/*
 * Copyright 2002-2012 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.lookup;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;
import javax.sql.DataSource;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.jdbc.datasource.AbstractDataSource;
import org.springframework.util.Assert;

/**
 * Abstract {@link javax.sql.DataSource} implementation that routes {@link #getConnection()}
 * calls to one of various target DataSources based on a lookup key. The latter is usually
 * (but not necessarily) determined through some thread-bound transaction context.
 *
 * @author Juergen Hoeller
 * @since 2.0.1
 * @see #setTargetDataSources
 * @see #setDefaultTargetDataSource
 * @see #determineCurrentLookupKey()
 */
public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {

        private Map<Object, Object> targetDataSources;

        private Object defaultTargetDataSource;

        private boolean lenientFallback = true;

        private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup();

        private Map<Object, DataSource> resolvedDataSources;

        private DataSource resolvedDefaultDataSource;


        /**
         * Specify the map of target DataSources, with the lookup key as key.
         * The mapped value can either be a corresponding {@link javax.sql.DataSource}
         * instance or a data source name String (to be resolved via a
         * {@link #setDataSourceLookup DataSourceLookup}).
         * <p>The key can be of arbitrary type; this class implements the
         * generic lookup process only. The concrete key representation will
         * be handled by {@link #resolveSpecifiedLookupKey(Object)} and
         * {@link #determineCurrentLookupKey()}.
         */
        public void setTargetDataSources(Map<Object, Object> targetDataSources) {
                this.targetDataSources = targetDataSources;
        }

        /**
         * Specify the default target DataSource, if any.
         * <p>The mapped value can either be a corresponding {@link javax.sql.DataSource}
         * instance or a data source name String (to be resolved via a
         * {@link #setDataSourceLookup DataSourceLookup}).
         * <p>This DataSource will be used as target if none of the keyed
         * {@link #setTargetDataSources targetDataSources} match the
         * {@link #determineCurrentLookupKey()} current lookup key.
         */
        public void setDefaultTargetDataSource(Object defaultTargetDataSource) {
                this.defaultTargetDataSource = defaultTargetDataSource;
        }

        /**
         * Specify whether to apply a lenient fallback to the default DataSource
         * if no specific DataSource could be found for the current lookup key.
         * <p>Default is "true", accepting lookup keys without a corresponding entry
         * in the target DataSource map - simply falling back to the default DataSource
         * in that case.
         * <p>Switch this flag to "false" if you would prefer the fallback to only apply
         * if the lookup key was {@code null}. Lookup keys without a DataSource
         * entry will then lead to an IllegalStateException.
         * @see #setTargetDataSources
         * @see #setDefaultTargetDataSource
         * @see #determineCurrentLookupKey()
         */
        public void setLenientFallback(boolean lenientFallback) {
                this.lenientFallback = lenientFallback;
        }

        /**
         * Set the DataSourceLookup implementation to use for resolving data source
         * name Strings in the {@link #setTargetDataSources targetDataSources} map.
         * <p>Default is a {@link JndiDataSourceLookup}, allowing the JNDI names
         * of application server DataSources to be specified directly.
         */
        public void setDataSourceLookup(DataSourceLookup dataSourceLookup) {
                this.dataSourceLookup = (dataSourceLookup != null ? dataSourceLookup : new JndiDataSourceLookup());
        }


        @Override
        public void afterPropertiesSet() {
                if (this.targetDataSources == null) {
                        throw new IllegalArgumentException("Property 'targetDataSources' is required");
                }
                this.resolvedDataSources = new HashMap<Object, DataSource>(this.targetDataSources.size());
                for (Map.Entry<Object, Object> entry : this.targetDataSources.entrySet()) {
                        Object lookupKey = resolveSpecifiedLookupKey(entry.getKey());
                        DataSource dataSource = resolveSpecifiedDataSource(entry.getValue());
                        this.resolvedDataSources.put(lookupKey, dataSource);
                }
                if (this.defaultTargetDataSource != null) {
                        this.resolvedDefaultDataSource = resolveSpecifiedDataSource(this.defaultTargetDataSource);
                }
        }

        /**
         * Resolve the given lookup key object, as specified in the
         * {@link #setTargetDataSources targetDataSources} map, into
         * the actual lookup key to be used for matching with the
         * {@link #determineCurrentLookupKey() current lookup key}.
         * <p>The default implementation simply returns the given key as-is.
         * @param lookupKey the lookup key object as specified by the user
         * @return the lookup key as needed for matching
         */
        protected Object resolveSpecifiedLookupKey(Object lookupKey) {
                return lookupKey;
        }

        /**
         * Resolve the specified data source object into a DataSource instance.
         * <p>The default implementation handles DataSource instances and data source
         * names (to be resolved via a {@link #setDataSourceLookup DataSourceLookup}).
         * @param dataSource the data source value object as specified in the
         * {@link #setTargetDataSources targetDataSources} map
         * @return the resolved DataSource (never {@code null})
         * @throws IllegalArgumentException in case of an unsupported value type
         */
        protected DataSource resolveSpecifiedDataSource(Object dataSource) throws IllegalArgumentException {
                if (dataSource instanceof DataSource) {
                        return (DataSource) dataSource;
                }
                else if (dataSource instanceof String) {
                        return this.dataSourceLookup.getDataSource((String) dataSource);
                }
                else {
                        throw new IllegalArgumentException(
                                        "Illegal data source value - only [javax.sql.DataSource] and String supported: " + dataSource);
                }
        }


        @Override
        public Connection getConnection() throws SQLException {
                return determineTargetDataSource().getConnection();
        }

        @Override
        public Connection getConnection(String username, String password) throws SQLException {
                return determineTargetDataSource().getConnection(username, password);
        }

        @Override
        @SuppressWarnings("unchecked")
        public <T> T unwrap(Class<T> iface) throws SQLException {
                if (iface.isInstance(this)) {
                        return (T) this;
                }
                return determineTargetDataSource().unwrap(iface);
        }

        @Override
        public boolean isWrapperFor(Class<?> iface) throws SQLException {
                return (iface.isInstance(this) || determineTargetDataSource().isWrapperFor(iface));
        }

        /**
         * Retrieve the current target DataSource. Determines the
         * {@link #determineCurrentLookupKey() current lookup key}, performs
         * a lookup in the {@link #setTargetDataSources targetDataSources} map,
         * falls back to the specified
         * {@link #setDefaultTargetDataSource default target DataSource} if necessary.
         * @see #determineCurrentLookupKey()
         */
        protected DataSource determineTargetDataSource() {
                Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
                Object lookupKey = determineCurrentLookupKey();
                DataSource dataSource = this.resolvedDataSources.get(lookupKey);
                if (dataSource == null && (this.lenientFallback || lookupKey == null)) {
                        dataSource = this.resolvedDefaultDataSource;
                }
                if (dataSource == null) {
                        throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");
                }
                return dataSource;
        }

        /**
         * Determine the current lookup key. This will typically be
         * implemented to check a thread-bound transaction context.
         * <p>Allows for arbitrary keys. The returned key needs
         * to match the stored lookup key type, as resolved by the
         * {@link #resolveSpecifiedLookupKey} method.
         */
        protected abstract Object determineCurrentLookupKey();

}