import { randomBytes, createCipheriv, createDecipheriv } from "node:crypto";

function key(): Buffer {
  const hex = process.env.PM_ENCRYPTION_KEY;
  if (!hex || hex.length !== 64) {
    throw new Error("PM_ENCRYPTION_KEY must be 64 hex chars (32 bytes)");
  }
  return Buffer.from(hex, "hex");
}

// format: base64(iv[12] | tag[16] | ciphertext)
export function encrypt(plain: string): string {
  const iv = randomBytes(12);
  const cipher = createCipheriv("aes-256-gcm", key(), iv);
  const ct = Buffer.concat([cipher.update(plain, "utf8"), cipher.final()]);
  const tag = cipher.getAuthTag();
  return Buffer.concat([iv, tag, ct]).toString("base64");
}

export function decrypt(payload: string): string {
  const buf = Buffer.from(payload, "base64");
  if (buf.length < 28) throw new Error("ciphertext too short");
  const iv = buf.subarray(0, 12);
  const tag = buf.subarray(12, 28);
  const ct = buf.subarray(28);
  const decipher = createDecipheriv("aes-256-gcm", key(), iv);
  decipher.setAuthTag(tag);
  return Buffer.concat([decipher.update(ct), decipher.final()]).toString("utf8");
}