/*-------------------------------------------------------------------------
*
* Copyright (c) 2004-2008, PostgreSQL Global Development Group
*
* IDENTIFICATION
*   $PostgreSQL: pgjdbc/org/postgresql/ds/jdbc23/AbstractJdbc23PooledConnection.java,v 1.6 2009/01/15 04:18:03 jurka Exp $
*
*-------------------------------------------------------------------------
*/
package org.postgresql.ds.jdbc23;

import javax.sql.*;
import java.sql.*;
import java.util.*;
import java.lang.reflect.*;
import org.postgresql.PGConnection;
import org.postgresql.util.GT;
import org.postgresql.util.PSQLException;
import org.postgresql.util.PSQLState;

/**
 * PostgreSQL implementation of the PooledConnection interface.  This shouldn't
 * be used directly, as the pooling client should just interact with the
 * ConnectionPool instead.
 * @see org.postgresql.ds.PGConnectionPoolDataSource
 *
 * @author Aaron Mulder (ammulder@chariotsolutions.com)
 * @author Csaba Nagy (ncsaba@yahoo.com)
 */
public abstract class AbstractJdbc23PooledConnection
{
    private List listeners = new LinkedList();
    private Connection con;
    private ConnectionHandler last;
    private final boolean autoCommit;
    private final boolean isXA;

    /**
     * Creates a new PooledConnection representing the specified physical
     * connection.
     */
    public AbstractJdbc23PooledConnection(Connection con, boolean autoCommit, boolean isXA)
    {
        this.con = con;
        this.autoCommit = autoCommit;
        this.isXA = isXA;
    }

    /**
     * Adds a listener for close or fatal error events on the connection
     * handed out to a client.
     */
    public void addConnectionEventListener(ConnectionEventListener connectionEventListener)
    {
        listeners.add(connectionEventListener);
    }

    /**
     * Removes a listener for close or fatal error events on the connection
     * handed out to a client.
     */
    public void removeConnectionEventListener(ConnectionEventListener connectionEventListener)
    {
        listeners.remove(connectionEventListener);
    }

    /**
     * Closes the physical database connection represented by this
     * PooledConnection.  If any client has a connection based on
     * this PooledConnection, it is forcibly closed as well.
     */
    public void close() throws SQLException
    {
        if (last != null)
        {
            last.close();
            if (!con.getAutoCommit())
            {
                try
                {
                    con.rollback();
                }
                catch (SQLException e)
                {
                }
            }
        }
        try
        {
            con.close();
        }
        finally
        {
            con = null;
        }
    }

    /**
     * Gets a handle for a client to use.  This is a wrapper around the
     * physical connection, so the client can call close and it will just
     * return the connection to the pool without really closing the
     * pgysical connection.
     *
     * <p>According to the JDBC 2.0 Optional Package spec (6.2.3), only one
     * client may have an active handle to the connection at a time, so if
     * there is a previous handle active when this is called, the previous
     * one is forcibly closed and its work rolled back.</p>
     */
    public Connection getConnection() throws SQLException
    {
        if (con == null)
        {
            // Before throwing the exception, let's notify the registered listeners about the error
            PSQLException sqlException = new PSQLException(GT.tr("This PooledConnection has already been closed."),
                                                           PSQLState.CONNECTION_DOES_NOT_EXIST);
            fireConnectionFatalError(sqlException);
            throw sqlException;
        }
        // If any error occures while opening a new connection, the listeners
        // have to be notified. This gives a chance to connection pools to
        // eliminate bad pooled connections.
        try
        {
            // Only one connection can be open at a time from this PooledConnection.  See JDBC 2.0 Optional Package spec section 6.2.3
            if (last != null)
            {
                last.close();
                if (!con.getAutoCommit())
                {
                    try
                    {
                        con.rollback();
                    }
                    catch (SQLException e)
                    {
                    }
                }
                con.clearWarnings();
            }
            /*
             * In XA-mode, autocommit is handled in PGXAConnection,
             * because it depends on whether an XA-transaction is open
             * or not
             */
            if (!isXA)
                con.setAutoCommit(autoCommit);
        }
        catch (SQLException sqlException)
        {
            fireConnectionFatalError(sqlException);
            throw (SQLException)sqlException.fillInStackTrace();
        }
        ConnectionHandler handler = new ConnectionHandler(con);
        last = handler;

