/*
  Fyro Finance — formattazione numeri e date.
  Unico punto dell'app che trasforma numeri in testo da mostrare.
  Regole: vedi "05 — Number formatting" nel design system.
*/

export type Locale = "en" | "it";
export type CurrencyCode = "EUR" | "USD" | "GBP" | "HKD" | "BGN";

const MINUS = "\u2212";
const NBSP = "\u00A0";
const DASH = "—";

const SYMBOLS: Record<string, string> = { EUR: "€", USD: "$", GBP: "£", HKD: "HK$", BGN: "BGN" };

const MONTHS: Record<Locale, string[]> = {
  en: ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"],
  it: ["gen", "feb", "mar", "apr", "mag", "giu", "lug", "ago", "set", "ott", "nov", "dic"],
};

const isMissing = (v: unknown): boolean => v === null || v === undefined || (typeof v === "number" && !Number.isFinite(v));

/** Cifre con separatori del locale. IT raggruppa sempre le migliaia (1.234,56). */
function digits(abs: number, decimals: number, locale: Locale, grouping = true): string {
  const en = abs.toLocaleString("en-US", { minimumFractionDigits: decimals, maximumFractionDigits: decimals, useGrouping: grouping });
  if (locale === "en") return en;
  return en.replace(/,/g, "§").replace(/\./g, ",").replace(/§/g, ".");
}

/** Arrotonda a `decimals` e toglie lo zero negativo, così −0.00 diventa 0.00. */
function round(v: number, decimals: number): number {
  const f = 10 ** decimals;
  const r = Math.round(v * f) / f;
  return Object.is(r, -0) ? 0 : r;
}

function withSymbol(sign: string, num: string, currency: string, locale: Locale): string {
  const sym = SYMBOLS[currency] ?? currency;
  return locale === "en" ? `${sign}${sym}${NBSP}${num}` : `${sign}${num}${NBSP}${sym}`;
}

export interface MoneyOptions {
  locale?: Locale;
  /** Mostra "+" davanti ai positivi (delta, movimenti). */
  signed?: boolean;
  /** Solo valore assoluto: righe dentro una sezione (−) del P&L, dove il segno è già nel titolo. */
  magnitude?: boolean;
  decimals?: number;
}

/** € 1,234.56 · −€ 8,420.00 · 1.234,56 € · — (dato mancante) */
export function formatMoney(value: number | null | undefined, currency: CurrencyCode | string, opts: MoneyOptions = {}): string {
  if (isMissing(value)) return DASH;
  const { locale = "en", signed = false, magnitude = false, decimals = 2 } = opts;
  const r = round(value as number, decimals);
  const sign = r < 0 && !magnitude ? MINUS : r > 0 && signed ? "+" : "";
  return withSymbol(sign, digits(Math.abs(r), decimals, locale), currency, locale);
}

/** Importo in tabella senza simbolo: la valuta sta nell'intestazione di colonna. */
export function formatAmount(value: number | null | undefined, opts: MoneyOptions = {}): string {
  if (isMissing(value)) return DASH;
  const { locale = "en", signed = false, magnitude = false, decimals = 2 } = opts;
  const r = round(value as number, decimals);
  const sign = r < 0 && !magnitude ? MINUS : r > 0 && signed ? "+" : "";
  return sign + digits(Math.abs(r), decimals, locale);
}

/** KPI: € 840 · € 74.2k · € 1.24M  |  IT: 840 € · 74,2k € · 1,24 Mln € */
export function formatMoneyCompact(value: number | null | undefined, currency: CurrencyCode | string, opts: { locale?: Locale; signed?: boolean } = {}): string {
  if (isMissing(value)) return DASH;
  const { locale = "en", signed = false } = opts;
  const v = value as number;
  const abs = Math.abs(v);
  let num: string;
  if (abs >= 1_000_000) {
    num = digits(round(abs / 1_000_000, 2), 2, locale) + (locale === "en" ? "M" : `${NBSP}Mln`);
  } else if (abs >= 1_000) {
    const k = round(abs / 1_000, 1);
    num = k >= 1000 ? digits(round(abs / 1_000_000, 2), 2, locale) + (locale === "en" ? "M" : `${NBSP}Mln`) : digits(k, 1, locale) + "k";
  } else {
    num = digits(round(abs, 0), 0, locale);
  }
  const isZero = round(v, 0) === 0 && abs < 1_000;
  const sign = isZero ? "" : v < 0 ? MINUS : signed ? "+" : "";
  return withSymbol(sign, num, currency, locale);
}

