# 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 app.exceptions import (
    ProductNotFoundException,
    ValidationException,
    InsufficientInventoryException
)

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.

        Note: This is a simple in-memory implementation.
        In production, you'd store carts in Redis or database.
        """
        # For now, return empty cart structure
        # TODO: Implement persistent cart storage
        return {
            "vendor_id": vendor_id,
            "session_id": session_id,
            "items": [],
            "subtotal": 0.0,
            "total": 0.0
        }

    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
        """
        # 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:
            raise ProductNotFoundException(str(product_id))

        # Check inventory
        if product.available_inventory < quantity:
            raise InsufficientInventoryException(
                product_id=product_id,
                requested=quantity,
                available=product.available_inventory
            )

        # TODO: Add to persistent cart storage
        # For now, return success response
        logger.info(
            f"Added product {product_id} (qty: {quantity}) to cart "
            f"for session {session_id}"
        )

        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."""
        if quantity < 1:
            raise ValidationException("Quantity must be at least 1")

        # Verify product
        product = db.query(Product).filter(
            and_(
                Product.id == product_id,
                Product.vendor_id == vendor_id
            )
        ).first()

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

        # Check inventory
        if product.available_inventory < quantity:
            raise InsufficientInventoryException(
                product_id=product_id,
                requested=quantity,
                available=product.available_inventory
            )

        # TODO: Update persistent cart
        logger.info(f"Updated cart item {product_id} quantity to {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."""
        # TODO: Remove from persistent cart
        logger.info(f"Removed product {product_id} from cart {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."""
        # TODO: Clear persistent cart
        logger.info(f"Cleared cart for session {session_id}")

        return {
            "message": "Cart cleared"
        }


# Create service instance
cart_service = CartService()