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package com.google.refine.expr.functions;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.IllformedLocaleException;
import java.util.List;
import java.util.Locale;
import java.util.Properties;
import java.util.TimeZone;

import org.apache.commons.lang3.StringUtils;

import com.google.refine.expr.EvalError;
import com.google.refine.expr.util.CalendarParser;
import com.google.refine.expr.util.CalendarParserException;
import com.google.refine.grel.ControlFunctionRegistry;
import com.google.refine.grel.Function;
import com.google.refine.util.ParsingUtilities;

public class ToDate implements Function {

    @Override
    public Object call(Properties bindings, Object[] args) {
        String o1;
        Boolean month_first = null;
        List<String> formats =  new ArrayList<>();
        OffsetDateTime date = null;
        
        //Check there is at least one argument
        if (args.length == 0) {
            return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects at least one argument");
        } else {
            Object arg0 = args[0];
            //check the first argument is something that can be parsed as a date
            if (arg0 instanceof OffsetDateTime) {
                return arg0;
            } else if (arg0 instanceof Long) {
                o1 =  ((Long) arg0).toString(); // treat integers as years
            } else if (arg0 instanceof String && arg0.toString().trim().length() > 0) {
                o1 = (String) arg0;
            } else {
                // ignore cell values that aren't Date, Calendar, Long or String 
                return new EvalError("Unable to parse as date");
            }
        }
        
        if(args.length==1) {
            try {
                date = parse(o1, true, formats);
            } catch (DateFormatException e) {
                // Should never happen since we're using an empty format list
            }
        } else if (args.length > 1) {
            if(args[1] instanceof Boolean) {
                month_first = (Boolean) args[1];
            } else if (args[1] instanceof String) {
                formats.add(StringUtils.trim((String) args[1]));
            } else {
                return new EvalError("Invalid argument");
            }
            for (int i = 2; i < args.length; i++) {
                if (!(args[i] instanceof String)) {
                    return new EvalError("Invalid non-string format argument " + args[i].toString());
                }
                formats.add(StringUtils.trim((String) args[i]));
            }
            try {
                if (month_first != null) {
                    date = parse(o1, month_first, formats);
                } else {
                    date = parse(o1, formats);
                }
            } catch (DateFormatException e) {
                return new EvalError(e.getMessage());
            }
        }
        if(date != null) {
            return date;
        }
        return new EvalError("Unable to convert to a date");
    }
    
    private OffsetDateTime parse(String o1, Boolean month_first, List<String> formats) throws DateFormatException {
        if(month_first != null) {
            try {
               return CalendarParser.parseAsOffsetDateTime( o1, (month_first) ? CalendarParser.MM_DD_YY : CalendarParser.DD_MM_YY);
            } catch (CalendarParserException e) {
           }
        }
        return parse(o1,formats);
    }

    private Locale getLocale(List<String> formats) {
        Locale locale = Locale.getDefault();
        if (formats.size() > 0) {
            String possibleLanguageTag = formats.get(0);
            try {
                Locale possibleLocale = new Locale.Builder().setLanguageTag(possibleLanguageTag).build();
                // Check if it's in our list of supported date locales
                for (Locale l : DateFormat.getAvailableLocales()) {
                    if (l.equals(possibleLocale)) {
                        locale = possibleLocale;
                        formats.remove(0);
                    }
                }
            } catch (IllformedLocaleException e) {
                // We ignore this. It PROBABLY means we got a date format string, not a language code
                // although it could be a malformed language tag like zh_TW instead of zh-TW
            }
        }
        return locale;
    }

    private OffsetDateTime parse(String o1, List<String> formats) throws DateFormatException {
        Locale locale = getLocale(formats);
        DateFormat formatter;
        OffsetDateTime date;
        //need to try using each format in the formats list!
        if(formats.size()>0) {
            for(int i=0;i<formats.size();i++) {
                try {
                    formatter = new SimpleDateFormat(formats.get(i),locale);
                } catch (IllegalArgumentException e) {
                    throw new DateFormatException("Unable to parse date format " + formats.get(i));
                }
                date = parse(o1, formatter);
                if (date != null) {
                    return date;
                }
            }
        } 
        date = ParsingUtilities.stringToDate(o1);
        if (date != null) {
            return date;
        } else {
            try {
                Calendar parsedDate = javax.xml.bind.DatatypeConverter.parseDateTime(o1);
                int offsetMillis = parsedDate.getTimeZone().getOffset(parsedDate.getTimeInMillis());
                return parsedDate.toInstant().plusMillis(offsetMillis).atOffset(ZoneOffset.of("Z"));
            } catch (IllegalArgumentException e2) {
                return null;
            }
        }
    }
    
    private OffsetDateTime parse(String o1, DateFormat formatter) {
        try {
            formatter.setTimeZone(TimeZone.getTimeZone("Z"));
            Date date = formatter.parse(o1);
            GregorianCalendar c = new GregorianCalendar();
            c.setTime(date);
            return ParsingUtilities.calendarToOffsetDateTime(c);
        } catch (java.text.ParseException e) {
            return null;
        }
    }
    
    @Override
    public String getDescription() {
        return "Returns o converted to a date object, you can hint if the day or the month is listed first, or give an ordered list of possible formats using this syntax: http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html";
    }
    
    @Override
    public String getParams() {
        return "o, boolean month_first / format1, format2, ... (all optional)";
    }
    
    @Override
    public String getReturns() {
        return "date";
    }

    class DateFormatException extends Exception {
        private static final long serialVersionUID = -6506736145451835731L;

        public DateFormatException(String string) {
            super(string);
        }
    }

}