        Connection proxyCon = (Connection)Proxy.newProxyInstance(getClass().getClassLoader(), new Class[]{Connection.class, PGConnection.class}, handler);
        last.setProxy(proxyCon);
        return proxyCon;
    }

    /**
     * Used to fire a connection closed event to all listeners.
     */
    void fireConnectionClosed()
    {
        ConnectionEvent evt = null;
        // Copy the listener list so the listener can remove itself during this method call
        ConnectionEventListener[] local = (ConnectionEventListener[]) listeners.toArray(new ConnectionEventListener[listeners.size()]);
        for (int i = 0; i < local.length; i++)
        {
            ConnectionEventListener listener = local[i];
            if (evt == null)
            {
                evt = createConnectionEvent(null);
            }
            listener.connectionClosed(evt);
        }
    }

    /**
     * Used to fire a connection error event to all listeners.
     */
    void fireConnectionFatalError(SQLException e)
    {
        ConnectionEvent evt = null;
        // Copy the listener list so the listener can remove itself during this method call
        ConnectionEventListener[] local = (ConnectionEventListener[])listeners.toArray(new ConnectionEventListener[listeners.size()]);
        for (int i = 0; i < local.length; i++)
        {
            ConnectionEventListener listener = local[i];
            if (evt == null)
            {
                evt = createConnectionEvent(e);
            }
            listener.connectionErrorOccurred(evt);
        }
    }

    protected abstract ConnectionEvent createConnectionEvent(SQLException e);

    // Classes we consider fatal.
    private static String[] fatalClasses = {
        "08",  // connection error
        "53",  // insufficient resources

        // nb: not just "57" as that includes query cancel which is nonfatal
        "57P01",  // admin shutdown
        "57P02",  // crash shutdown
        "57P03",  // cannot connect now

        "58",  // system error (backend)
        "60",  // system error (driver)
        "99",  // unexpected error
        "F0",  // configuration file error (backend)
        "XX",  // internal error (backend)
    };

    private static boolean isFatalState(String state) {
        if (state == null)      // no info, assume fatal
            return true;
        if (state.length() < 2) // no class info, assume fatal
            return true;

        for (int i = 0; i < fatalClasses.length; ++i)
            if (state.startsWith(fatalClasses[i]))
                return true; // fatal

        return false;
    }

    /**
     * Fires a connection error event, but only if we
     * think the exception is fatal.
     *
     * @param e the SQLException to consider
     */    
    private void fireConnectionError(SQLException e) 
    {
        if (!isFatalState(e.getSQLState()))
            return;

        fireConnectionFatalError(e);
    }

    /**
     * Instead of declaring a class implementing Connection, which would have
     * to be updated for every JDK rev, use a dynamic proxy to handle all
     * calls through the Connection interface. This is the part that
     * requires JDK 1.3 or higher, though JDK 1.2 could be supported with a
     * 3rd-party proxy package.
     */
    private class ConnectionHandler implements InvocationHandler
    {
        private Connection con;
        private Connection proxy; // the Connection the client is currently using, which is a proxy
        private boolean automatic = false;

        public ConnectionHandler(Connection con)
        {
            this.con = con;
        }

        public Object invoke(Object proxy, Method method, Object[] args)
        throws Throwable
        {
            // From Object
            if (method.getDeclaringClass().getName().equals("java.lang.Object"))
            {
                if (method.getName().equals("toString"))
                {
                    return "Pooled connection wrapping physical connection " + con;
                }
                if (method.getName().equals("equals"))
                {
                    return new Boolean(proxy == args[0]);
                }
                if (method.getName().equals("hashCode"))
                {
                    return new Integer(System.identityHashCode(proxy));
                }
                try
                {
                    return method.invoke(con, args);
                }
                catch (InvocationTargetException e)
                {
                    throw e.getTargetException();
                }
            }
            // All the rest is from the Connection or PGConnection interface
            if (method.getName().equals("isClosed"))
            {
                return con == null ? Boolean.TRUE : Boolean.FALSE;
            }
            if (con == null && !method.getName().equals("close"))
            {
                throw new PSQLException(automatic ? GT.tr("Connection has been closed automatically because a new connection was opened for the same PooledConnection or the PooledConnection has been closed.") : GT.tr("Connection has been closed."),
                                        PSQLState.CONNECTION_DOES_NOT_EXIST);
            }
            if (method.getName().equals("close"))
            {
                // we are already closed and a double close
                // is not an error.
                if (con == null)
                    return null;

