import os
import re
import argparse

def main(path, extensions, padding, number, dry_run):
    extensions = r"\.(?:" + "|".join(extensions) + ")" if extensions else ""
    st = r"(?:\D*\d+)+\D*(?:" + extensions + r")"

    reg = re.compile(st)
    if number > 1:
        st = r"((?:\D*(\d+)){" + str(number - 1) + r"})"
    else:
        st = r""
    st += r"(?:(\D*)(\d+)){1}(.*)"
    reg_sub = re.compile(st)

    for fn in os.listdir(path):
        if reg.match(fn):
            t = reg_sub.match(fn)
            if t:
                if number > 1:
                    tmp = t.group(3).zfill(padding)
                    new_name = reg_sub.sub(r"\1\2" + tmp + r"\4", fn)
                else:
                    tmp = t.group(2).zfill(padding)
                    new_name = reg_sub.sub(tmp + r"\3", fn)
                print(fn, end=" -> ")
                print(new_name)
                print("***")
                if not dry_run:
                    os.rename(os.path.join(path, fn), os.path.join(path, new_name))

if __name__ == "__main__":
    ap = argparse.ArgumentParser(description="Zero padding to number in file name")
    ap.add_argument("-e", "--extensions", action="append", help="List file extentions")
    ap.add_argument("-n", "--number", type=int, default=1, help="Number's group number")
    ap.add_argument("-p", "--padding", type=int, default=2, help="Number of zero for padding")
    ap.add_argument("--dry-run", dest="dry_run", action="store_true", help="Only print changed name")
    ap.set_defaults(dry_run=False)
    ap.add_argument("path", nargs="?", default=os.getcwd)

    args = ap.parse_args()
    main(args.path, args.extensions, args.padding, args.number, args.dry_run)