/*
 * Copyright 2002-2020 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.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.SQLException;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

/**
 * Implementation of {@link SmartDataSource} that wraps a single JDBC Connection
 * which is not closed after use. Obviously, this is not multi-threading capable.
 *
 * <p>Note that at shutdown, someone should close the underlying Connection
 * via the {@code close()} method. Client code will never call close
 * on the Connection handle if it is SmartDataSource-aware (e.g. uses
 * {@code DataSourceUtils.releaseConnection}).
 *
 * <p>If client code will call {@code close()} in the assumption of a pooled
 * Connection, like when using persistence tools, set "suppressClose" to "true".
 * This will return a close-suppressing proxy instead of the physical Connection.
 *
 * <p>This is primarily intended for testing. For example, it enables easy testing
 * outside an application server, for code that expects to work on a DataSource.
 * In contrast to {@link DriverManagerDataSource}, it reuses the same Connection
 * all the time, avoiding excessive creation of physical Connections.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see #getConnection()
 * @see java.sql.Connection#close()
 * @see DataSourceUtils#releaseConnection
 */
public class SingleConnectionDataSource extends DriverManagerDataSource implements SmartDataSource, DisposableBean {

        /** Create a close-suppressing proxy?. */
        private boolean suppressClose;

        /** Override auto-commit state?. */
        @Nullable
        private Boolean autoCommit;

        /** Wrapped Connection. */
        @Nullable
        private Connection target;

        /** Proxy Connection. */
        @Nullable
        private Connection connection;

        /** Synchronization monitor for the shared Connection. */
        private final Object connectionMonitor = new Object();


        /**
         * Constructor for bean-style configuration.
         */
        public SingleConnectionDataSource() {
        }

        /**
         * Create a new SingleConnectionDataSource with the given standard
         * DriverManager parameters.
         * @param url the JDBC URL to use for accessing the DriverManager
         * @param username the JDBC username to use for accessing the DriverManager
         * @param password the JDBC password to use for accessing the DriverManager
         * @param suppressClose if the returned Connection should be a
         * close-suppressing proxy or the physical Connection
         * @see java.sql.DriverManager#getConnection(String, String, String)
         */
        public SingleConnectionDataSource(String url, String username, String password, boolean suppressClose) {
                super(url, username, password);
                this.suppressClose = suppressClose;
        }

        /**
         * Create a new SingleConnectionDataSource with the given standard
         * DriverManager parameters.
         * @param url the JDBC URL to use for accessing the DriverManager
         * @param suppressClose if the returned Connection should be a
         * close-suppressing proxy or the physical Connection
         * @see java.sql.DriverManager#getConnection(String, String, String)
         */
        public SingleConnectionDataSource(String url, boolean suppressClose) {
                super(url);
                this.suppressClose = suppressClose;
        }

        /**
         * Create a new SingleConnectionDataSource with a given Connection.
         * @param target underlying target Connection
         * @param suppressClose if the Connection should be wrapped with a Connection that
         * suppresses {@code close()} calls (to allow for normal {@code close()}
         * usage in applications that expect a pooled Connection but do not know our
         * SmartDataSource interface)
         */
        public SingleConnectionDataSource(Connection target, boolean suppressClose) {
                Assert.notNull(target, "Connection must not be null");
                this.target = target;
                this.suppressClose = suppressClose;
                this.connection = (suppressClose ? getCloseSuppressingConnectionProxy(target) : target);
        }


        /**
         * Set whether the returned Connection should be a close-suppressing proxy
         * or the physical Connection.
         */
        public void setSuppressClose(boolean suppressClose) {
                this.suppressClose = suppressClose;
        }

        /**
         * Return whether the returned Connection will be a close-suppressing proxy
         * or the physical Connection.
         */
        protected boolean isSuppressClose() {
                return this.suppressClose;
        }

        /**
         * Set whether the returned Connection's "autoCommit" setting should be overridden.
         */
        public void setAutoCommit(boolean autoCommit) {
                this.autoCommit = (autoCommit);
        }

        /**
         * Return whether the returned Connection's "autoCommit" setting should be overridden.
         * @return the "autoCommit" value, or {@code null} if none to be applied
         */
        @Nullable
        protected Boolean getAutoCommitValue() {
                return this.autoCommit;
        }


        @Override
        public Connection getConnection() throws SQLException {
                synchronized (this.connectionMonitor) {
                        if (this.connection == null) {
                                // No underlying Connection -> lazy init via DriverManager.
                                initConnection();
                        }
                        if (this.connection.isClosed()) {
                                throw new SQLException(
                                                "Connection was closed in SingleConnectionDataSource. Check that user code checks " +
                                                "shouldClose() before closing Connections, or set 'suppressClose' to 'true'");
                        }
                        return this.connection;
                }
        }

