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

class Food(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

    @validator('price')
    def price_must_be_positive(cls, value):
        if value <= 0:
            raise ValueError('Price must be a positive value')
        return value

def get_all_foods(foods: List[Food]) -> List[Dict]:
    return [food.dict() for food in foods]

def filter_foods_by_category(foods: List[Food], category: str) -> List[Dict]:
    filtered_foods = [food for food in foods if food.category == category]
    return [food.dict() for food in filtered_foods]

def filter_available_foods(foods: List[Food]) -> List[Dict]:
    available_foods = [food for food in foods if food.is_available]
    return [food.dict() for food in available_foods]

def sort_foods_by_price(foods: List[Food], ascending: bool = True) -> List[Dict]:
    sorted_foods = sorted(foods, key=lambda food: food.price, reverse=not ascending)
    return [food.dict() for food in sorted_foods]