import { cookies } from "next/headers";
import { NextResponse } from "next/server";
import { isSessionTokenRevoked, isActionTokenUsed } from "./token-blacklist";

const encoder = new TextEncoder();

interface AdminSession {
  id: string;
  email: string;
  name: string;
  exp: number;
}

interface ActionToken {
  anfrageId: string;
  status: "in_bearbeitung" | "abgeschlossen";
  exp: number;
}

function toBase64Url(buffer: ArrayBuffer | Uint8Array): string {
  const bytes = buffer instanceof Uint8Array ? buffer : new Uint8Array(buffer);
  return btoa(String.fromCharCode(...bytes))
    .replace(/\+/g, "-").replace(/\//g, "_").replace(/=/g, "");
}

function fromBase64Url(str: string): ArrayBuffer {
  const b64 = str.replace(/-/g, "+").replace(/_/g, "/");
  const bytes = Uint8Array.from(atob(b64), (c) => c.charCodeAt(0));
  return bytes.buffer as ArrayBuffer;
}

async function getKey(secret: string): Promise<CryptoKey> {
  return crypto.subtle.importKey(
    "raw",
    encoder.encode(secret),
    { name: "HMAC", hash: "SHA-256" },
    false,
    ["sign", "verify"]
  );
}

export async function createSessionToken(
  session: Omit<AdminSession, "exp">
): Promise<string> {
  const secret = process.env.ADMIN_SESSION_TOKEN!;
  const payload: AdminSession = {
    ...session,
    exp: Math.floor(Date.now() / 1000) + 60 * 60 * 2,
  };
  const data = toBase64Url(encoder.encode(JSON.stringify(payload)));
  const key = await getKey(secret);
  const sig = toBase64Url(await crypto.subtle.sign("HMAC", key, encoder.encode(data)));
  return `${data}.${sig}`;
}

export async function requireAdmin(): Promise<AdminSession | NextResponse> {
  const cookieStore = await cookies();
  const token = cookieStore.get("admin_session")?.value;

  if (!token) {
    return NextResponse.json({ error: "Nicht authentifiziert" }, { status: 401 });
  }

  const session = await verifySessionToken(token);
  if (!session) {
    return NextResponse.json({ error: "Session ungültig" }, { status: 401 });
  }

  return session;
}

export async function verifySessionToken(token: string): Promise<AdminSession | null> {
  try {
    const secret = process.env.ADMIN_SESSION_TOKEN!;
    const [data, sig] = token.split(".");
    if (!data || !sig) return null;

    if (await isSessionTokenRevoked(sig)) return null;

    const key = await getKey(secret);
    const valid = await crypto.subtle.verify(
      "HMAC",
      key,
      fromBase64Url(sig),
      encoder.encode(data)
    );
    if (!valid) return null;

    const session: AdminSession = JSON.parse(
      new TextDecoder().decode(new Uint8Array(fromBase64Url(data)))
    );
    if (session.exp < Math.floor(Date.now() / 1000)) return null;

    return session;
  } catch {
    return null;
  }
}

export async function createActionToken(
  anfrageId: string,
  status: "in_bearbeitung" | "abgeschlossen",
  ablaufTage = 7
): Promise<string> {
  const secret = process.env.ADMIN_SESSION_TOKEN!;
  const payload: ActionToken = {
    anfrageId,
    status,
    exp: Math.floor(Date.now() / 1000) + 60 * 60 * 24 * ablaufTage,
  };
  const data = toBase64Url(encoder.encode(JSON.stringify(payload)));
  const key = await getKey(secret);
  const sig = toBase64Url(await crypto.subtle.sign("HMAC", key, encoder.encode(data)));
  return `${data}.${sig}`;
}

export async function verifyActionToken(
  token: string
): Promise<{ anfrageId: string; status: string } | null> {
  try {
    const secret = process.env.ADMIN_SESSION_TOKEN!;
    const [data, sig] = token.split(".");
    if (!data || !sig) return null;

    if (await isActionTokenUsed(sig)) return null;

    const key = await getKey(secret);
    const valid = await crypto.subtle.verify(
      "HMAC",
      key,
      fromBase64Url(sig),
      encoder.encode(data)
    );
    if (!valid) return null;

    const actionToken: ActionToken = JSON.parse(
      new TextDecoder().decode(new Uint8Array(fromBase64Url(data)))
    );
    if (actionToken.exp < Math.floor(Date.now() / 1000)) return null;

    return { anfrageId: actionToken.anfrageId, status: actionToken.status };
  } catch {
    return null;
  }
}