"""Timezone helpers.

Everything is stored in UTC and *reported* in the user's timezone, so there is
exactly one place that knows how to turn "now" into "which day does this count
for" — here.
"""

from __future__ import annotations

from datetime import date, datetime, time, timedelta, timezone
from zoneinfo import ZoneInfo


def tz(name: str) -> ZoneInfo:
    try:
        return ZoneInfo(name)
    except Exception:  # pragma: no cover - bad tz falls back rather than crashing
        return ZoneInfo("UTC")


def now_utc() -> datetime:
    return datetime.now(timezone.utc)


def ensure_utc(moment: datetime | None) -> datetime | None:
    """Attach UTC to a naive datetime.

    SQLite has no timezone type, so a column declared `DateTime(timezone=True)`
    comes back naive from SQLite and aware from Postgres. Everything we store is
    UTC, so normalising on read keeps the arithmetic valid on both.
    """
    if moment is None:
        return None
    return moment if moment.tzinfo is not None else moment.replace(tzinfo=timezone.utc)


def to_local(moment: datetime, tz_name: str) -> datetime:
    if moment.tzinfo is None:
        moment = moment.replace(tzinfo=timezone.utc)
    return moment.astimezone(tz(tz_name))


def local_date(tz_name: str, moment: datetime | None = None) -> date:
    """The day a moment belongs to for the user (the report's unit of grouping)."""
    return to_local(moment or now_utc(), tz_name).date()


def local_time(tz_name: str, moment: datetime | None = None) -> time:
    return to_local(moment or now_utc(), tz_name).timetz().replace(tzinfo=None)


def day_bounds_utc(day: date, tz_name: str) -> tuple[datetime, datetime]:
    """The UTC half-open interval `[start, end)` covering a local calendar day."""
    zone = tz(tz_name)
    start = datetime.combine(day, time.min, tzinfo=zone)
    end = start + timedelta(days=1)
    return start.astimezone(timezone.utc), end.astimezone(timezone.utc)


def in_window(moment: time, start: time, end: time) -> bool:
    """Whether a clock time is inside a window, handling windows that wrap midnight."""
    if start <= end:
        return start <= moment <= end
    return moment >= start or moment <= end


def humanize_minutes(total_minutes: int | float) -> str:
    """`95` -> `1h 35m`, `40` -> `40m`, `0` -> `0m`."""
    minutes = round(total_minutes)
    hours, rest = divmod(minutes, 60)
    if hours and rest:
        return f"{hours}h {rest}m"
    if hours:
        return f"{hours}h"
    return f"{rest}m"