced document resides:

  * {@code $ref}.</li>

  * <li>The value of the _id field in the referenced document: {@code $id}.</li>

  * <li>The name of the database where the referenced document resides:

  * {@code $db} (Optional).</li>

  * </ol>

  * 

  * @see <a

  *      href="http://docs.mongodb.org/manual/applications/database-references/#dbref">MongoDB

  *      DBRef Information</a>

  * @api.yes This class is part of the driver's API. Public and protected members

  *          will be deprecated for at least 1 non-bugfix release (version

  *          numbers are <major>.<minor>.<bugfix>) before being

  *          removed or modified.

  * @copyright 2012-2013, Allanbank Consulting, Inc., All Rights Reserved

  */

 public class DocumentReference implements DocumentAssignable, Serializable {

     /** The name for the collection name field. */

     public static final String COLLECTION_FIELD_NAME = "$ref";

     /** The name for the database name field. */

     public static final String DATABASE_FIELD_NAME = "$db";

     /** The name for the id field. */

     public static final String ID_FIELD_NAME = "$id";

     /** The serialization version for the class. */

     private static final long serialVersionUID = 7597767390422754639L;

     /** The name of the collection being referenced. */

     private final String myCollectionName;

     /** The name of the database being referenced. */

     private final String myDatabaseName;

     /** The id of the document being referenced. */

     private final Element myId;

     /**

      * Creates a new DocumentReference.

      * 

      * @param collectionName

      *            The name of the collection being referenced.

      * @param id

      *            The id of the document being referenced. The name of the

      *            element is ignored within the {@link DocumentReference}.

      * @throws IllegalArgumentException

      *             If the {@code collectionName} or {@code id} are

      *             <code>null</code>.

      */

     public DocumentReference(final String collectionName, final Element id)

             throws IllegalArgumentException {

         this(null, collectionName, id);

     }

     /**

      * Creates a new DocumentReference.

      * 

      * @param databaseName

      *            The name of the database being referenced.

      * @param collectionName

      *            The name of the collection being referenced.

      * @param id

      *            The id of the document being referenced. The name of the

      *            element is ignored within the {@link DocumentReference}.

      * @throws IllegalArgumentException

      *             If the {@code collectionName} or {@code id} are

      *             <code>null</code>.

      */

     public DocumentReference(final String databaseName,

             final String collectionName, final Element id)

             throws IllegalArgumentException {

         assertNotNull(collectionName,

                 "The collection name of a Document Reference (DBRef) cannot be null.");

         assertNotNull(id,

                 "The id of a Document Reference (DBRef) cannot be null.");

         myDatabaseName = databaseName;

         myCollectionName = collectionName;

         myId = id.withName(ID_FIELD_NAME);

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to return a DBRef style document. This is the reference as a

      * document <em>not</em> the referenced document.

      * </p>

      */

     @Override

     public Document asDocument() {

         final DocumentBuilder builder = BuilderFactory.start();

         builder.add(COLLECTION_FIELD_NAME, myCollectionName);

         builder.add(myId.withName(ID_FIELD_NAME));

         if (myDatabaseName != null) {

             builder.add(DATABASE_FIELD_NAME, myDatabaseName);

         }

         return builder.asDocument();

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to compare the {@code object} to this

      * {@link DocumentReference} .

      * </p>

      */

     @Override

     public boolean equals(final Object object) {

         boolean result = false;

         if (this == object) {

             result = true;

         }

         else if ((object != null) && (getClass() == object.getClass())) {

             final DocumentReference other = (DocumentReference) object;

             result = myCollectionName.equals(other.myCollectionName)

                     && myId.withName(ID_FIELD_NAME).equals(

                             other.myId.withName(ID_FIELD_NAME))

                     && nullSafeEquals(myDatabaseName, other.myDatabaseName);

         }

         return result;

     }

     /**

      * Returns the name of the collection being referenced.

      * 

      * @return The name of the collection being referenced.

      */

     public String getCollectionName() {

         return myCollectionName;

     }

     /**

      * Returns the name of the database being referenced. This may be

      * <code>null</code>.

      * 

      * @return The name of the database being referenced.

      */

     public String getDatabaseName() {

         return myDatabaseName;

     }

     /**

      * Returns the id of the document being referenced.

      * 

      * @return The id of the document being referenced.

      */

     public Element getId() {

         return myId;

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to compute a reasonable hash for this

      * {@link DocumentReference}.

      * </p>

      */

     @Override

     public int hashCode() {

         int result = 1;

         result = (31 * result) + myCollectionName.hashCode();

         result = (31 * result) + myId.withName(ID_FIELD_NAME).hashCode();

         result = (31 * result)

                 + ((myDatabaseName != null) ? myDatabaseName.hashCode() : 3);

         return result;

     }

     /**

      * {@inheritDoc}

      * <p>

      * Overridden to return a JSON like representation of the

      * {@link DocumentReference}.

      * </p>

      */

     @Override

     public String toString() {

         final StringBuilder builder = new StringBuilder("{ '");

         builder.append(COLLECTION_FIELD_NAME);

         builder.append("' : '");

         builder.append(myCollectionName);

         builder.append("', ");

         builder.append(myId.withName(ID_FIELD_NAME));

         if (myDatabaseName != null) {

             builder.append(", '");

             builder.append(DATABASE_FIELD_NAME);

             builder.append("' : '");

             builder.append(myDatabaseName);

             builder.append("'");

         }

         builder.append(" }");

         return builder.toString();

     }

     /**

      * Does a null safe equals comparison.

      * 

      * @param rhs

      *            The right-hand-side of the comparison.

      * @param lhs

      *            The left-hand-side of the comparison.

      * @return True if the rhs equals the lhs. Note: nullSafeEquals(null, null)

      *         returns true.

      */

     protected boolean nullSafeEquals(final Object rhs, final Object lhs) {

         return (rhs == lhs) || ((rhs != null) && rhs.equals(lhs));

     }

 }