/** 18.4% · 18,4%. `value` è già in punti percentuali (18.4, non 0.184). */
export function formatPct(value: number | null | undefined, opts: { locale?: Locale; decimals?: number; signed?: boolean } = {}): string {
  if (isMissing(value)) return DASH;
  const { locale = "en", decimals = 1, signed = false } = opts;
  const r = round(value as number, decimals);
  const sign = r < 0 ? MINUS : r > 0 && signed ? "+" : "";
  return `${sign}${digits(Math.abs(r), decimals, locale)}%`;
}

/** Variazione % tra due valori: +8.3% · −1.6% · >999% · n/a (base zero o mancante). */
export function formatDelta(current: number | null | undefined, previous: number | null | undefined, opts: { locale?: Locale } = {}): string {
  const { locale = "en" } = opts;
  if (isMissing(current) || isMissing(previous) || previous === 0) return "n/a";
  const pct = (((current as number) - (previous as number)) / Math.abs(previous as number)) * 100;
  if (Math.abs(pct) > 999) return `${pct < 0 ? MINUS : ""}>999%`;
  return formatPct(pct, { locale, signed: true });
}

/** Variazione tra due margini, in punti: +1.2 pp · −1,6 p.p. */
export function formatPp(delta: number | null | undefined, opts: { locale?: Locale } = {}): string {
  const { locale = "en" } = opts;
  if (isMissing(delta)) return DASH;
  const r = round(delta as number, 1);
  const sign = r < 0 ? MINUS : r > 0 ? "+" : "";
  return `${sign}${digits(Math.abs(r), 1, locale)}${NBSP}${locale === "en" ? "pp" : "p.p."}`;
}

/** Colore di un delta. higherIsBetter=false per i costi. */
export function deltaTone(current: number | null | undefined, previous: number | null | undefined, higherIsBetter = true): "positive" | "negative" | "neutral" {
  if (isMissing(current) || isMissing(previous) || previous === 0 || current === previous) return "neutral";
  const up = (current as number) > (previous as number);
  return up === higherIsBetter ? "positive" : "negative";
}

/** Tasso di cambio: sempre 6 decimali, niente separatore delle migliaia. 1.086420 · 1,086420 */
export function formatRate(rate: number | null | undefined, opts: { locale?: Locale } = {}): string {
  if (isMissing(rate)) return DASH;
  return digits(rate as number, 6, opts.locale ?? "en", false);
}

/** Legge "YYYY-MM-DD" come data locale (evita lo slittamento di un giorno per fuso orario). */
function toDate(d: string | Date): Date | null {
  if (d instanceof Date) return Number.isNaN(d.getTime()) ? null : d;
  const m = /^(\d{4})-(\d{2})-(\d{2})/.exec(d);
  if (m) return new Date(Number(m[1]), Number(m[2]) - 1, Number(m[3]));
  const p = new Date(d);
  return Number.isNaN(p.getTime()) ? null : p;
}

/** 12 Mar 2026 · 12 mar 2026 */
export function formatDate(d: string | Date | null | undefined, opts: { locale?: Locale } = {}): string {
  if (!d) return DASH;
  const date = toDate(d);
  if (!date) return DASH;
  const locale = opts.locale ?? "en";
  return `${date.getDate()}${NBSP}${MONTHS[locale][date.getMonth()]}${NBSP}${date.getFullYear()}`;
}

/** Mar 2026 · mar 2026. monthIndex 0–11. */
export function formatMonth(year: number, monthIndex: number, opts: { locale?: Locale } = {}): string {
  return `${MONTHS[opts.locale ?? "en"][monthIndex]}${NBSP}${year}`;
}