/**
 * wc-timer
 * @version 1.1.0
 * @description A lightweight, efficient countdown/uptimer Web Component.
 * @license MIT
 */

/**
 * Internal cache for Intl objects to optimize performance.
 * @private
 */
const IntlCache = (() => {
  const cache = new Map();

  function get(Ctor, locale, opts = {}) {
    const key = `${Ctor.name}:${locale}:${JSON.stringify(opts)}`;
    if (!cache.has(key)) {
      cache.set(key, new Ctor(locale, opts));
    }
    return cache.get(key);
  }

  return {
    dtf: (loc, opts) => get(Intl.DateTimeFormat, loc, opts),
    pr: (loc) => get(Intl.PluralRules, loc),
    df: (loc, opts) => get(Intl.DurationFormat, loc, opts),
    hasIDF: typeof Intl !== 'undefined' && 'DurationFormat' in Intl
  };
})();

/**
 * Centralized ticker to sync all instances and prevent drift.
 * @private
 */
const TickHub = (() => {
  const subs = new Set();
  let timer = null;

  function scheduleNext() {
    if (subs.size === 0) return;
    const now = performance.now();
    const msToNext = 1000 - (Math.floor(now) % 1000);

    timer = setTimeout(() => {
      const t = Date.now();
      for (const cb of [...subs]) {
        try { cb(t); } catch (e) { console.error(e); }
      }
      scheduleNext();
    }, msToNext);
  }

  return {
    sub(cb) {
      subs.add(cb);
      if (!timer) scheduleNext();
      return () => {
        subs.delete(cb);
        if (subs.size === 0 && timer) {
          clearTimeout(timer);
          timer = null;
        }
      };
    }
  };
})();

/* ---------------- Locale Helpers ---------------- */
const LABELS = {
  en: {
    y: { long: { one: 'year', other: 'years' }, short: 'y' },
    M: { long: { one: 'month', other: 'months' }, short: 'mo' },
    d: { long: { one: 'day', other: 'days' }, short: 'd' },
    h: { long: { one: 'hour', other: 'hours' }, short: 'h' },
    m: { long: { one: 'minute', other: 'minutes' }, short: 'min' },
    s: { long: { one: 'second', other: 'seconds' }, short: 's' },
  },
  pl: {
    y: { long: { one: 'rok', few: 'lata', many: 'lat', other: 'lat' }, short: 'r.' },
    M: { long: { one: 'miesiąc', few: 'miesiące', many: 'miesięcy', other: 'miesięcy' }, short: 'mies.' },
    d: { long: { one: 'dzień', few: 'dni', many: 'dni', other: 'dni' }, short: 'd' },
    h: { long: { one: 'godzina', few: 'godziny', many: 'godzin', other: 'godzin' }, short: 'godz.' },
    m: { long: { one: 'minuta', few: 'minuty', many: 'minut', other: 'minut' }, short: 'min' },
    s: { long: { one: 'sekunda', few: 'sekundy', many: 'sekund', other: 'sekund' }, short: 's' },
  }
};

function resolveLocale(el) {
  const attr = el.getAttribute('locale') || el.getAttribute('lang');
  if (attr) return attr.toLowerCase();
  return (navigator.language || 'en').toLowerCase();
}

/* ---------------- Date Logic ---------------- */

function diffCalendar(a, b, wantY, wantM) {
  let anchor = new Date(a);
  let y = 0;
  let M = 0;

  if (wantY) {
    y = b.getFullYear() - anchor.getFullYear();
    const probe = new Date(anchor);
    probe.setFullYear(anchor.getFullYear() + y);
    if (probe > b) y--;
    anchor.setFullYear(anchor.getFullYear() + y);
  }

  if (wantM) {
    M = (b.getFullYear() - anchor.getFullYear()) * 12 + (b.getMonth() - anchor.getMonth());
    const probe = new Date(anchor);
    probe.setMonth(anchor.getMonth() + M);
    if (probe > b) M--;
    anchor.setMonth(anchor.getMonth() + M);
  }

  return { y, M, anchor };
}

function collapseForUnits(start, end, show) {
  const { y, M, anchor } = diffCalendar(start, end, !!show.y, !!show.M);
  const base = (show.y || show.M) ? anchor : start;
  let rest = Math.max(0, end - base);

  const MS = { d: 86400000, h: 3600000, m: 60000, s: 1000 };
  const res = { years: y, months: M, days: 0, hours: 0, minutes: 0, seconds: 0 };

