/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.commons.dbcp2;

import java.lang.management.ManagementFactory;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Collection;

import javax.management.InstanceAlreadyExistsException;
import javax.management.MBeanRegistrationException;
import javax.management.MBeanServer;
import javax.management.NotCompliantMBeanException;
import javax.management.ObjectName;

import org.apache.commons.pool2.ObjectPool;

/**
 * A delegating connection that, rather than closing the underlying connection, returns itself to an {@link ObjectPool}
 * when closed.
 *
 * @author Rodney Waldhoff
 * @author Glenn L. Nielsen
 * @author James House
 * @since 2.0
 */
public class PoolableConnection extends DelegatingConnection<Connection> implements PoolableConnectionMXBean {

    private static MBeanServer MBEAN_SERVER = null;

    static {
        try {
            MBEAN_SERVER = ManagementFactory.getPlatformMBeanServer();
        } catch (NoClassDefFoundError | Exception ex) {
            // ignore - JMX not available
        }
    }

    /** The pool to which I should return. */
    private final ObjectPool<PoolableConnection> _pool;

    private final ObjectNameWrapper _jmxObjectName;

    // Use a prepared statement for validation, retaining the last used SQL to
    // check if the validation query has changed.
    private PreparedStatement validationPreparedStatement = null;
    private String lastValidationSql = null;

    /**
     * Indicate that unrecoverable SQLException was thrown when using this connection. Such a connection should be
     * considered broken and not pass validation in the future.
     */
    private boolean _fatalSqlExceptionThrown = false;

    /**
     * SQL_STATE codes considered to signal fatal conditions. Overrides the defaults in
     * {@link Utils#DISCONNECTION_SQL_CODES} (plus anything starting with {@link Utils#DISCONNECTION_SQL_CODE_PREFIX}).
     */
    private final Collection<String> _disconnectionSqlCodes;

    /** Whether or not to fast fail validation after fatal connection errors */
    private final boolean _fastFailValidation;

    /**
     *
     * @param conn
     *            my underlying connection
     * @param pool
     *            the pool to which I should return when closed
     * @param jmxObjectName
     *            JMX name
     * @param disconnectSqlCodes
     *            SQL_STATE codes considered fatal disconnection errors
     * @param fastFailValidation
     *            true means fatal disconnection errors cause subsequent validations to fail immediately (no attempt to
     *            run query or isValid)
     */
    public PoolableConnection(final Connection conn, final ObjectPool<PoolableConnection> pool,
            final ObjectName jmxObjectName, final Collection<String> disconnectSqlCodes,
            final boolean fastFailValidation) {
        super(conn);
        _pool = pool;
        _jmxObjectName = ObjectNameWrapper.wrap(jmxObjectName);
        _disconnectionSqlCodes = disconnectSqlCodes;
        _fastFailValidation = fastFailValidation;

        if (jmxObjectName != null) {
            try {
                MBEAN_SERVER.registerMBean(this, jmxObjectName);
            } catch (InstanceAlreadyExistsException | MBeanRegistrationException | NotCompliantMBeanException e) {
                // For now, simply skip registration
            }
        }
    }

    /**
     *
     * @param conn
     *            my underlying connection
     * @param pool
     *            the pool to which I should return when closed
     * @param jmxName
     *            JMX name
     */
    public PoolableConnection(final Connection conn, final ObjectPool<PoolableConnection> pool,
            final ObjectName jmxName) {
        this(conn, pool, jmxName, null, false);
    }

    @Override
    protected void passivate() throws SQLException {
        super.passivate();
        setClosedInternal(true);
    }

    /**
     * {@inheritDoc}
     * <p>
     * This method should not be used by a client to determine whether or not a connection should be return to the
     * connection pool (by calling {@link #close()}). Clients should always attempt to return a connection to the pool
     * once it is no longer required.
     */
    @Override
    public boolean isClosed() throws SQLException {
        if (isClosedInternal()) {
            return true;
        }

        if (getDelegateInternal().isClosed()) {
            // Something has gone wrong. The underlying connection has been
            // closed without the connection being returned to the pool. Return
            // it now.
            close();
            return true;
        }

        return false;
    }

    /**
     * Returns me to my pool.
     */
    @Override
    public synchronized void close() throws SQLException {
        if (isClosedInternal()) {
            // already closed
            return;
        }

        boolean isUnderlyingConnectionClosed;
        try {
            isUnderlyingConnectionClosed = getDelegateInternal().isClosed();
        } catch (final SQLException e) {
            try {
                _pool.invalidateObject(this);
            } catch (final IllegalStateException ise) {
                // pool is closed, so close the connection
                passivate();
                getInnermostDelegate().close();
            } catch (final Exception ie) {
                // DO NOTHING the original exception will be rethrown
            }
            throw new SQLException("Cannot close connection (isClosed check failed)", e);
        }

