const crypto = require("node:crypto");

function toBase64Url(value) {
  const source = typeof value === "string" ? value : JSON.stringify(value);
  return Buffer.from(source).toString("base64url");
}

function fromBase64Url(value) {
  return Buffer.from(value, "base64url").toString("utf8");
}

function signPayload(payload, secret) {
  const body = toBase64Url(payload);
  const signature = crypto.createHmac("sha256", secret).update(body).digest("base64url");
  return `${body}.${signature}`;
}

function verifyToken(token, secret) {
  if (typeof token !== "string") {
    return { ok: false, reason: "invalid_format" };
  }

  const segments = token.split(".");
  if (segments.length !== 2) {
    return { ok: false, reason: "invalid_format" };
  }

  const [body, signature] = segments;
  const expected = crypto.createHmac("sha256", secret).update(body).digest("base64url");
  if (signature !== expected) {
    return { ok: false, reason: "invalid_signature" };
  }

  try {
    const payload = JSON.parse(fromBase64Url(body));
    return { ok: true, payload };
  } catch {
    return { ok: false, reason: "invalid_payload" };
  }
}

module.exports = {
  signPayload,
  verifyToken,
};