module.exports = {
  slug: "present-value-of-lump-sum",
  title: "Present value of a lump sum",
  deck_category: "finance",
  description: "Computes the present value of a single future cash amount, discounted at a given annual rate.",
  inputs: [
    { name: "future_value", type: "number", unit: "currency units", required: true, description: "Amount to be received in the future", min: 0 },
    { name: "annual_discount_rate_percent", type: "number", unit: "%", required: true, description: "Annual discount rate", min: 0 },
    { name: "years", type: "number", unit: "years", required: true, description: "Number of years until the amount is received", min: 0 }
  ],
  outputs: [
    { name: "present_value", unit: "currency units", description: "Value of the future amount in today's terms" }
  ],
  steps: [
    "Convert the annual rate to a decimal: r = annual_discount_rate_percent / 100.",
    "present_value = future_value / (1 + r) ^ years.",
    "Round present_value to 2 decimals (money to cents)."
  ],
  constants: [],
  sources: [
    { kind: "edition_page", value: "Brealey, Myers, Allen, Principles of Corporate Finance, 13th ed., Chapter 2, section 2-1 (Present Values)", title: "Principles of Corporate Finance", publisher: "McGraw-Hill", retrieved_utc: "2026-09-30T19:31:29Z", note: "PV = FV / (1+r)^n" }
  ],
  disclaimer: null,
  questionText(inputs) {
    return `What is the present value of $${inputs.future_value} to be received in ${inputs.years} years, discounted at ${inputs.annual_discount_rate_percent}% per year?`;
  },
  run(inputs) {
    const { future_value, annual_discount_rate_percent, years } = inputs;
    if (typeof future_value !== "number" || future_value < 0) throw new Error("future_value must be a non-negative number");
    if (typeof annual_discount_rate_percent !== "number" || annual_discount_rate_percent < 0) throw new Error("annual_discount_rate_percent must be a non-negative number");
    if (typeof years !== "number" || years < 0) throw new Error("years must be a non-negative number");
    const r = annual_discount_rate_percent / 100;
    const present_value = Math.round((future_value / Math.pow(1 + r, years)) * 100) / 100;
    const fmt = (n) => n.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g, ",");
    return {
      answer: `$${fmt(present_value)}`,
      values: { present_value }
    };
  },
  examples: [
    {
      name: "worked example",
      inputs: { future_value: 10000, annual_discount_rate_percent: 5, years: 10 },
      expected: { answer: "$6,139.13" },
      check: "hand computation: PV = 10000 / (1.05)^10 = 10000/1.628894... = 6139.1325..., rounds to 6139.13"
    },
    {
      name: "test vector: short horizon",
      inputs: { future_value: 1000, annual_discount_rate_percent: 8, years: 1 },
      expected: { answer: "$925.93" },
      check: "hand computation: PV = 1000 / 1.08 = 925.9259..., rounds to 925.93"
    }
  ]
};