"""User-timezone helpers.

All datetimes in the DB are stored as UTC. The helpers here bridge between
that UTC storage and the user's configured local timezone (IANA string in
the ``user_timezone`` setting). Use these anywhere the model or UI talks
in terms of "today", "tomorrow", or a bare calendar date — never
``date.today()`` or ``datetime.now(timezone.utc)`` inside a per-user flow.
"""
from __future__ import annotations

from datetime import date, datetime, timedelta
from zoneinfo import ZoneInfo, ZoneInfoNotFoundError

from fabledassistant.services.settings import get_setting

# Briefing day boundary — kept in sync with the compilation slot in
# ``briefing_scheduler.SLOTS``. The briefing day flips at this local hour
# (not midnight) so the 00:00–04:00 local window still shows yesterday's
# briefing until the 4am compilation generates the new one.
BRIEFING_DAY_START_HOUR = 4


async def get_user_tz(user_id: int) -> ZoneInfo:
    """Return the user's IANA ``ZoneInfo``, falling back to UTC."""
    tz_str = await get_setting(user_id, "user_timezone") or "UTC"
    try:
        return ZoneInfo(tz_str)
    except (ZoneInfoNotFoundError, KeyError):
        return ZoneInfo("UTC")


async def user_today(user_id: int) -> date:
    """Return today's calendar date in the user's local timezone."""
    tz = await get_user_tz(user_id)
    return datetime.now(tz).date()


async def user_briefing_date(user_id: int) -> date:
    """Return the current "briefing day" in the user's local timezone.

    The briefing day flips at ``BRIEFING_DAY_START_HOUR`` (4am local),
    aligned with the compilation slot that generates the day's briefing.
    Between 00:00 and 04:00 local this still returns *yesterday*, so the
    UI keeps showing the in-progress briefing until the new one is built.
    """
    tz = await get_user_tz(user_id)
    return (datetime.now(tz) - timedelta(hours=BRIEFING_DAY_START_HOUR)).date()