import contextvars
from datetime import date, datetime, timedelta, timezone, tzinfo
from zoneinfo import ZoneInfo

# Costa Rica has no DST; a fixed offset is exact year-round. This is the
# FALLBACK when the request doesn't declare a timezone (n8n posts, tests).
CR_TZ = timezone(timedelta(hours=-6))

# Per-request client timezone, set by the agent middleware from the
# X-Client-Timezone header (IANA name sent by the browser). Falls back to
# Costa Rica so headless callers keep the owner's local semantics.
_client_tz: contextvars.ContextVar[tzinfo] = contextvars.ContextVar(
    "client_tz", default=CR_TZ
)


def set_client_timezone(name: str | None) -> contextvars.Token | None:
    """Bind the request's IANA timezone; ignores unknown/absent names.

    Proxies that see the header twice merge the values into a comma list
    ("Zone, Zone") — take the first entry.
    """
    if not name:
        return None
    try:
        return _client_tz.set(ZoneInfo(name.split(",")[0].strip()))
    except (KeyError, ValueError):
        return None


def reset_client_timezone(token: contextvars.Token | None) -> None:
    if token is not None:
        _client_tz.reset(token)


def client_tz() -> tzinfo:
    return _client_tz.get()


def today_client() -> date:
    """Current date where the USER is (request timezone, CR fallback).

    The server clock is UTC — at 6 pm in Costa Rica it is already "tomorrow"
    in UTC. Anything user-facing that means "today" (agent answers, date
    defaults) must come from here, never date.today().
    """
    return datetime.now(client_tz()).date()


def today_cr() -> date:
    """Current date in Costa Rica (UTC-6) — timezone-independent fallback."""
    return datetime.now(CR_TZ).date()


def utcnow() -> datetime:
    """Naive UTC now, via the non-deprecated API.

    Every datetime column in the schema is TIMESTAMP WITHOUT TIME ZONE, so the
    whole app speaks naive-UTC. Replacing datetime.utcnow() call sites with
    this helper removes the Python 3.12 deprecation without changing any
    stored value or comparison. When the columns move to TIMESTAMPTZ
    (Phase 2), this becomes `datetime.now(timezone.utc)` and the type change
    happens in exactly one place.
    """
    return datetime.now(timezone.utc).replace(tzinfo=None)