  if (show.d) { res.days = Math.floor(rest / MS.d); rest %= MS.d; }
  if (show.h) { res.hours = Math.floor(rest / MS.h); rest %= MS.h; }
  if (show.m) { res.minutes = Math.floor(rest / MS.m); rest %= MS.m; }
  if (show.s) { res.seconds = Math.floor(rest / MS.s); }

  return res;
}

/* ---------------- Formatting ---------------- */
const pad2 = (n) => String(n ?? 0).padStart(2, '0');

function formatDurationSmart(locale, labelsMode, show, parts) {
  if (labelsMode === 'none') {
    const head = [];
    if (show.y) head.push(parts.years);
    if (show.M) head.push(parts.months);
    if (show.d) head.push(parts.days);

    const hms = [pad2(parts.hours), pad2(parts.minutes), pad2(parts.seconds)];
    if (!show.h) hms.shift();

    return [...head, hms.join(':')].join(' ');
  }

  if (IntlCache.hasIDF) {
    const opts = { style: labelsMode === 'short' ? 'short' : 'long' };
    if (show.h) opts.hours = '2-digit';
    if (show.m) opts.minutes = '2-digit';
    if (show.s) opts.seconds = '2-digit';

    const inParts = {};
    for (const key in parts) {
      if (show[key.slice(0, 1)] || show[key.slice(0, 2)]) inParts[key] = parts[key];
    }
    return IntlCache.df(locale, opts).format(inParts);
  }

  // Fallback
  const lang2 = LABELS[locale.slice(0, 2)] ? locale.slice(0, 2) : 'en';
  const L = LABELS[lang2];
  const pr = IntlCache.pr(locale);
  const out = [];

  const add = (k, v, forcePad = false) => {
    const cat = pr.select(v);
    const word = L[k].long[cat] ?? L[k].long.other;
    const num = forcePad ? pad2(v) : v;
    const suffix = labelsMode === 'short' ? L[k].short : word;
    out.push(`${num} ${suffix}`);
  };

  if (show.y) add('y', parts.years);
  if (show.M) add('M', parts.months);
  if (show.d) add('d', parts.days);
  if (show.h) add('h', parts.hours, true);
  if (show.m) add('m', parts.minutes, true);
  if (show.s) add('s', parts.seconds, true);

  return out.join(' ');
}

function getShowConfig(preset, diffMs) {
  const base = { y: false, M: false, d: true, h: true, m: true, s: true };

  switch (preset) {
    case 'hms': return { ...base, d: false };
    case 'dhms': return base;
    case 'ydhms': return { y: true, M: true, d: true, h: true, m: true, s: true };
    case 'auto':
      return diffMs >= 2592000000 ? base : { ...base, d: false };
    default: return base;
  }
}

/* ---------------- Web Component ---------------- */

const sheet = new CSSStyleSheet();
sheet.replaceSync(`
  :host {
    display:inline-block;
    color: inherit;
    user-select: text; -webkit-user-select: text;
    font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
    font-variant-numeric: tabular-nums;
    white-space: nowrap;
    min-height: 1.2em;
    line-height: 1.2;
  }
`);

/**
 * A versatile countdown/uptimer Web Component that renders as selectable text.
 * @element wc-timer
 * @attr {string} target - The target date/time (ISO string or anything Date.parse accepts).
 * @attr {string} [preset="auto"] - Display configuration ('auto', 'hms', 'dhms', 'ydhms', 'date').
 * @attr {string} [labels="short"] - Label style ('none', 'short', 'long').
 * @attr {boolean} [compact] - If set, hides high-order units that are zero.
 * @attr {string} [locale] - Force a specific locale (e.g. 'pl', 'en-US').
 * @example
 * <wc-timer target="2025-01-01T00:00:00Z"></wc-timer>
 * <wc-timer preset="dhms" labels="long" compact></wc-timer>
 */
class WcTimer extends HTMLElement {
  static get observedAttributes() { return ['target', 'preset', 'labels', 'locale', 'lang', 'compact']; }

  #target = new Date();
  #preset = 'auto';
  #labels = 'short';
  #compact = false;
  #locale = 'en';
  #unsub = null;
  #textNode = null;
  #isAttrUpdate = false;

  constructor() {
    super();
    const shadow = this.attachShadow({ mode: 'open' });
    shadow.adoptedStyleSheets = [sheet];
    shadow.appendChild(document.createElement('slot'));
  }

  connectedCallback() {
    // Ensures element has dimensions before JS runs (CLS prevention)
    if (!this.firstChild || this.firstChild.nodeType !== Node.TEXT_NODE) {
      this.textContent = '';
      this.#textNode = document.createTextNode('\u00A0');
      this.appendChild(this.#textNode);
    } else {
      this.#textNode = this.firstChild;
    }

    this.#syncAttrs();
    this.#startTicking();
  }

  disconnectedCallback() {
    this.#stopTicking();
  }

  attributeChangedCallback() {
    if (this.#isAttrUpdate) return;
    this.#syncAttrs();
    this.#render(Date.now());
    this.#checkRestart();
  }

