import React, { useEffect, useMemo, useState } from 'react';
import { Avatar, Card, EmptyState, ErrorBox, Segmented, Spinner, inputClass } from '../ui/controls';
import { Icon } from '../ui/Icon';
import { MonthGrid } from './MonthGrid';
import { Timeline } from './Timeline';
import { calendarApi, type CalendarUser } from '../../lib/api';
import { useLoader, usePersistentState } from '../../lib/hooks';
import { MONTHS, addDays, addMonths, formatDate, fromIso, mondayOf, monthEnd, monthStart, todayIso } from '../../lib/format';
import { subordinates } from '../team/hierarchy';
import { buildIndex, holidaysOn, shortNames, userColor, vacationRanges, vacationsOn } from './calendarData';

type Mode = 'month' | 'timeline';

/** Tage als "5.10." bzw. "5.–9.10." / "28.9.–2.10." */
function rangeLabel(from: string, to: string) {
  const a = fromIso(from);
  const b = fromIso(to);
  if (from === to) return `${a.getDate()}.${a.getMonth() + 1}.`;
  if (a.getMonth() === b.getMonth()) return `${a.getDate()}.–${b.getDate()}.${b.getMonth() + 1}.`;
  return `${a.getDate()}.${a.getMonth() + 1}.–${b.getDate()}.${b.getMonth() + 1}.`;
}

const dayCount = (n: number) => `${n.toLocaleString('de-DE')} ${n === 1 ? 'Tag' : 'Tage'}`;

/**
 * Kalender fuer alle: genehmigte Urlaube und Feiertage aus HRworks, auch in
 * der Zukunft. Monatsansicht als Standard, dazu eine Zeitleiste je Person.
 */
export const Calendar: React.FC = () => {
  const today = todayIso();
  // Bewusst nicht gemerkt: der Kalender oeffnet immer in der Monatsansicht.
  const [mode, setMode] = useState<Mode>('month');
  const [month, setMonth] = useState(monthStart(today));
  const [selected, setSelected] = useState<string | null>(today);
  const [team, setTeam] = usePersistentState<string>('pulse_calendar_team', 'all');
  const [search, setSearch] = useState('');
  const [onlyAway, setOnlyAway] = usePersistentState('pulse_calendar_only_away', false);

  const gridStart = mondayOf(month);
  const end = monthEnd(month);
  const weeks = Math.ceil(((fromIso(end).getTime() - fromIso(gridStart).getTime()) / 86400000 + 1) / 7);
  const gridEnd = addDays(gridStart, weeks * 7 - 1);

  const data = useLoader(() => calendarApi.get(gridStart, gridEnd), [gridStart, gridEnd]);

  const shift = (delta: number) => {
    const next = addMonths(month, delta);
    setMonth(next);
    setSelected(today.slice(0, 7) === next.slice(0, 7) ? today : null);
  };
  const goToday = () => {
    setMonth(monthStart(today));
    setSelected(today);
  };

  useEffect(() => {
    const onKey = (e: KeyboardEvent) => {
      const target = e.target as HTMLElement | null;
      if (target && ['INPUT', 'SELECT', 'TEXTAREA'].includes(target.tagName)) return;
      if (e.key === 'ArrowLeft') shift(-1);
      if (e.key === 'ArrowRight') shift(1);
    };
    window.addEventListener('keydown', onKey);
    return () => window.removeEventListener('keydown', onKey);
  });

  const users = data.data?.users ?? [];

  // Teams: jeder, dem jemand unterstellt ist, samt allen darunter.
  const leads = useMemo(() => {
    const ids = new Set(users.map((u) => u.manager_id).filter((id): id is number => id != null));
    return users.filter((u) => ids.has(u.id)).sort((a, b) => a.name.localeCompare(b.name, 'de'));
  }, [users]);

  const visibleUsers = useMemo(() => {
    let list: CalendarUser[] = users;
    if (team.startsWith('lead:')) {
      const leadId = Number(team.slice(5));
      const lead = users.find((u) => u.id === leadId);
      // Unbekanntes Team (Vorgesetzter weg): alle zeigen statt einer leeren Seite.
      if (lead) list = [lead, ...subordinates(users, leadId)];
    }
    const q = search.trim().toLowerCase();
    if (q) list = list.filter((u) => u.name.toLowerCase().includes(q));
    return [...list].sort((a, b) => a.name.localeCompare(b.name, 'de'));
  }, [users, team, search]);

  const index = useMemo(
    () => buildIndex(data.data?.days ?? [], new Set(visibleUsers.map((u) => u.id))),
    [data.data, visibleUsers]
  );
  const userMap = useMemo(() => new Map(users.map((u) => [u.id, u])), [users]);
  const names = useMemo(() => shortNames(users), [users]);

