getParseRegExp = function()

in globalize/globalize.ts [935:1025]
76 lines of code
36 McCabe index (conditional complexity)

    getParseRegExp = function (cal, format) {
        // converts a format string into a regular expression with groups that
        // can be used to extract date fields from a date string.
        // check for a cached parse regex.
        var re = cal._parseRegExp;
        if (!re) {
            cal._parseRegExp = re = {};
        }
        else {
            var reFormat = re[format];
            if (reFormat) {
                return reFormat;
            }
        }

        // expand single digit formats, then escape regular expression characters.
        var expFormat = expandFormat(cal, format).replace(/([\^\$\.\*\+\?\|\[\]\(\)\{\}])/g, "\\\\$1"),
            regexp = ["^"],
            groups = [],
            index = 0,
            quoteCount = 0,
            tokenRegExp = getTokenRegExp(),
            match;

        // iterate through each date token found.
        while ((match = tokenRegExp.exec(expFormat)) !== null) {
            var preMatch = expFormat.slice(index, match.index);
            index = tokenRegExp.lastIndex;

            // don't replace any matches that occur inside a string literal.
            quoteCount += appendPreOrPostMatch(preMatch, regexp);
            if (quoteCount % 2) {
                regexp.push(match[0]);
                continue;
            }

            // add a regex group for the token.
            var m = match[0],
                len = m.length,
                add;
            switch (m) {
                case "dddd": case "ddd":
                case "MMMM": case "MMM":
                case "gg": case "g":
                    add = "(\\D+)";
                    break;
                case "tt": case "t":
                    add = "(\\D*)";
                    break;
                case "yyyy":
                case "fff":
                case "ff":
                case "f":
                    add = "(\\d{" + len + "})";
                    break;
                case "dd": case "d":
                case "MM": case "M":
                case "yy": case "y":
                case "HH": case "H":
                case "hh": case "h":
                case "mm": case "m":
                case "ss": case "s":
                    add = "(\\d\\d?)";
                    break;
                case "zzz":
                    add = "([+-]?\\d\\d?:\\d{2})";
                    break;
                case "zz": case "z":
                    add = "([+-]?\\d\\d?)";
                    break;
                case "/":
                    add = "(\\" + cal["/"] + ")";
                    break;
                default:
                    throw "Invalid date format pattern \'" + m + "\'.";
            }
            if (add) {
                regexp.push(add);
            }
            groups.push(match[0]);
        }
        appendPreOrPostMatch(expFormat.slice(index), regexp);
        regexp.push("$");

        // allow whitespace to differ when matching formats.
        var regexpStr = regexp.join("").replace(/\s+/g, "\\s+"),
            parseRegExp = { "regExp": regexpStr, "groups": groups };

        // cache the regex for this format.
        return re[format] = parseRegExp;
    };