/*
 * 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.builtin;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.pig.EvalFunc;
import org.apache.pig.FuncSpec;
import org.apache.pig.data.DataType;
import org.apache.pig.data.Tuple;
import org.apache.pig.impl.logicalLayer.FrontendException;
import org.apache.pig.impl.logicalLayer.schema.Schema;
import org.joda.time.DateTime;

/**
 * <p>
 * ToMilliSeconds converts the DateTime to the number of milliseconds that have passed
 * since January 1, 1970 00:00:00.000 GMT.
 * </p>
 * <ul>
 * <li>Jodatime: http://joda-time.sourceforge.net/</li>
 * <li>ISO8601 Date Format: http://en.wikipedia.org/wiki/ISO_8601</li>
 * <li>Unix Time: http://en.wikipedia.org/wiki/Unix_time</li>
 * </ul>
 * <br />
 * <pre>
 * Example usage:
 *
 * ISOin = LOAD 'test.tsv' USING PigStorage('\t') AS (dt:datetime, dt2:datetime);
 *
 * DESCRIBE ISOin;
 * ISOin: {dt: datetime,dt2: datetime}
 *
 * DUMP ISOin;
 *
 * (2009-01-07T01:07:01.000Z,2008-02-01T00:00:00.000Z)
 * (2008-02-06T02:06:02.000Z,2008-02-01T00:00:00.000Z)
 * (2007-03-05T03:05:03.000Z,2008-02-01T00:00:00.000Z)
 * ...
 *
 * toMilliSeconds = FOREACH ISOin GENERATE ToMilliSeconds(dt) AS unixTime:long;
 *
 * DESCRIBE toMilliSeconds;
 * toMilliSeconds: {unixTime: long}
 *
 * DUMP toMilliSeconds;
 *
 * (1231290421000L)
 * (1202263562000L)
 * (1173063903000L)
 * ...
 *</pre>
 */
public class ToMilliSeconds extends EvalFunc<Long> {

    @Override
    public Long exec(Tuple input) throws IOException
    {
        if (input == null || input.size() < 1 || input.get(0) == null) {
            return null;
        }

        DateTime result = (DateTime) input.get(0);

        return result.getMillis();
    }

    @Override
    public Schema outputSchema(Schema input) {
        return new Schema(new Schema.FieldSchema(getSchemaName(this.getClass().getName().toLowerCase(), input), DataType.LONG));
    }

    @Override
    public List<FuncSpec> getArgToFuncMapping() throws FrontendException {
        List<FuncSpec> funcList = new ArrayList<FuncSpec>();
        funcList.add(new FuncSpec(this.getClass().getName(), new Schema(new Schema.FieldSchema(null, DataType.DATETIME))));

        return funcList;
    }

    @Override
    public boolean allowCompileTimeCalculation() {
        return true;
    }
}