// Utility class for string compression (LZW algorithm)
// Used to reduce save file size in localStorage
class Compression {
    static compress(s) {
        if (s == null) return "";
        var dict = {}, data = (s + "").split(""), out = [], currChar, phrase = data[0], code = 256;
        for (var i = 1; i < data.length; i++) {
            currChar = data[i];
            if (dict[phrase + currChar] != null) {
                phrase += currChar;
            } else {
                out.push(phrase.length > 1 ? dict[phrase] : phrase.charCodeAt(0));
                dict[phrase + currChar] = code;
                code++;
                phrase = currChar;
            }
        }
        out.push(phrase.length > 1 ? dict[phrase] : phrase.charCodeAt(0));
        for (var i = 0; i < out.length; i++) {
            out[i] = String.fromCharCode(out[i]);
        }
        return out.join("");
    }

    static decompress(s) {
        if (s == null) return "";
        if (s == "") return null;
        var dict = {}, data = (s + "").split(""), currChar = data[0], oldPhrase = currChar, out = [currChar], code = 256, phrase;
        for (var i = 1; i < data.length; i++) {
            var currCode = data[i].charCodeAt(0);
            if (currCode < 256) {
                phrase = data[i];
            } else {
                phrase = dict[currCode] ? dict[currCode] : (oldPhrase + oldPhrase.charAt(0));
            }
            out.push(phrase);
            currChar = phrase.charAt(0);
            dict[code] = oldPhrase + currChar;
            code++;
            oldPhrase = phrase;
        }
        return out.join("");
    }
}