"""Helpers for converting ingredient portions to gram quantities."""

from __future__ import annotations

from collections.abc import Sequence

from parsing_pipeline.db.usda_ingredient_tables import IngredientPortion


def convert_quantity_to_grams_from_portions(
    portions: Sequence[IngredientPortion],
    quantity: float,
    unit: str,
) -> float | None:
    """Find the first portion whose modifier matches *unit* and return the gram conversion.

    Matching: normalized modifier equals normalized unit, or unit is a substring
    of the modifier (e.g. "cup" matches "cup, chopped").
    Returns ``(quantity / portion.amount) * portion.gram_weight`` on match, else None.
    """
    normalized_unit = unit.strip().lower()
    for portion in portions:
        if portion.amount is None or portion.amount <= 0:
            continue
        if portion.gram_weight <= 0:
            continue
        portion_modifier = (portion.modifier or "").strip().lower()
        if portion_modifier == normalized_unit or normalized_unit in portion_modifier:
            return (quantity / portion.amount) * portion.gram_weight
    return None