        /**
         * Specifying a custom username and password doesn't make sense
         * with a single Connection. Returns the single Connection if given
         * the same username and password; throws an SQLException else.
         */
        @Override
        public Connection getConnection(String username, String password) throws SQLException {
                if (ObjectUtils.nullSafeEquals(username, getUsername()) &&
                                ObjectUtils.nullSafeEquals(password, getPassword())) {
                        return getConnection();
                }
                else {
                        throw new SQLException("SingleConnectionDataSource does not support custom username and password");
                }
        }

        /**
         * This is a single Connection: Do not close it when returning to the "pool".
         */
        @Override
        public boolean shouldClose(Connection con) {
                synchronized (this.connectionMonitor) {
                        return (con != this.connection && con != this.target);
                }
        }

        /**
         * Close the underlying Connection.
         * The provider of this DataSource needs to care for proper shutdown.
         * <p>As this bean implements DisposableBean, a bean factory will
         * automatically invoke this on destruction of its cached singletons.
         */
        @Override
        public void destroy() {
                synchronized (this.connectionMonitor) {
                        closeConnection();
                }
        }


        /**
         * Initialize the underlying Connection via the DriverManager.
         */
        public void initConnection() throws SQLException {
                if (getUrl() == null) {
                        throw new IllegalStateException("'url' property is required for lazily initializing a Connection");
                }
                synchronized (this.connectionMonitor) {
                        closeConnection();
                        this.target = getConnectionFromDriver(getUsername(), getPassword());
                        prepareConnection(this.target);
                        if (logger.isDebugEnabled()) {
                                logger.debug("Established shared JDBC Connection: " + this.target);
                        }
                        this.connection = (isSuppressClose() ? getCloseSuppressingConnectionProxy(this.target) : this.target);
                }
        }

        /**
         * Reset the underlying shared Connection, to be reinitialized on next access.
         */
        public void resetConnection() {
                synchronized (this.connectionMonitor) {
                        closeConnection();
                        this.target = null;
                        this.connection = null;
                }
        }

        /**
         * Prepare the given Connection before it is exposed.
         * <p>The default implementation applies the auto-commit flag, if necessary.
         * Can be overridden in subclasses.
         * @param con the Connection to prepare
         * @see #setAutoCommit
         */
        protected void prepareConnection(Connection con) throws SQLException {
                Boolean autoCommit = getAutoCommitValue();
                if (autoCommit != null && con.getAutoCommit() != autoCommit) {
                        con.setAutoCommit(autoCommit);
                }
        }

        /**
         * Close the underlying shared Connection.
         */
        private void closeConnection() {
                if (this.target != null) {
                        try {
                                this.target.close();
                        }
                        catch (Throwable ex) {
                                logger.info("Could not close shared JDBC Connection", ex);
                        }
                }
        }

        /**
         * Wrap the given Connection with a proxy that delegates every method call to it
         * but suppresses close calls.
         * @param target the original Connection to wrap
         * @return the wrapped Connection
         */
        protected Connection getCloseSuppressingConnectionProxy(Connection target) {
                return (Connection) Proxy.newProxyInstance(
                                ConnectionProxy.class.getClassLoader(),
                                new Class<?>[] {ConnectionProxy.class},
                                new CloseSuppressingInvocationHandler(target));
        }


        /**
         * Invocation handler that suppresses close calls on JDBC Connections.
         */
        private static class CloseSuppressingInvocationHandler implements InvocationHandler {

                private final Connection target;

                public CloseSuppressingInvocationHandler(Connection target) {
                        this.target = target;
                }

                @Override
                @Nullable
                public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        // Invocation on ConnectionProxy interface coming in...

                        if (method.getName().equals("equals")) {
                                // Only consider equal when proxies are identical.
                                return (proxy == args[0]);
                        }
                        else if (method.getName().equals("hashCode")) {
                                // Use hashCode of Connection proxy.
                                return System.identityHashCode(proxy);
                        }
                        else if (method.getName().equals("unwrap")) {
                                if (((Class<?>) args[0]).isInstance(proxy)) {
                                        return proxy;
                                }
                        }
                        else if (method.getName().equals("isWrapperFor")) {
                                if (((Class<?>) args[0]).isInstance(proxy)) {
                                        return true;
                                }
                        }
                        else if (method.getName().equals("close")) {
                                // Handle close method: don't pass the call on.
                                return null;
                        }
                        else if (method.getName().equals("isClosed")) {
                                return this.target.isClosed();
                        }
                        else if (method.getName().equals("getTargetConnection")) {
                                // Handle getTargetConnection method: return underlying Connection.
                                return this.target;
                        }

                        // Invoke method on target Connection.
                        try {
                                return method.invoke(this.target, args);
                        }
                        catch (InvocationTargetException ex) {
                                throw ex.getTargetException();
                        }
                }
        }

}