class FilenameUtils {

    public static int getPrefixLength(String filename) {
        if (filename == null) {
            return -1;
        }
        int len = filename.length();
        if (len == 0) {
            return 0;
        }
        char ch0 = filename.charAt(0);
        if (ch0 == ':') {
            return -1;
        }
        if (len == 1) {
            if (ch0 == '~') {
                return 2;  // return a length greater than the input
            }
            return (isSeparator(ch0) ? 1 : 0);
        } else {
            if (ch0 == '~') {
                int posUnix = filename.indexOf(UNIX_SEPARATOR, 1);
                int posWin = filename.indexOf(WINDOWS_SEPARATOR, 1);
                if (posUnix == -1 && posWin == -1) {
                    return len + 1;  // return a length greater than the input
                }
                posUnix = (posUnix == -1 ? posWin : posUnix);
                posWin = (posWin == -1 ? posUnix : posWin);
                return Math.min(posUnix, posWin) + 1;
            }
            char ch1 = filename.charAt(1);
            if (ch1 == ':') {
                ch0 = Character.toUpperCase(ch0);
                if (ch0 >= 'A' && ch0 <= 'Z') {
                    if (len == 2 || isSeparator(filename.charAt(2)) == false) {
                        return 2;
                    }
                    return 3;
                }
                return -1;
                
            } else if (isSeparator(ch0) && isSeparator(ch1)) {
                int posUnix = filename.indexOf(UNIX_SEPARATOR, 2);
                int posWin = filename.indexOf(WINDOWS_SEPARATOR, 2);
                if ((posUnix == -1 && posWin == -1) || posUnix == 2 || posWin == 2) {
                    return -1;
                }
                posUnix = (posUnix == -1 ? posWin : posUnix);
                posWin = (posWin == -1 ? posUnix : posWin);
                return Math.min(posUnix, posWin) + 1;
            } else {
                return (isSeparator(ch0) ? 1 : 0);
            }
        }
    }

    public  FilenameUtils();

}