script.js

function gregorianToPersian(gDate) {
  const gy = gDate.getFullYear();
  const gm = gDate.getMonth() + 1;
  const gd = gDate.getDate();
  const gDayOffsets = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334];
  const gy2 = gm > 2 ? gy + 1 : gy;

  let days = 355666 + (365 * gy)
    + Math.floor((gy2 + 3) / 4)
    - Math.floor((gy2 + 99) / 100)
    + Math.floor((gy2 + 399) / 400)
    + gd
    + gDayOffsets[gm - 1];

  let jy = -1595 + (33 * Math.floor(days / 12053));
  days %= 12053;

  jy += 4 * Math.floor(days / 1461);
  days %= 1461;

  if (days > 365) {
    jy += Math.floor((days - 1) / 365);
    days = (days - 1) % 365;
  }

  let jm;
  let jd;

  if (days < 186) {
    jm = 1 + Math.floor(days / 31);
    jd = 1 + (days % 31);
  } else {
    jm = 7 + Math.floor((days - 186) / 30);
    jd = 1 + ((days - 186) % 30);
  }

  return { year: jy, month: jm, date: jd };
}

function persianToGregorian(jy, jm, jd) {
  jy += 1595;

  let days = -355668
    + (365 * jy)
    + (Math.floor(jy / 33) * 8)
    + Math.floor(((jy % 33) + 3) / 4)
    + jd
    + (jm < 7 ? (jm - 1) * 31 : ((jm - 7) * 30) + 186);

  let gy = 400 * Math.floor(days / 146097);
  days %= 146097;

  if (days > 36524) {
    gy += 100 * Math.floor(--days / 36524);
    days %= 36524;
    if (days >= 365) {
      days++;
    }
  }

  gy += 4 * Math.floor(days / 1461);
  days %= 1461;

  if (days > 365) {
    gy += Math.floor((days - 1) / 365);
    days = (days - 1) % 365;
  }

  let gd = days + 1;
  const gregorianMonthDays = [
    0,
    31,
    ((gy % 4 === 0 && gy % 100 !== 0) || (gy % 400 === 0)) ? 29 : 28,
    31,
    30,
    31,
    30,
    31,
    31,
    30,
    31,
    30,
    31
  ];

  let gm = 0;
  for (; gm < 13 && gd > gregorianMonthDays[gm]; gm++) {
    gd -= gregorianMonthDays[gm];
  }

  return new Date(gy, gm - 1, gd);
}

function gregorianToHijri(gDate) {
  const year = gDate.getFullYear();
  const month = gDate.getMonth() + 1;
  const day = gDate.getDate();
  const jd = Math.floor((1461 * (year + 4800 + Math.floor((month - 14) / 12))) / 4) +
    Math.floor((367 * (month - 2 - 12 * Math.floor((month - 14) / 12))) / 12) -
    Math.floor((3 * Math.floor((year + 4900 + Math.floor((month - 14) / 12)) / 100)) / 4) +
    day - 32075;

  let l = jd - 1948440 + 10632;
  const n = Math.floor((l - 1) / 10631);
  l = l - (10631 * n) + 354;

  const j = (Math.floor((10985 - l) / 5316)) * (Math.floor((50 * l) / 17719))
    + (Math.floor(l / 5670)) * (Math.floor((43 * l) / 15238));

  l = l
    - (Math.floor((30 - j) / 15)) * (Math.floor((17719 * j) / 50))
    - (Math.floor(j / 16)) * (Math.floor((15238 * j) / 43))
    + 29;

  const hm = Math.floor((24 * l) / 709);
  const hd = l - Math.floor((709 * hm) / 24);
  const hy = 30 * n + j - 30;

  return { year: hy, month: hm, date: hd };
}

function hijriToGregorian(hy, hm, hd) {
  let jd = Math.floor((11 * hy + 3) / 30) + 354 * hy + 30 * hm - Math.floor((hm - 1) / 2) + hd + 1948440 - 385;
  let l = jd + 68569;
  let n = Math.floor((4 * l) / 146097);
  l = l - Math.floor((146097 * n + 3) / 4);
  let i = Math.floor((4000 * (l + 1)) / 1461001);
  l = l - Math.floor((1461 * i) / 4) + 31;
  let j = Math.floor((80 * l) / 2447);
  let d = l - Math.floor((2447 * j) / 80);
  l = Math.floor(j / 11);
  let m = j + 2 - 12 * l;
  let y = 100 * (n - 49) + i + l;
  return new Date(y, m - 1, d);
}

const dayNamesGreg = ['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'];
const dayNamesPers = ['یکشنبه','دوشنبه','سه‌شنبه','چهارشنبه','پنج‌شنبه','جمعه','شنبه'];
const dayNamesHijri = ['الأحد','الاثنين','الثلاثاء','الأربعاء','الخميس','الجمعة','السبت'];

