// Calendar grid for the trip's date range. Real weeks as rows (Mon–Sun
// columns); days outside the range are greyed. Each in-range day shows its
// entries as compact, type-coloured chips. Clicking a day opens the editor.
import { el } from '../dom.js';
import {
  ENTRY_TYPES,
  typeInfo,
  parseYMD,
  ymd,
  addDays,
  startOfWeekMon,
  formatMoney,
  flightChain,
  hasSegments,
  hasRental,
  isMultiDay,
} from '../format.js';
import { computeStayLayout, renderWeekBands } from './stayBands.js';
import { makeChipDraggable, makeDayDropTarget } from './dragdrop.js';

const WEEKDAYS = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];

export function renderCalendar(tctx) {
  const { trip, entries } = tctx.trip;
  const currency = trip.currency || 'USD';

  // Group entries by date for quick per-cell lookup.
  const byDate = new Map();
  // Derived "dropoff" chips: a rental whose dropoff day differs from its
  // (pickup) entry date gets a secondary chip on the dropoff day.
  const dropoffByDate = new Map();
  // Continuation ghosts: a non-stay multi-day entry marks each following day
  // through end_date with a "…continues" chip.
  const contByDate = new Map();
  for (const entry of entries) {
    if (!byDate.has(entry.date)) byDate.set(entry.date, []);
    byDate.get(entry.date).push(entry);
    if (hasRental(entry)) {
      const dropDate = entry.rental.dropoff && entry.rental.dropoff.date;
      if (dropDate && dropDate !== entry.date) {
        if (!dropoffByDate.has(dropDate)) dropoffByDate.set(dropDate, []);
        dropoffByDate.get(dropDate).push(entry);
      }
    }
    if (entry.type !== 'stay' && isMultiDay(entry)) {
      let d = addDays(parseYMD(entry.date), 1);
      const end = parseYMD(entry.end_date);
      while (d <= end) {
        const k = ymd(d);
        if (!contByDate.has(k)) contByDate.set(k, []);
        contByDate.get(k).push(entry);
        d = addDays(d, 1);
      }
    }
  }

  const stayLayout = computeStayLayout(entries);
  // id -> entry, for the drop handler to resolve the dragged chip.
  const entriesById = new Map(entries.map((e) => [e.id, e]));

  const rangeStart = parseYMD(trip.start_date);
  const rangeEnd = parseYMD(trip.end_date);
  const gridStart = startOfWeekMon(rangeStart);

  const section = el(
    'section',
    { class: 'card calendar-section' },
    el(
      'div',
      { class: 'section-head' },
      el('h2', {}, 'Calendar'),
      el('p', { class: 'muted' }, 'Click a day to add or edit entries.'),
    ),
    legend(),
  );

  // Collect whole weeks (Mon–Sun) covering the range.
  const weeks = [];
  let cursor = gridStart;
  let guard = 0;
  while (cursor <= rangeEnd && guard < 400) {
    const week = [];
    for (let i = 0; i < 7; i++) {
      week.push(cursor);
      cursor = addDays(cursor, 1);
    }
    weeks.push(week);
    guard += 7;
  }

  const cal = el('div', { class: 'calendar' });
  const header = el('div', { class: 'cal-weekdays' });
  for (const label of WEEKDAYS) header.appendChild(el('div', { class: 'cal-weekday' }, label));
  cal.appendChild(header);

  for (const week of weeks) {
    // Each week is a stay-bands strip (all-day bars) above a row of day cells.
    const weekEl = el('div', { class: 'cal-week' });
    const bands = renderWeekBands(week.map(ymd), stayLayout, tctx);
    if (bands) weekEl.appendChild(bands);
    const daysRow = el('div', { class: 'cal-week-days' });
    for (const date of week) {
      daysRow.appendChild(dayCell(date, rangeStart, rangeEnd, byDate, contByDate, dropoffByDate, entriesById, tctx, currency));
    }
    weekEl.appendChild(daysRow);
    cal.appendChild(weekEl);
  }

  // A cancelled drag (released outside a cell) fires dragend on the source chip,
  // which bubbles up here — sweep any lingering drop highlight.
  cal.addEventListener('dragend', () => {
    for (const n of cal.querySelectorAll('.cal-day-drop')) n.classList.remove('cal-day-drop');
  });

  section.appendChild(cal);
  return section;
}

function dayCell(date, rangeStart, rangeEnd, byDate, contByDate, dropoffByDate, entriesById, tctx, currency) {
  const key = ymd(date);
  const inRange = date >= rangeStart && date <= rangeEnd;
  // Stays render as bands, not chips, so exclude them from the day cell.
  const dayEntries = (byDate.get(key) || []).filter((e) => e.type !== 'stay');
  const conts = contByDate.get(key) || [];
  const dropoffs = dropoffByDate.get(key) || [];
  const hasAny = dayEntries.length || conts.length || dropoffs.length;
  const isFirstOfMonth = date.getDate() === 1;

  const cell = el('div', {
    class: `cal-day${inRange ? '' : ' cal-out'}${hasAny ? ' cal-has' : ''}`,
  });

