/*
 Copyright (c) 2002, 2012, Oracle and/or its affiliates. All rights reserved.
 

  The MySQL Connector/J is licensed under the terms of the GPLv2
  <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
  There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
  this software, see the FLOSS License Exception
  <http://www.mysql.com/about/legal/licensing/foss-exception.html>.

  This program is free software; you can redistribute it and/or modify it under the terms
  of the GNU General Public License as published by the Free Software Foundation; version 2
  of the License.

  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 General Public License for more details.

  You should have received a copy of the GNU General Public License along with this
  program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
  Floor, Boston, MA 02110-1301  USA
 */

package com.mysql.jdbc;

import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

/**
 * Model for result set data backed by a cursor. Only works for forward-only
 * result sets (but still works with updatable concurrency).
 * 
 * @version $Id: CursorRowProvider.java,v 1.1.2.1 2005/05/19 18:31:49 mmatthews
 *          Exp $
 */
public class RowDataCursor implements RowData {

	private final static int BEFORE_START_OF_ROWS = -1;

	/**
	 * The cache of rows we have retrieved from the server.
	 */
	private List<ResultSetRow> fetchedRows;

	/**
	 * Where we are positionaly in the entire result set, used mostly to
	 * facilitate easy 'isBeforeFirst()' and 'isFirst()' methods.
	 */
	private int currentPositionInEntireResult = BEFORE_START_OF_ROWS;

	/**
	 * Position in cache of rows, used to determine if we need to fetch more
	 * rows from the server to satisfy a request for the next row.
	 */
	private int currentPositionInFetchedRows = BEFORE_START_OF_ROWS;

	/**
	 * The result set that we 'belong' to.
	 */
	private ResultSetImpl owner;

	/**
	 * Have we been told from the server that we have seen the last row?
	 */
	private boolean lastRowFetched = false;

	/**
	 * Field-level metadata from the server. We need this, because it is not
	 * sent for each batch of rows, but we need the metadata to unpack the
	 * results for each field.
	 */
	private Field[] metadata;

	/**
	 * Communications channel to the server
	 */
	private MysqlIO mysql;

	/**
	 * Identifier for the statement that created this cursor.
	 */
	private long statementIdOnServer;

	/**
	 * The prepared statement that created this cursor.
	 */
	private ServerPreparedStatement prepStmt;

	/**
	 * The server status for 'last-row-sent'...This might belong in mysqldefs,
	 * but it it only ever referenced from here.
	 */
	private static final int SERVER_STATUS_LAST_ROW_SENT = 128;

	/**
	 * Have we attempted to fetch any rows yet?
	 */
	private boolean firstFetchCompleted = false;

	private boolean wasEmpty = false;

	private boolean useBufferRowExplicit = false;
	
	/**
	 * Creates a new cursor-backed row provider.
	 * 
	 * @param ioChannel
	 *            connection to the server.
	 * @param creatingStatement
	 *            statement that opened the cursor.
	 * @param metadata
	 *            field-level metadata for the results that this cursor covers.
	 */
	public RowDataCursor(MysqlIO ioChannel,
			ServerPreparedStatement creatingStatement, Field[] metadata) {
		this.currentPositionInEntireResult = BEFORE_START_OF_ROWS;
		this.metadata = metadata;
		this.mysql = ioChannel;
		this.statementIdOnServer = creatingStatement.getServerStatementId();
		this.prepStmt = creatingStatement;
		this.useBufferRowExplicit = MysqlIO.useBufferRowExplicit(this.metadata);
		
	}

	/**
	 * Returns true if we got the last element.
	 * 
	 * @return DOCUMENT ME!
	 */
	public boolean isAfterLast() {
		return lastRowFetched
				&& this.currentPositionInFetchedRows > this.fetchedRows.size();
	}

	/**
	 * Only works on non dynamic result sets.
	 * 
	 * @param index
	 *            row number to get at
	 * @return row data at index
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public ResultSetRow getAt(int ind) throws SQLException {
		notSupported();

		return null;
	}

	/**
	 * Returns if iteration has not occured yet.
	 * 
	 * @return true if before first row
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public boolean isBeforeFirst() throws SQLException {
		return this.currentPositionInEntireResult < 0;
	}

	/**
	 * Moves the current position in the result set to the given row number.
	 * 
	 * @param rowNumber
	 *            row to move to
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public void setCurrentRow(int rowNumber) throws SQLException {
		notSupported();
	}

	/**
	 * Returns the current position in the result set as a row number.
	 * 
	 * @return the current row number
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public int getCurrentRowNumber() throws SQLException {
		return this.currentPositionInEntireResult + 1;
	}

	/**
	 * Returns true if the result set is dynamic.
	 * 
	 * This means that move back and move forward won't work because we do not
	 * hold on to the records.
	 * 
	 * @return true if this result set is streaming from the server
	 */
	public boolean isDynamic() {
		return true;
	}

	/**
	 * Has no records.
	 * 
	 * @return true if no records
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public boolean isEmpty() throws SQLException {
		return this.isBeforeFirst() && this.isAfterLast();
	}

	/**
	 * Are we on the first row of the result set?
	 * 
	 * @return true if on first row
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public boolean isFirst() throws SQLException {
		return this.currentPositionInEntireResult == 0;
	}

	/**
	 * Are we on the last row of the result set?
	 * 
	 * @return true if on last row
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public boolean isLast() throws SQLException {
		return this.lastRowFetched
				&& this.currentPositionInFetchedRows == (this.fetchedRows
						.size() - 1);
	}

