Fixup JSON dates exported by .NET JavaScriptSerializer

fix_json_dates.py

#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-3.0-or-later

# For issues or updated versions of this script, browse to the following URL:
# https://gist.github.com/AfroThundr3007730/1ec8a10df9345b337c19363a8094ab04

"""
Fixup JSON dates exported by .NET JavaScriptSerializer

Example input file:

> $FormatEnumerationLimit = -1
> Get-ADUser -Filter * -Properties * |
>     ConvertTo-Json -Compress | Out-File AD_Users.json
"""

__author__ = "AfroThundr"
__modified__ = "2026-04-23"
__version__ = "0.3.2"

from collections.abc import Callable
from datetime import datetime, UTC
from json import dump, load
from os import stat
from re import search
from sys import argv, maxsize

type NStr = str | None
type JVal = str | int | float | bool | None
type JDoc = dict[str, JVal | JDoc] | list[JVal | JDoc]
type JData = JDoc | JVal
type NodeFilter = Callable[[JData, NStr, NStr], JData]
type NodeWalker = Callable[[JData], JData]


def parse_netdate(obj: JData, _: NStr = None, regex: NStr = None) -> JData:
    """Reads .NET JSON timestamps and returns ISO-8601 timestamps"""
    regex = regex or r"\/Date\((-?\d+)\)\/"
    if isinstance(obj, str) and (match := search(regex, obj)):
        return datetime.fromtimestamp(
            int(match.groups()[0]) / 1000, UTC
        ).strftime("%FT%TZ")
    if isinstance(obj, int) and 18 <= len(str(obj)) <= 19:
        if obj == maxsize:
            return "Never"
        epoch1 = -int(datetime.strptime("0001", "%Y").strftime("%s"))
        epoch2 = -int(datetime.strptime("1601", "%Y").strftime("%s"))
        obj /= 10_000_000
        obj = obj - epoch1 if obj > epoch1 else obj - epoch2
        return datetime.fromtimestamp(obj, UTC).strftime("%FT%TZ")
    return obj


def make_walker(func: NodeFilter) -> NodeWalker:
    """Create a function that walks an object and calls a method on members"""

    def _walk(node: JData, key: NStr = None) -> JData:
        """Walks an object and calls a method on members"""
        if isinstance(node, dict):
            return {k: _walk(v, k) for k, v in node.items()}
        if isinstance(node, list):
            return [_walk(v, key) for v in node]
        return func(node, key, None)

    return _walk


if __name__ == "__main__":
    hook: NodeWalker = make_walker(parse_netdate)
    for entry in argv[1:]:
        if stat(entry).st_size == 0:
            print("Empty file:", entry)
            continue
        print("Processing:", entry)
        with (
            open(entry, "r", encoding="utf-8") as f1,
            open(entry, "r+", encoding="utf-8") as f2,
        ):
            dump(load(f1, object_hook=hook), f2, ensure_ascii=False, indent=2)
            f2.truncate()