One API for every network

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

export type VerifyError = "malformed" | "no_signature" | "timestamp" | "mismatch";

/**
 * Verifies a Nowgate-Signature header ("t=<unix seconds>,v1=<hex HMAC-SHA256>")
 * against the raw request body. Pass the exact bytes you received, before any JSON
 * parsing, and every endpoint secret you accept (two while rotating).
 * Returns null when the event is genuine, or the reason it is not.
 */
export function verifyNowgateSignature(
  header: string,
  rawBody: Buffer | string,
  secrets: string[],
  { toleranceSeconds = 300, now = Math.floor(Date.now() / 1000) } = {},
): VerifyError | null {
  let timestamp = 0;
  const signatures: Buffer[] = [];
  for (const part of header.split(",")) {
    const item = part.trim();
    const eq = item.indexOf("=");
    if (eq < 0) return "malformed";
    const key = item.slice(0, eq);
    const value = item.slice(eq + 1);
    if (key === "t") {
      if (timestamp !== 0 || !/^[0-9]+$/.test(value) || Number(value) <= 0) return "malformed";
      timestamp = Number(value);
    } else if (key === "v1") {
      if (!/^[0-9a-fA-F]{64}$/.test(value)) return "malformed";
      signatures.push(Buffer.from(value, "hex"));
    } // other schemes are ignored
  }
  if (timestamp === 0) return "malformed";
  if (signatures.length === 0) return "no_signature";
  if (Math.abs(now - timestamp) > toleranceSeconds) return "timestamp";

  const body = typeof rawBody === "string" ? Buffer.from(rawBody, "utf8") : rawBody;
  let match = false;
  for (const secret of secrets) {
    const expected = createHmac("sha256", secret).update(`${timestamp}.`).update(body).digest();
    for (const signature of signatures) {
      match = timingSafeEqual(expected, signature) || match; // no early exit
    }
  }
  return match ? null : "mismatch";
}