from __future__ import annotations

from datetime import UTC, datetime, timedelta, timezone
from zoneinfo import ZoneInfo, ZoneInfoNotFoundError


TIME_FORMAT = "%Y-%m-%d %H:%M:%S.%f"


def resolve_timezone(timezone_name: str):
    try:
        return ZoneInfo(timezone_name)
    except ZoneInfoNotFoundError:
        fallback_mapping = {
            "Asia/Shanghai": timezone(timedelta(hours=8)),
            "Asia/Hong_Kong": timezone(timedelta(hours=8)),
            "UTC": UTC,
        }
        return fallback_mapping.get(timezone_name, UTC)


def format_now(timezone_name: str) -> str:
    current = datetime.now(resolve_timezone(timezone_name))
    return current.strftime(TIME_FORMAT)[:-3]


def parse_timestamp(value: str | None) -> datetime | None:
    if not value:
        return None
    try:
        return datetime.strptime(value, TIME_FORMAT)
    except ValueError:
        return None


def compute_duration_ms(started_at: str | None, finished_at: str | None) -> int | None:
    started = parse_timestamp(started_at)
    finished = parse_timestamp(finished_at)
    if not started or not finished:
        return None
    duration_ms = int((finished - started).total_seconds() * 1000)
    return max(duration_ms, 0)