/**
 * 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;
import org.joda.time.DateTimeZone;
import org.joda.time.format.DateTimeFormatter;
import org.joda.time.format.ISODateTimeFormat;

/**
 *
 * <p>ToDate converts the ISO or the customized string or the Unix timestamp to the DateTime object.</p>
 * <p>ToDate is overloaded.</p>
 *
 * <dl>
 * <dt><b>Syntax:</b></dt>
 * <dd><code>DateTime ToDate(Long millis)</code>.</dd>
 * <dt><b>Input:</b></dt>
 * <dd><code>the milliseconds</code>.</dd>
 * <dt><b>Output:</b></dt>
 * <dd><code>the DateTime object</code>.</dd>
 * </dl>
 *
 * <dl>
 * <dt><b>Syntax:</b></dt>
 * <dd><code>DateTime ToDate(String dtStr)</code>.</dd>
 * <dt><b>Input:</b></dt>
 * <dd><code>the ISO format date time string</code>.</dd>
 * <dt><b>Output:</b></dt>
 * <dd><code>the DateTime object</code>.</dd>
 * </dl>
 *
 * <dl>
 * <dt><b>Syntax:</b></dt>
 * <dd><code>DateTime ToDate(String dtStr, String format)</code>.</dd>
 * <dt><b>Input:</b></dt>
 * <dd><code>dtStr: the string that represents a date time</code>.</dd>
 * <dd><code>format: the format string</code>.</dd>
 * <dt><b>Output:</b></dt>
 * <dd><code>the DateTime object</code>.</dd>
 * </dl>
 *
 * <dl>
 * <dt><b>Syntax:</b></dt>
 * <dd><code>DateTime ToDate(String dtStr, String format, String timezone)</code>.</dd>
 * <dt><b>Input:</b></dt>
 * <dd><code>dtStr: the string that represents a date time</code>.</dd>
 * <dd><code>format: the format string</code>.</dd>
 * <dd><code>timezone: the timezone string</code>.</dd>
 * <dt><b>Output:</b></dt>
 * <dd><code>the DateTime object</code>.</dd>
 * </dl>
 */
public class ToDate extends EvalFunc<DateTime> {

    private static final DateTimeFormatter isoDateTimeFormatter = ISODateTimeFormat
            .dateOptionalTimeParser().withOffsetParsed();

    public DateTime exec(Tuple input) throws IOException {
        if (input == null || input.size() < 1 || input.get(0) == null) {
            return null;
        }
        return new DateTime(DataType.toLong(input.get(0)));
    }

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

    @Override
    public List<FuncSpec> getArgToFuncMapping() throws FrontendException {
        List<FuncSpec> funcList = new ArrayList<FuncSpec>();
        Schema s = new Schema();
        s.add(new Schema.FieldSchema(null, DataType.LONG));
        funcList.add(new FuncSpec(this.getClass().getName(), s));
        s = new Schema();
        s.add(new Schema.FieldSchema(null, DataType.CHARARRAY));
        funcList.add(new FuncSpec(ToDateISO.class.getName(), s));
        s = new Schema();
        s.add(new Schema.FieldSchema(null, DataType.CHARARRAY));
        s.add(new Schema.FieldSchema(null, DataType.CHARARRAY));
        funcList.add(new FuncSpec(ToDate2ARGS.class.getName(), s));
        s = new Schema();
        s.add(new Schema.FieldSchema(null, DataType.CHARARRAY));
        s.add(new Schema.FieldSchema(null, DataType.CHARARRAY));
        s.add(new Schema.FieldSchema(null, DataType.CHARARRAY));
        funcList.add(new FuncSpec(ToDate3ARGS.class.getName(), s));
        return funcList;
    }

    public static DateTimeZone extractDateTimeZone(String dtStr) {
        return isoDateTimeFormatter.parseDateTime(allowIso8601Space(dtStr)).getZone();
    }

    public static DateTime extractDateTime(String dtStr) {
        return isoDateTimeFormatter.parseDateTime(allowIso8601Space(dtStr));
    }
    
	/*
	 * ISO-8601 format and JDBC timestamp format are similar but not the same.
	 * 
	 * Strict ISO-8601 specifies a 'T' between the date portion and
	 * the time portion:
	 *   2015-05-29T10:41:30.123
	 *   
	 * ISO-8601 allows a space instead of a 'T' as a looser variant. 
	 * This variant is often adopted because it increases human readability. 
	 * The JDBC timestamp format uses the ' ' space variant. 
	 *   2015-05-29 10:41:30.123
	 * 
	 * Hive & Impala are database-oriented and generate JDBC timestamps
	 * with a ' ' space. 
	 * 
	 * We would like to accept both 'T' and ' ' space formats. 
	 * 
	 * org.joda.time.format.ISODateTimeFormatter requires the 'T'. 
	 * The cleanest way to get joda-time to accept both is to convert
	 * the ' ' space to a a 'T' before feeding the string to the
	 * ISODateTimeFormatter. 
	 */
    private static String allowIso8601Space(String dtStr) {
    	if (dtStr == null || dtStr.length() <= 10 || dtStr.charAt(10) != ' ') {
    		return dtStr;
    	}
    	return dtStr.substring(0, 10) + 'T' + dtStr.substring(11);
    }

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