from typing import Generic, TypeVar

from fastapi import Query
from pydantic import BaseModel
from sqlalchemy import Select, func, select
from sqlalchemy.orm import Session

T = TypeVar("T")


class PageParams:
    def __init__(
        self,
        page: int = Query(1, ge=1),
        page_size: int = Query(50, ge=1, le=200),
    ):
        self.page = page
        self.page_size = page_size

    @property
    def offset(self) -> int:
        return (self.page - 1) * self.page_size


class Page(BaseModel, Generic[T]):
    items: list[T]
    total: int
    page: int
    page_size: int


def paginate(db: Session, stmt: Select, params: PageParams) -> tuple[list, int]:
    total = db.scalar(select(func.count()).select_from(stmt.subquery())) or 0
    rows = db.scalars(stmt.offset(params.offset).limit(params.page_size)).all()
    return list(rows), total