var WEEKDAYS = ["Пн", "Вт", "Ср", "Чт", "Пт", "Сб", "Вс"];
var MONTHS = [
  "Январь", "Февраль", "Март", "Апрель", "Май", "Июнь",
  "Июль", "Август", "Сентябрь", "Октябрь", "Ноябрь", "Декабрь"
];

var now = new Date();
var view = { year: now.getFullYear(), month: now.getMonth() };
var selected = null;

var gridEl = document.getElementById("grid");
var monthNameEl = document.getElementById("monthName");
var hintEl = document.getElementById("hint");

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

function fmt(d) {
  return pad(d.getDate()) + "." + pad(d.getMonth() + 1) + "." + d.getFullYear();
}

function renderWeekdays() {
  document.getElementById("weekdays").innerHTML =
    WEEKDAYS.map(function (w) { return "<span>" + w + "</span>"; }).join("");
}

function render() {
  monthNameEl.textContent = MONTHS[view.month] + " " + view.year;

  var first = new Date(view.year, view.month, 1);
  var startPad = (first.getDay() + 6) % 7;
  var daysInMonth = new Date(view.year, view.month + 1, 0).getDate();
  var prevDays = new Date(view.year, view.month, 0).getDate();

  var html = "";

  for (var i = startPad - 1; i >= 0; i--) {
    html += '<div class="day empty">' + (prevDays - i) + "</div>";
  }

  for (var d = 1; d <= daysInMonth; d++) {
    var cls = "day";
    var date = new Date(view.year, view.month, d);

    var isToday =
      date.getFullYear() === now.getFullYear() &&
      date.getMonth() === now.getMonth() &&
      date.getDate() === now.getDate();
    if (isToday) cls += " today";

    if (selected && fmt(date) === fmt(selected)) cls += " selected";

    html += '<div class="' + cls + '" data-date="' + fmt(date) + '">' + d + "</div>";
  }

  var endPad = 7 - ((startPad + daysInMonth) % 7);
  if (endPad < 7) {
    for (var j = 1; j <= endPad; j++) {
      html += '<div class="day empty">' + j + "</div>";
    }
  }

  gridEl.innerHTML = html;
}

function changeMonth(delta) {
  view.month += delta;
  if (view.month < 0) { view.month = 11; view.year--; }
  if (view.month > 11) { view.month = 0; view.year++; }
  selected = null;
  render();
}

function goToday() {
  now = new Date();
  view = { year: now.getFullYear(), month: now.getMonth() };
  selected = null;
  render();
}

gridEl.addEventListener("click", function (e) {
  var day = e.target.closest(".day");
  if (!day || day.classList.contains("empty")) return;
  selected = new Date(view.year, view.month, parseInt(day.textContent, 10));
  hintEl.textContent = "Выбрано: " + fmt(selected);
  render();
});

document.getElementById("prev").addEventListener("click", function () { changeMonth(-1); });
document.getElementById("next").addEventListener("click", function () { changeMonth(1); });
document.getElementById("today").addEventListener("click", goToday);

renderWeekdays();
render();