  #syncAttrs() {
    const tRaw = this.getAttribute('target');
    this.#target = tRaw ? new Date(tRaw) : new Date();
    if (isNaN(this.#target)) this.#target = new Date();

    this.#preset = (this.getAttribute('preset') || 'auto').toLowerCase();
    this.#labels = (this.getAttribute('labels') || 'short').toLowerCase();
    this.#compact = this.hasAttribute('compact');
    this.#locale = resolveLocale(this);
  }

  #startTicking() {
    if (!this.#unsub) {
      this.#unsub = TickHub.sub((now) => this.#render(now));
      this.#render(Date.now());
    }
  }

  #stopTicking() {
    if (this.#unsub) {
      this.#unsub();
      this.#unsub = null;
    }
  }

  #checkRestart() {
    const now = Date.now();
    if (this.#target > now && !this.#unsub) {
      this.#startTicking();
    }
  }

  #render(nowMs) {
    if (!this.#textNode) return;

    if (this.#preset === 'date') {
      const dtf = IntlCache.dtf(this.#locale, {
        year: 'numeric', month: '2-digit', day: '2-digit',
        hour: '2-digit', minute: '2-digit', second: '2-digit',
        hour12: false
      });
      const txt = dtf.format(this.#target);
      if (this.#textNode.data !== txt) this.#textNode.data = txt;
      return;
    }

    const now = new Date(nowMs);
    const diff = this.#target - now;
    const isFuture = diff >= 0;

    if (!isFuture && this.#unsub) {
      this.#stopTicking();
    }

    const start = isFuture ? now : this.#target;
    const end = isFuture ? this.#target : now;

    let show = getShowConfig(this.#preset, Math.abs(diff));

    if (this.#compact) {
      const probe = collapseForUnits(start, end, show);
      if (show.y && probe.years === 0) show.y = false;
      if (show.M && !show.y && probe.months === 0) show.M = false;
      if (show.d && !show.y && !show.M && probe.days === 0) show.d = false;

      const probe2 = collapseForUnits(start, end, show);
      if (show.d && show.h && probe2.hours === 0) show.h = false;
    }

    const parts = collapseForUnits(start, end, show);

    let txt = formatDurationSmart(this.#locale, this.#labels, show, parts);
    if (!txt) txt = '00:00:00';

    if (this.#textNode.data !== txt) this.#textNode.data = txt;
  }

  /* Public API */

  /**
   * The target date object.
   * @type {Date}
   */
  get target() { return new Date(this.#target); }
  set target(val) {
    const d = new Date(val);
    if (isNaN(d)) return;
    this.#target = d;
    this.#reflect('target', d.toISOString());
    this.#render(Date.now());
    this.#checkRestart();
  }

  /**
   * Current preset configuration.
   * @type {string} - 'auto' | 'hms' | 'dhms' | 'ydhms' | 'date'
   */
  get preset() { return this.#preset; }
  set preset(val) {
    this.#preset = String(val).toLowerCase();
    this.#reflect('preset', this.#preset);
    this.#render(Date.now());
  }

  /**
   * Label display mode.
   * @type {string} - 'none' | 'short' | 'long'
   */
  get labels() { return this.#labels; }
  set labels(val) {
    this.#labels = String(val).toLowerCase();
    this.#reflect('labels', this.#labels);
    this.#render(Date.now());
  }

  /**
   * Whether compact mode is enabled (hides empty high units).
   * @type {boolean}
   */
  get compact() { return this.#compact; }
  set compact(val) {
    this.#compact = !!val;
    if (this.#compact) this.setAttribute('compact', '');
    else this.removeAttribute('compact');
    this.#isAttrUpdate = true;
    this.#render(Date.now());
    this.#isAttrUpdate = false;
  }

  /**
   * Current locale override.
   * @type {string}
   */
  set locale(val) {
    if (!val) return;
    this.#locale = String(val).toLowerCase();
    this.#reflect('locale', this.#locale);
    this.#render(Date.now());
  }

  #reflect(name, val) {
    this.#isAttrUpdate = true;
    this.setAttribute(name, val);
    this.#isAttrUpdate = false;
  }
}

customElements.define('wc-timer', WcTimer);