AR Date reformat

// ### Stuff you can change, right below
//Possible date separator in original filename. You can put more in there.
const DATE_SEP = '-_';

// date separator for the final filename. Can be changed to taste.
const NEW_DATE_SEP = '-';

// Possible characters before the date to remove
const BFR_DATE_SEP = ' _';

// Filename displayed when the regex expression can't find what it's looking for
const REGEX_ERROR = '-Regex Error-';

// Day and month digit size minimum (pad with zero if necessary)
const MNT_DAY_SIZE = 2

// ### From here, mostly Stuff you shouldn't change, unless you know what you're doing of course.
// positions of the regex resulting array, to clarify things
const FULL_RSLT = 0, BEF_DATE = 1, DATE_DAY = 2, DATE_MNT = 3, DATE_YR = 4, AFT_DATE = 5;

//final values for the date components will be stored here.
var newDay = "", newMonth = "", newYear = "";

// Regular expression to split the filename around the date.
var reDateExtract = new RegExp("(.*?)[" + BFR_DATE_SEP + "]?0?(\\d{1,2})[" + DATE_SEP + "]0?(\\d{1,2})[" + DATE_SEP + "](\\d{2})[\\s_]?(.*)", "");

if (reDateExtract.test(item.newBasename) == False)
  { return REGEX_ERROR; }

// Run the regex and return it in an array
aDate_n_Extra = reDateExtract.exec(item.newBasename);

// add proper century to the year
if (aDate_n_Extra[DATE_YR] >= 30 && aDate_n_Extra[DATE_YR] <=99)
    { newYear = '19' + aDate_n_Extra[DATE_YR]; }
else
    { newYear = '20' + aDate_n_Extra[DATE_YR]; }

// padding day and month with a zeros
newDay = zpad(aDate_n_Extra[DATE_DAY], MNT_DAY_SIZE);
newMonth = zpad(aDate_n_Extra[DATE_MNT], MNT_DAY_SIZE);

// Final filename
return aDate_n_Extra[BEF_DATE] + aDate_n_Extra[AFT_DATE]  + ' ' + [newYear, newMonth, newDay].join(NEW_DATE_SEP);

// add leading zeros to any string
function zpad(str, nb_digits)
{
    if (str.length < nb_digits)
        { return (Array(nb_digits - str.length + 1).join('0') + str); }
    else
        { return str; }
}