"use strict";

function round2(x) { return Math.round(x * 100) / 100; }

module.exports = {
  slug: "circle-measures",
  title: "Circle circumference and area",
  deck_category: "geometry",
  description: "Computes a circle's circumference and area from its radius or diameter.",
  inputs: [
    { name: "which_given", type: "string", required: true, description: "Whether value is a radius or a diameter.", enum: ["radius", "diameter"] },
    { name: "value", type: "number", unit: "length units", required: true, description: "The radius or diameter, per which_given.", min: 0 }
  ],
  outputs: [
    { name: "circumference", unit: "length units", description: "Circle circumference." },
    { name: "area", unit: "square length units", description: "Circle area." }
  ],
  steps: [
    "If which_given is diameter, radius = value / 2; otherwise radius = value.",
    "circumference = 2 * pi * radius.",
    "area = pi * radius^2.",
    "Round both to 2 decimals."
  ],
  constants: [
    { name: "pi", value: 3.14159265358979, unit: "dimensionless", source: 0 }
  ],
  sources: [
    { kind: "edition_page", value: "Standard geometry reference (e.g. Coxeter, H.S.M. Introduction to Geometry, 2nd ed., Wiley, 1969).", title: "Circle circumference and area formulas", publisher: "Wiley", retrieved_utc: "2026-09-30T19:48:00Z", note: "Standard formulas C=2*pi*r and A=pi*r^2." }
  ],
  disclaimer: null,
  questionText(inputs) {
    return `What are the circumference and area of a circle with ${inputs.which_given} ${inputs.value}?`;
  },
  run(inputs) {
    const { which_given, value } = inputs || {};
    if (which_given !== "radius" && which_given !== "diameter") throw new Error("which_given must be radius or diameter");
    if (typeof value !== "number" || value <= 0) throw new Error("value must be a positive number");
    const r = which_given === "diameter" ? value / 2 : value;
    const circumference = round2(2 * Math.PI * r);
    const area = round2(Math.PI * r * r);
    return { answer: `circumference ${circumference.toFixed(2)}, area ${area.toFixed(2)}`, values: { circumference, area } };
  },
  examples: [
    {
      name: "worked example",
      inputs: { which_given: "radius", value: 7 },
      expected: { answer: "circumference 43.98, area 153.94" },
      check: "By hand: circumference=2*3.14159265*7=43.9823 rounds to 43.98; area=3.14159265*49=153.9380 rounds to 153.94."
    },
    {
      name: "test vector: given diameter",
      inputs: { which_given: "diameter", value: 10 },
      expected: { answer: "circumference 31.42, area 78.54" },
      check: "By hand: radius=5; circumference=2*3.14159265*5=31.4159 rounds to 31.42; area=3.14159265*25=78.5398 rounds to 78.54; matches the well known fact that a circle of diameter 10 has circumference pi*10=31.4159."
    }
  ]
};