// This software is released into the Public Domain.  See copying.txt for details.
package org.openstreetmap.osmosis.apidb.common;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.openstreetmap.osmosis.core.OsmosisRuntimeException;
import org.openstreetmap.osmosis.core.database.ReleasableStatementContainer;


/**
 * Postgresql implementation of an identity value loader.
 * 
 * @author Brett Henderson
 */
public class PostgresqlIdentityValueLoader implements IdentityValueLoader {
	private static final String SQL_SELECT_LAST_INSERT_ID =
		"SELECT lastval() AS lastInsertId";
	private static final String SQL_SELECT_LAST_SEQUENCE_ID =
		"SELECT currval(?) AS lastSequenceId";
	
	private DatabaseContext dbCtx;
	private ReleasableStatementContainer statementContainer;
	private PreparedStatement selectInsertIdStatement;
	private PreparedStatement selectSequenceIdStatement;
	
	
	/**
	 * Creates a new instance.
	 * 
	 * @param dbCtx
	 *            The database context to use for all database access.
	 */
	public PostgresqlIdentityValueLoader(DatabaseContext dbCtx) {
		this.dbCtx = dbCtx;
		
		statementContainer = new ReleasableStatementContainer();
	}
	
	
	/**
	 * Returns the id of the most recently inserted row on the current
	 * connection.
	 * 
	 * @return The newly inserted id.
	 */
	public long getLastInsertId() {
		if (selectInsertIdStatement == null) {
			selectInsertIdStatement =
				statementContainer.add(dbCtx.prepareStatementForStreaming(SQL_SELECT_LAST_INSERT_ID));
		}
		
		try (ResultSet lastInsertQuery = selectInsertIdStatement.executeQuery()) {
			lastInsertQuery.next();
			return lastInsertQuery.getLong("lastInsertId");
			
		} catch (SQLException e) {
			throw new OsmosisRuntimeException(
				"Unable to retrieve the id of the newly inserted record.",
				e
			);
		}
	}


	/**
	 * {@inheritDoc}
	 */
	@Override
	public long getLastSequenceId(String sequenceName) {
		if (selectSequenceIdStatement == null) {
			selectSequenceIdStatement =
				statementContainer.add(dbCtx.prepareStatementForStreaming(SQL_SELECT_LAST_SEQUENCE_ID));
		}

		try {
			selectSequenceIdStatement.setString(1, sequenceName);
			try (ResultSet lastSequenceQuery = selectSequenceIdStatement.executeQuery()) {

				lastSequenceQuery.next();
				return lastSequenceQuery.getLong("lastSequenceId");
			}
		} catch (SQLException e) {
			throw new OsmosisRuntimeException("Unable to retrieve the last sequence id.", e);
		}
	}
	
	
	/**
	 * {@inheritDoc}
	 */
	@Override
	public void close() {
		statementContainer.close();
	}
}