import { state, saveState } from './app.js';
import { getWorkdays, generatePlan } from './algorithm.js';
import { toggleHoliday, toggleClosure, addHistoryEntries, removeHistoryEntry } from './data.js';
import { exportSchedule, downloadBlob } from './excel.js';

const MONTHS = ['Januar','Februar','März','April','Mai','Juni',
  'Juli','August','September','Oktober','November','Dezember'];
const WD_LABELS = ['Mo','Di','Mi','Do','Fr','Sa','So'];

let currentYear = new Date().getFullYear();
let currentMonth = Math.min(Math.max(new Date().getMonth() + 1, 1), 12);
let currentPlan = []; // [{ date, employeeId, manual }] for displayed month

export function renderCalendar() {
  const container = document.getElementById('tab-planning');
  container.replaceChildren();

  // Title
  const title = document.createElement('h2');
  title.className = 'section-title';
  title.textContent = 'Monatsplanung';
  container.appendChild(title);

  // Controls row
  const controls = document.createElement('div');
  controls.className = 'row';

  const monthLabel = document.createElement('label');
  monthLabel.textContent = 'Monat:';

  const monthSel = document.createElement('select');
  MONTHS.forEach((m, i) => {
    const opt = document.createElement('option');
    opt.value = String(i + 1);
    opt.textContent = m;
    if (i + 1 === currentMonth) opt.selected = true;
    monthSel.appendChild(opt);
  });

  const yearLabel = document.createElement('label');
  yearLabel.textContent = 'Jahr:';

  const yearSel = document.createElement('select');
  const thisYear = new Date().getFullYear();
  for (let y = thisYear - 1; y <= thisYear + 2; y++) {
    const opt = document.createElement('option');
    opt.value = String(y);
    opt.textContent = String(y);
    if (y === currentYear) opt.selected = true;
    yearSel.appendChild(opt);
  }

  const slotsLabel = document.createElement('label');
  slotsLabel.textContent = 'Pro Tag:';

  const slotsSel = document.createElement('select');
  for (let n = 1; n <= 5; n++) {
    const opt = document.createElement('option');
    opt.value = String(n);
    opt.textContent = String(n);
    if (n === state.settings.moderatorsPerDay) opt.selected = true;
    slotsSel.appendChild(opt);
  }

  const genBtn = document.createElement('button');
  genBtn.type = 'button';
  genBtn.className = 'primary';
  genBtn.textContent = 'Plan generieren';

  const exportBtn = document.createElement('button');
  exportBtn.type = 'button';
  exportBtn.textContent = 'Als Excel exportieren';
  exportBtn.style.display = 'none';

  controls.append(monthLabel, monthSel, yearLabel, yearSel, slotsLabel, slotsSel, genBtn, exportBtn);
  container.appendChild(controls);

  // Legend
  const legend = document.createElement('div');
  legend.className = 'cal-legend';
  legend.innerHTML =
    '<span><span class="cal-legend-dot" style="background:#fde68a"></span>Feiertag</span>' +
    '<span><span class="cal-legend-dot" style="background:#fecaca"></span>Betriebsurlaub</span>';
  container.appendChild(legend);

  const warnBox = document.createElement('div');
  warnBox.id = 'skipped-warning';
  warnBox.style.display = 'none';
  container.appendChild(warnBox);

  // Calendar grid wrapper
  const wrapper = document.createElement('div');
  wrapper.className = 'calendar-outer';
  wrapper.id = 'calendar-wrapper';
  container.appendChild(wrapper);

  loadPlanFromHistory();
  renderGrid(wrapper, exportBtn);

  monthSel.addEventListener('change', () => {
    currentMonth = parseInt(monthSel.value);
    loadPlanFromHistory();
    renderGrid(wrapper, exportBtn);
  });

  yearSel.addEventListener('change', () => {
    currentYear = parseInt(yearSel.value);
    loadPlanFromHistory();
    renderGrid(wrapper, exportBtn);
  });

  slotsSel.addEventListener('change', () => {
    state.settings.moderatorsPerDay = parseInt(slotsSel.value, 10);
    saveState();
    renderGrid(wrapper, exportBtn);
  });

