import { createCipheriv, createDecipheriv, randomBytes } from "node:crypto";
import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
import { join } from "node:path";

export function loadOrCreateKey(dataDir: string): Buffer {
  mkdirSync(dataDir, { recursive: true });
  const path = join(dataDir, "secret.key");
  if (!existsSync(path)) writeFileSync(path, randomBytes(32), { mode: 0o600 });
  const key = readFileSync(path);
  if (key.length !== 32) throw new Error(`secret.key must be 32 bytes, got ${key.length}`);
  return key;
}

export function encrypt(key: Buffer, plaintext: string): string {
  const iv = randomBytes(12);
  const cipher = createCipheriv("aes-256-gcm", key, iv);
  const ct = Buffer.concat([cipher.update(plaintext, "utf8"), cipher.final()]);
  return "enc:" + Buffer.concat([iv, cipher.getAuthTag(), ct]).toString("base64");
}

export function decrypt(key: Buffer, sealed: string): string {
  if (!sealed.startsWith("enc:")) throw new Error("not an encrypted value");
  const buf = Buffer.from(sealed.slice(4), "base64");
  const decipher = createDecipheriv("aes-256-gcm", key, buf.subarray(0, 12));
  decipher.setAuthTag(buf.subarray(12, 28));
  return Buffer.concat([decipher.update(buf.subarray(28)), decipher.final()]).toString("utf8");
}

export function mask(secret: string): string {
  return secret.length >= 5 ? "…" + secret.slice(-4) : "…";
}