/**
 * Kalenderansicht (plan.md Abschnitt 7): Monat / Woche / Tag.
 *
 * Serverkomponente: laedt Kalender + Reservierungen des Zeitraums
 * serverseitig (Berechtigungspruefung via requireCalendarContext).
 * Die Ansicht selbst ist eine reine Darstellung; das Umschalten der
 * Ansicht/Periode erfolgt ueber URL-Parameter (sharebar, kein State).
 */
import { redirect } from 'next/navigation';
import { prisma } from '@/lib/db/client';
import { requireCalendarContext } from '@/lib/api/context';
import { displayName } from '@/lib/privacy/display';
import { CalendarView } from '@/components/calendar/CalendarView';
import { NewReservationButton } from '@/components/reservation/NewReservationButton';

interface PageProps {
  params: Promise<{ id: string }>;
  searchParams: Promise<{ view?: string; date?: string }>;
}

export default async function CalendarPage({ params, searchParams }: PageProps) {
  const { id } = await params;
  const { view = 'week', date } = await searchParams;

  const context = await requireCalendarContext(id).catch(() => null);
  if (!context) {
    redirect('/login');
  }

  // Zeitfenster bestimmen (UTC-Grenzen; Anzeige in Kalender-Zeitzone).
  const referenceDate = date ? new Date(date) : new Date();
  const { windowStart, windowEnd } = computeWindow(view, referenceDate);

  const reservations = await prisma.reservation.findMany({
    where: {
      calendarId: id,
      status: 'CONFIRMED',
      startAt: { lt: windowEnd },
      endAt: { gt: windowStart },
    },
    orderBy: { startAt: 'asc' },
    select: {
      id: true,
      userId: true,
      title: true,
      startAt: true,
      endAt: true,
      user: { select: { email: true, username: true } },
    },
  });

  return (
    <main className="mx-auto max-w-6xl px-4 py-8">
      <header className="mb-6">
        <h1 className="text-2xl font-bold">{context.calendar.title}</h1>
        {context.calendar.description && (
          <p className="mt-1 text-sm text-slate-600">{context.calendar.description}</p>
        )}
        {!context.calendar.isActive && (
          <p className="mt-2 rounded-md bg-slate-100 px-3 py-2 text-sm text-slate-700 dark:bg-slate-800 dark:text-slate-300">
            Dieser Kalender ist deaktiviert; neue Reservierungen sind nicht moeglich.
          </p>
        )}
      </header>

      <CalendarView
        view={view}
        referenceDate={referenceDate.toISOString()}
        calendarId={id}
        reservations={reservations.map((reservation) => ({
          id: reservation.id,
          title: reservation.title,
          startAt: reservation.startAt.toISOString(),
          endAt: reservation.endAt.toISOString(),
          ownerName: displayName(
            reservation.user.username,
            reservation.user.email,
          ),
          isOwn: reservation.userId === context.user.id,
        }))}
      />

      <div className="mt-6">
        <NewReservationButton
          calendarId={id}
          maxReservationMinutes={context.calendar.maxReservationMinutes}
        />
      </div>
    </main>
  );
}

/** Berechnet das Zeitfenster der gewaehlten Ansicht. */
function computeWindow(
  view: string,
  reference: Date,
): { windowStart: Date; windowEnd: Date } {
  const start = new Date(reference);
  start.setHours(0, 0, 0, 0);
  const end = new Date(start);

  switch (view) {
    case 'day':
      end.setDate(end.getDate() + 1);
      break;
    case 'month':
      start.setDate(1);
      end.setMonth(end.getMonth() + 1, 1);
      break;
    case 'week':
    default:
      // Woche startet montags.
      const weekday = (start.getDay() + 6) % 7;
      start.setDate(start.getDate() - weekday);
      end.setTime(start.getTime());
      end.setDate(end.getDate() + 7);
      break;
  }
  return { windowStart: start, windowEnd: end };
}