/*
 * JBoss, the OpenSource J2EE webOS
 *
 * Distributable under LGPL license.
 * See terms of license at gnu.org.
 */

package org.jboss.ejb.plugins.cmp.jdbc;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.List;
import javax.ejb.EJBException;
import javax.ejb.NoSuchEntityException;

import org.jboss.ejb.EntityEnterpriseContext;
import org.jboss.ejb.plugins.cmp.jdbc.bridge.JDBCFieldBridge;
import org.jboss.ejb.plugins.cmp.jdbc.bridge.JDBCCMPFieldBridge;
import org.jboss.ejb.plugins.cmp.jdbc.bridge.JDBCEntityBridge;
import org.jboss.ejb.plugins.cmp.jdbc.metadata.JDBCFunctionMappingMetaData;
import org.jboss.logging.Logger;
import org.jboss.deployment.DeploymentException;

/**
 * JDBCLoadEntityCommand loads the data for an instance from the table.
 * This command implements specified eager loading. For CMP 2.x, the
 * entity can be configured to only load some of the fields, which is
 * helpful for entitys with lots of data.
 *
 * @author <a href="mailto:dain@daingroup.com">Dain Sundstrom</a>
 * @author <a href="mailto:on@ibis.odessa.ua">Oleg Nitz</a>
 * @author <a href="mailto:rickard.oberg@telkel.com">Rickard �berg</a>
 * @author <a href="mailto:marc.fleury@telkel.com">Marc Fleury</a>
 * @author <a href="mailto:shevlandj@kpi.com.au">Joe Shevland</a>
 * @author <a href="mailto:justin@j-m-f.demon.co.uk">Justin Forder</a>
 * @author <a href="mailto:dirk@jboss.de">Dirk Zimmermann</a>
 * @author <a href="mailto:danch@nvisia.com">danch (Dan Christopherson)</a>
 * @author <a href="mailto:alex@jboss.org">Alexey Loubyansky</a>
 * @version $Revision: 1.36.2.1 $
 */
public final class JDBCLoadEntityCommand
{
   private final JDBCStoreManager manager;
   private final JDBCEntityBridge entity;
   private final Logger log;
   private final JDBCFunctionMappingMetaData rowLockingTemplate;

   public JDBCLoadEntityCommand(JDBCStoreManager manager) throws DeploymentException
   {
      this.manager = manager;
      entity = (JDBCEntityBridge) manager.getEntityBridge();
      boolean rawLocking = entity.getMetaData().hasRowLocking();
      rowLockingTemplate = rawLocking ? entity.getMetaData().getTypeMapping().getRowLockingTemplate() : null;

      // Create the Log
      log = Logger.getLogger(
              this.getClass().getName() +
              "." +
              manager.getMetaData().getName());
   }

   /**
    * Loads entity.
    * If failIfNotFound is true and entity wasn't found then NoSuchEntityException is thrown.
    * Otherwise, if entity wasn't found, returns false.
    * If entity was loaded successfully return true.
    * @param ctx - entity context;
    * @param failIfNotFound - whether to fail if entity wasn't found;
    * @return true if entity was loaded, false - otherwise.
    */
   public boolean execute(EntityEnterpriseContext ctx, boolean failIfNotFound)
   {
      return execute(null, ctx, failIfNotFound);
   }

   /**
    * Loads entity or required field. If entity not found throws NoSuchEntityException.
    * @param requiredField - required field or null;
    * @param ctx - the corresponding context;
    */
   public void execute(JDBCCMPFieldBridge requiredField, EntityEnterpriseContext ctx)
   {
      execute(requiredField, ctx, true);
   }


   /**
    * Loads entity or required field.
    * If failIfNotFound is set to true, then NoSuchEntityException is thrown if the
    * entity wasn't found.
    * If failIfNotFound is false then if the entity wasn't found returns false,
    * if the entity was loaded successfully, returns true.
    * @param requiredField - required field;
    * @param ctx - entity context;
    * @param failIfNotFound - whether to fail if entity wasn't loaded.
    * @return true if entity was loaded, false - otherwise.
    */
   private boolean execute(JDBCCMPFieldBridge requiredField,
                           EntityEnterpriseContext ctx,
                           boolean failIfNotFound)
   {
      // load the instance primary key fields into the context
      Object id = ctx.getId();
      // TODO: when exactly do I need to do the following?
      entity.injectPrimaryKeyIntoInstance(ctx, id);

      // get the read ahead cache
      ReadAheadCache readAheadCache = manager.getReadAheadCache();

      // load any preloaded fields into the context
      if(readAheadCache.load(ctx))
      {
         if(requiredField == null || (requiredField != null && requiredField.isLoaded(ctx)))
         {
            return true;
         }
      }

      // get the finder results associated with this context, if it exists
      ReadAheadCache.EntityReadAheadInfo info = readAheadCache.getEntityReadAheadInfo(id);

      // determine the fields to load
      JDBCEntityBridge.FieldIterator loadIter = entity.getLoadIterator(requiredField, info.getReadAhead(), ctx);
      if(!loadIter.hasNext())
         return true;

      // get the keys to load
      List loadKeys = info.getLoadKeys();

      // generate the sql
      String sql = (rowLockingTemplate != null ? getRawLockingSQL(loadIter, loadKeys.size()) : getSQL(loadIter, loadKeys.size()));

