import { UNIT_INFO, type Unit } from "@app/shared-types";

export interface ScalableIngredient {
  canonicalIngredientId: string;
  displayNameSv: string;
  quantity: number;
  unit: Unit;
  optional: boolean;
}

/** Enheter som avrundas till "köksvänliga" mängder vid skalning. */
const SPOON_UNITS: ReadonlySet<Unit> = new Set(["TABLESPOON", "TEASPOON", "PINCH"]);

/**
 * Skala recept till annat antal portioner (Cooking Mode: "skala till sex personer").
 * Kryddmått avrundas till halva mått; styck till kvartar.
 */
export function scaleIngredients(
  ingredients: ScalableIngredient[],
  fromPortions: number,
  toPortions: number,
): ScalableIngredient[] {
  if (fromPortions <= 0 || toPortions <= 0) {
    throw new Error("Portioner måste vara > 0");
  }
  const factor = toPortions / fromPortions;
  return ingredients.map((ing) => ({
    ...ing,
    quantity: roundForUnit(ing.quantity * factor, ing.unit),
  }));
}

function roundForUnit(value: number, unit: Unit): number {
  if (SPOON_UNITS.has(unit)) return Math.round(value * 2) / 2;
  if (UNIT_INFO[unit].kind === "count") return Math.round(value * 4) / 4;
  if (unit === "KILOGRAM" || unit === "LITER" || unit === "POUND")
    return Math.round(value * 100) / 100;
  if (unit === "CUP_US") return Math.round(value * 4) / 4;
  return Math.round(value * 10) / 10;
}