        /*
         * Can't set close before this code block since the connection needs to be open when validation runs. Can't set
         * close after this code block since by then the connection will have been returned to the pool and may have
         * been borrowed by another thread. Therefore, the close flag is set in passivate().
         */
        if (isUnderlyingConnectionClosed) {
            // Abnormal close: underlying connection closed unexpectedly, so we
            // must destroy this proxy
            try {
                _pool.invalidateObject(this);
            } catch (final IllegalStateException e) {
                // pool is closed, so close the connection
                passivate();
                getInnermostDelegate().close();
            } catch (final Exception e) {
                throw new SQLException("Cannot close connection (invalidating pooled object failed)", e);
            }
        } else {
            // Normal close: underlying connection is still open, so we
            // simply need to return this proxy to the pool
            try {
                _pool.returnObject(this);
            } catch (final IllegalStateException e) {
                // pool is closed, so close the connection
                passivate();
                getInnermostDelegate().close();
            } catch (final SQLException e) {
                throw e;
            } catch (final RuntimeException e) {
                throw e;
            } catch (final Exception e) {
                throw new SQLException("Cannot close connection (return to pool failed)", e);
            }
        }
    }

    /**
     * Actually close my underlying {@link Connection}.
     */
    @Override
    public void reallyClose() throws SQLException {
        if (_jmxObjectName != null) {
            _jmxObjectName.unregisterMBean();
        }

        if (validationPreparedStatement != null) {
            try {
                validationPreparedStatement.close();
            } catch (final SQLException sqle) {
                // Ignore
            }
        }

        super.closeInternal();
    }

    /**
     * Expose the {@link #toString()} method via a bean getter so it can be read as a property via JMX.
     */
    @Override
    public String getToString() {
        return toString();
    }

    /**
     * Validates the connection, using the following algorithm:
     * <ol>
     * <li>If {@code fastFailValidation} (constructor argument) is {@code true} and this connection has previously
     * thrown a fatal disconnection exception, a {@code SQLException} is thrown.</li>
     * <li>If {@code sql} is null, the driver's #{@link Connection#isValid(int) isValid(timeout)} is called. If it
     * returns {@code false}, {@code SQLException} is thrown; otherwise, this method returns successfully.</li>
     * <li>If {@code sql} is not null, it is executed as a query and if the resulting {@code ResultSet} contains at
     * least one row, this method returns successfully. If not, {@code SQLException} is thrown.</li>
     * </ol>
     * 
     * @param sql
     *            validation query
     * @param timeout
     *            validation timeout
     * @throws SQLException
     *             if validation fails or an SQLException occurs during validation
     */
    public void validate(final String sql, int timeout) throws SQLException {
        if (_fastFailValidation && _fatalSqlExceptionThrown) {
            throw new SQLException(Utils.getMessage("poolableConnection.validate.fastFail"));
        }

        if (sql == null || sql.length() == 0) {
            if (timeout < 0) {
                timeout = 0;
            }
            if (!isValid(timeout)) {
                throw new SQLException("isValid() returned false");
            }
            return;
        }

        if (!sql.equals(lastValidationSql)) {
            lastValidationSql = sql;
            // Has to be the innermost delegate else the prepared statement will
            // be closed when the pooled connection is passivated.
            validationPreparedStatement = getInnermostDelegateInternal().prepareStatement(sql);
        }

        if (timeout > 0) {
            validationPreparedStatement.setQueryTimeout(timeout);
        }

        try (ResultSet rs = validationPreparedStatement.executeQuery()) {
            if (!rs.next()) {
                throw new SQLException("validationQuery didn't return a row");
            }
        } catch (final SQLException sqle) {
            throw sqle;
        }
    }

    /**
     * Checks the SQLState of the input exception and any nested SQLExceptions it wraps.
     * <p>
     * If {@link #getDisconnectSqlCodes() disconnectSQLCodes} has been set, sql states are compared to those in the
     * configured list of fatal exception codes. If this property is not set, codes are compared against the default
     * codes in #{@link Utils.DISCONNECTION_SQL_CODES} and in this case anything starting with #{link
     * Utils.DISCONNECTION_SQL_CODE_PREFIX} is considered a disconnection.
     * </p>
     *
     * @param e
     *            SQLException to be examined
     * @return true if the exception signals a disconnection
     */
    private boolean isDisconnectionSqlException(final SQLException e) {
        boolean fatalException = false;
        final String sqlState = e.getSQLState();
        if (sqlState != null) {
            fatalException = _disconnectionSqlCodes == null
                    ? sqlState.startsWith(Utils.DISCONNECTION_SQL_CODE_PREFIX)
                            || Utils.DISCONNECTION_SQL_CODES.contains(sqlState)
                    : _disconnectionSqlCodes.contains(sqlState);
            if (!fatalException) {
                final SQLException nextException = e.getNextException();
                if (nextException != null && nextException != e) {
                    fatalException = isDisconnectionSqlException(e.getNextException());
                }
            }
        }
        return fatalException;
    }

    @Override
    protected void handleException(final SQLException e) throws SQLException {
        _fatalSqlExceptionThrown |= isDisconnectionSqlException(e);
        super.handleException(e);
    }
}