  genBtn.addEventListener('click', () => {
    if (state.employees.length === 0) {
      alert('Bitte zuerst Mitarbeiter hinzufügen.');
      return;
    }
    const workdays = getWorkdays(currentYear, currentMonth,
      state.calendar.holidays, state.calendar.companyClosures);
    const prefix = currentYear + '-' + String(currentMonth).padStart(2, '0');
    // Preserve manual picks for this month; only auto-entries get regenerated.
    const manualEntries = state.history.filter(h => h.date.startsWith(prefix) && h.manual);
    const historyWithoutMonth = state.history.filter(h => !h.date.startsWith(prefix));
    // Drop stale auto-entries for the month, keep history + manual picks
    state.history = historyWithoutMonth.concat(manualEntries);
    const result = generatePlan(workdays, state.employees, historyWithoutMonth,
      Math.random, state.settings.moderatorsPerDay, manualEntries);
    addHistoryEntries(state, result.assignments);
    currentPlan = manualEntries.concat(result.assignments);
    saveState();
    renderSkippedWarning(warnBox, result.skippedDates);
    renderGrid(wrapper, exportBtn);
  });

  exportBtn.addEventListener('click', () => {
    if (typeof XLSX === 'undefined') {
      alert('Excel-Export nicht verfügbar (SheetJS konnte nicht geladen werden).');
      return;
    }
    const blob = exportSchedule(currentPlan, state.employees);
    downloadBlob(blob, 'Moderationsplan-' + MONTHS[currentMonth-1] + '-' + currentYear + '.xlsx');
  });
}

function loadPlanFromHistory() {
  const prefix = currentYear + '-' + String(currentMonth).padStart(2,'0');
  currentPlan = state.history
    .filter(h => h.date.startsWith(prefix))
    .map(h => ({ ...h }));
}

function renderGrid(wrapper, exportBtn) {
  wrapper.replaceChildren();

  const daysInMonth = new Date(currentYear, currentMonth, 0).getDate();
  const empNameById = Object.fromEntries(state.employees.map(e => [e.id, e.name]));
  const updateExportVisibility = () => {
    exportBtn.style.display = currentPlan.length > 0 ? 'inline-block' : 'none';
  };

  // Build one day cell. Self-contained so a change to a single day re-renders
  // just that cell (cell.replaceWith) instead of rebuilding the whole grid.
  function makeDayCell(d) {
    const iso = currentYear + '-' + String(currentMonth).padStart(2,'0') + '-' + String(d).padStart(2,'0');
    const wdNum = (() => { const x = new Date(iso + 'T12:00:00Z').getUTCDay(); return x === 0 ? 7 : x; })();
    const isWeekend = wdNum >= 6;
    const isHoliday = state.calendar.holidays.includes(iso);
    const isClosure = state.calendar.companyClosures.includes(iso);

    const cell = document.createElement('div');
    cell.className = 'cal-day';
    if (isWeekend) cell.classList.add('weekend');
    else if (isHoliday) cell.classList.add('holiday');
    else if (isClosure) cell.classList.add('closure');

    const dayNum = document.createElement('div');
    dayNum.className = 'day-num';
    dayNum.textContent = d + ' ';
    const wdSpan = document.createElement('span');
    wdSpan.className = 'day-tag';
    wdSpan.textContent = WD_LABELS[wdNum - 1];
    dayNum.appendChild(wdSpan);
    cell.appendChild(dayNum);

    // Re-render only this cell after a change affecting this day
    const refresh = () => { cell.replaceWith(makeDayCell(d)); updateExportVisibility(); };

    if (!isWeekend) {
      if (isHoliday || isClosure) {
        const tag = document.createElement('div');
        tag.className = 'cal-day-tag-label';
        tag.textContent = isHoliday ? 'Feiertag' : 'Betriebsurlaub';
        const removeBtn = document.createElement('button');
        removeBtn.type = 'button';
        removeBtn.textContent = '✕';
        removeBtn.addEventListener('click', () => {
          if (isHoliday) toggleHoliday(state, iso);
          else toggleClosure(state, iso);
          saveState();
          refresh();
        });
        tag.appendChild(removeBtn);
        cell.appendChild(tag);
      } else {
        const slotCount = state.settings.moderatorsPerDay;
        const dayEntries = currentPlan
          .filter(a => a.date === iso)
          .sort((x, y) =>
            (empNameById[x.employeeId] ?? '').localeCompare(empNameById[y.employeeId] ?? '', 'de'));
        const slotValues = []; // employeeId per slot index, '' if empty
        for (let s = 0; s < slotCount; s++) slotValues.push(dayEntries[s]?.employeeId ?? '');

