/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed 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
 *
 *      https://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.springframework.jdbc.datasource;

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Savepoint;

import org.springframework.lang.Nullable;
import org.springframework.transaction.support.ResourceHolderSupport;
import org.springframework.util.Assert;

/**
 * Resource holder wrapping a JDBC {@link Connection}.
 * {@link DataSourceTransactionManager} binds instances of this class
 * to the thread, for a specific {@link javax.sql.DataSource}.
 *
 * <p>Inherits rollback-only support for nested JDBC transactions
 * and reference count functionality from the base class.
 *
 * <p>Note: This is an SPI class, not intended to be used by applications.
 *
 * @author Juergen Hoeller
 * @since 06.05.2003
 * @see DataSourceTransactionManager
 * @see DataSourceUtils
 */
public class ConnectionHolder extends ResourceHolderSupport {

        /**
         * Prefix for savepoint names.
         */
        public static final String SAVEPOINT_NAME_PREFIX = "SAVEPOINT_";


        @Nullable
        private ConnectionHandle connectionHandle;

        @Nullable
        private Connection currentConnection;

        private boolean transactionActive = false;

        @Nullable
        private Boolean savepointsSupported;

        private int savepointCounter = 0;


        /**
         * Create a new ConnectionHolder for the given ConnectionHandle.
         * @param connectionHandle the ConnectionHandle to hold
         */
        public ConnectionHolder(ConnectionHandle connectionHandle) {
                Assert.notNull(connectionHandle, "ConnectionHandle must not be null");
                this.connectionHandle = connectionHandle;
        }

        /**
         * Create a new ConnectionHolder for the given JDBC Connection,
         * wrapping it with a {@link SimpleConnectionHandle},
         * assuming that there is no ongoing transaction.
         * @param connection the JDBC Connection to hold
         * @see SimpleConnectionHandle
         * @see #ConnectionHolder(java.sql.Connection, boolean)
         */
        public ConnectionHolder(Connection connection) {
                this.connectionHandle = new SimpleConnectionHandle(connection);
        }

        /**
         * Create a new ConnectionHolder for the given JDBC Connection,
         * wrapping it with a {@link SimpleConnectionHandle}.
         * @param connection the JDBC Connection to hold
         * @param transactionActive whether the given Connection is involved
         * in an ongoing transaction
         * @see SimpleConnectionHandle
         */
        public ConnectionHolder(Connection connection, boolean transactionActive) {
                this(connection);
                this.transactionActive = transactionActive;
        }


        /**
         * Return the ConnectionHandle held by this ConnectionHolder.
         */
        @Nullable
        public ConnectionHandle getConnectionHandle() {
                return this.connectionHandle;
        }

        /**
         * Return whether this holder currently has a Connection.
         */
        protected boolean hasConnection() {
                return (this.connectionHandle != null);
        }

        /**
         * Set whether this holder represents an active, JDBC-managed transaction.
         * @see DataSourceTransactionManager
         */
        protected void setTransactionActive(boolean transactionActive) {
                this.transactionActive = transactionActive;
        }

        /**
         * Return whether this holder represents an active, JDBC-managed transaction.
         */
        protected boolean isTransactionActive() {
                return this.transactionActive;
        }


        /**
         * Override the existing Connection handle with the given Connection.
         * Reset the handle if given {@code null}.
         * <p>Used for releasing the Connection on suspend (with a {@code null}
         * argument) and setting a fresh Connection on resume.
         */
        protected void setConnection(@Nullable Connection connection) {
                if (this.currentConnection != null) {
                        if (this.connectionHandle != null) {
                                this.connectionHandle.releaseConnection(this.currentConnection);
                        }
                        this.currentConnection = null;
                }
                if (connection != null) {
                        this.connectionHandle = new SimpleConnectionHandle(connection);
                }
                else {
                        this.connectionHandle = null;
                }
        }

        /**
         * Return the current Connection held by this ConnectionHolder.
         * <p>This will be the same Connection until {@code released}
         * gets called on the ConnectionHolder, which will reset the
         * held Connection, fetching a new Connection on demand.
         * @see ConnectionHandle#getConnection()
         * @see #released()
         */
        public Connection getConnection() {
                Assert.notNull(this.connectionHandle, "Active Connection is required");
                if (this.currentConnection == null) {
                        this.currentConnection = this.connectionHandle.getConnection();
                }
                return this.currentConnection;
        }

        /**
         * Return whether JDBC 3.0 Savepoints are supported.
         * Caches the flag for the lifetime of this ConnectionHolder.
         * @throws SQLException if thrown by the JDBC driver
         */
        public boolean supportsSavepoints() throws SQLException {
                if (this.savepointsSupported == null) {
                        this.savepointsSupported = getConnection().getMetaData().supportsSavepoints();
                }
                return this.savepointsSupported;
        }

        /**
         * Create a new JDBC 3.0 Savepoint for the current Connection,
         * using generated savepoint names that are unique for the Connection.
         * @return the new Savepoint
         * @throws SQLException if thrown by the JDBC driver
         */
        public Savepoint createSavepoint() throws SQLException {
                this.savepointCounter++;
                return getConnection().setSavepoint(SAVEPOINT_NAME_PREFIX + this.savepointCounter);
        }

        /**
         * Releases the current Connection held by this ConnectionHolder.
         * <p>This is necessary for ConnectionHandles that expect "Connection borrowing",
         * where each returned Connection is only temporarily leased and needs to be
         * returned once the data operation is done, to make the Connection available
         * for other operations within the same transaction.
         */
        @Override
        public void released() {
                super.released();
                if (!isOpen() && this.currentConnection != null) {
                        if (this.connectionHandle != null) {
                                this.connectionHandle.releaseConnection(this.currentConnection);
                        }
                        this.currentConnection = null;
                }
        }


        @Override
        public void clear() {
                super.clear();
                this.transactionActive = false;
                this.savepointsSupported = null;
                this.savepointCounter = 0;
        }

}