// ==UserScript==
// @name           ISO 8601 Dates
// @namespace      http://chocolatey.com/code/js
// @description    Converts US dates to the ISO 8601 YYYY-MM-DD format
// @include        http://*.gov/*
// @include        http://*.us/*
// @author         chocolateboy <chocolate.boy@email.com>
// @version        0.02 (2007-11-24) leap year fix
// @version        0.01 (2007-11-21)
// ==/UserScript==

// test suite: http://chocolatey.com/code/js/iso_8601_dates_test.html

const $xpath = '//body//text()';
const $date  = new RegExp(
      '(?:\\b(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])-(\\d{4}|\\d{2})\\b(?!-))'
    + '|'
    + '(?:\\b(0[1-9]|1[0-2])/(0[1-9]|[12][0-9]|3[01])/(\\d{4}|\\d{2})\\b(?!/))',
    'g'
);

//              Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
const $days = [ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ]; 

function $leap_year ($year) {
    if (($year % 400) == 0) {           // multiples of 400 are leap years
        return true;
    } else if (($year % 100) == 0) {    // the remaining multiples of 100 are not leap years
        return false;
    } else if (($year % 4) == 0) {      // the remaining multiples of 4 are leap years
        return true;
    } else {                            // the rest are common years
        return false;
    }
}

// https://bugzilla.mozilla.org/show_bug.cgi?id=392378
function $replace ($match, $m1, $d1, $y1, $m2, $d2, $y2, $offset, $string) {
    var $year  = $y1 || $y2; // depending on the above, non-matches are either empty or undefined, both of which are false
    var $month = $m1 || $m2;
    var $day   = $d1 || $d2;

    // manual negative look-behind: see: http://blog.stevenlevithan.com/archives/mimic-lookbehind-javascript
    if ($offset > 0) {
        var $prefix = $string[$offset - 1];
        if (($prefix == '-') || ($prefix == '/')) {
            return $match;
        }
    }

    if ($day > $days[$month - 1]) {
        return $match;
    }

    if ($year.length == 2) {
        // Internet Founding Fathers, forgive us. From the epoch to 1999, we knew not what to do...
        $year = ((($year >= 70) && ($year <= 99)) ? '19' : '20') + $year;
    }

    if (($month == '02') && ($day == '29') && !$leap_year($year)) {
        return $match;
    }

    return $year + '-' + $month + '-' + $day;
}

var $nodes  = document.evaluate($xpath, document, null, XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE, null);

for (var $i = 0; $i < $nodes.snapshotLength; ++$i) {
    var $text = $nodes.snapshotItem($i);
    $text.data = $text.data.replace($date, $replace);
}