/*

  * Copyright 2012-2013 smartics, Kronseder & Reiner GmbH

  *

  * 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 de.smartics.properties.spi.config.ds;

 import java.sql.Connection;

 import java.sql.ResultSet;

 import java.sql.SQLException;

 import java.util.Iterator;

 import java.util.NoSuchElementException;

 import javax.annotation.concurrent.NotThreadSafe;

 import de.smartics.properties.api.config.domain.Property;

 import de.smartics.properties.api.config.domain.PropertyCollection;

 import de.smartics.properties.api.config.domain.PropertyLocation;

 /**

  * Implementation of {@link PropertyCollection} based on accessing a data

  * source.

  */

 @NotThreadSafe

 public final class DsPropertyCollection implements PropertyCollection

 {

   // ********************************* Fields *********************************

   // --- constants ------------------------------------------------------------

   // --- members --------------------------------------------------------------

   /**

    * The identifier of the data source the properties are read from.

    */

   private final String dataSourceId;

   /**

    * The underlying connection of the result set.

    */

   private final Connection connection;

   /**

    * The properties to iterate over.

    */

   private final ResultSet resultSet;

   // ****************************** Initializer *******************************

   // ****************************** Constructors ******************************

   /**

    * Default constructor.

    *

    * @param dataSourceId the identifier of the data source the properties are

    *          read from.

    * @param connection the underlying connection of the result set.

    * @param resultSet the properties to iterate over.

    */

   public DsPropertyCollection(final String dataSourceId,

       final Connection connection, final ResultSet resultSet)

   {

     this.dataSourceId = dataSourceId;

     this.connection = connection;

     this.resultSet = resultSet;

   }

   // ****************************** Inner Classes *****************************

   /**

    * Maps the result set iteration to a Java iterator.

    */

   private final class ResultSetIterator implements Iterator<Property>

   {

     // ******************************** Fields ********************************

     // --- constants ----------------------------------------------------------

     // --- members ------------------------------------------------------------

     /**

      * A reference to the next property to return.

      */

     private Property nextProperty;

     // ***************************** Initializer ******************************

     // ***************************** Constructors *****************************

     // ***************************** Inner Classes ****************************

     // ******************************** Methods *******************************

     // --- init ---------------------------------------------------------------

     // --- get&set ------------------------------------------------------------

     // --- business -----------------------------------------------------------

     @Override

     public boolean hasNext()

     {

       provideProperty();

       return nextProperty != null;

     }

     @Override

     public Property next()

     {

       provideProperty();

       if (nextProperty == null)

       {

         throw new NoSuchElementException(

             "No further elements in collection from data source '"

                 + dataSourceId + "'.");

       }

       final Property currentProperty = nextProperty;

       nextProperty = null;

       return currentProperty;

     }

     /**

      * {@inheritDoc}

      * <p>

      * Not supported by this implementation.

      * </p>

      *

      * @throws UnsupportedOperationException always.

      */

     @Override

     public void remove() throws UnsupportedOperationException

     {

       throw new UnsupportedOperationException("Remove not supported.");

     }

     private void provideProperty()

     {

       if (nextProperty == null)

       {

         try

         {

           if (resultSet.next())

           {

             final String name = resultSet.getString(1);

             final String value = resultSet.getString(2);

             nextProperty =

                 new Property(new PropertyLocation(dataSourceId), name, value);

           }

           else

           {

             close();

           }

         }

         catch (final SQLException e)

         {

           close();

           throw new IllegalStateException(

               "Cannot read next property from data source '" + dataSourceId

                   + "'.");

         }

       }

     }

     // --- object basics ------------------------------------------------------

   }

   // ********************************* Methods ********************************

   // --- init -----------------------------------------------------------------

   // --- get&set --------------------------------------------------------------

   // --- business -------------------------------------------------------------

   /**

    * {@inheritDoc}

    *

    * @see java.lang.Iterable#iterator()

    */

   @Override

   public Iterator<Property> iterator()

   {

     return new ResultSetIterator();

   }

   /**

    * Closes the collection to release the underlying connection.

    * <p>

    * The connection is automatically closed when the iterator reaches the last

    * element.

    * </p>

    */

   @Override

   public void close()

   {

     try

     {

       if (!connection.isClosed())

       {

         connection.close();

       }

     }

     catch (final SQLException e)

     {

       // Ignore

     }

   }

   // --- object basics --------------------------------------------------------

 }