(() => {
  const weeksEl = document.querySelector("#weeks");
  if (!weeksEl) return;

  const appShell = document.querySelector(".app-shell");
  const today = fromISO(appShell.dataset.today);
  const saveUrl = appShell.dataset.saveUrl;
  const statusUrl = appShell.dataset.statusUrl;
  const deleteUrl = appShell.dataset.deleteUrl;
  const savedChoices = JSON.parse(document.querySelector("#saved-choices").textContent);
  const savedStatuses = JSON.parse(document.querySelector("#saved-statuses").textContent);
  const monthLabel = document.querySelector("#visible-month");
  const selectedLabel = document.querySelector("#selected-date");
  const amountControls = document.querySelector("#amount-controls");
  const customAmount = document.querySelector("#custom-amount");
  const saveStatus = document.querySelector("#save-status");
  const dayFormatter = new Intl.DateTimeFormat(undefined, { weekday: "long", month: "long", day: "numeric", year: "numeric" });
  const monthFormatter = new Intl.DateTimeFormat(undefined, { month: "long", year: "numeric" });
  let firstSunday = startOfWeek(addDays(today, -14));
  let lastSunday = addDays(firstSunday, 7 * 13);
  let selectedButton = null;
  let loading = false;
  let previousScrollTop = 0;
  let lastExpansionAt = 0;

  function fromISO(value) {
    const [year, month, day] = value.split("-").map(Number);
    return new Date(year, month - 1, day, 12);
  }

  function addDays(date, count) {
    const next = new Date(date);
    next.setDate(next.getDate() + count);
    return next;
  }

  function startOfWeek(date) { return addDays(date, -date.getDay()); }
  function iso(date) {
    const year = date.getFullYear();
    const month = String(date.getMonth() + 1).padStart(2, "0");
    const day = String(date.getDate()).padStart(2, "0");
    return `${year}-${month}-${day}`;
  }

  function createWeek(sunday) {
    const row = document.createElement("div");
    row.className = "week";
    row.dataset.sunday = iso(sunday);
    row.setAttribute("role", "row");

    for (let index = 0; index < 7; index += 1) {
      const date = addDays(sunday, index);
      const button = document.createElement("button");
      button.type = "button";
      button.className = `day${index === 0 || index === 6 ? " is-weekend" : ""}${iso(date) === iso(today) ? " is-today" : ""}`;
      button.dataset.date = iso(date);
      button.innerHTML = `<span class="day-number">${date.getDate()}</span><span class="day-amount"></span>`;
      button.setAttribute("role", "gridcell");
      button.setAttribute("aria-label", dayFormatter.format(date));
      if (iso(date) === iso(today)) button.setAttribute("aria-current", "date");
      applySavedChoice(button);
      applySavedStatus(button);
      button.addEventListener("click", () => selectDate(button, date));
      row.appendChild(button);
    }
    return row;
  }

  function appendWeeks(count) {
    const fragment = document.createDocumentFragment();
    for (let i = 0; i < count; i += 1) {
      lastSunday = addDays(lastSunday, 7);
      fragment.appendChild(createWeek(lastSunday));
    }
    weeksEl.appendChild(fragment);
  }

  function prependWeeks(count) {
    const oldHeight = weeksEl.scrollHeight;
    const fragment = document.createDocumentFragment();
    for (let i = count; i >= 1; i -= 1) fragment.appendChild(createWeek(addDays(firstSunday, -7 * i)));
    firstSunday = addDays(firstSunday, -7 * count);
    weeksEl.prepend(fragment);
    weeksEl.scrollTop += weeksEl.scrollHeight - oldHeight;
  }

  function selectDate(button, date) {
    selectedButton?.classList.remove("is-selected");
    selectedButton?.removeAttribute("aria-selected");
    selectedButton = button;
    button.classList.add("is-selected");
    button.setAttribute("aria-selected", "true");
    selectedLabel.textContent = dayFormatter.format(date);
    amountControls.hidden = false;
    saveStatus.textContent = savedChoices[iso(date)] === undefined ? "Choose an amount." : `${formatAmount(savedChoices[iso(date)])} saved.`;
    customAmount.value = "";
    updateStatusButtons(savedStatuses[iso(date)] || "worked");
  }

  function formatAmount(cents) {
    return new Intl.NumberFormat(undefined, { style: "currency", currency: "EUR" }).format(cents / 100);
  }

  function applySavedChoice(button) {
    const cents = savedChoices[button.dataset.date];
    button.classList.toggle("has-amount", cents !== undefined);
    const amountLabel = button.querySelector(".day-amount");
    if (amountLabel) amountLabel.textContent = cents === undefined ? "" : formatAmount(cents);
  }

  function applySavedStatus(button) {
    const status = savedStatuses[button.dataset.date] || "worked";
    button.classList.toggle("is-vacation", status === "vacation");
    button.classList.toggle("is-sick", status === "sick");
  }

