# ForwardResults.java

    /*
    ** Module   : ForwardResults.java
    ** Abstract : Implementation of Results which wraps ScrollableResults, used for ResultSet.TYPE_FORWARD_ONLY
    **
    ** Copyright (c) 2023-2024, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- ---------------------------------------Description----------------------------------------
    ** 001 SR  20230713 Created initial version.
    ** 002 AL2 20231025 Added rowNumber to be stored internally.
    ** 003 AL2 20240906 Implemented get(forceOnlyId).
    ** 004 OM  20241128 Multi-tenant runtime support: selected the proper persistence context, eventually
    **                  based on [sharedDb] parameter.
    */

    /*
    ** 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.
    **
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    **
    **     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.persist;

    import java.util.logging.*;
    import com.goldencode.p2j.persist.orm.*;
    import com.goldencode.p2j.util.logging.*;

    /**
     * A simple, forward only implementation of the {@code Results} interface, which offers a thin layer
     * around the internal, {@code ScrollableResults} object provided by the query.
     */
    final class ForwardResults
    implements Results
    {
       /** Logger */
       private static final CentralLogger LOG = CentralLogger.get(ForwardResults.class.getName());

       /** Scrollable result set;  primary keys or {@code Record}s */
       private final ScrollableResults<Object> results;

       /** Persistence object which provided the underlying ScrollableResults */
       private final Persistence persistence;

       /**
        * The {@link Persistence} context. Only used at cleanup time when the getter is not accessible
        * any more.
        */
       private final Persistence.Context persistenceContext;

       /** Track closed state of the {@link #results}. */
       private boolean closed = false;

       /** Flag to check if the result set is empty */
       private boolean hasResults = true;

       /** Flag to check if the cursor is after last row */
       private boolean isAfterLast = false;

       /** Cache the row number */
       private int rowNumber = -1;

       /**
        * Construct an instance of this object from a scrollable result set
        * provided by query execution.
        *
        * @param   persistence
        *          The associated persistence service object.
        * @param   results
        *          Scrollable result set generated by the query.
        */
       ForwardResults(Persistence persistence, ScrollableResults<Object> results)
       throws PersistenceException
       {
          this.results = results;
          this.persistence = persistence;
          this.persistenceContext = persistence.getContext(results.isSharedTenantDatabase());
          persistenceContext.useSession();
       }

       /**
        * Move cursor to the first result row only if the cursor is behind it.
        *
        * @return  <code>true</code> if the cursor is already first or behind it.
        */
       public boolean first()
       {
          if (!hasResults)
          {
             return false;
          }

          int rn = getRowNumber();
          if (isAfterLast || rn > 0)
          {
             LOG.log(Level.SEVERE, "Cannot call first in FORWARD_ONLY mode if the record is after first");
             return false;
          }

          if (rn == 0)
          {
             return true;
          }

          if (rn == -1)
          {
             return next();
          }

          LOG.log(Level.SEVERE, "Cannot call first in FORWARD_ONLY mode if the record is after first");
          return false;
       }

       /**
        * Move cursor to the last result row.
        *
        * @return  <code>true</code> if there are any results.
        */
       public boolean last()
       {
          if (!hasResults)
          {
             return false;
          }

          if (isLast())
          {
             return true;
          }

          while (!isLast() && next());

          if (!isLast())
          {
             hasResults = false;
             isAfterLast = true;
             rowNumber = -1;
             return false;
          }

          return true;
       }

       /**
        * Move cursor to the next result row.
        *
        * @return  <code>true</code> if there is a result under the cursor.
        */
       public boolean next()
       {
          if (isAfterLast)
          {
             return false;
          }

          if (!hasResults || isLast())
          {
             isAfterLast = true;
             rowNumber = -1;
             return false;
          }

          boolean nxt = results.next();
          if (!nxt)
          {
             hasResults = false;
             isAfterLast = true;
             rowNumber = -1;
          }
          else
          {
             rowNumber++;
          }

          return nxt;
       }

       /**
        * Should move cursor to the previous result row, but it cannot be done in FORWARD_ONLY mode.
        *
        * @return  <code>false</code> .
        */
       public boolean previous()
       {
          LOG.log(Level.SEVERE, "Cannot call previous in FORWARD_ONLY mode");
          return false;
       }

       /**
        * Is the cursor on the first row in the result set?
        *
        * @return  <code>true</code> if the cursor is on the first row.
        */
       public boolean isFirst()
       {
          return rowNumber == 0;
       }

