Script that converts selected text to a GREP find - Experimental script

I started working on this script some time ago and it's since fallen to the wayside - I'm not using it. But I was tinkering around some unused and unfinished script projects 

I've taken it as far as I can go in terms of a learning curve for me - if anyone wants it or wants to tinker with it and make it better feel free.

All it was meant to do is give a starting point to a GREP search for people not familiar with GREP to give them a leg up on the starting point of the GREP. 

But I feel it could be more robust.

#target indesign

(function () {

    if (app.documents.length === 0) {
        alert("No document open.");
        return;
    }

    if (app.selection.length === 0 || !app.selection[0].hasOwnProperty("contents")) {
        alert("Please select some text.");
        return;
    }

    var txt = app.selection[0].contents;
    var grep = "";

    var i = 0;

    function isDigit(c) { return /\d/.test(c); }
    function isLower(c) { return /[a-z]/.test(c); }
    function isUpper(c) { return /[A-Z]/.test(c); }
    function isLetter(c) { return /[A-Za-z]/.test(c); }
    function isSpace(c) { return /\s/.test(c); }

    while (i < txt.length) {
        var c = txt[i];

        // DIGITS (collapse runs)
        if (isDigit(c)) {
            var start = i;
            while (i < txt.length && isDigit(txt[i])) i++;
            var count = i - start;
            grep += (count === 1) ? "\\d" : "\\d{" + count + "}";
            continue;
        }

        // LOWERCASE LETTERS
        if (isLower(c)) {
            var start = i;
            while (i < txt.length && isLower(txt[i])) i++;
            var count = i - start;
            grep += (count === 1) ? "[a-z]" : "[a-z]{" + count + "}";
            continue;
        }

        // UPPERCASE LETTERS
        if (isUpper(c)) {
            var start = i;
            while (i < txt.length && isUpper(txt[i])) i++;
            var count = i - start;
            grep += (count === 1) ? "[A-Z]" : "[A-Z]{" + count + "}";
            continue;
        }

        // SPACES
        if (isSpace(c)) {
            while (i < txt.length && isSpace(txt[i])) i++;
            grep += "\\s+";
            continue;
        }

        // ESCAPED GREP METACHARACTERS
        if (/[\\.^$*+?()[\]{}|]/.test(c)) {
            grep += "\\" + c;
            i++;
            continue;
        }

        // EVERYTHING ELSE (commas, hyphens, slashes, etc.)
        grep += c;
        i++;
    }

    // Push to Find GREP
    app.findGrepPreferences = NothingEnum.nothing;
    app.findGrepPreferences.findWhat = grep;

    alert("Generated GREP:\n\n" + grep);

})();

 
This is another iteration of the same thing 

#target indesign

(function () {

    if (app.documents.length === 0) {
        alert("No document open.");
        return;
    }

    if (app.selection.length === 0 || !app.selection[0].hasOwnProperty("contents")) {
        alert("Please select some text.");
        return;
    }

    var txt = app.selection[0].contents;
    var grep = "";
    var i = 0;

    function isDigit(c) { return /\d/.test(c); }
    function isLower(c) { return /[a-z]/.test(c); }
    function isUpper(c) { return /[A-Z]/.test(c); }
    function isLetter(c) { return /[A-Za-z]/.test(c); }
    function isSpace(c) { return /\s/.test(c); }

    while (i < txt.length) {
        var c = txt[i];

        /* =========================
           NUMBERS (smart handling)
           ========================= */

        if (isDigit(c)) {
            var start = i;
            while (i < txt.length && /[\d,.]/.test(txt[i])) i++;
            var token = txt.substring(start, i);

            // Comma-grouped number
            if (/^\d{1,3}(,\d{3})+$/.test(token)) {
                grep += "\\d{1,3}(,\\d{3})*";
                continue;
            }

            // Decimal number
            if (/^\d+(\.\d+)?$/.test(token)) {
                grep += "\\d+(\\.\\d+)?";
                continue;
            }

            // Plain digits
            grep += "\\d{" + token.replace(/\D/g, "").length + "}";
            continue;
        }

        /* =========================
           LETTERS
           ========================= */

        if (isLower(c)) {
            var start = i;
            while (i < txt.length && isLower(txt[i])) i++;
            grep += "[a-z]{" + (i - start) + "}";
            continue;
        }

        if (isUpper(c)) {
            var start = i;
            while (i < txt.length && isUpper(txt[i])) i++;
            grep += "[A-Z]{" + (i - start) + "}";
            continue;
        }

        /* =========================
           SPACES
           ========================= */

        if (isSpace(c)) {
            while (i < txt.length && isSpace(txt[i])) i++;
            grep += "\\s+";
            continue;
        }

        /* =========================
           ESCAPED METACHARACTERS
           ========================= */

        if (/[\\.^$*+?()[\]{}|]/.test(c)) {
            grep += "\\" + c;
            i++;
            continue;
        }

        /* =========================
           EVERYTHING ELSE
           ========================= */

        grep += c;
        i++;
    }

    app.findGrepPreferences = NothingEnum.nothing;
    app.findGrepPreferences.findWhat = grep;

    alert("Generated GREP:\n\n" + grep);

})();