from sqlalchemy import Column, Integer, DateTime, Boolean, String, JSON, func, inspect
from sqlalchemy.orm import declarative_mixin, declarative_base, NO_VALUE

Base = declarative_base()

def _safe_get_loaded_attr(obj, name):
    try:
        st = inspect(obj)
        attr = st.attrs.get(name)
        if attr is not None:
            val = attr.loaded_value
            return None if val is NO_VALUE else val
        if name in st.dict:
            return st.dict.get(name)
        return None
    except Exception:
        return None

@declarative_mixin
class CRUDMixin:
    id = Column(Integer, primary_key=True)
    created_at = Column(DateTime, default=func.now(), nullable=False)
    updated_at = Column(DateTime, default=func.now(), nullable=False, onupdate=func.now())

    def as_dict(self, fields: list[str] | None = None):
        """
        Serialize the instance.
            - If 'fields' (possibly dotted) is provided, emit exactly those keys.
            - Else, if '__crudkit_projection__' is set on the instance, emit those keys.
            - Else, fall back to all mapped columns on this class hierarchy.
        Always includes 'id' when present unless explicitly excluded.
        """
        if fields is None:
            fields = getattr(self, "__crudkit_projection__", None)

        if fields:
            out = {}
            if "id" not in fields and hasattr(self, "id"):
                out["id"] = getattr(self, "id")
            for f in fields:
                cur = self
                for part in f.split("."):
                    if cur is None:
                        break
                    cur = getattr(cur, part, None)
                out[f] = cur
            return out

        result = {}
        for cls in self.__class__.__mro__:
            if hasattr(cls, "__table__"):
                for column in cls.__table__.columns:
                    name = column.name
                    result[name] = getattr(self, name)
        return result


class Version(Base):
    __tablename__ = "versions"

    id = Column(Integer, primary_key=True)
    model_name = Column(String, nullable=False)
    object_id = Column(Integer, nullable=False)
    change_type = Column(String, nullable=False)
    data = Column(JSON, nullable=True)
    timestamp = Column(DateTime, default=func.now())

    actor = Column(String, nullable=True)
    meta = Column('metadata', JSON, nullable=True)