# app/services/cart_service.py
"""
Shopping cart service.

This module provides:
- Session-based cart management
- Cart item operations (add, update, remove)
- Cart total calculations
"""

import logging
from typing import Dict, List, Optional
from datetime import datetime, timezone

from sqlalchemy.orm import Session
from sqlalchemy import and_

from models.database.product import Product
from models.database.vendor import Vendor
from models.database.cart import CartItem
from app.exceptions import (
    ProductNotFoundException,
    CartItemNotFoundException,
    CartValidationException,
    InsufficientInventoryForCartException,
    InvalidCartQuantityException,
    ProductNotAvailableForCartException,
)

logger = logging.getLogger(__name__)


class CartService:
    """Service for managing shopping carts."""

    def get_cart(
            self,
            db: Session,
            vendor_id: int,
            session_id: str
    ) -> Dict:
        """
        Get cart contents for a session.

        Args:
            db: Database session
            vendor_id: Vendor ID
            session_id: Session ID

        Returns:
            Cart data with items and totals
        """
        logger.info(
            f"[CART_SERVICE] get_cart called",
            extra={
                "vendor_id": vendor_id,
                "session_id": session_id,
            }
        )

        # Fetch cart items from database
        cart_items = db.query(CartItem).filter(
            and_(
                CartItem.vendor_id == vendor_id,
                CartItem.session_id == session_id
            )
        ).all()

        logger.info(
            f"[CART_SERVICE] Found {len(cart_items)} items in database",
            extra={"item_count": len(cart_items)}
        )

        # Build response
        items = []
        subtotal = 0.0

        for cart_item in cart_items:
            product = cart_item.product
            line_total = cart_item.line_total

            items.append({
                "product_id": product.id,
                "product_name": product.marketplace_product.title,
                "quantity": cart_item.quantity,
                "price": cart_item.price_at_add,
                "line_total": line_total,
                "image_url": product.marketplace_product.image_link if product.marketplace_product else None,
            })

            subtotal += line_total

        cart_data = {
            "vendor_id": vendor_id,
            "session_id": session_id,
            "items": items,
            "subtotal": subtotal,
            "total": subtotal  # Could add tax/shipping later
        }

        logger.info(
            f"[CART_SERVICE] get_cart returning: {len(cart_data['items'])} items, total: {cart_data['total']}",
            extra={"cart": cart_data}
        )

        return cart_data

    def add_to_cart(
            self,
            db: Session,
            vendor_id: int,
            session_id: str,
            product_id: int,
            quantity: int = 1
    ) -> Dict:
        """
        Add product to cart.

        Args:
            db: Database session
            vendor_id: Vendor ID
            session_id: Session ID
            product_id: Product ID
            quantity: Quantity to add

        Returns:
            Updated cart

        Raises:
            ProductNotFoundException: If product not found
            InsufficientInventoryException: If not enough inventory
        """
        logger.info(
            f"[CART_SERVICE] add_to_cart called",
            extra={
                "vendor_id": vendor_id,
                "session_id": session_id,
                "product_id": product_id,
                "quantity": quantity
            }
        )

        # Verify product exists and belongs to vendor
        product = db.query(Product).filter(
            and_(
                Product.id == product_id,
                Product.vendor_id == vendor_id,
                Product.is_active == True
            )
        ).first()

        if not product:
            logger.error(
                f"[CART_SERVICE] Product not found",
                extra={"product_id": product_id, "vendor_id": vendor_id}
            )
            raise ProductNotFoundException(product_id=product_id, vendor_id=vendor_id)

        logger.info(
            f"[CART_SERVICE] Product found: {product.marketplace_product.title}",
            extra={
                "product_id": product_id,
                "product_name": product.marketplace_product.title,
                "available_inventory": product.available_inventory
            }
        )

        # Get current price (use sale_price if available, otherwise regular price)
        current_price = product.sale_price if product.sale_price else product.price

        # Check if item already exists in cart
        existing_item = db.query(CartItem).filter(
            and_(
                CartItem.vendor_id == vendor_id,
                CartItem.session_id == session_id,
                CartItem.product_id == product_id
            )
        ).first()

        if existing_item:
            # Update quantity
            new_quantity = existing_item.quantity + quantity

            # Check inventory for new total quantity
            if product.available_inventory < new_quantity:
                logger.warning(
                    f"[CART_SERVICE] Insufficient inventory for update",
                    extra={
                        "product_id": product_id,
                        "current_in_cart": existing_item.quantity,
                        "adding": quantity,
                        "requested_total": new_quantity,
                        "available": product.available_inventory
                    }
                )
                raise InsufficientInventoryForCartException(
                    product_id=product_id,
                    product_name=product.marketplace_product.title,
                    requested=new_quantity,
                    available=product.available_inventory
                )

            existing_item.quantity = new_quantity
            db.commit()
            db.refresh(existing_item)

            logger.info(
                f"[CART_SERVICE] Updated existing cart item",
                extra={
                    "cart_item_id": existing_item.id,
                    "new_quantity": new_quantity
                }
            )

            return {
                "message": "Product quantity updated in cart",
                "product_id": product_id,
                "quantity": new_quantity
            }
        else:
            # Check inventory for new item
            if product.available_inventory < quantity:
                logger.warning(
                    f"[CART_SERVICE] Insufficient inventory",
                    extra={
                        "product_id": product_id,
                        "requested": quantity,
                        "available": product.available_inventory
                    }
                )
                raise InsufficientInventoryForCartException(
                    product_id=product_id,
                    product_name=product.marketplace_product.title,
                    requested=quantity,
                    available=product.available_inventory
                )

