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/*

  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.managed;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.Map;
import java.util.Objects;
import java.util.WeakHashMap;

import javax.transaction.SystemException;
import javax.transaction.Transaction;
import javax.transaction.TransactionManager;
import javax.transaction.TransactionSynchronizationRegistry;
import javax.transaction.xa.XAResource;

import org.apache.commons.dbcp2.DelegatingConnection;

/**
 * TransactionRegistry tracks Connections and XAResources in a transacted environment for a single XAConnectionFactory.
 * 
 * The TransactionRegistry hides the details of transaction processing from the existing DBCP pooling code, and gives
 * the ManagedConnection a way to enlist connections in a transaction, allowing for the maximal rescue of DBCP.
 * 
 *
 * @since 2.0
 */
public class TransactionRegistry {
    private final TransactionManager transactionManager;
    private final Map caches = new WeakHashMap<>();
    private final Map xaResources = new WeakHashMap<>();
    private final TransactionSynchronizationRegistry transactionSynchronizationRegistry;

    /**
     * Provided for backwards compatibility
     * @param transactionManager the transaction manager used to enlist connections
     */
    public TransactionRegistry(final TransactionManager transactionManager) {
        this (transactionManager, null);
    }

    /**
     * Creates a TransactionRegistry for the specified transaction manager.
     *
     * @param transactionManager
     *            the transaction manager used to enlist connections.
     * @param transactionSynchronizationRegistry
     *              The optional TSR to register synchronizations with
     * @since 2.6.0
     */
    public TransactionRegistry(final TransactionManager transactionManager, final TransactionSynchronizationRegistry transactionSynchronizationRegistry) {
        this.transactionManager = transactionManager;
        this.transactionSynchronizationRegistry = transactionSynchronizationRegistry;
    }

    /**
     * Gets the active TransactionContext or null if not Transaction is active.
     *
     * @return The active TransactionContext or null if no Transaction is active.
     * @throws SQLException
     *             Thrown when an error occurs while fetching the transaction.
     */
    public TransactionContext getActiveTransactionContext() throws SQLException {
        Transaction transaction = null;
        try {
            transaction = transactionManager.getTransaction();

            // was there a transaction?
            if (transaction == null) {
                return null;
            }

            // This is the transaction on the thread so no need to check it's status - we should try to use it and
            // fail later based on the subsequent status
        } catch (final SystemException e) {
            throw new SQLException("Unable to determine current transaction ", e);
        }

        // register the context (or create a new one)
        synchronized (this) {
            TransactionContext cache = caches.get(transaction);
            if (cache == null) {
                cache = new TransactionContext(this, transaction, transactionSynchronizationRegistry);
                caches.put(transaction, cache);
            }
            return cache;
        }
    }

    private Connection getConnectionKey(final Connection connection) {
        final Connection result;
        if (connection instanceof DelegatingConnection) {
            result = ((DelegatingConnection) connection).getInnermostDelegateInternal();
        } else {
            result = connection;
        }
        return result;
    }

    /**
     * Gets the XAResource registered for the connection.
     *
     * @param connection
     *            the connection
     * @return The XAResource registered for the connection; never null.
     * @throws SQLException
     *             Thrown when the connection does not have a registered XAResource.
     */
    public synchronized XAResource getXAResource(final Connection connection) throws SQLException {
        Objects.requireNonNull(connection, "connection is null");
        final Connection key = getConnectionKey(connection);
        final XAResource xaResource = xaResources.get(key);
        if (xaResource == null) {
            throw new SQLException("Connection does not have a registered XAResource " + connection);
        }
        return xaResource;
    }

    /**
     * Registers the association between a Connection and a XAResource. When a connection is enlisted in a transaction,
     * it is actually the XAResource that is given to the transaction manager.
     *
     * @param connection
     *            The JDBC connection.
     * @param xaResource
     *            The XAResource which managed the connection within a transaction.
     */
    public synchronized void registerConnection(final Connection connection, final XAResource xaResource) {
        Objects.requireNonNull(connection, "connection is null");
        Objects.requireNonNull(xaResource, "xaResource is null");
        xaResources.put(connection, xaResource);
    }

    /**
     * Unregisters a destroyed connection from {@link TransactionRegistry}.
     *
     * @param connection
     *            A destroyed connection from {@link TransactionRegistry}.
     */
    public synchronized void unregisterConnection(final Connection connection) {
        final Connection key = getConnectionKey(connection);
        xaResources.remove(key);
    }
}