(function () {
  const MONTHS = [
    "Январь", "Февраль", "Март", "Апрель", "Май", "Июнь",
    "Июль", "Август", "Сентябрь", "Октябрь", "Ноябрь", "Декабрь"
  ];

  let current = new Date();
  const calendarEl = document.getElementById("calendar");
  const monthTitleEl = document.getElementById("monthTitle");
  const dutyListEl = document.getElementById("dutyList");
  const loadingEl = document.getElementById("loading");
  const errorEl = document.getElementById("error");

  function isoDate(d) {
    return d.toISOString().slice(0, 10);
  }

  function firstDayOfMonth(d) {
    return new Date(d.getFullYear(), d.getMonth(), 1);
  }

  function lastDayOfMonth(d) {
    return new Date(d.getFullYear(), d.getMonth() + 1, 0);
  }

  function getMonday(d) {
    const day = d.getDay();
    const diff = d.getDate() - day + (day === 0 ? -6 : 1);
    return new Date(d.getFullYear(), d.getMonth(), diff);
  }

  async function fetchDuties(from, to) {
    const base = window.location.origin;
    const url = base + "/api/duties?from=" + encodeURIComponent(from) + "&to=" + encodeURIComponent(to);
    const res = await fetch(url);
    if (!res.ok) throw new Error("Ошибка загрузки");
    return res.json();
  }

  function renderCalendar(year, month, dutiesByDate) {
    const first = firstDayOfMonth(new Date(year, month, 1));
    const last = lastDayOfMonth(new Date(year, month, 1));
    const start = getMonday(first);
    const today = isoDate(new Date());

    calendarEl.innerHTML = "";
    let d = new Date(start);
    const cells = 42;
    for (let i = 0; i < cells; i++) {
      const key = isoDate(d);
      const isOther = d.getMonth() !== month;
      const dayDuties = dutiesByDate[key] || [];
      const isToday = key === today;

      const cell = document.createElement("div");
      cell.className = "day" + (isOther ? " other-month" : "") + (isToday ? " today" : "") + (dayDuties.length ? " has-duty" : "");
      cell.innerHTML =
        "<span class=\"num\">" + d.getDate() + "</span>" +
        (dayDuties.length ? "<span class=\"day-duties\">" + dayDuties.map(function (x) { return x.full_name; }).join(", ") + "</span>" : "");
      calendarEl.appendChild(cell);
      d.setDate(d.getDate() + 1);
    }

    monthTitleEl.textContent = MONTHS[month] + " " + year;
  }

  function renderDutyList(duties) {
    if (duties.length === 0) {
      dutyListEl.innerHTML = "<p class=\"muted\">В этом месяце дежурств нет.</p>";
      return;
    }
    const grouped = {};
    duties.forEach(function (d) {
      const date = d.start_at.slice(0, 10);
      if (!grouped[date]) grouped[date] = [];
      grouped[date].push(d);
    });
    const dates = Object.keys(grouped).sort();
    let html = "";
    dates.forEach(function (date) {
      const list = grouped[date];
      html += "<h2>" + date + "</h2>";
      list.forEach(function (d) {
        const start = d.start_at.slice(11, 16);
        const end = d.end_at.slice(11, 16);
        html += "<div class=\"duty-item\"><span class=\"name\">" + escapeHtml(d.full_name) + "</span><div class=\"time\">" + start + " – " + end + "</div></div>";
      });
    });
    dutyListEl.innerHTML = html;
  }

  function escapeHtml(s) {
    const div = document.createElement("div");
    div.textContent = s;
    return div.innerHTML;
  }

  function dutiesByDate(duties) {
    const byDate = {};
    duties.forEach(function (d) {
      const start = new Date(d.start_at);
      const end = new Date(d.end_at);
      for (let t = new Date(start); t <= end; t.setDate(t.getDate() + 1)) {
        const key = isoDate(t);
        if (!byDate[key]) byDate[key] = [];
        byDate[key].push(d);
      }
    });
    return byDate;
  }

  function showError(msg) {
    errorEl.textContent = msg;
    errorEl.hidden = false;
    loadingEl.classList.add("hidden");
  }

  async function loadMonth() {
    loadingEl.classList.remove("hidden");
    errorEl.hidden = true;
    const from = isoDate(firstDayOfMonth(current));
    const to = isoDate(lastDayOfMonth(current));
    try {
      const duties = await fetchDuties(from, to);
      const byDate = dutiesByDate(duties);
      renderCalendar(current.getFullYear(), current.getMonth(), byDate);
      renderDutyList(duties);
    } catch (e) {
      showError(e.message || "Не удалось загрузить данные.");
      return;
    }
    loadingEl.classList.add("hidden");
  }

  document.getElementById("prevMonth").addEventListener("click", function () {
    current.setMonth(current.getMonth() - 1);
    loadMonth();
  });
  document.getElementById("nextMonth").addEventListener("click", function () {
    current.setMonth(current.getMonth() + 1);
    loadMonth();
  });

  loadMonth();
})();