            # Create new cart item
            cart_item = CartItem(
                vendor_id=vendor_id,
                session_id=session_id,
                product_id=product_id,
                quantity=quantity,
                price_at_add=current_price
            )
            db.add(cart_item)
            db.commit()
            db.refresh(cart_item)

            logger.info(
                f"[CART_SERVICE] Created new cart item",
                extra={
                    "cart_item_id": cart_item.id,
                    "quantity": quantity,
                    "price": current_price
                }
            )

            return {
                "message": "Product added to cart",
                "product_id": product_id,
                "quantity": quantity
            }

    def update_cart_item(
            self,
            db: Session,
            vendor_id: int,
            session_id: str,
            product_id: int,
            quantity: int
    ) -> Dict:
        """
        Update quantity of item in cart.

        Args:
            db: Database session
            vendor_id: Vendor ID
            session_id: Session ID
            product_id: Product ID
            quantity: New quantity (must be >= 1)

        Returns:
            Success message

        Raises:
            ValidationException: If quantity < 1
            ProductNotFoundException: If product not found
            InsufficientInventoryException: If not enough inventory
        """
        if quantity < 1:
            raise InvalidCartQuantityException(quantity=quantity, min_quantity=1)

        # Find cart item
        cart_item = db.query(CartItem).filter(
            and_(
                CartItem.vendor_id == vendor_id,
                CartItem.session_id == session_id,
                CartItem.product_id == product_id
            )
        ).first()

        if not cart_item:
            raise CartItemNotFoundException(product_id=product_id, session_id=session_id)

        # Verify product still exists and is active
        product = db.query(Product).filter(
            and_(
                Product.id == product_id,
                Product.vendor_id == vendor_id,
                Product.is_active == True
            )
        ).first()

        if not product:
            raise ProductNotFoundException(str(product_id))

        # Check inventory
        if product.available_inventory < quantity:
            raise InsufficientInventoryForCartException(
                product_id=product_id,
                product_name=product.marketplace_product.title,
                requested=quantity,
                available=product.available_inventory
            )

        # Update quantity
        cart_item.quantity = quantity
        db.commit()
        db.refresh(cart_item)

        logger.info(
            f"[CART_SERVICE] Updated cart item quantity",
            extra={
                "cart_item_id": cart_item.id,
                "product_id": product_id,
                "new_quantity": quantity
            }
        )

        return {
            "message": "Cart updated",
            "product_id": product_id,
            "quantity": quantity
        }

    def remove_from_cart(
            self,
            db: Session,
            vendor_id: int,
            session_id: str,
            product_id: int
    ) -> Dict:
        """
        Remove item from cart.

        Args:
            db: Database session
            vendor_id: Vendor ID
            session_id: Session ID
            product_id: Product ID

        Returns:
            Success message

        Raises:
            ProductNotFoundException: If product not in cart
        """
        # Find and delete cart item
        cart_item = db.query(CartItem).filter(
            and_(
                CartItem.vendor_id == vendor_id,
                CartItem.session_id == session_id,
                CartItem.product_id == product_id
            )
        ).first()

        if not cart_item:
            raise CartItemNotFoundException(product_id=product_id, session_id=session_id)

        db.delete(cart_item)
        db.commit()

        logger.info(
            f"[CART_SERVICE] Removed item from cart",
            extra={
                "cart_item_id": cart_item.id,
                "product_id": product_id,
                "session_id": session_id
            }
        )

        return {
            "message": "Item removed from cart",
            "product_id": product_id
        }

    def clear_cart(
            self,
            db: Session,
            vendor_id: int,
            session_id: str
    ) -> Dict:
        """
        Clear all items from cart.

        Args:
            db: Database session
            vendor_id: Vendor ID
            session_id: Session ID

        Returns:
            Success message with count of items removed
        """
        # Delete all cart items for this session
        deleted_count = db.query(CartItem).filter(
            and_(
                CartItem.vendor_id == vendor_id,
                CartItem.session_id == session_id
            )
        ).delete()

        db.commit()

        logger.info(
            f"[CART_SERVICE] Cleared cart",
            extra={
                "session_id": session_id,
                "vendor_id": vendor_id,
                "items_removed": deleted_count
            }
        )

        return {
            "message": "Cart cleared",
            "items_removed": deleted_count
        }


# Create service instance
cart_service = CartService()