"""SQL-backed CartService implementation.

Queries ``shared.models.market.CartItem`` — only this module may write
to cart-domain tables on behalf of other domains.
"""
from __future__ import annotations

from decimal import Decimal

from sqlalchemy import select, update, func
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from shared.models.market import CartItem
from shared.models.market_place import MarketPlace
from shared.models.calendars import CalendarEntry, Calendar
from shared.contracts.dtos import CartItemDTO, CartSummaryDTO


def _item_to_dto(ci: CartItem) -> CartItemDTO:
    product = ci.product
    return CartItemDTO(
        id=ci.id,
        product_id=ci.product_id,
        quantity=ci.quantity,
        product_title=product.title if product else None,
        product_slug=product.slug if product else None,
        product_image=product.image if product else None,
        unit_price=Decimal(str(product.special_price or product.regular_price or 0)) if product else None,
        market_place_id=ci.market_place_id,
    )


class SqlCartService:

    async def cart_summary(
        self, session: AsyncSession, *,
        user_id: int | None, session_id: str | None,
        page_slug: str | None = None,
    ) -> CartSummaryDTO:
        """Build a lightweight cart summary for the current identity."""
        # Resolve page filter
        page_post_id: int | None = None
        if page_slug:
            from shared.services.registry import services
            post = await services.blog.get_post_by_slug(session, page_slug)
            if post and post.is_page:
                page_post_id = post.id

        # --- product cart ---
        cart_q = select(CartItem).where(CartItem.deleted_at.is_(None))
        if user_id is not None:
            cart_q = cart_q.where(CartItem.user_id == user_id)
        elif session_id is not None:
            cart_q = cart_q.where(CartItem.session_id == session_id)
        else:
            return CartSummaryDTO()

        if page_post_id is not None:
            mp_ids = select(MarketPlace.id).where(
                MarketPlace.container_type == "page",
                MarketPlace.container_id == page_post_id,
                MarketPlace.deleted_at.is_(None),
            ).scalar_subquery()
            cart_q = cart_q.where(CartItem.market_place_id.in_(mp_ids))

        cart_q = cart_q.options(selectinload(CartItem.product))
        result = await session.execute(cart_q)
        cart_items = result.scalars().all()

        count = sum(ci.quantity for ci in cart_items)
        total = sum(
            Decimal(str(ci.product.special_price or ci.product.regular_price or 0)) * ci.quantity
            for ci in cart_items
            if ci.product and (ci.product.special_price or ci.product.regular_price)
        )

        # --- calendar entries ---
        from shared.services.registry import services
        if page_post_id is not None:
            cal_entries = await services.calendar.entries_for_page(
                session, page_post_id,
                user_id=user_id,
                session_id=session_id,
            )
        else:
            cal_entries = await services.calendar.pending_entries(
                session,
                user_id=user_id,
                session_id=session_id,
            )

        calendar_count = len(cal_entries)
        calendar_total = sum(Decimal(str(e.cost or 0)) for e in cal_entries if e.cost is not None)

        # --- tickets ---
        if page_post_id is not None:
            tickets = await services.calendar.tickets_for_page(
                session, page_post_id,
                user_id=user_id,
                session_id=session_id,
            )
        else:
            tickets = await services.calendar.pending_tickets(
                session,
                user_id=user_id,
                session_id=session_id,
            )

        ticket_count = len(tickets)
        ticket_total = sum(Decimal(str(t.price or 0)) for t in tickets)

        items = [_item_to_dto(ci) for ci in cart_items]

        return CartSummaryDTO(
            count=count,
            total=total,
            calendar_count=calendar_count,
            calendar_total=calendar_total,
            items=items,
            ticket_count=ticket_count,
            ticket_total=ticket_total,
        )

    async def cart_items(
        self, session: AsyncSession, *,
        user_id: int | None, session_id: str | None,
    ) -> list[CartItemDTO]:
        cart_q = select(CartItem).where(CartItem.deleted_at.is_(None))
        if user_id is not None:
            cart_q = cart_q.where(CartItem.user_id == user_id)
        elif session_id is not None:
            cart_q = cart_q.where(CartItem.session_id == session_id)
        else:
            return []

        cart_q = cart_q.options(selectinload(CartItem.product)).order_by(CartItem.created_at.desc())
        result = await session.execute(cart_q)
        return [_item_to_dto(ci) for ci in result.scalars().all()]

    async def adopt_cart_for_user(
        self, session: AsyncSession, user_id: int, session_id: str,
    ) -> None:
        """Adopt anonymous cart items for a logged-in user."""
        anon_result = await session.execute(
            select(CartItem).where(
                CartItem.deleted_at.is_(None),
                CartItem.user_id.is_(None),
                CartItem.session_id == session_id,
            )
        )
        anon_items = anon_result.scalars().all()

        if anon_items:
            # Soft-delete existing user cart
            await session.execute(
                update(CartItem)
                .where(CartItem.deleted_at.is_(None), CartItem.user_id == user_id)
                .values(deleted_at=func.now())
            )
            for ci in anon_items:
                ci.user_id = user_id