/**
 * Locale-aware dates, times and numbers, for both halves of the site.
 *
 * One object per locale, built from that locale's translator, so a page and the island
 * that updates it in place format the same timestamp the same way. Everything that used
 * to be a hand-rolled `toLocaleDateString('en-GB', …)` goes through here now.
 *
 * This file ships to the browser, so it stays small: three cached Intl instances and
 * some arithmetic.
 */
import { intlTag, type Locale } from './config.js';
import type { Translator } from './translate.js';

const MINUTE = 60;
const HOUR = 3600;
const DAY = 86_400;
const WEEK = 604_800;
const MONTH = 2_592_000;
const YEAR = 31_536_000;

/** Largest first: the first threshold a difference clears is the unit it is said in. */
const UNITS: Array<{ key: string; intl: Intl.RelativeTimeFormatUnit; seconds: number }> = [
  { key: 'year', intl: 'year', seconds: YEAR },
  { key: 'month', intl: 'month', seconds: MONTH },
  { key: 'week', intl: 'week', seconds: WEEK },
  { key: 'day', intl: 'day', seconds: DAY },
  { key: 'hour', intl: 'hour', seconds: HOUR },
  { key: 'minute', intl: 'minute', seconds: MINUTE },
];

const relativeFormats = new Map<string, Intl.RelativeTimeFormat>();
const dateFormats = new Map<string, Intl.DateTimeFormat>();
const numberFormats = new Map<string, Intl.NumberFormat>();

function relativeFormat(tag: string): Intl.RelativeTimeFormat {
  let found = relativeFormats.get(tag);
  if (!found) {
    found = new Intl.RelativeTimeFormat(tag, { style: 'short', numeric: 'always' });
    relativeFormats.set(tag, found);
  }
  return found;
}

function dateFormat(tag: string, options: Intl.DateTimeFormatOptions, id: string): Intl.DateTimeFormat {
  const cacheKey = `${tag}:${id}`;
  let found = dateFormats.get(cacheKey);
  if (!found) {
    found = new Intl.DateTimeFormat(tag, options);
    dateFormats.set(cacheKey, found);
  }
  return found;
}

function numberFormat(tag: string): Intl.NumberFormat {
  let found = numberFormats.get(tag);
  if (!found) {
    found = new Intl.NumberFormat(tag);
    numberFormats.set(tag, found);
  }
  return found;
}

export interface Formatters {
  locale: Locale;
  t: Translator;
  /** "4d ago", "hace 4 d", "4 d geleden". The dense form, used in rows and card feet. */
  relative(unix: number | null, now?: number): string;
  /** Magnitude only: "4d". The big number in the verdict strip. */
  shortDuration(unix: number | null, now?: number): string;
  /** "3 Aug 2026". Precise, for a banner where a fuzzy date is not good enough. */
  date(unix: number | null): string;
  /** "3 August 2026". The long form, for a day heading in the review feed. */
  longDate(unix: number): string;
  /** "Mar 2024", for "first seen". */
  monthYear(unix: number): string;
  /** "03/08/2026, 14:20 UTC". The mint's own clock, always in UTC. */
  serverTime(unix: number): string;
  /** Grouped: 1,000,000 in English, 1.000.000 in Spanish and Dutch. */
  number(n: number): string;
  /** Compact: "500K" / "500 mil", for a limit quoted inside a meta description. */
  compact(n: number): string;
  /** A rating to one decimal, with the locale's own decimal separator. */
  decimal(n: number, digits?: number): string;
}

/**
 * Build the formatter set for one locale.
 *
 * Cheap enough to call per component: the Intl instances behind it are cached by tag,
 * and the object itself is a handful of closures.
 */
export function formatters(t: Translator): Formatters {
  const tag = intlTag(t.locale);

  /**
   * The relative form, catalog first.
   *
   * `Intl.RelativeTimeFormat` knows every language's grammar and is the right default,
   * but its short forms are not short enough for this layout: English gives "4 days
   * ago" where the design has room for "4d ago", and these strings sit in card feet and
   * dense review rows that were measured against the compact form.
   *
   * So the catalog gets first refusal, per unit, and Intl is the fallback. A fourth
   * language that never adds a single `time.ago.*` key still renders correct, natural
   * relative times from day one; the three launch languages tune theirs for width.
   */
  const relative = (unix: number | null, now = Date.now() / 1000): string => {
    if (unix === null) return t('time.never');
    const diff = Math.max(0, Math.floor(now - unix));
    if (diff < MINUTE) return t('time.justNow');

    for (const unit of UNITS) {
      if (diff < unit.seconds) continue;
      const n = Math.floor(diff / unit.seconds);
      const key = `time.ago.${unit.key}`;
      if (t.has(key)) return t(key, { n });
      return relativeFormat(tag).format(-n, unit.intl);
    }

    return t('time.justNow');
  };

  const shortDuration = (unix: number | null, now = Date.now() / 1000): string => {
    if (unix === null) return t('time.none');
    const diff = Math.max(0, Math.floor(now - unix));
    // Under a minute still reads as one minute here: this is a magnitude in a big
    // display number, and "0m" says less than "1m".
    if (diff < HOUR) return t('time.short.minute', { n: Math.max(1, Math.floor(diff / MINUTE)) });

    for (const unit of UNITS) {
      if (diff < unit.seconds) continue;
      return t(`time.short.${unit.key}`, { n: Math.floor(diff / unit.seconds) });
    }

    return t('time.short.minute', { n: 1 });
  };

  return {
    locale: t.locale,
    t,
    relative,
    shortDuration,

    date: (unix) =>
      unix === null
        ? t('time.unknownDate')
        : dateFormat(tag, { day: 'numeric', month: 'short', year: 'numeric' }, 'short').format(unix * 1000),

    longDate: (unix) =>
      dateFormat(tag, { day: 'numeric', month: 'long', year: 'numeric' }, 'long').format(unix * 1000),

    monthYear: (unix) =>
      dateFormat(tag, { month: 'short', year: 'numeric' }, 'monthYear').format(unix * 1000),

    serverTime: (unix) =>
      dateFormat(
        tag,
        { dateStyle: 'short', timeStyle: 'short', timeZone: 'UTC' },
        'serverTime',
      ).format(unix * 1000) + ' UTC',

    number: (n) => numberFormat(tag).format(n),

    compact: (n) =>
      new Intl.NumberFormat(tag, { notation: 'compact', maximumFractionDigits: 1 }).format(n),

    decimal: (n, digits = 1) =>
      new Intl.NumberFormat(tag, {
        minimumFractionDigits: digits,
        maximumFractionDigits: digits,
      }).format(n),
  };
}

/** Locale-free, so it lives here beside the rest rather than in two places. */
export function starString(rating: number | null): string {
  if (rating === null) return '☆☆☆☆☆';
  // Ratings are integers 0 to 5 in the data; anything else is clamped rather than
  // trusted, so a stray fractional or out-of-range value can never emit a malformed
  // row (six stars, negative repeat counts, a half glyph).
  const filled = Math.min(5, Math.max(0, Math.round(rating)));
  return '★'.repeat(filled) + '☆'.repeat(5 - filled);
}