       /**
        * Is the cursor on the last row in the result set?
        *
        * @return  <code>true</code> if the cursor is on the last row.
        */
       public boolean isLast()
       {
          if (!hasResults || isAfterLast || rowNumber == -1)
          {
             return false;
          }

          return results.isLast();
       }

       /**
        * Returns the row at the current position. It can be either only an array of PK or
        * an array of DMOs.
        *
        * @param   forceOnlyId
        *          Indicates whether it's only the primary keys that must be returned,
        *          or original data found is returned (either PK or DMO).
        *
        * @return  Object array or {@code null}.
        */
       public Object[] get(boolean forceOnlyId)
       {
          if (!hasResults || isAfterLast || rowNumber == -1)
          {
             return null;
          }

          return results.get(forceOnlyId);
       }

       /**
        * Get the object at the current result row, at the specified column.
        *
        * @param   column
        *          Zero-based index column of the desired object.
        *
        * @return  Object at <code>column</code> or <code>null</code>.
        */
       public Object get(int column)
       {
          if (!hasResults || isAfterLast || rowNumber == -1)
          {
             return null;
          }

          Object[] row = get();
          return (row != null) ? row[column] : null;
       }

       /**
        * Get the primary key ID at the current result row, at the specified
        * column.
        *
        * @param   column
        *          Zero-based index column of the desired ID.
        *
        * @return  ID of the record or <code>null</code>.
        */
       public Long getID(int column)
       {
          if (!hasResults || isAfterLast || rowNumber == -1)
          {
             return null;
          }

          Object result = get(column);
          if (result instanceof Record)
          {
             return ((Record) result).primaryKey();
          }

          return (Long) result;
       }

       /**
        * Get the row number currently under the cursor.
        *
        * @return  Zero-based index of the current row, or <code>-1</code>
        *          if the cursor is not currently on a result.
        */
       public int getRowNumber()
       {
          if (!hasResults || isAfterLast || rowNumber < 0)
          {
             return -1;
          }

          return rowNumber;
       }

       /**
        * Set the cursor at the row number.
        *
        * @param   row
        *          Zero-based index of the row to be set as the current row.
        *
        * @return  <code>true</code> if the row number is after the current position and before last;
        *          else <code>false</code>.
        */
       public boolean setRowNumber(int row)
       {
          if (!hasResults || isAfterLast)
          {
             LOG.log(Level.SEVERE, "Cannot call setRowNumber on empty or "
                      + "fully iterated results in FORWARD_ONLY mode");
             return false;
          }

          int nrOfSteps = row - rowNumber;
          if (nrOfSteps < 0)
          {
             LOG.log(Level.SEVERE, "Cannot call setRowNumber if the row is "
                      + "smaller than the current position in FORWARD_ONLY mode");
             return false;
          }

          return scroll(nrOfSteps);
       }

       /**
        * Scroll the cursor ahead by the specified number of rows.
        *
        * @param   rows
        *          Number of rows to jump ahead or back.
        *
        * @return  <code>true</code> if there is a row at the new location;
        *          else <code>false</code>.
        */
       public boolean scroll(int rows)
       {
          if (rows < 0)
          {
             LOG.log(Level.SEVERE, "Cannot call scroll with negative number of rows in FORWARD_ONLY mode");
             return false;
          }

          for (int i = 0; i < rows; i++)
          {
             if (!next())
             {
                return false;
             }
          }
          return true;
       }

       /**
        * Should reset the cursor to its natural starting position, before the first
        * result row, but it cannot be done in FORWARD_ONLY mode.
        */
       public void reset()
       {
          LOG.log(Level.SEVERE, "Cannot call reset in FORWARD_ONLY mode");
       }

       /**
        * Invoked when the current Hibernate session is about to close.  Gives
        * the implementation an opportunity to perform appropriate processing in
        * response to this event.
        */
       public void sessionClosing()
       {
          cleanup();
       }

       /**
        * Close the wrapped {@code ScrollableResults} object.
        */
       public void cleanup()
       {
          if (closed)
          {
             return;
          }

          try
          {
             results.close();
          }
          catch (PersistenceException exc)
          {
             DBUtils.handleException(persistence.getDatabase(Persistence.PRIVATE_CTX), exc);

             // Non-critical operation;  logging the error is sufficient.
             if (LOG.isLoggable(Level.FINE))
             {
                LOG.log(Level.FINE, exc.getMessage(), exc);
             }
             else if (LOG.isLoggable(Level.WARNING))
             {
                LOG.log(Level.WARNING, exc.getMessage());
             }
          }
          finally
          {
             closed = true;
             persistenceContext.releaseSession();
          }
       }
    }