const persianMonthNames = {
  en: ["Farvardin","Ordibehesht","Khordad","Tir","Mordad","Shahrivar","Mehr","Aban","Azar","Dey","Bahman","Esfand"],
  fa: ["فروردین","اردیبهشت","خرداد","تیر","مرداد","شهریور","مهر","آبان","آذر","دی","بهمن","اسفند"]
};

const hijriMonthNames = {
  en: ["Muharram","Safar","Rabi' al-Awwal","Rabi' al-Thani","Jumada al-Awwal","Jumada al-Thani","Rajab","Sha'ban","Ramadan","Shawwal","Dhu al-Qa'dah","Dhu al-Hijjah"],
  fa: ["محرم","صفر","ربيع الأول","ربيع الثاني","جمادى الأولى","جمادى الثانية","رجب","شعبان","رمضان","شوال","ذو القعدة","ذو الحجة"]
};

const translations = {
  en: {
    pageTitle: "Date Converter",
    gregTitle: "Gregorian (Miladi)",
    persianTitle: "Persian (Jalali)",
    hijriTitle: "Hijri (Qamari)",
    todayBtn: "Set to Today",
    footerDescription: "Universal date converter for Gregorian, Persian, and Hijri calendars.",
    repoLabel: "GitHub Repository",
    seoTitle: "TimeBridge | Universal Date Converter",
    seoDescription: "TimeBridge: Universal date converter for Gregorian, Persian, and Hijri calendars."
  },
  fa: {
    pageTitle: "تبدیل تاریخ‌ها",
    gregTitle: "میلادی",
    persianTitle: "هجری شمسی",
    hijriTitle: "هجری قمری",
    todayBtn: "امروز",
    footerDescription: "تبدیل‌گر تاریخ برای تقویم‌های میلادی، شمسی و قمری.",
    repoLabel: "مخزن گیت‌هاب",
    seoTitle: "TimeBridge | تبدیل تاریخ‌ها",
    seoDescription: "TimeBridge: تبدیل‌گر تاریخ برای تقویم‌های میلادی، شمسی و قمری."
  }
};

let currentLang = 'en';
const byId = (id) => document.getElementById(id);
const gregInput = byId('gregorian');
const persianInput = byId('persian');
const hijriInput = byId('hijri');
const gregDisplay = byId('gregorian-display');
const persianDisplay = byId('persian-display');
const hijriDisplay = byId('hijri-display');
const themeBtn = byId('theme-btn');
const langButtons = { en: byId('lang-en-btn'), fa: byId('lang-fa-btn') };
const textElements = {
  pageTitle: byId('page-title'),
  gregTitle: byId('greg-title'),
  persianTitle: byId('persian-title'),
  hijriTitle: byId('hijri-title'),
  todayBtn: byId('today-btn-text'),
  footerDescription: byId('footer-description'),
  repoLabel: byId('repo-link')
};
const digitMaps = {
  fa: ['۰', '۱', '۲', '۳', '۴', '۵', '۶', '۷', '۸', '۹'],
  ar: ['٠', '١', '٢', '٣', '٤', '٥', '٦', '٧', '٨', '٩']
};

function pad(n) { return n < 10 ? '0' + n : n; }

function convertDigits(value, digits) {
  return String(value).replace(/\d/g, (digit) => digits[Number(digit)]);
}

function localizeNumber(value, locale) {
  return locale ? convertDigits(value, digitMaps[locale]) : String(value);
}

function normalizeDigits(value) {
  return String(value)
    .replace(/[۰-۹]/g, (digit) => String(digit.charCodeAt(0) - 1728))
    .replace(/[٠-٩]/g, (digit) => String(digit.charCodeAt(0) - 1632));
}

function normalizeTextInputValue(input) {
  const normalizedValue = normalizeDigits(input.value);
  if (input.value !== normalizedValue) input.value = normalizedValue;
  return normalizedValue;
}

function localizeInputValue(input, locale) {
  if (!locale || currentLang !== 'fa') return;
  const start = input.selectionStart;
  const end = input.selectionEnd;
  const localizedValue = localizeNumber(normalizeDigits(input.value), locale);
  if (input.value !== localizedValue) {
    input.value = localizedValue;
    if (start !== null && end !== null) input.setSelectionRange(start, end);
  }
}

function getCurrentDate() {
  return gregInput.value ? new Date(gregInput.value) : new Date();
}

function formatCalendarText(date, monthName, weekday, locale) {
  const year = localizeNumber(date.year, locale);
  const day = localizeNumber(date.date, locale);
  return currentLang === 'fa'
    ? `${day} <span class="font-semibold">${monthName}</span> ${year}`
    : `<span class="font-semibold">${monthName}</span> ${day}, ${year}`;
}

