from __future__ import annotations

from decimal import Decimal

from fastapi import Request
from sqlalchemy import func, select
from sqlalchemy.orm import Session

from app.models import Product, ProductKey


def get_cart_map(request: Request) -> dict[str, int]:
    raw = request.session.get("cart") or {}
    cart: dict[str, int] = {}
    for key, value in raw.items():
        try:
            qty = int(value)
        except (TypeError, ValueError):
            continue
        if qty > 0:
            cart[str(key)] = qty
    return cart


def save_cart(request: Request, cart: dict[str, int]) -> None:
    request.session["cart"] = {str(k): int(v) for k, v in cart.items() if int(v) > 0}


def cart_count(request: Request) -> int:
    return sum(get_cart_map(request).values())


def available_stock(db: Session, product_id: int) -> int:
    return int(
        db.scalar(
            select(func.count())
            .select_from(ProductKey)
            .where(ProductKey.product_id == product_id, ProductKey.is_sold.is_(False))
        )
        or 0
    )


def build_cart_items(db: Session, request: Request) -> tuple[list[dict], Decimal]:
    cart = get_cart_map(request)
    items: list[dict] = []
    total = Decimal("0.00")
    if not cart:
        return items, total

    product_ids = [int(pid) for pid in cart.keys()]
    products = {
        p.id: p
        for p in db.scalars(select(Product).where(Product.id.in_(product_ids))).all()
    }

    clean_cart = dict(cart)
    for pid_str, qty in cart.items():
        product = products.get(int(pid_str))
        if not product or not product.is_active:
            clean_cart.pop(pid_str, None)
            continue
        stock = available_stock(db, product.id)
        qty = min(qty, max(stock, 0))
        if qty <= 0:
            clean_cart.pop(pid_str, None)
            continue
        clean_cart[pid_str] = qty
        line_total = product.price * qty
        total += line_total
        items.append(
            {
                "product": product,
                "quantity": qty,
                "stock": stock,
                "line_total": line_total,
            }
        )

    if clean_cart != cart:
        save_cart(request, clean_cart)
    return items, total