from typing import List, Dict, Optional
from pydantic import BaseModel
from datetime import datetime

class FoodItem(BaseModel):
    id: int
    name: str
    description: Optional[str] = None
    price: float
    category: str
    is_available: bool = True
    created_at: datetime
    updated_at: Optional[datetime] = None

def validate_food_item(food_item: FoodItem) -> Dict[str, str]:
    errors = {}
    if not food_item.name.strip():
        errors["name"] = "Name cannot be empty"
    if food_item.price <= 0:
        errors["price"] = "Price must be greater than zero"
    if not food_item.category.strip():
        errors["category"] = "Category cannot be empty"
    return errors

def get_available_food_items(food_items: List[FoodItem]) -> List[FoodItem]:
    return [item for item in food_items if item.is_available]

def get_food_items_by_category(food_items: List[FoodItem], category: str) -> List[FoodItem]:
    return [item for item in food_items if item.category.lower() == category.lower()]

def get_food_item_by_id(food_items: List[FoodItem], item_id: int) -> Optional[FoodItem]:
    for item in food_items:
        if item.id == item_id:
            return item
    return None

def update_food_item_availability(food_item: FoodItem, is_available: bool) -> FoodItem:
    food_item.is_available = is_available
    food_item.updated_at = datetime.now()
    return food_item