  cell.appendChild(
    el(
      'div',
      { class: 'cal-day-head' },
      el('span', { class: 'cal-daynum' }, String(date.getDate())),
      isFirstOfMonth
        ? el('span', { class: 'cal-month' }, date.toLocaleDateString(undefined, { month: 'short' }))
        : null,
      !inRange && hasAny
        ? el('span', { class: 'cal-flag', title: 'Outside the trip date range' }, '⚠')
        : null,
    ),
  );

  const chips = el('div', { class: 'cal-chips' });
  for (const entry of dayEntries) chips.appendChild(chip(entry, currency));
  // "…continues" ghosts for multi-day entries; click opens the start day.
  for (const entry of conts) chips.appendChild(continuationChip(entry, tctx));
  // Secondary dropoff chips: clicking opens the pickup day where the entry lives.
  for (const entry of dropoffs) chips.appendChild(dropoffChip(entry, tctx));
  cell.appendChild(chips);

  // In-range days are always clickable; out-of-range days only when they hold
  // something (a chip, continuation, or dropoff marker).
  if (inRange || hasAny) {
    cell.classList.add('clickable');
    cell.tabIndex = 0;
    cell.setAttribute('role', 'button');
    cell.addEventListener('click', () => tctx.openDay(key));
    cell.addEventListener('keydown', (e) => {
      if (e.key === 'Enter' || e.key === ' ') {
        e.preventDefault();
        tctx.openDay(key);
      }
    });
  }

  // Only in-range days accept dropped entries; new sort_order appends after the
  // day's current entries (byDate holds every entry, incl. stays, for that day).
  if (inRange) {
    makeDayDropTarget(cell, key, (byDate.get(key) || []).length, entriesById, tctx);
  }

  return cell;
}

function chip(entry, currency) {
  const info = typeInfo(entry.type);
  const hasPrice = entry.price != null;
  const chain = hasSegments(entry) ? flightChain(entry.segments) : '';
  const car = hasRental(entry) ? [entry.rental.brand, entry.rental.model].filter(Boolean).join(' ') : '';
  const label = chain || car || entry.title;
  const node = el(
    'div',
    {
      class: 'cal-chip',
      style: { '--chip': info.color },
      title: `${info.label}: ${chain ? `${entry.title} (${chain})` : entry.title}${hasPrice ? ` · ${formatMoney(entry.price, currency, { compact: true })}` : ''}`,
    },
    el('span', { class: 'chip-icon' }, info.icon),
    el('span', { class: 'chip-text' }, label),
    hasPrice
      ? el('span', { class: 'chip-price' }, formatMoney(entry.price, currency, { compact: true }))
      : null,
  );
  // Regular chips are drag sources (move the entry to another day). The
  // "…continues" and "dropoff" ghost chips and stay bands stay non-draggable.
  makeChipDraggable(node, entry);
  return node;
}

// Ghost chip on the days a multi-day entry spans after its start. Clicking
// opens the START day's editor (where the entry lives).
function continuationChip(entry, tctx) {
  const info = typeInfo(entry.type);
  const node = el(
    'div',
    {
      class: 'cal-chip cal-chip-cont',
      style: { '--chip': info.color },
      role: 'button',
      tabindex: '0',
      title: `${info.label}: ${entry.title} (continues) — opens the start day`,
    },
    el('span', { class: 'chip-icon' }, '⤷'),
    el('span', { class: 'chip-text' }, 'continues'),
  );
  const open = (e) => { e.stopPropagation(); tctx.openDay(entry.date); };
  node.addEventListener('click', open);
  node.addEventListener('keydown', (e) => {
    if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); open(e); }
  });
  return node;
}

// Secondary, outlined chip shown on a rental's dropoff day. Clicking opens the
// PICKUP day's editor (the day the entry actually lives on).
function dropoffChip(entry, tctx) {
  const info = typeInfo(entry.type);
  const car = [entry.rental.brand, entry.rental.model].filter(Boolean).join(' ');
  const node = el(
    'div',
    {
      class: 'cal-chip cal-chip-dropoff',
      style: { '--chip': info.color },
      role: 'button',
      tabindex: '0',
      title: `Rental dropoff${car ? `: ${car}` : ''} — opens the pickup day`,
    },
    el('span', { class: 'chip-icon' }, info.icon),
    el('span', { class: 'chip-text' }, 'dropoff'),
  );
  const open = (e) => { e.stopPropagation(); tctx.openDay(entry.date); };
  node.addEventListener('click', open);
  node.addEventListener('keydown', (e) => {
    if (e.key === 'Enter' || e.key === ' ') { e.preventDefault(); open(e); }
  });
  return node;
}

function legend() {
  const wrap = el('div', { class: 'legend' });
  for (const [type, info] of Object.entries(ENTRY_TYPES)) {
    wrap.appendChild(
      el(
        'span',
        { class: 'legend-item', 'data-type': type },
        el('span', { class: 'legend-dot', style: { background: info.color } }),
        el('span', {}, `${info.icon} ${info.label}`),
      ),
    );
  }
  return wrap;
}