import { createHmac, timingSafeEqual } from "node:crypto";

function getKey(): string {
  const key = process.env["TOKEN_ENCRYPTION_KEY"];
  if (!key) throw new Error("Missing TOKEN_ENCRYPTION_KEY for reply token verification");
  return key;
}

interface ReplyTokenData {
  actionId: string;
  missionId: string;
  nonce: string;
}

function base64UrlEncode(value: string): string {
  return Buffer.from(value, "utf8").toString("base64url");
}

function base64UrlDecode(value: string): string {
  return Buffer.from(value, "base64url").toString("utf8");
}

function sign(payload: string): string {
  return createHmac("sha256", getKey()).update(payload).digest("base64url");
}

function isReplyTokenData(value: unknown): value is ReplyTokenData {
  if (!value || typeof value !== "object") return false;
  const candidate = value as Record<string, unknown>;
  return (
    typeof candidate["actionId"] === "string" &&
    typeof candidate["missionId"] === "string" &&
    typeof candidate["nonce"] === "string"
  );
}

export function parseReplyAddress(address: string): { token: string } | null {
  const match = address.match(/^reply\+([A-Za-z0-9_-]+\.[A-Za-z0-9_-]+)@/i);
  if (!match) return null;
  return { token: match[1]! };
}

export function verifyReplyToken(token: string): ReplyTokenData | null {
  const [payload, signature] = token.split(".");
  if (!payload || !signature) return null;

  const expected = sign(payload);
  if (!tokensMatch(signature, expected)) return null;

  try {
    const decoded: unknown = JSON.parse(base64UrlDecode(payload));
    return isReplyTokenData(decoded) ? decoded : null;
  } catch {
    return null;
  }
}

export function generateReplyToken(
  actionId: string,
  missionId: string,
  nonce: string,
): string {
  const payload = base64UrlEncode(JSON.stringify({ actionId, missionId, nonce }));
  return `${payload}.${sign(payload)}`;
}

export function tokensMatch(a: string, b: string): boolean {
  try {
    return timingSafeEqual(Buffer.from(a), Buffer.from(b));
  } catch {
    return false;
  }
}