function flattenInstructions(instructions) {
  return instructions.flatMap((instruction) => {
    if (typeof instruction === "string") return [instruction];
    if (Array.isArray(instruction?.itemListElement)) return flattenInstructions(instruction.itemListElement);
    return instruction?.text ? [instruction.text] : [];
  });
}

function normalizeProgress(progress = {}) {
  return {
    completedIngredients: [...new Set((progress.completedIngredients || []).filter(Number.isInteger))],
    completedSteps: [...new Set((progress.completedSteps || []).filter(Number.isInteger))]
  };
}

function updateProgress(recipe, progress, { kind, index, completed }) {
  if (!recipe || !["ingredient", "step"].includes(kind)
    || !Number.isInteger(index) || typeof completed !== "boolean") {
    throw new Error("Invalid progress update");
  }
  const limit = kind === "ingredient"
    ? (recipe.recipeIngredient || []).length
    : flattenInstructions(recipe.recipeInstructions || []).length;
  if (index < 0 || index >= limit) throw new Error("Progress item does not exist");

  const key = kind === "ingredient" ? "completedIngredients" : "completedSteps";
  const next = normalizeProgress(progress);
  const items = new Set(next[key]);
  if (completed) items.add(index);
  else items.delete(index);
  next[key] = [...items].sort((left, right) => left - right);
  return next;
}

module.exports = { flattenInstructions, normalizeProgress, updateProgress };