/*
    * 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 --------------------------------------------------------
 
 }