                SQLException ex = null;
                if (!isXA && !con.getAutoCommit())
                {
                    try
                    {
                        con.rollback();
                    }
                    catch (SQLException e)
                    {
                        ex = e;
                    }
                }
                con.clearWarnings();
                con = null;
                this.proxy = null;
                last = null;
                fireConnectionClosed();
                if (ex != null)
                {
                    throw ex;
                }
                return null;
            }
            
            // From here on in, we invoke via reflection, catch exceptions,
            // and check if they're fatal before rethrowing.

            try {            
                if (method.getName().equals("createStatement"))
                {
                    Statement st = (Statement)method.invoke(con, args);
                    return Proxy.newProxyInstance(getClass().getClassLoader(), new Class[]{Statement.class, org.postgresql.PGStatement.class}, new StatementHandler(this, st));
                }
                else if (method.getName().equals("prepareCall"))
                {
                    Statement st = (Statement)method.invoke(con, args);
                    return Proxy.newProxyInstance(getClass().getClassLoader(), new Class[]{CallableStatement.class, org.postgresql.PGStatement.class}, new StatementHandler(this, st));
                }
                else if (method.getName().equals("prepareStatement"))
                {
                    Statement st = (Statement)method.invoke(con, args);
                    return Proxy.newProxyInstance(getClass().getClassLoader(), new Class[]{PreparedStatement.class, org.postgresql.PGStatement.class}, new StatementHandler(this, st));
                }
                else
                {
                    return method.invoke(con, args);
                }
            } catch (InvocationTargetException e) {
                Throwable te = e.getTargetException();
                if (te instanceof SQLException)
                    fireConnectionError((SQLException)te); // Tell listeners about exception if it's fatal
                throw te;
            }
        }

        Connection getProxy() {
            return proxy;
        }

        void setProxy(Connection proxy) {
            this.proxy = proxy;
        }

        public void close()
        {
            if (con != null)
            {
                automatic = true;
            }
            con = null;
            proxy = null;
            // No close event fired here: see JDBC 2.0 Optional Package spec section 6.3
        }

        public boolean isClosed() {
            return con == null;
        }
    }

    /**
     * Instead of declaring classes implementing Statement, PreparedStatement,
     * and CallableStatement, which would have to be updated for every JDK rev,
     * use a dynamic proxy to handle all calls through the Statement
     * interfaces. This is the part that requires JDK 1.3 or higher, though
     * JDK 1.2 could be supported with a 3rd-party proxy package.
     *
     * The StatementHandler is required in order to return the proper
     * Connection proxy for the getConnection method.
     */
    private class StatementHandler implements InvocationHandler {
        private AbstractJdbc23PooledConnection.ConnectionHandler con;
        private Statement st;

        public StatementHandler(AbstractJdbc23PooledConnection.ConnectionHandler con, Statement st) {
            this.con = con;
            this.st = st;
        }
        public Object invoke(Object proxy, Method method, Object[] args)
        throws Throwable
        {
            // From Object
            if (method.getDeclaringClass().getName().equals("java.lang.Object"))
            {
                if (method.getName().equals("toString"))
                {
                    return "Pooled statement wrapping physical statement " + st;
                }
                if (method.getName().equals("hashCode"))
                {
                    return new Integer(System.identityHashCode(proxy));
                }
                if (method.getName().equals("equals"))
                {
                    return new Boolean(proxy == args[0]);
                }
                return method.invoke(st, args);
            }
            // All the rest is from the Statement interface
            if (method.getName().equals("close"))
            {
                // closing an already closed object is a no-op
                if (st == null || con.isClosed())
                    return null;

                try
                {
                    st.close();
                }
                finally
                {
                    con = null;
                    st = null;
                }
                return null;
            }
            if (st == null || con.isClosed())
            {
                throw new PSQLException(GT.tr("Statement has been closed."),
                                        PSQLState.OBJECT_NOT_IN_STATE);
            }
            
            if (method.getName().equals("getConnection"))
            {
                return con.getProxy(); // the proxied connection, not a physical connection
            }

            try
            {
                return method.invoke(st, args);
            } catch (InvocationTargetException e) {
                Throwable te = e.getTargetException();
                if (te instanceof SQLException)
                    fireConnectionError((SQLException)te); // Tell listeners about exception if it's fatal
                throw te;
            }
        }
    }
}