/*
 * Copyright 2002-2017 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
 *
 *      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.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.lang.Nullable;
import org.springframework.util.Assert;

Abstract DataSource implementation that routes 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
See Also:
setTargetDataSources
setDefaultTargetDataSource
determineCurrentLookupKey()
Since:
2.0.1/**
 * 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 {

	@Nullable
	private Map<Object, Object> targetDataSources;

	@Nullable
	private Object defaultTargetDataSource;

	private boolean lenientFallback = true;

	private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup();

	@Nullable
	private Map<Object, DataSource> resolvedDataSources;

	@Nullable
	private DataSource resolvedDefaultDataSource;


	
Specify the map of target DataSources, with the lookup key as key. The mapped value can either be a corresponding DataSource instance or a data source name String (to be resolved via a DataSourceLookup). 
The key can be of arbitrary type; this class implements the generic lookup process only. The concrete key representation will be handled by resolveSpecifiedLookupKey(Object) and determineCurrentLookupKey(). /**
	 * 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.
The mapped value can either be a corresponding DataSource instance or a data source name String (to be resolved via a DataSourceLookup). 
This DataSource will be used as target if none of the keyed targetDataSources match the determineCurrentLookupKey() current lookup key. /**
	 * 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.
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.
Switch this flag to "false" if you would prefer the fallback to only apply if the lookup key was null. Lookup keys without a DataSource entry will then lead to an IllegalStateException. 
See Also:
setTargetDataSources
setDefaultTargetDataSource
determineCurrentLookupKey()/**
	 * 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 targetDataSources map. 
Default is a JndiDataSourceLookup, allowing the JNDI names of application server DataSources to be specified directly. /**
	 * 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(@Nullable 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<>(this.targetDataSources.size());
		this.targetDataSources.forEach((key, value) -> {
			Object lookupKey = resolveSpecifiedLookupKey(key);
			DataSource dataSource = resolveSpecifiedDataSource(value);
			this.resolvedDataSources.put(lookupKey, dataSource);
		});
		if (this.defaultTargetDataSource != null) {
			this.resolvedDefaultDataSource = resolveSpecifiedDataSource(this.defaultTargetDataSource);
		}
	}

	
Resolve the given lookup key object, as specified in the targetDataSources map, into the actual lookup key to be used for matching with the current lookup key. 
The default implementation simply returns the given key as-is.
Params:
lookupKey – the lookup key object as specified by the user
Returns:
the lookup key as needed for matching/**
	 * 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.
The default implementation handles DataSource instances and data source names (to be resolved via a DataSourceLookup). 
Params:
dataSource – the data source value object as specified in the targetDataSources map
Throws:
IllegalArgumentException – in case of an unsupported value type
Returns:
the resolved DataSource (never null)/**
	 * 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 current lookup key, performs a lookup in the targetDataSources map, falls back to the specified default target DataSource if necessary. 
See Also:
determineCurrentLookupKey()/**
	 * 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.
Allows for arbitrary keys. The returned key needs to match the stored lookup key type, as resolved by the resolveSpecifiedLookupKey method. /**
	 * 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.
	 */
	@Nullable
	protected abstract Object determineCurrentLookupKey();

}