      Connection con = null;
      PreparedStatement ps = null;
      ResultSet rs = null;
      try
      {
         // create the statement
         if (log.isDebugEnabled())
         {
            log.debug("Executing SQL: " + sql);
         }

         // get the connection
         con = entity.getDataSource().getConnection();
         ps = con.prepareStatement(sql);

         // Set the fetch size of the statement
         if (entity.getFetchSize() > 0)
         {
            ps.setFetchSize(entity.getFetchSize());
         }

         // set the parameters
         int paramIndex = 1;
         for (int i = 0; i < loadKeys.size(); i++)
         {
            paramIndex = entity.setPrimaryKeyParameters(ps, paramIndex, loadKeys.get(i));
         }

         // execute statement
         rs = ps.executeQuery();

         // load results
         boolean mainEntityLoaded = false;
         Object[] ref = new Object[1];
         while (rs.next())
         {
            // reset the column index for this row
            int index = 1;

            // ref must be reset to null before load
            ref[0] = null;

            // if we are loading more then one entity, load the pk from the row
            Object pk = null;
            if (loadKeys.size() > 1)
            {
               // load the pk
               index = entity.loadPrimaryKeyResults(rs, index, ref);
               pk = ref[0];
            }

            // is this the main entity or a preload entity
            if (loadKeys.size() == 1 || pk.equals(id))
            {
               // main entity; load the values into the context
               loadIter.reset();
               while(loadIter.hasNext())
               {
                  JDBCCMPFieldBridge field = loadIter.next();
                  index = field.loadInstanceResults(rs, index, ctx);
                  field.setClean(ctx);
               }
               mainEntityLoaded = true;
            }
            else
            {
               // preload entity; load the values into the read ahead cahce
               loadIter.reset();
               while(loadIter.hasNext())
               {
                  JDBCCMPFieldBridge field = loadIter.next();
                  // ref must be reset to null before load
                  ref[0] = null;

                  // load the result of the field
                  index = field.loadArgumentResults(rs, index, ref);

                  // cache the field value
                  readAheadCache.addPreloadData(pk, field, ref[0]);
               }
            }
         }

         // clear LOAD_REQUIRED flag
         loadIter.removeAll();

         // did we load the main results
         if (!mainEntityLoaded)
         {
            if (failIfNotFound)
               throw new NoSuchEntityException("Entity not found: primaryKey=" + ctx.getId());
            else
               return false;
         }
         else
            return true;
      }
      catch (EJBException e)
      {
         throw e;
      }
      catch (Exception e)
      {
         throw new EJBException("Load failed", e);
      }
      finally
      {
         JDBCUtil.safeClose(rs);
         JDBCUtil.safeClose(ps);
         JDBCUtil.safeClose(con);
      }
   }

   private String getSQL(JDBCEntityBridge.FieldIterator loadIter, int keyCount)
   {
      StringBuffer sql = new StringBuffer(250);
      sql.append(SQLUtil.SELECT);

      // if we are loading more then one entity we need to add the primry
      // key to the load fields to match up the results with the correct entity.
      JDBCFieldBridge[] primaryKeyFields = entity.getPrimaryKeyFields();
      if (keyCount > 1)
      {
         SQLUtil.getColumnNamesClause(primaryKeyFields, sql);
         sql.append(SQLUtil.COMMA);
      }
      SQLUtil.getColumnNamesClause(loadIter, sql);
      sql.append(SQLUtil.FROM)
              .append(entity.getQualifiedTableName())
              .append(SQLUtil.WHERE);

      //
      // where clause
      String pkWhere = SQLUtil.getWhereClause(primaryKeyFields, new StringBuffer(50)).toString();
      sql.append('(').append(pkWhere).append(')');
      for (int i = 1; i < keyCount; i++)
      {
         sql.append(SQLUtil.OR).append('(').append(pkWhere).append(')');
      }

      return sql.toString();
   }

   private String getRawLockingSQL(JDBCEntityBridge.FieldIterator loadIter, int keyCount)
   {
      //
      // column names clause
      StringBuffer columnNamesClause = new StringBuffer(250);
      // if we are loading more then one entity we need to add the primry
      // key to the load fields to match up the results with the correct
      // entity.
      if (keyCount > 1)
      {
         SQLUtil.getColumnNamesClause(entity.getPrimaryKeyFields(), columnNamesClause);
         columnNamesClause.append(SQLUtil.COMMA);
      }

      SQLUtil.getColumnNamesClause(loadIter, columnNamesClause);

      //
      // table name clause
      String tableName = entity.getQualifiedTableName();

      //
      // where clause
      String whereClause = SQLUtil.
              getWhereClause(entity.getPrimaryKeyFields(), new StringBuffer(50)).toString();
      if (keyCount > 0)
      {
         StringBuffer sb = new StringBuffer((whereClause.length() + 6) * keyCount + 4);
         for (int i = 0; i < keyCount; i++)
         {
            if (i > 0)
               sb.append(SQLUtil.OR);
            sb.append('(').append(whereClause).append(')');
         }
         whereClause = sb.toString();
      }

      String[] args = new String[]{
         columnNamesClause.toString(),
         tableName,
         whereClause,
         null // order by
      };
      return rowLockingTemplate.getFunctionSql(args, new StringBuffer(300)).toString();
   }
}