  function updateStatusButtons(status) {
    document.querySelectorAll("[data-status]").forEach((button) => {
      const selected = button.dataset.status === status;
      button.classList.toggle("is-active", selected);
      button.setAttribute("aria-pressed", String(selected));
    });
  }

  async function saveAmount(amount) {
    if (!selectedButton) return;
    saveStatus.textContent = "Saving…";
    try {
      const response = await fetch(saveUrl, {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ date: selectedButton.dataset.date, amount }),
      });
      const result = await response.json();
      if (!response.ok) throw new Error(result.error || "Could not save the amount.");
      savedChoices[result.date] = result.amount_cents;
      applySavedChoice(selectedButton);
      saveStatus.textContent = `${formatAmount(result.amount_cents)} saved.`;
    } catch (error) {
      saveStatus.textContent = error.message;
    }
  }

  async function saveDayStatus(status) {
    if (!selectedButton) return;
    saveStatus.textContent = "Saving…";
    try {
      const response = await fetch(statusUrl, {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ date: selectedButton.dataset.date, status }),
      });
      const result = await response.json();
      if (!response.ok) throw new Error(result.error || "Could not save the day status.");
      savedStatuses[result.date] = result.status;
      applySavedStatus(selectedButton);
      updateStatusButtons(result.status);
      saveStatus.textContent = `${result.status[0].toUpperCase()}${result.status.slice(1)} saved.`;
    } catch (error) {
      saveStatus.textContent = error.message;
    }
  }

  async function deleteDateData() {
    if (!selectedButton) return;
    const selectedDate = selectedButton.dataset.date;
    if (!window.confirm(`Delete all saved data for ${dayFormatter.format(fromISO(selectedDate))}?`)) return;
    saveStatus.textContent = "Deleting…";
    try {
      const response = await fetch(deleteUrl, {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ date: selectedDate }),
      });
      const result = await response.json();
      if (!response.ok) throw new Error(result.error || "Could not delete the date data.");
      delete savedChoices[result.date];
      delete savedStatuses[result.date];
      applySavedChoice(selectedButton);
      applySavedStatus(selectedButton);
      updateStatusButtons("worked");
      customAmount.value = "";
      saveStatus.textContent = "All saved data for this date was deleted.";
    } catch (error) {
      saveStatus.textContent = error.message;
    }
  }

  function updateMonth() {
    const rows = [...weeksEl.querySelectorAll(".week")];
    const marker = weeksEl.getBoundingClientRect().top + Math.min(100, weeksEl.clientHeight / 3);
    const visible = rows.find((row) => row.getBoundingClientRect().bottom >= marker) || rows[0];
    if (visible) monthLabel.textContent = monthFormatter.format(addDays(fromISO(visible.dataset.sunday), 3));
  }

  for (let i = 0; i < 14; i += 1) weeksEl.appendChild(createWeek(addDays(firstSunday, i * 7)));
  lastSunday = addDays(firstSunday, 13 * 7);
  updateMonth();

  weeksEl.addEventListener("scroll", () => {
    if (loading) return;
    const currentScrollTop = weeksEl.scrollTop;
    const direction = currentScrollTop > previousScrollTop ? "down" : "up";
    previousScrollTop = currentScrollTop;
    loading = true;
    requestAnimationFrame(() => {
      const now = Date.now();
      const canExpand = now - lastExpansionAt > 250;
      if (canExpand && direction === "up" && weeksEl.scrollTop < 80) {
        prependWeeks(3);
        previousScrollTop = weeksEl.scrollTop;
        lastExpansionAt = now;
      } else if (canExpand && direction === "down" && weeksEl.scrollHeight - weeksEl.scrollTop - weeksEl.clientHeight < 160) {
        appendWeeks(3);
        lastExpansionAt = now;
      }
      updateMonth();
      loading = false;
    });
  }, { passive: true });

  document.querySelectorAll("[data-today-button]").forEach((button) => {
    button.addEventListener("click", () => {
      const target = weeksEl.querySelector(`[data-date="${iso(today)}"]`);
      if (target) {
        target.scrollIntoView({ block: "center", behavior: "smooth" });
        selectDate(target, today);
      } else {
        window.location.reload();
      }
    });
  });

  document.querySelectorAll("[data-amount]").forEach((button) => {
    button.addEventListener("click", () => saveAmount(button.dataset.amount));
  });

  document.querySelectorAll("[data-status]").forEach((button) => {
    button.addEventListener("click", () => saveDayStatus(button.dataset.status));
  });

  document.querySelector("#custom-amount-form").addEventListener("submit", (event) => {
    event.preventDefault();
    if (customAmount.reportValidity()) saveAmount(customAmount.value);
  });

  document.querySelector("#delete-date-button").addEventListener("click", deleteDateData);
})();