/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.pig.piggybank.evaluation.datetime.truncate;

import org.apache.pig.data.Tuple;
import org.joda.time.DateTime;
import org.joda.time.DateTimeZone;
import org.joda.time.format.ISODateTimeFormat;
import org.apache.pig.backend.executionengine.ExecException;

/**
 * ISOHelper provides helper methods for the other classes in this package.
 *
 * <ul>
 * <li>Jodatime: http://joda-time.sourceforge.net/</li>
 * <li>ISO8601 Date Format: http://en.wikipedia.org/wiki/ISO_8601</li>
 * </ul>
 * This class is public so that it can be tested in TestTruncateDateTime. 
 * Otherwise, it would have "package" visibility.
 */
public class ISOHelper {

    /**
     * Default time zone for use in parsing, regardless of System or JDK's
     * default time zone.
     */
    public static final DateTimeZone DEFAULT_DATE_TIME_ZONE = DateTimeZone.UTC;

    /**
     * @param input a non-null, non-empty Tuple,
     *  whose first element is a ISO 8601 string representation of a date, time, or dateTime;
     *  with optional time zone.
     * @return a DateTime representing the date, 
     *  with DateTimeZone set to the time zone parsed from the string,
     *  or else DateTimeZone.defaultTimeZone() if one is set,
     *  or else UTC.
     * @throws ExecException if input is a malformed or empty tuple.
     * This method is public so that it can be tested in TestTruncateDateTime. 
     * Otherwise, it would have "package" visibility.
     */
    public static DateTime parseDateTime(Tuple input) throws ExecException {    
            
        // Save previous default time zone for restore later.
        DateTimeZone previousDefaultTimeZone = DateTimeZone.getDefault();

        // Temporarily set default time zone to UTC, for this parse.
        DateTimeZone.setDefault(DEFAULT_DATE_TIME_ZONE);

        String isoDateString = input.get(0).toString();
        DateTime dt = ISODateTimeFormat.dateTimeParser().withOffsetParsed().parseDateTime(isoDateString);            

        // restore previous default TimeZone.
        DateTimeZone.setDefault(previousDefaultTimeZone);

        return dt;
    }
    
}

