/**
 * Presentation helpers for MoR EIMS tax documents (ADD-P001 print layout).
 *
 * The layout these serve is modelled on the Ministry's own portal rendering of a registered EDR
 * invoice (portal.mor.gov.et), which is the authoritative source for the bilingual field labels —
 * not on any one vendor's template.
 */

/** Ethiopian month names, index 0 = መስከረም. */
const ETHIOPIAN_MONTHS = [
  "መስከረም",
  "ጥቅምት",
  "ኅዳር",
  "ታኅሣሥ",
  "ጥር",
  "የካቲት",
  "መጋቢት",
  "ሚያዝያ",
  "ግንቦት",
  "ሰኔ",
  "ሐምሌ",
  "ነሐሴ",
  "ጳጉሜ",
] as const;

export interface EthiopianDate {
  year: number;
  month: number;
  day: number;
}

/**
 * Gregorian → Ethiopian, via Julian Day Number.
 *
 * JDN rather than day-of-year arithmetic because the Ethiopian new year drifts against September
 * 11/12 on the Gregorian leap cycle; JDN is the same conversion the passenger portal already uses.
 */
export function gregorianToEthiopian(date: Date): EthiopianDate {
  const year = date.getFullYear();
  const month = date.getMonth() + 1;
  const day = date.getDate();

  const a = Math.floor((14 - month) / 12);
  const y = year + 4800 - a;
  const m = month + 12 * a - 3;
  const jdn =
    day +
    Math.floor((153 * m + 2) / 5) +
    365 * y +
    Math.floor(y / 4) -
    Math.floor(y / 100) +
    Math.floor(y / 400) -
    32045;

  // 1723856 is the JDN of 1 መስከረም 1 E.C.
  const r = (jdn - 1723856) % 1461;
  const n = (r % 365) + 365 * Math.floor(r / 1460);
  const ethYear = 4 * Math.floor((jdn - 1723856) / 1461) + Math.floor(r / 365) - Math.floor(r / 1460);
  const ethMonth = Math.floor(n / 30) + 1;
  const ethDay = (n % 30) + 1;

  return { year: ethYear, month: ethMonth, day: ethDay };
}

/** `25-12-2018 ዓ/ም` — the numeric form the MoR portal prints beside the Gregorian date. */
export function formatEthiopianDate(value: Date | string | null | undefined): string {
  const date = value ? new Date(value) : null;
  if (!date || Number.isNaN(date.getTime())) return "-";
  const { year, month, day } = gregorianToEthiopian(date);
  const pad = (n: number) => String(n).padStart(2, "0");
  return `${pad(day)}-${pad(month)}-${year} ዓ/ም`;
}

/** `ሐምሌ 25, 2018` — the long form, when a document has room for it. */
export function formatEthiopianDateLong(value: Date | string | null | undefined): string {
  const date = value ? new Date(value) : null;
  if (!date || Number.isNaN(date.getTime())) return "-";
  const { year, month, day } = gregorianToEthiopian(date);
  return `${ETHIOPIAN_MONTHS[month - 1] ?? ""} ${day}, ${year}`;
}

/** `31-08-2026 G.C` — Gregorian, labelled the way the MoR portal labels it. */
export function formatGregorianDate(value: Date | string | null | undefined): string {
  const date = value ? new Date(value) : null;
  if (!date || Number.isNaN(date.getTime())) return "-";
  const pad = (n: number) => String(n).padStart(2, "0");
  return `${pad(date.getDate())}-${pad(date.getMonth() + 1)}-${date.getFullYear()} G.C`;
}

/** `10:58:30`, 24-hour, to match the portal's `ሰአት/Time` row. */
export function formatDocumentTime(value: Date | string | null | undefined): string {
  const date = value ? new Date(value) : null;
  if (!date || Number.isNaN(date.getTime())) return "-";
  const pad = (n: number) => String(n).padStart(2, "0");
  return `${pad(date.getHours())}:${pad(date.getMinutes())}:${pad(date.getSeconds())}`;
}

const ONES = [
  "",
  "one",
  "two",
  "three",
  "four",
  "five",
  "six",
  "seven",
  "eight",
  "nine",
  "ten",
  "eleven",
  "twelve",
  "thirteen",
  "fourteen",
  "fifteen",
  "sixteen",
  "seventeen",
  "eighteen",
  "nineteen",
];
const TENS = ["", "", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"];
const SCALES: [number, string][] = [
  [1_000_000_000, "billion"],
  [1_000_000, "million"],
  [1_000, "thousand"],
];

/** 0-999 in words. */
function underThousand(value: number): string {
  if (value < 20) return ONES[value];
  if (value < 100) {
    const rest = value % 10;
    return TENS[Math.floor(value / 10)] + (rest ? `-${ONES[rest]}` : "");
  }
  const rest = value % 100;
  return `${ONES[Math.floor(value / 100)]} hundred${rest ? ` and ${underThousand(rest)}` : ""}`;
}

/** Whole number in words. Returns "zero" for 0. */
export function numberToWords(value: number): string {
  const n = Math.floor(Math.abs(value));
  if (n === 0) return "zero";

  const parts: string[] = [];
  let remaining = n;
  for (const [scale, name] of SCALES) {
    const count = Math.floor(remaining / scale);
    if (count > 0) {
      parts.push(`${numberToWords(count)} ${name}`);
      remaining %= scale;
    }
  }
  if (remaining > 0) {
    // "and" only before a trailing sub-hundred group, matching how the amount reads aloud
    // ("three thousand seven hundred and fifty-nine", not "three thousand and seven hundred").
    parts.push(parts.length > 0 && remaining < 100 ? `and ${underThousand(remaining)}` : underThousand(remaining));
  }
  return parts.join(" ");
}

/**
 * `Total including Tax (in words)` — the legally required spelling-out of the payable amount.
 *
 * Computed here rather than read back from MoR: the Ministry renders its own copy on the portal,
 * but returns nothing carrying it on `/v1/register`, and the line has to print on a document that
 * may not be registered yet.
 */
export function amountInWords(value: number, currencyLabel = "Birr", fractionLabel = "Cents"): string {
  const amount = Number.isFinite(value) ? Math.abs(value) : 0;
  const birr = Math.floor(amount);
  // Round the remainder rather than truncate: 0.155 must read as sixteen cents, not fifteen.
  const cents = Math.round((amount - birr) * 100);
  // Rounding cents can carry into the next Birr (x.999 -> 100 cents).
  const [wholeBirr, wholeCents] = cents === 100 ? [birr + 1, 0] : [birr, cents];

  const head = `${numberToWords(wholeBirr)} ${currencyLabel}`;
  const text = wholeCents > 0 ? `${head} and ${numberToWords(wholeCents)} ${fractionLabel}` : head;
  return text.charAt(0).toUpperCase() + text.slice(1);
}