import { NextResponse } from "next/server";
import { getPayload } from "payload";
import config from "@payload-config";
import { checkRateLimit, getClientIp } from "@/lib/auth/rateLimit";

export const dynamic = "force-dynamic";

// Registration capacity is checked before the insert. Serialize registrations
// for the same event so two simultaneous requests cannot both observe the
// same free seat in this single-process deployment.
const registrationLocks = new Map<string, Promise<void>>();

async function withEventRegistrationLock<T>(eventId: string, action: () => Promise<T>): Promise<T> {
  const previous = registrationLocks.get(eventId) ?? Promise.resolve();
  let release!: () => void;
  const current = new Promise<void>((resolve) => {
    release = resolve;
  });
  registrationLocks.set(eventId, current);
  await previous;
  try {
    return await action();
  } finally {
    release();
    if (registrationLocks.get(eventId) === current) registrationLocks.delete(eventId);
  }
}

type Args = { params: Promise<{ slug: string }> };

export async function POST(request: Request, { params }: Args) {
  const { slug } = await params;

  if (!checkRateLimit(`event-registration:ip:${getClientIp(request)}`, { max: 20, windowMs: 60 * 60 * 1000 })) {
    return NextResponse.json({ error: "Zu viele Anmeldungen. Bitte versuche es später erneut." }, { status: 429 });
  }

  let body: { name?: unknown; email?: unknown };
  try {
    body = await request.json();
  } catch {
    return NextResponse.json({ error: "Ungültige Anfrage." }, { status: 400 });
  }

  const name = typeof body.name === "string" ? body.name.trim() : "";
  const email = typeof body.email === "string" ? body.email.trim().toLowerCase() : "";
  if (!name || name.length > 120 || !email || email.length > 254 || !email.includes("@")) {
    return NextResponse.json({ error: "Bitte gib deinen Namen und eine gültige E-Mail-Adresse an." }, { status: 400 });
  }

  try {
    const payload = await getPayload({ config });

    const { docs } = await payload.find({
      collection: "events",
      where: { slug: { equals: slug } },
      limit: 1,
    });
    const event = docs[0];
    if (!event || event._status !== "published" || !event.registrationRequired) {
      return NextResponse.json({ error: "Dieser Termin wurde nicht gefunden." }, { status: 404 });
    }
    if (!checkRateLimit(`event-registration:email:${event.id}:${email}`, { max: 3, windowMs: 60 * 60 * 1000 })) {
      return NextResponse.json({ error: "Zu viele Anmeldeversuche für diese Adresse. Bitte versuche es später erneut." }, { status: 429 });
    }

    return await withEventRegistrationLock(String(event.id), async () => {
      const { docs: existingForEmail } = await payload.find({
        collection: "event-registrations",
        where: {
          and: [
            { event: { equals: event.id } },
            { email: { equals: email } },
            { status: { equals: "registered" } },
          ],
        },
        limit: 1,
      });
      if (existingForEmail[0]) {
        return NextResponse.json({ ok: true, alreadyRegistered: true });
      }

      if (event.maxParticipants) {
        const { totalDocs } = await payload.count({
          collection: "event-registrations",
          where: { and: [{ event: { equals: event.id } }, { status: { equals: "registered" } }] },
        });
        if (totalDocs >= event.maxParticipants) {
          return NextResponse.json({ error: "Dieser Termin ist bereits ausgebucht." }, { status: 409 });
        }
      }

      await payload.create({
        collection: "event-registrations",
        data: { event: event.id, name, email, status: "registered" },
      });

      return NextResponse.json({ ok: true });
    });
  } catch (error) {
    console.error("event registration failed", error);
    return NextResponse.json({ error: "Die Anmeldung ist gerade nicht möglich. Bitte versuche es später erneut." }, { status: 500 });
  }
}