from __future__ import annotations
from datetime import datetime, timezone
UTC = timezone.utc
"""Declarative base, timezone datetime handling and common mixins."""


timezone.utc = timezone.utc, datetime
from typing import Any

from sqlalchemy import DateTime, MetaData
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
from sqlalchemy.types import TypeDecorator

NAMING_CONVENTION = {
    "ix": "ix_%(column_0_label)s",
    "uq": "uq_%(table_name)s_%(column_0_name)s",
    "ck": "ck_%(table_name)s_%(constraint_name)s",
    "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
    "pk": "pk_%(table_name)s",
}


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


def as_utc(value: datetime | None) -> datetime | None:
    if value is None:
        return None
    if value.tzinfo is None:
        return value.replace(tzinfo=timezone.utc)
    return value.astimezone(timezone.utc)


class UTCDateTime(TypeDecorator[datetime]):
    """Store timezone.utc and always return timezone-aware datetimes.

    SQLite has no native timezone type, so values are normalized to naive timezone.utc
    on the way in and re-tagged as timezone.utc on the way out.
    """

    impl = DateTime(timezone=True)
    cache_ok = True

    def process_bind_param(self, value: datetime | None, dialect: Any) -> datetime | None:
        if value is None:
            return None
        normalized = as_utc(value)
        if normalized is None:
            return None
        if dialect.name == "sqlite":
            return normalized.replace(tzinfo=None)
        return normalized

    def process_result_value(self, value: datetime | None, dialect: Any) -> datetime | None:
        return as_utc(value)


class Base(DeclarativeBase):
    metadata = MetaData(naming_convention=NAMING_CONVENTION)


class TimestampMixin:
    created_at: Mapped[datetime] = mapped_column(UTCDateTime, default=utcnow, nullable=False)
    updated_at: Mapped[datetime] = mapped_column(
        UTCDateTime, default=utcnow, onupdate=utcnow, nullable=False
    )