import { addDays, isoToDate, todayISO } from './stats.js';

const DOW = ['mon', 'tue', 'wed', 'thu', 'fri', 'sat', 'sun'];

function startOfMonth(year, month) {
  return new Date(year, month, 1);
}
function endOfMonth(year, month) {
  return new Date(year, month + 1, 0);
}
function isoOf(d) {
  const y = d.getFullYear();
  const m = String(d.getMonth() + 1).padStart(2, '0');
  const day = String(d.getDate()).padStart(2, '0');
  return `${y}-${m}-${day}`;
}

/**
 * Render a month grid into `root`.
 *
 * @param {HTMLElement} root
 * @param {object} opts
 * @param {number} opts.year
 * @param {number} opts.month        0-indexed (Jan = 0)
 * @param {Array}  opts.goals        all goals
 * @param {Array}  opts.completions  flat completions array
 * @param {string} opts.activeUser   'ray' | 'cer'
 * @param {(args: {iso: string}) => void} opts.onDayClick
 * @param {() => void} opts.onPrev
 * @param {() => void} opts.onNext
 */
export function renderCalendar(root, opts) {
  const { year, month, goals, completions, activeUser, onDayClick, onPrev, onNext } = opts;
  const today = todayISO();

  const goalRange = goals.reduce(
    (acc, g) => ({
      min: g.start_date < acc.min ? g.start_date : acc.min,
      max: g.end_date > acc.max ? g.end_date : acc.max,
    }),
    { min: '9999-12-31', max: '0000-01-01' }
  );

  // Index completions by date for O(1) lookup
  const byDate = new Map();
  for (const c of completions) {
    if (!c.completed) continue;
    if (!byDate.has(c.date)) byDate.set(c.date, []);
    byDate.get(c.date).push(c);
  }

  const first = startOfMonth(year, month);
  const last = endOfMonth(year, month);

  // Use Mon as first column. JS getDay(): 0=Sun..6=Sat → mon-index = (d+6)%7
  const leadBlanks = (first.getDay() + 6) % 7;
  const totalCells = leadBlanks + last.getDate();
  const trailBlanks = (7 - (totalCells % 7)) % 7;

  const monthName = first.toLocaleString(undefined, { month: 'long' });

  // sort goals deterministically (sugar before social)
  const orderedGoals = [...goals].sort((a, b) => {
    if (a.start_date !== b.start_date) return a.start_date.localeCompare(b.start_date);
    return a.id.localeCompare(b.id);
  });

  root.innerHTML = '';

  const head = document.createElement('div');
  head.className = 'cal-head';
  head.innerHTML = `
    <div class="cal-title">${monthName} ${year}</div>
    <div class="cal-nav">
      <button class="iconbtn" data-prev aria-label="Previous month">&lt;</button>
      <button class="iconbtn" data-today aria-label="Today">today</button>
      <button class="iconbtn" data-next aria-label="Next month">&gt;</button>
    </div>
  `;
  head.querySelector('[data-prev]').addEventListener('click', onPrev);
  head.querySelector('[data-next]').addEventListener('click', onNext);
  head.querySelector('[data-today]').addEventListener('click', () => {
    const t = new Date();
    if (opts.onJumpToday) opts.onJumpToday(t.getFullYear(), t.getMonth());
  });
  root.appendChild(head);

  const grid = document.createElement('div');
  grid.className = 'cal-grid';

  // DOW header row
  const dow = document.createElement('div');
  dow.className = 'cal-dow';
  for (const name of DOW) {
    const c = document.createElement('div');
    c.className = 'cal-dow__cell';
    c.textContent = name;
    dow.appendChild(c);
  }
  grid.appendChild(dow);

  // Leading blanks
  for (let i = 0; i < leadBlanks; i++) {
    const c = document.createElement('div');
    c.className = 'cal-cell cal-cell--off';
    grid.appendChild(c);
  }

  // Days
  for (let day = 1; day <= last.getDate(); day++) {
    const d = new Date(year, month, day);
    const iso = isoOf(d);
    const inRange = iso >= goalRange.min && iso <= goalRange.max;
    const isFuture = iso > today;

    const cell = document.createElement('button');
    cell.type = 'button';
    cell.className = 'cal-cell';
    if (!inRange) cell.classList.add('cal-cell--out-of-range');
    if (isFuture) cell.classList.add('cal-cell--future');
    if (iso === today) cell.classList.add('cal-cell--today');
    cell.dataset.iso = iso;

    const dateEl = document.createElement('span');
    dateEl.className = 'cal-cell__date';
    dateEl.textContent = String(day);
    cell.appendChild(dateEl);

    if (inRange) {
      const dotsWrap = document.createElement('div');
      dotsWrap.className = 'cal-cell__grid';
      // 4 dots: rows = goals (orderedGoals[0], orderedGoals[1]); cols = users (ray, cer)
      // Order in DOM: row1col1, row1col2, row2col1, row2col2
      const todays = byDate.get(iso) || [];
      const has = (user, goalId) =>
        todays.some((c) => c.user === user && c.goal_id === goalId && c.completed);

      const layout = [
        ['ray', orderedGoals[0]?.id],
        ['cer', orderedGoals[0]?.id],
        ['ray', orderedGoals[1]?.id],
        ['cer', orderedGoals[1]?.id],
      ];
      for (const [user, goalId] of layout) {
        const dot = document.createElement('span');
        dot.className = `cal-cell__dot cal-cell__dot--${user}`;
        if (goalId && has(user, goalId)) dot.classList.add('cal-cell__dot--on');
        dotsWrap.appendChild(dot);
      }
      cell.appendChild(dotsWrap);
    }

    if (inRange && !isFuture) {
      cell.addEventListener('click', () => onDayClick({ iso }));
    } else {
      cell.disabled = true;
    }

    grid.appendChild(cell);
  }

  // Trailing blanks
  for (let i = 0; i < trailBlanks; i++) {
    const c = document.createElement('div');
    c.className = 'cal-cell cal-cell--off';
    grid.appendChild(c);
  }

  root.appendChild(grid);
}

/* convenient util re-exports */
export { addDays, isoToDate, todayISO };