#!/usr/bin/python3

# usage: sync-mtime src dst
#
# synchronize atime/mtime on files between src and dst.
#
# src and dst are directories, where dst is expected to contain a subset of the
# files found in src. for each file present in dst or a subdirectory thereof,
# if atime/mtime differ between the same file in src and that file in dst,
# update atime/mtime on the file in dst.

import os
import sys
from pathlib import Path


def time_eq(a: os.stat_result, b: os.stat_result) -> bool:
    return (
        (a.st_mtime_ns == b.st_mtime_ns) and
        (a.st_atime_ns == b.st_atime_ns)
    )


src, dst = sys.argv[1:]
for dirpath, dirnames, filenames in Path(dst).walk():
    for filename in filenames:
        dst_file = dirpath / filename
        if not dst_file.is_file():
            continue
        src_file = src / dst_file.relative_to(dst)

        src_stat = src_file.stat(follow_symlinks=False)
        dst_stat = dst_file.stat(follow_symlinks=False)
        if time_eq(src_stat, dst_stat):
            continue

        ns = (src_stat.st_atime_ns, src_stat.st_mtime_ns)
        os.utime(dst_file, ns=ns, follow_symlinks=False)