from typing import TypeVar, Generic, Type, Sequence
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import select, delete as sa_delete, ColumnElement
from sqlalchemy.exc import IntegrityError
from sqlalchemy.sql import Select
from fooder.domain import Base
from fooder.exc import Conflict, NotFound

T = TypeVar("T", bound=Base)


DEFAULT_LIMIT = 20


class RepositoryBase(Generic[T]):
    def __init__(self, model: Type[T], session: AsyncSession):
        self.model = model
        self.session = session

    def _build_select(self, *expressions: ColumnElement) -> Select[tuple[T]]:
        stmt = select(self.model)

        if expressions:
            stmt = stmt.where(*expressions)

        return stmt

    async def _get(self, *expressions: ColumnElement) -> T:
        stmt = self._build_select(*expressions)
        result = await self.session.execute(stmt)
        obj = result.scalar_one_or_none()

        if obj is None:
            raise NotFound()

        return obj

    async def _list(self, *expressions: ColumnElement, offset: int = 0, limit: int | None = DEFAULT_LIMIT) -> Sequence[T]:
        stmt = self._build_select(*expressions)

        if offset:
            stmt = stmt.offset(offset)

        if limit is not None:
            stmt = stmt.limit(limit)

        result = await self.session.execute(stmt)
        return result.scalars().all()

    async def create(self, obj: T) -> T:
        self.session.add(obj)
        try:
            await self.session.flush()
        except IntegrityError:
            raise Conflict()
        await self.session.refresh(obj)
        return obj

    async def update(self, obj: T) -> T:
        try:
            await self.session.flush()
        except IntegrityError:
            raise Conflict()
        return obj

    async def _delete(self, *expressions: ColumnElement):
        stmt = sa_delete(self.model)

        if expressions:
            stmt = stmt.where(*expressions)

        await self.session.execute(stmt)