  // Wer ist in diesem Monat weg, und wann?
  const monthly = useMemo(
    () =>
      visibleUsers
        .map((u) => ({ user: u, ranges: vacationRanges(index.byUser.get(u.id), month, end) }))
        .filter((x) => x.ranges.length > 0),
    [visibleUsers, index, month, end]
  );

  const timelineUsers = onlyAway ? visibleUsers.filter((u) => monthly.some((m) => m.user.id === u.id)) : visibleUsers;
  const selectedAway = selected
    ? vacationsOn(index, selected)
        .map((d) => ({ entry: d, user: userMap.get(d.user_id)! }))
        .filter((x) => x.user)
        .sort((a, b) => a.user.name.localeCompare(b.user.name, 'de'))
    : [];
  const selectedHolidays = selected ? holidaysOn(index, selected) : [];
  const monthHolidays = useMemo(() => {
    const out: { day: string; labels: string[] }[] = [];
    for (let d = month; d <= end; d = addDays(d, 1)) {
      const labels = holidaysOn(index, d);
      if (labels.length) out.push({ day: d, labels });
    }
    return out;
  }, [index, month, end]);

  const label = `${MONTHS[fromIso(month).getMonth()]} ${fromIso(month).getFullYear()}`;

  return (
    <div className="mx-auto max-w-[1500px]">
      {/* Werkzeugleiste */}
      <div className="mb-4 flex flex-wrap items-center gap-2 sm:gap-3">
        <div className="flex items-center rounded-xl border border-ink-200 bg-surface shadow-card">
          <button onClick={() => shift(-1)} className="rounded-l-xl p-2.5 text-ink-500 hover:bg-ink-50 hover:text-ink-900" aria-label="Vorheriger Monat">
            <Icon name="chevronLeft" className="h-4 w-4" strokeWidth={2.2} />
          </button>
          <button onClick={goToday} className="border-x border-ink-200 px-3 py-2 text-xs font-bold text-ink-600 hover:bg-ink-50">
            Heute
          </button>
          <button onClick={() => shift(1)} className="rounded-r-xl p-2.5 text-ink-500 hover:bg-ink-50 hover:text-ink-900" aria-label="Nächster Monat">
            <Icon name="chevronRight" className="h-4 w-4" strokeWidth={2.2} />
          </button>
        </div>
        <h2 className="tabular min-w-0 flex-1 truncate text-base text-ink-900 sm:flex-none sm:text-lg">{label}</h2>

        <div className="order-last flex w-full flex-wrap items-center gap-2 sm:order-none sm:ml-auto sm:w-auto sm:flex-nowrap">
          <Segmented
            value={mode}
            onChange={setMode}
            className="flex-1 sm:flex-none"
            options={[
              { value: 'month', label: 'Monat', icon: 'calendar', title: 'Monatsansicht' },
              { value: 'timeline', label: 'Zeitleiste', icon: 'list', title: 'Eine Zeile je Mitarbeiter' },
            ]}
          />
          <select
            className={`${inputClass} w-auto min-w-0 max-w-[200px] flex-1 py-2 text-xs font-bold sm:flex-none`}
            value={team.startsWith('lead:') && !leads.some((l) => `lead:${l.id}` === team) ? 'all' : team}
            onChange={(e) => setTeam(e.target.value)}
            title="Team filtern"
          >
            <option value="all">Alle Mitarbeiter</option>
            {leads.map((l) => (
              <option key={l.id} value={`lead:${l.id}`}>
                Team {l.name}
              </option>
            ))}
          </select>
          <div className="relative min-w-0 flex-1 sm:w-44 sm:flex-none">
            <Icon name="search" className="pointer-events-none absolute left-2.5 top-1/2 h-3.5 w-3.5 -translate-y-1/2 text-ink-400" />
            <input
              className={`${inputClass} py-2 pl-8 text-xs`}
              placeholder="Name suchen"
              value={search}
              onChange={(e) => setSearch(e.target.value)}
              aria-label="Name suchen"
            />
          </div>
        </div>
      </div>

      {data.error && <ErrorBox message={data.error} onRetry={data.reload} />}
      {data.loading && !data.data ? (
        <Spinner />
      ) : data.data && !data.data.last_run && data.data.days.length === 0 ? (
        <EmptyState
          icon="calendar"
          title="Noch keine Urlaube übernommen"
          text="Der Kalender füllt sich mit dem nächsten Abgleich aus HRworks (morgens und mittags)."
        />
      ) : (
        <div className="grid gap-4 xl:grid-cols-[minmax(0,1fr)_320px]">
          <div key={`${mode}-${month}`} className="animate-fade min-w-0 space-y-3">
            {mode === 'month' ? (
              <MonthGrid
                month={month}
                gridStart={gridStart}
                weeks={weeks}
                index={index}
                users={userMap}
                names={names}
                selected={selected}
                onSelect={setSelected}
              />
            ) : (
              <>
                <label className="flex w-fit cursor-pointer items-center gap-2 text-xs font-bold text-ink-600">
                  <input type="checkbox" className="accent-[var(--color-brand-500)]" checked={onlyAway} onChange={(e) => setOnlyAway(e.target.checked)} />
                  Nur Mitarbeiter mit Urlaub in diesem Monat
                </label>
                {timelineUsers.length ? (
                  <Timeline month={month} index={index} users={timelineUsers} selected={selected} onSelect={setSelected} />
                ) : (
                  <EmptyState icon="calendar" title="Niemand im Urlaub" text="In diesem Monat ist für die Auswahl kein Urlaub eingetragen." />
                )}
              </>
            )}
            <Legend lastRun={data.data?.last_run ?? null} />
          </div>

