fix: normalize nutrition units and retain zero-valued nutrients

lib/nutrition.ts

@@ -0,0 +1,24 @@
+/** Normalização dos valores nutricionais recebidos do Open Food Facts. */
+export function getNutrientValue(value: unknown): number | null {
+  if (typeof value !== "number" && typeof value !== "string") return null;
+  if (typeof value === "string" && value.trim() === "") return null;
+  const number = Number(value);
+  return Number.isFinite(number) && number >= 0 ? number : null;
+}
+
+/**
+ * Prefere o campo explícito em kcal. Os campos energy/energy-kj usam kJ;
+ * 1 kcal = 4.184 kJ. Zero é um valor válido, distinto de dado ausente.
+ * https://openfoodfacts.github.io/openfoodfacts-server/api/tutorial-off-api/
+ */
+export function getEnergyKcal(nutriments?: {
+  "energy-kcal_100g"?: unknown;
+  "energy-kj_100g"?: unknown;
+  energy_100g?: unknown;
+}): number | null {
+  const kcal = getNutrientValue(nutriments?.["energy-kcal_100g"]);
+  if (kcal !== null) return kcal;
+  const kj = getNutrientValue(nutriments?.["energy-kj_100g"])
+    ?? getNutrientValue(nutriments?.energy_100g);
+  return kj === null ? null : kj / 4.184;
+}