const FRACTIONS = new Map([
  ["¼", 1 / 4], ["½", 1 / 2], ["¾", 3 / 4], ["⅓", 1 / 3],
  ["⅔", 2 / 3], ["⅛", 1 / 8], ["⅜", 3 / 8], ["⅝", 5 / 8], ["⅞", 7 / 8]
]);

function parseYield(value) {
  const match = String(value ?? "").match(/\d+(?:\.\d+)?/);
  if (!match) return null;
  const portions = Number(match[0]);
  return Number.isFinite(portions) && portions > 0 ? portions : null;
}

function parseQuantity(value) {
  if (FRACTIONS.has(value)) return FRACTIONS.get(value);
  if (value.includes("/")) {
    const [numerator, denominator] = value.split("/").map(Number);
    return denominator ? numerator / denominator : null;
  }
  return Number(value);
}

function formatQuantity(value) {
  const whole = Math.floor(value + 1e-8);
  const remainder = value - whole;
  const candidates = [[0, ""], [1 / 8, "⅛"], [1 / 4, "¼"], [1 / 3, "⅓"],
    [3 / 8, "⅜"], [1 / 2, "½"], [5 / 8, "⅝"], [2 / 3, "⅔"],
    [3 / 4, "¾"], [7 / 8, "⅞"], [1, ""]];
  const [fraction, symbol] = candidates.reduce((best, candidate) => (
    Math.abs(candidate[0] - remainder) < Math.abs(best[0] - remainder) ? candidate : best
  ));
  if (Math.abs(fraction - remainder) <= 0.02) {
    const adjustedWhole = fraction === 1 ? whole + 1 : whole;
    return `${adjustedWhole || ""}${adjustedWhole && symbol ? " " : ""}${symbol}` || "0";
  }
  return Number(value.toFixed(2)).toString();
}

function scaleIngredient(ingredient, factor) {
  if (typeof ingredient !== "string" || factor === 1) return ingredient;
  const match = ingredient.match(/^(\s*)(?:(\d+)\s+)?(\d+\/\d+|\d+(?:\.\d+)?|[¼½¾⅓⅔⅛⅜⅝⅞])(?=\s|[a-zA-Z])/);
  if (!match) return ingredient;
  const whole = Number(match[2] || 0);
  const quantity = parseQuantity(match[3]);
  if (!Number.isFinite(quantity)) return ingredient;
  const replacement = `${match[1]}${formatQuantity((whole + quantity) * factor)}`;
  return replacement + ingredient.slice(match[0].length);
}

function scaleRecipe(recipe, portions) {
  const basePortions = parseYield(recipe?.recipeYield);
  if (!basePortions || !Number.isInteger(portions) || portions < 1) return recipe;
  const suffix = String(recipe.recipeYield).replace(/^\s*\d+(?:\.\d+)?\s*/, "");
  return {
    ...recipe,
    recipeYield: suffix ? `${portions} ${suffix}` : portions,
    recipeIngredient: (recipe.recipeIngredient || []).map((ingredient) => (
      scaleIngredient(ingredient, portions / basePortions)
    ))
  };
}

module.exports = { parseYield, scaleIngredient, scaleRecipe };