from datetime import UTC, date, datetime
from typing import Annotated
from zoneinfo import ZoneInfo

from pydantic import AfterValidator

from app.core.config import get_settings
from app.core.errors import DomainValidationError


def utcnow() -> datetime:
    return datetime.now(UTC)


def resolve_tz(tz: str | None) -> ZoneInfo:
    name = tz or get_settings().timezone
    try:
        return ZoneInfo(name)
    except Exception as exc:
        raise DomainValidationError(f"Fuseau horaire inconnu : {name}") from exc


def local_day(dt_utc: datetime, tz: ZoneInfo) -> date:
    return dt_utc.astimezone(tz).date()


def as_utc(value: datetime) -> datetime:
    """Normalise a *stored* instant to UTC-aware.

    Every instant is persisted in UTC (CONVENTIONS C2.3), but the driver decides
    what comes back: PostgreSQL `TIMESTAMPTZ` yields an aware datetime while
    SQLite yields a naive one. Stamping UTC on naive values keeps responses
    compliant with the `Z` suffix required by architecture §8.4 on both engines.
    """
    return value.replace(tzinfo=UTC) if value.tzinfo is None else value.astimezone(UTC)


def require_utc(value: datetime) -> datetime:
    """Validate an *inbound* instant: naive is refused, aware is converted to UTC.

    Architecture §8.4: "entrée avec offset acceptée et convertie en UTC ; entrée
    naïve refusée (422)". Silently reading a naive datetime as UTC would record a
    local wall-clock time off by the client's offset.
    """
    if value.tzinfo is None or value.utcoffset() is None:
        raise ValueError(
            "Horodatage sans fuseau horaire : précisez le décalage "
            "(par exemple « 2026-08-13T06:31:00Z »)."
        )
    return value.astimezone(UTC)


# Use in request schemas (XxxCreate/XxxUpdate) for any client-supplied instant.
UtcDatetime = Annotated[datetime, AfterValidator(require_utc)]

# Use in response schemas (XxxRead) for any instant read back from the database.
StoredUtcDatetime = Annotated[datetime, AfterValidator(as_utc)]