"use strict";
// Day-number kernel: Howard Hinnant, "chrono-Compatible Low-Level Date Algorithms",
// https://howardhinnant.github.io/date_algorithms.html (days_from_civil). No host clock, no
// Date.now(), no time zone database.
function daysFromCivil(y, m, d) {
  y = m <= 2 ? y - 1 : y;
  const era = Math.floor((y >= 0 ? y : y - 399) / 400);
  const yoe = y - era * 400;
  const doy = Math.floor((153 * (m + (m > 2 ? -3 : 9)) + 2) / 5) + d - 1;
  const doe = yoe * 365 + Math.floor(yoe / 4) - Math.floor(yoe / 100) + doy;
  return era * 146097 + doe - 719468;
}
const EPOCH_JDN = 2440588;
function toJDN(y, m, d) { return daysFromCivil(y, m, d) + EPOCH_JDN; }
function isLeapGregorian(y) { return (y % 4 === 0 && y % 100 !== 0) || (y % 400 === 0); }
function daysInMonth(y, m) {
  const dim = [31, isLeapGregorian(y) ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
  return dim[m - 1];
}
function parseISODate(s, label) {
  const m = /^(-?\d{4})-(\d{2})-(\d{2})$/.exec(String(s).trim());
  if (!m) throw new Error((label || "date") + " must be an ISO 8601 date YYYY-MM-DD, got: " + s);
  const year = parseInt(m[1], 10), month = parseInt(m[2], 10), day = parseInt(m[3], 10);
  if (month < 1 || month > 12) throw new Error((label || "date") + " month out of range 1-12");
  if (day < 1 || day > daysInMonth(year, month)) throw new Error((label || "date") + " day out of range for that month");
  return { year, month, day };
}

module.exports = {
  slug: "day-of-year-and-days-remaining",
  title: "Day of year and days remaining",
  deck_category: "dates",
  description: "Computes a date's ordinal position within its calendar year and how many days are left in that year.",
  inputs: [
    { name: "date", type: "string", format: "date", required: true, description: "ISO 8601 date, YYYY-MM-DD" }
  ],
  outputs: [
    { name: "day_of_year", unit: "days", description: "Ordinal day within the year, 1 to 365 or 366" },
    { name: "days_remaining", unit: "days", description: "Days left in the calendar year after this date" }
  ],
  steps: [
    "Parse the date as a proleptic Gregorian civil date.",
    "Convert the date and January 1 of the same year to Julian Day Numbers (Hinnant days_from_civil, cited above).",
    "day_of_year = JDN(date) - JDN(year, 1, 1) + 1.",
    "days_in_year = 366 if the year is a Gregorian leap year, else 365.",
    "days_remaining = days_in_year - day_of_year."
  ],
  constants: [],
  sources: [
    { kind: "url", value: "https://howardhinnant.github.io/date_algorithms.html", title: "chrono-Compatible Low-Level Date Algorithms", publisher: "Howard Hinnant", retrieved_utc: "2026-09-30T19:41:35Z", note: "day-number kernel used for the ordinal-day subtraction" }
  ],
  disclaimer: null,
  questionText(inputs) {
    return "What day of the year is " + inputs.date + ", and how many days remain in that year?";
  },
  run(inputs) {
    const d = parseISODate(inputs.date, "date");
    const dayOfYear = toJDN(d.year, d.month, d.day) - toJDN(d.year, 1, 1) + 1;
    const daysInYear = isLeapGregorian(d.year) ? 366 : 365;
    const daysRemaining = daysInYear - dayOfYear;
    const answer = "Day " + dayOfYear + " of " + daysInYear + "; " + daysRemaining + " days remaining in the year";
    return { answer, values: { day_of_year: dayOfYear, days_remaining: daysRemaining } };
  },
  examples: [
    { name: "worked example", inputs: { date: "2024-03-01" },
      expected: { answer: "Day 61 of 366; 305 days remaining in the year" },
      check: "2024 is a leap year: January has 31 days and February has 29, so March 1 is day 31+29+1 = 61 of 366" },
    { name: "test vector: last day of a non-leap year", inputs: { date: "2023-12-31" },
      expected: { answer: "Day 365 of 365; 0 days remaining in the year" },
      check: "2023 is not a leap year, so it has 365 days and Dec 31 is the last one" },
    { name: "test vector: first day of year", inputs: { date: "2026-01-01" },
      expected: { answer: "Day 1 of 365; 364 days remaining in the year" },
      check: "2026 is not a leap year (not divisible by 4); January 1 is always day 1" }
  ]
};