function setCalendarOutput(input, display, date, monthNames, weekday, locale) {
  const rawValue = `${date.year}/${pad(date.month)}/${pad(date.date)}`;
  input.value = locale ? localizeNumber(rawValue, locale) : rawValue;
  display.innerHTML = `${formatCalendarText(date, monthNames[currentLang][date.month - 1], weekday, locale)} <span class="text-gray-500 dark:text-gray-400 mx-2">•</span> ${weekday}`;
}

function updateCalendars(date) {
  if (!date || isNaN(date.getTime())) return;
  const weekdayIndex = date.getDay();

  gregInput.value = `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())}`;
  gregDisplay.textContent = `${dayNamesGreg[weekdayIndex]}, ${date.toLocaleString('en-US', { month: 'short' })} ${date.getDate()}, ${date.getFullYear()}`;

  setCalendarOutput(
    persianInput,
    persianDisplay,
    gregorianToPersian(date),
    persianMonthNames,
    currentLang === 'fa' ? dayNamesPers[weekdayIndex] : dayNamesGreg[weekdayIndex],
    currentLang === 'fa' ? 'fa' : null
  );

  setCalendarOutput(
    hijriInput,
    hijriDisplay,
    gregorianToHijri(date),
    hijriMonthNames,
    currentLang === 'fa' ? dayNamesHijri[weekdayIndex] : dayNamesGreg[weekdayIndex],
    currentLang === 'fa' ? 'ar' : null
  );
}

function handleTextCalendarInput(input, converter, locale) {
  const normalizedValue = normalizeTextInputValue(input);
  localizeInputValue(input, locale);
  const parts = normalizedValue.split('/');
  if (parts.length !== 3) return;
  const [year, month, day] = parts.map(Number);
  if (year && month && day) updateCalendars(converter(year, month, day));
}

function switchLanguage(lang) {
  currentLang = lang;
  localStorage.setItem('lang', lang);

  Object.entries(textElements).forEach(([key, element]) => {
    element.textContent = translations[lang][key];
  });

  Object.entries(langButtons).forEach(([key, button]) => {
    button.classList.toggle('bg-blue-600', key === lang);
    button.classList.toggle('text-white', key === lang);
  });

  document.documentElement.dir = lang === 'fa' ? 'rtl' : 'ltr';
  document.documentElement.lang = lang;
  document.title = translations[lang].seoTitle;
  byId('repo-link').textContent = translations[lang].repoLabel;

  const metaDescription = document.querySelector('meta[name="description"]');
  const ogTitle = document.querySelector('meta[property="og:title"]');
  const ogDescription = document.querySelector('meta[property="og:description"]');
  const twitterTitle = document.querySelector('meta[name="twitter:title"]');
  const twitterDescription = document.querySelector('meta[name="twitter:description"]');
  const ogLocale = document.querySelector('meta[property="og:locale"]');

  metaDescription?.setAttribute('content', translations[lang].seoDescription);
  ogTitle?.setAttribute('content', translations[lang].seoTitle);
  ogDescription?.setAttribute('content', translations[lang].seoDescription);
  twitterTitle?.setAttribute('content', translations[lang].seoTitle);
  twitterDescription?.setAttribute('content', translations[lang].seoDescription);
  ogLocale?.setAttribute('content', lang === 'fa' ? 'fa_IR' : 'en_US');

  updateCalendars(getCurrentDate());
}

function toggleTheme() {
  const isDark = document.documentElement.classList.toggle('dark');
  themeBtn.textContent = isDark ? '🌙' : '🌞';
  localStorage.setItem('theme', isDark ? 'dark' : 'light');
}

function setToToday() {
  updateCalendars(new Date());
}

function init() {
  const savedTheme = localStorage.getItem('theme');
  const isDark = savedTheme ? savedTheme === 'dark' : window.matchMedia('(prefers-color-scheme: dark)').matches;
  document.documentElement.classList.toggle('dark', isDark);
  themeBtn.textContent = isDark ? '🌙' : '🌞';
  switchLanguage(localStorage.getItem('lang') || 'en');
  updateCalendars(new Date());
}

gregInput.addEventListener('input', () => {
  if (gregInput.value) updateCalendars(new Date(gregInput.value));
});
persianInput.addEventListener('input', () => handleTextCalendarInput(persianInput, persianToGregorian, 'fa'));
hijriInput.addEventListener('input', () => handleTextCalendarInput(hijriInput, hijriToGregorian, 'ar'));
langButtons.en.addEventListener('click', () => switchLanguage('en'));
langButtons.fa.addEventListener('click', () => switchLanguage('fa'));
themeBtn.addEventListener('click', toggleTheme);
byId('today-btn').addEventListener('click', setToToday);
window.addEventListener('load', init);