          <div className="min-w-0 space-y-4">
            {selected && (
              <Card className="animate-rise p-4">
                <h3 className="text-sm text-ink-900">{formatDate(selected, 'long')}</h3>
                {selectedHolidays.length > 0 && (
                  <p className="mt-2 inline-flex items-center gap-1.5 rounded-lg bg-amber-50 px-2 py-1 text-xs font-bold text-amber-700">
                    <Icon name="sun" className="h-3.5 w-3.5" />
                    {selectedHolidays.join(' · ')}
                  </p>
                )}
                {selectedAway.length ? (
                  <ul className="mt-3 space-y-2">
                    {selectedAway.map(({ entry, user }) => (
                      <li key={user.id} className="flex items-center gap-2.5">
                        <Avatar id={user.id} name={user.name} color={user.color} size={28} external={user.is_external} />
                        <span className="min-w-0 flex-1">
                          <span className="block truncate text-sm font-bold text-ink-800">{user.name}</span>
                          <span className="block text-xs text-ink-400">
                            {entry.label}
                            {entry.half ? ' · halber Tag' : ''}
                          </span>
                        </span>
                      </li>
                    ))}
                  </ul>
                ) : (
                  <p className="mt-2 text-xs text-ink-400">Niemand im Urlaub.</p>
                )}
              </Card>
            )}

            <Card className="animate-rise p-4" style={{ '--i': 1 } as React.CSSProperties}>
              <h3 className="text-sm text-ink-900">Urlaub im {MONTHS[fromIso(month).getMonth()]}</h3>
              {monthly.length ? (
                <ul className="mt-3 space-y-2.5">
                  {monthly.map(({ user, ranges }) => (
                    <li key={user.id} className="flex items-start gap-2.5">
                      <span className="mt-1.5 h-2.5 w-2.5 shrink-0 rounded-full" style={{ background: userColor(user) }} />
                      <span className="min-w-0 flex-1">
                        <span className="block truncate text-sm font-bold text-ink-800">{user.name}</span>
                        <span className="block text-xs text-ink-500">
                          {ranges.map((r) => `${rangeLabel(r.from, r.to)} (${dayCount(r.days)})`).join(', ')}
                        </span>
                      </span>
                    </li>
                  ))}
                </ul>
              ) : (
                <p className="mt-2 text-xs text-ink-400">In diesem Monat ist kein Urlaub eingetragen.</p>
              )}
              {monthHolidays.length > 0 && (
                <div className="mt-4 border-t border-ink-100 pt-3">
                  <p className="mb-1.5 text-[11px] font-extrabold uppercase tracking-wider text-ink-400">Feiertage</p>
                  <ul className="space-y-1 text-xs text-ink-600">
                    {monthHolidays.map((h) => (
                      <li key={h.day}>
                        <b className="tabular text-amber-700">{formatDate(h.day, 'day')}</b> {h.labels.join(' · ')}
                      </li>
                    ))}
                  </ul>
                </div>
              )}
            </Card>
          </div>
        </div>
      )}
    </div>
  );
};

const Legend: React.FC<{ lastRun: string | null }> = ({ lastRun }) => (
  <div className="flex flex-wrap items-center gap-x-4 gap-y-1 px-1 text-[11px] font-semibold text-ink-400">
    <span className="inline-flex items-center gap-1.5">
      <span className="h-2.5 w-4 rounded-sm bg-brand-500" /> Urlaub (genehmigt)
    </span>
    <span className="inline-flex items-center gap-1.5">
      <span className="h-2.5 w-4 rounded-sm bg-brand-500 opacity-50" /> halber Tag
    </span>
    <span className="inline-flex items-center gap-1.5">
      <span className="h-2.5 w-4 rounded-sm border border-amber-200 bg-amber-50" /> Feiertag
    </span>
    {lastRun && <span className="sm:ml-auto">Stand HRworks: {new Date(lastRun).toLocaleString('de-DE', { dateStyle: 'short', timeStyle: 'short' })}</span>}
  </div>
);