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/**
 * Copyright 2015 Netflix, Inc.
 *
 * 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 com.netflix.archaius.readers;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Callable;

import javax.sql.DataSource;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class JDCConfigReader implements Callable> {

    private static Logger log = LoggerFactory.getLogger(JDCConfigReader.class);

    // The datasource to connect to the database.
    private DataSource datasource;

    // The JDBC query to obtain properties stored in an RDBMS.
    // example:
    // "Select distinct property_key, property_value from SITE_PROPERTIES"
    private String query;

    // The column containing the keys
    private String keyColumnName = "property_key";
    
    // The column containing the values. 
    private String valueColumnName = "property_value";

    /**
     * Constructor
     * 
     * @param datasource
     *            The DataSource object for the JDBC; e.g.
     *            new OracleDataSource(databaseName, schema);
     * @param query
     *            The query statement to fetch the properties; e.g.
     *            "Select distinct property_key, property_value from SITE_PROPERTIES"
     * @param keyColumnName
     *            The column name which stores the property keys; e.g.
     *            property_key
     * @param valueColumnName
     *            The column name which stores the property values; e.g.
     *            property_value
     */
    public JDCConfigReader(DataSource datasource, String query, String keyColumnName, String valueColumnName) {
        this.datasource = datasource;
        this.query = query;
        this.keyColumnName = keyColumnName;
        this.valueColumnName = valueColumnName;
    }

    // ...
    @Override
    public Map call() throws Exception {
        Map map = new HashMap();
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;

        try {
            conn = getConnection();
            pstmt = conn.prepareStatement(query.toString());
            rs = pstmt.executeQuery();
            while (rs.next()) {
                String key = (String) rs.getObject(keyColumnName);
                Object value = rs.getObject(valueColumnName);
                map.put(key, value);
            }

        } catch (SQLException e) {
            throw e;
        } finally {
            close(conn, pstmt, rs);
        }
        return map;
    }

    /**
     * Returns the used DataSource object.
     * 
     * @return the data source
     * @since 1.4
     */
    public DataSource getDatasource() {
        return datasource;
    }

    /**
     * Returns a Connection object. This method is called when ever
     * the database is to be accessed. This implementation returns a connection
     * from the current DataSource.
     * 
     * @return the Connection object to be used
     * @throws SQLException
     *             if an error occurs
     * @since 1.4
     */
    protected Connection getConnection() throws SQLException {
        return getDatasource().getConnection();
    }

    /**
     * Close a Connection and, Statement. Avoid
     * closing if null and hide any SQLExceptions that occur.
     * 
     * @param conn
     *            The database connection to close
     * @param stmt
     *            The statement to close
     */
    private void close(Connection conn, Statement stmt, ResultSet rs) {
        try {
            if (rs != null) {
                rs.close();
            }
        } catch (SQLException e) {
            log.error("An error occured on closing the ResultSet", e);
        }

        try {
            if (stmt != null) {
                stmt.close();
            }
        } catch (SQLException e) {
            log.error("An error occured on closing the statement", e);
        }

        try {
            if (conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            log.error("An error occured on closing the connection", e);
        }
    }
}