	/**
	 * Adds a row to this row data.
	 * 
	 * @param row
	 *            the row to add
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public void addRow(ResultSetRow row) throws SQLException {
		notSupported();
	}

	/**
	 * Moves to after last.
	 * 
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public void afterLast() throws SQLException {
		notSupported();
	}

	/**
	 * Moves to before first.
	 * 
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public void beforeFirst() throws SQLException {
		notSupported();
	}

	/**
	 * Moves to before last so next el is the last el.
	 * 
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public void beforeLast() throws SQLException {
		notSupported();
	}

	/**
	 * We're done.
	 * 
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public void close() throws SQLException {

		this.metadata = null;
		this.owner = null;
	}

	/**
	 * Returns true if another row exists.
	 * 
	 * @return true if more rows
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public boolean hasNext() throws SQLException {

		if (this.fetchedRows != null && this.fetchedRows.size() == 0) {
			return false;
		}

		if (this.owner != null && this.owner.owningStatement != null) {
			int maxRows = this.owner.owningStatement.maxRows;
			
			if (maxRows != -1 && this.currentPositionInEntireResult + 1 > maxRows) {
				return false;
			}	
		}
		
		if (this.currentPositionInEntireResult != BEFORE_START_OF_ROWS) {
			// Case, we've fetched some rows, but are not at end of fetched
			// block
			if (this.currentPositionInFetchedRows < (this.fetchedRows.size() - 1)) {
				return true;
			} else if (this.currentPositionInFetchedRows == this.fetchedRows
					.size()
					&& this.lastRowFetched) {
				return false;
			} else {
				// need to fetch to determine
				fetchMoreRows();

				return (this.fetchedRows.size() > 0);
			}
		}

		// Okay, no rows _yet_, so fetch 'em

		fetchMoreRows();

		return this.fetchedRows.size() > 0;
	}

	/**
	 * Moves the current position relative 'rows' from the current position.
	 * 
	 * @param rows
	 *            the relative number of rows to move
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public void moveRowRelative(int rows) throws SQLException {
		notSupported();
	}

	/**
	 * Returns the next row.
	 * 
	 * @return the next row value
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public ResultSetRow next() throws SQLException {
		if (this.fetchedRows == null && this.currentPositionInEntireResult != BEFORE_START_OF_ROWS) {
			throw SQLError.createSQLException(
					Messages
							.getString("ResultSet.Operation_not_allowed_after_ResultSet_closed_144"), //$NON-NLS-1$
					SQLError.SQL_STATE_GENERAL_ERROR, mysql.getExceptionInterceptor());
		}
		
		if (!hasNext()) {
			return null;
		}
		
		this.currentPositionInEntireResult++;
		this.currentPositionInFetchedRows++;

		// Catch the forced scroll-passed-end
		if (this.fetchedRows != null && this.fetchedRows.size() == 0) {
			return null;
		}

		if (this.currentPositionInFetchedRows > (this.fetchedRows.size() - 1)) {
			fetchMoreRows();
			this.currentPositionInFetchedRows = 0;
		}

		ResultSetRow row = this.fetchedRows
				.get(this.currentPositionInFetchedRows);

		row.setMetadata(this.metadata);
		
		return row;
	}

	/**
	 * 
	 */
	private void fetchMoreRows() throws SQLException {
		if (this.lastRowFetched) {
			this.fetchedRows = new ArrayList<ResultSetRow>(0);
			return;
		}

		synchronized (this.owner.connection) {
			boolean oldFirstFetchCompleted = this.firstFetchCompleted;
			
			if (!this.firstFetchCompleted) {
				this.firstFetchCompleted = true;
			}

			int numRowsToFetch = this.owner.getFetchSize();

			if (numRowsToFetch == 0) {
				numRowsToFetch = this.prepStmt.getFetchSize();
			}
			
			if (numRowsToFetch == Integer.MIN_VALUE) {
				// Handle the case where the user used 'old'
				// streaming result sets

				numRowsToFetch = 1;
			}

			this.fetchedRows = this.mysql.fetchRowsViaCursor(this.fetchedRows,
					this.statementIdOnServer, this.metadata, numRowsToFetch, 
					this.useBufferRowExplicit);
			this.currentPositionInFetchedRows = BEFORE_START_OF_ROWS;

			if ((this.mysql.getServerStatus() & SERVER_STATUS_LAST_ROW_SENT) != 0) {
				this.lastRowFetched = true;
				
				if (!oldFirstFetchCompleted && this.fetchedRows.size() == 0) {
					this.wasEmpty  = true;
				}
			}
		}
	}

	/**
	 * Removes the row at the given index.
	 * 
	 * @param index
	 *            the row to move to
	 * @throws SQLException
	 *             if a database error occurs
	 */
	public void removeRow(int ind) throws SQLException {
		notSupported();
	}

	/**
	 * Only works on non dynamic result sets.
	 * 
	 * @return the size of this row data
	 */
	public int size() {
		return RESULT_SET_SIZE_UNKNOWN;
	}

	protected void nextRecord() throws SQLException {

	}

	private void notSupported() throws SQLException {
		throw new OperationNotSupportedException();
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see com.mysql.jdbc.RowProvider#setOwner(com.mysql.jdbc.ResultSet)
	 */
	public void setOwner(ResultSetImpl rs) {
		this.owner = rs;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see com.mysql.jdbc.RowProvider#getOwner()
	 */
	public ResultSetInternalMethods getOwner() {
		return this.owner;
	}

	public boolean wasEmpty() {
		return this.wasEmpty;
	}
	
	public void setMetadata(Field[] metadata) {
		this.metadata = metadata;
	}

}
