Could this regex be more efficient?

I modified a regex I got here. I needed to change it because I needed it to match the following additional criteria:

1. Dates with only Month and Year
2. Full dates in the form mm dd, yyyy
3. Dates with year only
4. Input 开发者_StackOverflowwith extraneous info (like Vol. 51, No. 1, Mar 2008)

This is what I have so far. I did this with RegexBuddy to help me parse the logic, but it's so complex I'm not certain I have the most efficient solution.

\b(?:((Jan(uary)?|Feb(ruary)?|Ma(r(ch)?|y)|Apr(il)?|Ju((ly?)|(ne?))|Aug(ust)?|Oct(ober)?|(Sept|Nov|Dec)(ember)?)|((((Jan(uary)?|Ma(r(ch)?|y)|Jul(y)?|Aug(ust)?|Oct(ober)?|Dec(ember)?) 31)|((Jan(uary)?|Ma(r(ch)?|y)|Apr(il)?|Ju((ly?)|(ne?))|Aug(ust)?|Oct(ober)?|(Sept|Nov|Dec)(ember)?) (0?[1-9]|([12]\d)|30))|(Feb(ruary)? (0?[1-9]|1\d|2[0-8]|(29(?=, ((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))))),)) ((1[6-9]|[2-9]\d)\d{2}))|((1[6-9]|[2-9]\d)\d{2})

Is there anything that could be done to preserve the functionality of both the original regex and my additional criteria?

Here is the code where I implement this, if it helps you see what I'm trying to do. The output of the parseDate function is supposed to be a string date in the form "yyyy mm dd" (i.e., example 4 should output "2008 Mar"):

//generalized RegEx function
function returnRegExMatch(ex,haystack) {
  var needle = ex.exec(haystack);
  if (needle) { return needle[0]; }
}

// date extraction (uses returnRegExMatch)
function parseDate(date) {
  //strip anything other than a valid date
  var dateRe = /\b(?:((Jan(uary)?|Feb(ruary)?|Ma(r(ch)?|y)|Apr(il)?|Ju((ly?)|(ne?))|Aug(ust)?|Oct(ober)?|(Sept|Nov|Dec)(ember)?)|((((Jan(uary)?|Ma(r(ch)?|y)|Jul(y)?|Aug(ust)?|Oct(ober)?|Dec(ember)?) 31)|((Jan(uary)?|Ma(r(ch)?|y)|Apr(il)?|Ju((ly?)|(ne?))|Aug(ust)?|Oct(ober)?|(Sept|Nov|Dec)(ember)?) (0?[1-9]|([12]\d)|30))|(Feb(ruary)? (0?[1-9]|1\d|2[0-8]|(29(?=, ((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))))),)) ((1[6-9]|[2-9]\d)\d{2}))|((1[6-9]|[2-9]\d)\d{2})/;
  date = returnRegExMatch(dateRe,date);

  var yearRe = /[0-9][0-9][0-9][0-9]/;
  var monthRe = /Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec/;
  var dayRe = /[0-9]?[0-9],/;

  var year = returnRegExMatch(yearRe,date);
  var month = returnRegExMatch(monthRe,date);
  var day = parseInt(returnRegExMatch(dayRe,date),10);

  var dateReturned = "";
  if (year) { dateReturned = year; }
  if (month) { dateReturned = dateReturned + " " + month; }
  if (month && day) { dateReturned = dateReturned + " " + day; }

  return dateReturned;
}

Thanks!

EDIT Thanks to all who took time to respond. You guys did what I was hoping for, pointing out the most ridiculous things in my implementation. I decided to simplify the main regex quite a bit. Here's the result:

\b(?:(?:Jan(?:uary)?|Feb(?:ruary)?|Ma(?:r(?:ch)?|y)|Apr(?:il)?|Ju(?:(?:ly?)|(?:ne?))|Aug(?:ust)?|Oct(?:ober)?|(?:Sept|Nov|Dec)(?:ember)?) (?:\d{1,2}, )?)?\d{4}

This doesn't worry about detect invalid dates based on leap years or whatever. @Bart convinced me that this is probably best done with native JS than regex. Thanks to @Tim too for pointing out the need for non-capturing parentheses.

If anyone has further suggestions for how I should refine this regex please fire away.

---

I must say that I'm having trouble grokking this monster :)

Two things that are immediately apparent:

1. It would be more efficient to use non-capturing parentheses (?:...) than regular parentheses if you're not planning on using their (sub-)matches later on.

2. If you have your parentheses nested to ten levels, something is wrong. It might work, but it's a b*tch to maintain. Or understand.

I'll check with RegexMagic if there's maybe a better way to get what you need. But since nobody is forcing you to do all you want to do in a single regex, why not break up the problem into components, using a single, simpler regex for each?

---

How about something like this:

#!/usr/bin/js

function getMonth(monthStr) {
    var monthMap = new Array();
    monthMap['jan'] = monthMap['january']   = 1;
    monthMap['feb'] = monthMap['february']  = 2;
    monthMap['mar'] = monthMap['march']     = 3;
    monthMap['apr'] = monthMap['april']     = 4;
    monthMap['may']                         = 5;
    monthMap['jun'] = monthMap['june']      = 6;
    monthMap['jul'] = monthMap['july']      = 7;
    monthMap['aug'] = monthMap['august']    = 8;
    monthMap['sep'] = monthMap['september'] = 9;
    monthMap['oct'] = monthMap['october']   = 10;
    monthMap['nov'] = monthMap['november']  = 11;
    monthMap['dec'] = monthMap['december']  = 12;
    return monthMap[monthStr.toLowerCase()];
}

function isLeapYear(year) {
    return year%400 == 0 || (year%100 != 0 && year%4 == 0);
}

function isPositiveNumber(str) {
    return str.match(/^\d+$/);
}

function parseDate(date) {
    var tokens = date.split(/,?\s+/);

    var m = getMonth(tokens[0]);
    var d = tokens[1];
    var y = tokens[2];

    if(!isPositiveNumber(d) || !m || !isPositiveNumber(y)) return false;

    if(
        ((m==4 || m==6 || m==9 || m==11) && d <= 30) ||
        (m==2 && ((isLeapYear(y) && d <= 29) || d <= 28)) ||
        ((m==1 || m==3 || m==5 || m==7 || m==8 || m==10 || m==12) && d <= 31)
    ) {
        var dateObj = new Date();
        dateObj.setFullYear(y, m-1, d);
        return dateObj;
    }

    return false;
}

var tests = new Array('January 31, 2009', 'Nov 31, 2009', 'Feb 29, 2001', 'Feb 29, 2000', 'Feb 29, 1900');

for(var i in tests) {
    var date = parseDate(tests[i]);
    print(date ? tests[i]+" is a valid date, parsed as: "+date : tests[i]+" invalid");
}

Output:

January 31, 2009 is a valid date, parsed as: Sat Jan 31 2009 20:31:33 GMT+0100 (CET)
Nov 31, 2009 invalid
Feb 29, 2001 invalid
Feb 29, 2000 is a valid date, parsed as: Tue Feb 29 2000 20:31:33 GMT+0100 (CET)
Feb 29, 1900 invalid