#!/usr/bin/env python3
"""Executes a UTS #35 rule file (e.g. collatz.txt) on real ICU.

Usage:
  python3 uts35.py collatz.txt aaaaaaa # Collatz of 7, ends at Ma

See also: uts35.sh, same runner through ICU's stock uconv, no Python.

pip install PyICU"""

import sys
from icu import Transliterator, ICU_VERSION

mk = lambda rules: Transliterator.createFromRules("", rules)

def fixed_point(compute, s, max_calls=1_000_000):
    prev, calls = None, 0
    while s != prev and calls < max_calls:
        prev, s = s, compute.transliterate(s)
        calls += 1
    return s, calls, s == prev

if __name__ == "__main__":
    if len(sys.argv) != 3:
        sys.exit("usage: uts35.py RULES.txt dataword")
    print(f"ICU {ICU_VERSION}")
    compute = mk(open(sys.argv[1]).read())
    s = "M" + sys.argv[2]
    print(f"{0:>3} - {s}")
    prev, calls, max_calls = None, 0, 100_000
    while s != prev and calls < max_calls:
        prev, s = s, compute.transliterate(s)
        calls += 1
        if s != prev:
            print(f"{calls:>3} - {s}")
    if s != prev:
        print(f"no fixed point after {calls} calls, system may never halt")