        for (let slotIdx = 0; slotIdx < slotCount; slotIdx++) {
          const sel = document.createElement('select');
          sel.dataset.slot = String(slotIdx);

          const emptyOpt = document.createElement('option');
          emptyOpt.value = '';
          emptyOpt.textContent = '— Leer —';
          sel.appendChild(emptyOpt);

          for (const emp of state.employees) {
            const opt = document.createElement('option');
            opt.value = emp.id;
            opt.textContent = emp.name; // textContent: safe
            // Disable if already picked in a different slot for this day
            const pickedElsewhere = slotValues.some((id, i) => i !== slotIdx && id === emp.id);
            if (pickedElsewhere) opt.disabled = true;
            if (emp.id === slotValues[slotIdx]) opt.selected = true;
            sel.appendChild(opt);
          }

          sel.addEventListener('change', () => {
            const newId = sel.value;
            const oldId = slotValues[slotIdx];
            if (oldId) {
              removeHistoryEntry(state, iso, oldId);
              currentPlan = currentPlan.filter(a => !(a.date === iso && a.employeeId === oldId));
            }
            if (newId) {
              const entry = { date: iso, employeeId: newId, manual: true };
              addHistoryEntries(state, [entry]);
              currentPlan.push(entry);
            }
            saveState();
            refresh();
          });

          cell.appendChild(sel);
        }

        const btnRow = document.createElement('div');
        btnRow.className = 'cal-btn-row';

        const ftBtn = document.createElement('button');
        ftBtn.type = 'button';
        ftBtn.textContent = 'Feiertag';
        ftBtn.addEventListener('click', () => { toggleHoliday(state, iso); saveState(); refresh(); });

        const buBtn = document.createElement('button');
        buBtn.type = 'button';
        buBtn.textContent = 'Betriebsurl.';
        buBtn.addEventListener('click', () => { toggleClosure(state, iso); saveState(); refresh(); });

        btnRow.append(ftBtn, buBtn);
        cell.appendChild(btnRow);
      }
    }

    return cell;
  }

  // Day-of-week header row
  const headerGrid = document.createElement('div');
  headerGrid.className = 'calendar-header-grid';
  WD_LABELS.forEach(lbl => {
    const cell = document.createElement('div');
    cell.className = 'cal-header-cell';
    cell.textContent = lbl;
    headerGrid.appendChild(cell);
  });
  wrapper.appendChild(headerGrid);

  // Body grid
  const bodyGrid = document.createElement('div');
  bodyGrid.className = 'calendar-body-grid';

  // Offset empty cells before first day
  const firstISO = currentYear + '-' + String(currentMonth).padStart(2,'0') + '-01';
  const firstWD = (() => { const d = new Date(firstISO + 'T12:00:00Z').getUTCDay(); return d === 0 ? 7 : d; })();
  for (let i = 1; i < firstWD; i++) {
    const empty = document.createElement('div');
    empty.className = 'cal-day empty-cell';
    bodyGrid.appendChild(empty);
  }

  // Day cells — each cell can re-render itself; no full-grid rebuild per click
  for (let d = 1; d <= daysInMonth; d++) {
    bodyGrid.appendChild(makeDayCell(d));
  }

  wrapper.appendChild(bodyGrid);
  updateExportVisibility();
}

function renderSkippedWarning(box, skippedDates) {
  box.replaceChildren();
  if (!skippedDates || skippedDates.length === 0) {
    box.style.display = 'none';
    return;
  }
  box.style.display = 'flex';
  box.className = 'skipped-warning';

  const formatted = skippedDates.map(d => {
    const [y, m, day] = d.split('-');
    return day + '.' + m + '.';
  }).join(', ');

  const text = document.createElement('span');
  text.textContent = skippedDates.length === 1
    ? '1 Tag konnte nicht vollständig besetzt werden: ' + formatted
    : skippedDates.length + ' Tage konnten nicht vollständig besetzt werden: ' + formatted;
  box.appendChild(text);

  const closeBtn = document.createElement('button');
  closeBtn.type = 'button';
  closeBtn.textContent = '✕';
  closeBtn.addEventListener('click', () => {
    box.replaceChildren();
    box.style.display = 'none';
  });
  box.appendChild(closeBtn);
}