module.exports = {
  slug: "recipe-scaling",
  title: "Recipe scaling",
  deck_category: "cooking",
  description: "Scales a list of ingredient quantities from an original serving count to a desired serving count.",
  inputs: [
    { name: "original_servings", type: "number", unit: "servings", required: true, description: "Servings the original recipe makes", min: 0 },
    { name: "desired_servings", type: "number", unit: "servings", required: true, description: "Servings wanted", min: 0 },
    { name: "ingredients", type: "array", required: true, description: "List of {name, quantity, unit} ingredient entries to scale" }
  ],
  outputs: [
    { name: "scale_factor", unit: null, description: "desired_servings / original_servings" },
    { name: "scaled_ingredients", unit: null, description: "Ingredient list with quantity multiplied by scale_factor" }
  ],
  steps: [
    "scale_factor = desired_servings / original_servings.",
    "For each ingredient, scaled_quantity = quantity * scale_factor, rounded to 2 decimals.",
    "Unit and name pass through unchanged; only quantity is scaled."
  ],
  constants: [],
  sources: [
    { kind: "edition_page", value: "Standard proportional recipe-scaling method (multiply every ingredient quantity by desired/original servings)", title: "Recipe yield scaling technique", publisher: "Standard culinary reference practice (e.g. The Professional Chef, Culinary Institute of America, chapter on recipe conversion)", retrieved_utc: "2026-09-30T19:50:00Z", note: "This card performs the standard linear scaling arithmetic; it does not adjust for non-linear items such as leavening or spice at extreme scale changes." }
  ],
  disclaimer: null,
  questionText(inputs) {
    const items = inputs.ingredients.map((i) => `${i.quantity} ${i.unit} ${i.name}`).join(", ");
    return `Scaling a recipe that serves ${inputs.original_servings} to serve ${inputs.desired_servings}, what are the scaled quantities for: ${items}?`;
  },
  run(inputs) {
    const { original_servings, desired_servings, ingredients } = inputs;
    if (typeof original_servings !== "number" || original_servings <= 0) throw new Error("original_servings must be a positive number");
    if (typeof desired_servings !== "number" || desired_servings <= 0) throw new Error("desired_servings must be a positive number");
    if (!Array.isArray(ingredients) || ingredients.length === 0) throw new Error("ingredients must be a non-empty array");
    const scaleFactorRaw = desired_servings / original_servings;
    const scaleFactor = Math.round(scaleFactorRaw * 10000) / 10000;
    const scaled = ingredients.map((ing) => {
      if (typeof ing.name !== "string" || typeof ing.quantity !== "number" || typeof ing.unit !== "string") {
        throw new Error("each ingredient needs name (string), quantity (number), unit (string)");
      }
      const q = Math.round(ing.quantity * scaleFactorRaw * 100) / 100;
      return { name: ing.name, quantity: q, unit: ing.unit };
    });
    const answer = scaled.map((s) => `${s.quantity} ${s.unit} ${s.name}`).join(", ");
    return { answer, values: { scale_factor: scaleFactor, scaled_ingredients: scaled } };
  },
  examples: [
    {
      name: "worked example",
      inputs: {
        original_servings: 4,
        desired_servings: 6,
        ingredients: [
          { name: "flour", quantity: 200, unit: "g" },
          { name: "sugar", quantity: 100, unit: "g" },
          { name: "eggs", quantity: 2, unit: "count" }
        ]
      },
      expected: { answer: "300 g flour, 150 g sugar, 3 count eggs" },
      check: "scale_factor = 6/4 = 1.5. 200*1.5=300. 100*1.5=150. 2*1.5=3."
    },
    {
      name: "test vector: fractional scale down",
      inputs: {
        original_servings: 12,
        desired_servings: 5,
        ingredients: [
          { name: "butter", quantity: 240, unit: "g" },
          { name: "chocolate chips", quantity: 360, unit: "g" }
        ]
      },
      expected: { answer: "100 g butter, 150 g chocolate chips" },
      check: "scale_factor = 5/12 = 0.416666... 240*0.416666=100.0 exactly. 360*0.416666=150.0 exactly."
    }
  ]
};