/*
 * 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
 *
 *      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.core.metadata;

import java.lang.reflect.Method;
import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.SQLException;
import java.sql.Types;

import org.springframework.dao.InvalidDataAccessApiUsageException;
import org.springframework.lang.Nullable;
import org.springframework.util.ReflectionUtils;

/**
 * Oracle-specific implementation of the {@link org.springframework.jdbc.core.metadata.TableMetaDataProvider}.
 * Supports a feature for including synonyms in the meta-data lookup. Also supports lookup of current schema
 * using the {@code sys_context}.
 *
 * <p>Thanks to Mike Youngstrom and Bruce Campbell for submitting the original suggestion for the Oracle
 * current schema lookup implementation.
 *
 * @author Thomas Risberg
 * @author Juergen Hoeller
 * @since 3.0
 */
public class OracleTableMetaDataProvider extends GenericTableMetaDataProvider {

	private final boolean includeSynonyms;

	@Nullable
	private final String defaultSchema;


	/**
	 * Constructor used to initialize with provided database meta-data.
	 * @param databaseMetaData meta-data to be used
	 */
	public OracleTableMetaDataProvider(DatabaseMetaData databaseMetaData) throws SQLException {
		this(databaseMetaData, false);
	}

	/**
	 * Constructor used to initialize with provided database meta-data.
	 * @param databaseMetaData meta-data to be used
	 * @param includeSynonyms whether to include synonyms
	 */
	public OracleTableMetaDataProvider(DatabaseMetaData databaseMetaData, boolean includeSynonyms)
			throws SQLException {

		super(databaseMetaData);
		this.includeSynonyms = includeSynonyms;
		this.defaultSchema = lookupDefaultSchema(databaseMetaData);
	}


	/*
	 * Oracle-based implementation for detecting the current schema.
	 */
	@Nullable
	private static String lookupDefaultSchema(DatabaseMetaData databaseMetaData) {
		try {
			CallableStatement cstmt = null;
			try {
				Connection con = databaseMetaData.getConnection();
				if (con == null) {
					logger.debug("Cannot check default schema - no Connection from DatabaseMetaData");
					return null;
				}
				cstmt = con.prepareCall("{? = call sys_context('USERENV', 'CURRENT_SCHEMA')}");
				cstmt.registerOutParameter(1, Types.VARCHAR);
				cstmt.execute();
				return cstmt.getString(1);
			}
			finally {
				if (cstmt != null) {
					cstmt.close();
				}
			}
		}
		catch (SQLException ex) {
			logger.debug("Exception encountered during default schema lookup", ex);
			return null;
		}
	}

	@Override
	@Nullable
	protected String getDefaultSchema() {
		if (this.defaultSchema != null) {
			return defaultSchema;
		}
		return super.getDefaultSchema();
	}


	@Override
	public void initializeWithTableColumnMetaData(DatabaseMetaData databaseMetaData,
			@Nullable String catalogName, @Nullable String schemaName, @Nullable String tableName)
			throws SQLException {

		if (!this.includeSynonyms) {
			logger.debug("Defaulting to no synonyms in table meta-data lookup");
			super.initializeWithTableColumnMetaData(databaseMetaData, catalogName, schemaName, tableName);
			return;
		}

		Connection con = databaseMetaData.getConnection();
		if (con == null) {
			logger.warn("Unable to include synonyms in table meta-data lookup - no Connection from DatabaseMetaData");
			super.initializeWithTableColumnMetaData(databaseMetaData, catalogName, schemaName, tableName);
			return;
		}

		try {
			Class<?> oracleConClass = con.getClass().getClassLoader().loadClass("oracle.jdbc.OracleConnection");
			con = (Connection) con.unwrap(oracleConClass);
		}
		catch (ClassNotFoundException | SQLException ex) {
			if (logger.isWarnEnabled()) {
				logger.warn("Unable to include synonyms in table meta-data lookup - no Oracle Connection: " + ex);
			}
			super.initializeWithTableColumnMetaData(databaseMetaData, catalogName, schemaName, tableName);
			return;
		}

		logger.debug("Including synonyms in table meta-data lookup");
		Method setIncludeSynonyms;
		Boolean originalValueForIncludeSynonyms;

		try {
			Method getIncludeSynonyms = con.getClass().getMethod("getIncludeSynonyms");
			ReflectionUtils.makeAccessible(getIncludeSynonyms);
			originalValueForIncludeSynonyms = (Boolean) getIncludeSynonyms.invoke(con);

			setIncludeSynonyms = con.getClass().getMethod("setIncludeSynonyms", boolean.class);
			ReflectionUtils.makeAccessible(setIncludeSynonyms);
			setIncludeSynonyms.invoke(con, Boolean.TRUE);
		}
		catch (Throwable ex) {
			throw new InvalidDataAccessApiUsageException("Could not prepare Oracle Connection", ex);
		}

		super.initializeWithTableColumnMetaData(databaseMetaData, catalogName, schemaName, tableName);

		try {
			setIncludeSynonyms.invoke(con, originalValueForIncludeSynonyms);
		}
		catch (Throwable ex) {
			throw new InvalidDataAccessApiUsageException("Could not reset Oracle Connection", ex);
		}
	}

}
