from __future__ import annotations

from typing import List, Set

from persons import Person
from meals.db import Meal


def get_duplicates(items: List[Person]) -> Set[str]:
    """Return the set of duplicate person names based on repeated ids."""
    seen: set[int] = set()
    duplicates: set[str] = set()
    for item in items:
        if item.id in seen:
            duplicates.add(item.name)
        seen.add(item.id)
    return duplicates


def validate_meal(meal: Meal) -> str | None:
    """Validate a Meal domain model.

    Returns:
        None if valid, otherwise a human-readable error message.
    """
    if not meal.chefs:
        return "Meal must have at least one chef"

    if not meal.cleanup:
        return "Meal must have at least one cleanup person"

    if not meal.consumers:
        return "Meal must have at least one consumer"

    if len(meal.recipes) == 0 and len(meal.extra_ingredients) == 0:
        return "Meal must have at least one recipe or ingredient"

    duplicates = get_duplicates(meal.chefs)
    if duplicates:
        return f"Duplicate chef: {', '.join(duplicates)}"

    duplicates = get_duplicates(meal.cleanup)
    if duplicates:
        return f"Duplicate cleanup person: {', '.join(duplicates)}"

    duplicates = get_duplicates(meal.consumers)
    if duplicates:
        return f"Duplicate consumer: {', '.join(duplicates)}"

    zero_servings = [r for r in meal.recipes if r.servings == 0]
    if zero_servings:
        return "Recipe servings must be greater than 0"

    return None