import datetime

from sqlalchemy import Column, DateTime, Binary, String, Float, Integer
from sqlalchemy.ext.declarative import declarative_base


ModelBase = declarative_base()


def as_group_singleton(cls):
    columns = {}
    for name, typ in cls.__annotations__.items():
        if name == "group_id":
            raise ValueError(f"Cannot have column named group_id in as_group_singleton class {cls.__name__}")
        if typ == int:
            columns[name] = Column(Integer)
        elif typ == float:
            columns[name] = Column(Float)
        elif typ == str:
            columns[name] = Column(String)
        elif typ in (object, "binary"):
            columns[name] = Column(Binary)
        elif typ == datetime.datetime:
            columns[name] = Column(DateTime)
        else:
            raise TypeError(f"Unsupported annotation {typ} for {name} in {cls.__name__}")

    cons_params = {k: getattr(cls, k, None) for k in columns}

    def get_or_create_standin(cls, db, group_id):
        sing = db.query(cls).get(group_id)
        if sing is None:
            sing = cls(group_id=group_id, **cons_params)
            db.add(sing)
        return sing

    columns["__tablename__"] = "".join(("_" + c.lower()) if "A" <= c <= "Z" else c for c in cls.__name__).strip("_")
    columns["group_id"] = Column(String, primary_key=True)

    return type(
        cls.__name__,
        (ModelBase, cls),
        dict(**columns, get_or_create=classmethod(get_or_create_standin))
    )