/**
 * GET    /api/calendars/[id]/members - Mitgliederliste (nur Admin).
 * POST   /api/calendars/[id]/members - User per E-Mail hinzufuegen (nur Admin).
 * DELETE /api/calendars/[id]/members - Mitglied entfernen (nur Admin).
 *
 * DB-basiertes Einladungssystem: Statt Invite-Links werden Benutzer
 * direkt per E-Mail-Suche ueber die Datenbank zugeordnet. Der Server
 * prueft die Verwaltungsberechtigung zentral (canManageCalendar).
 */
import { NextRequest, NextResponse } from 'next/server';
import { prisma } from '@/lib/db/client';
import { requireCalendarContext } from '@/lib/api/context';
import { addMemberSchema } from '@/lib/validation';
import { canManageCalendar } from '@/lib/permissions/permissions';
import { errorResponse, forbiddenResponse, notFoundResponse } from '@/lib/api/responses';

interface RouteParams {
  params: Promise<{ id: string }>;
}

/** Prueft Admin-Berechtigung fuer die Member-Verwaltung. */
async function requireManageContext(calendarId: string) {
  const context = await requireCalendarContext(calendarId);
  if (!canManageCalendar(context.user, context.calendar)) {
    return null;
  }
  return context;
}

export async function GET(
  _request: NextRequest,
  { params }: RouteParams,
): Promise<NextResponse> {
  try {
    const { id } = await params;
    const context = await requireManageContext(id);
    if (!context) {
      return forbiddenResponse();
    }

    const members = await prisma.calendarMember.findMany({
      where: { calendarId: id },
      orderBy: { createdAt: 'asc' },
      select: {
        id: true,
        createdAt: true,
        user: { select: { id: true, email: true, username: true } },
      },
    });

    return NextResponse.json({ members });
  } catch (error) {
    return errorResponse(error);
  }
}

export async function POST(
  request: NextRequest,
  { params }: RouteParams,
): Promise<NextResponse> {
  try {
    const { id } = await params;
    const context = await requireManageContext(id);
    if (!context) {
      return forbiddenResponse();
    }

    const body = addMemberSchema.parse(await request.json());

    const targetUser = await prisma.user.findUnique({
      where: { email: body.email },
      select: { id: true, email: true },
    });
    if (!targetUser) {
      return notFoundResponse(
        'Kein Benutzer mit dieser E-Mail gefunden. Der Benutzer muss sich zuerst registrieren.',
      );
    }

    // Ein User gehoert genau einem Kalender an (unique auf user_id).
    const existingMembership = await prisma.calendarMember.findUnique({
      where: { userId: targetUser.id },
      select: { calendarId: true },
    });
    if (existingMembership) {
      return NextResponse.json(
        {
          error:
            existingMembership.calendarId === id
              ? 'Dieser Benutzer ist bereits Mitglied dieses Kalenders.'
              : 'Dieser Benutzer ist bereits einem anderen Kalender zugeordnet.',
        },
        { status: 409 },
      );
    }

    const member = await prisma.calendarMember.create({
      data: { calendarId: id, userId: targetUser.id },
      select: {
        id: true,
        createdAt: true,
        user: { select: { id: true, email: true } },
      },
    });

    return NextResponse.json({ member }, { status: 201 });
  } catch (error) {
    return errorResponse(error);
  }
}

export async function DELETE(
  request: NextRequest,
  { params }: RouteParams,
): Promise<NextResponse> {
  try {
    const { id } = await params;
    const context = await requireManageContext(id);
    if (!context) {
      return forbiddenResponse();
    }

    const memberId = request.nextUrl.searchParams.get('memberId');
    if (!memberId) {
      return NextResponse.json(
        { error: 'memberId ist erforderlich.' },
        { status: 400 },
      );
    }

    const member = await prisma.calendarMember.findUnique({
      where: { id: memberId },
      select: { id: true, calendarId: true },
    });
    if (!member || member.calendarId !== id) {
      return notFoundResponse('Mitglied nicht gefunden.');
    }

    await prisma.calendarMember.delete({ where: { id: memberId } });
    return NextResponse.json({ ok: true });
  } catch (error) {
    return errorResponse(error);
  }
}