import crypto from 'node:crypto'
import { xchacha20poly1305 } from '@noble/ciphers/chacha.js'

/**
 * Authenticated encryption with a key from runtime config (`NUXT_ENCRYPTION_KEY`,
 * base64-encoded 32 bytes). Used to wrap anything sensitive at the app layer
 * before it lands in the DB: AT Proto session blobs, SSH private keys.
 *
 * The KEK is held only in env. If it's lost, every encrypted row becomes
 * unreadable. KEK rotation is a future concern; see PLAN.md.
 */
const NONCE_BYTES = 24
let cachedKey: Uint8Array | undefined

function getKey(): Uint8Array {
  if (cachedKey) return cachedKey
  // Read process.env directly rather than via useRuntimeConfig() so this helper
  // is callable from outside a Nitro request context (e.g. tests, scripts).
  // Nuxt's runtime config still declares the var for documentation; the env
  // name is the same.
  const raw = process.env.NUXT_ENCRYPTION_KEY
  if (!raw) {
    throw new Error('NUXT_ENCRYPTION_KEY is not set (expected base64-encoded 32 bytes)')
  }
  const decoded = Buffer.from(raw, 'base64')
  if (decoded.length !== 32) {
    throw new Error(`NUXT_ENCRYPTION_KEY must decode to 32 bytes, got ${decoded.length}`)
  }
  cachedKey = new Uint8Array(decoded)
  return cachedKey
}

export function encrypt(plaintext: string): { ciphertext: Buffer, nonce: Buffer } {
  const nonce = crypto.randomBytes(NONCE_BYTES)
  const cipher = xchacha20poly1305(getKey(), new Uint8Array(nonce))
  const ciphertext = cipher.encrypt(new TextEncoder().encode(plaintext))
  return { ciphertext: Buffer.from(ciphertext), nonce }
}

export function decrypt(ciphertext: Buffer, nonce: Buffer): string {
  const cipher = xchacha20poly1305(getKey(), new Uint8Array(nonce))
  const plaintext = cipher.decrypt(new Uint8Array(ciphertext))
  return new TextDecoder().decode(plaintext)
}

/** Test/utility hook: drop the cached key so the next call re-reads runtime config. */
export function clearEncryptionKeyCache() {
  cachedKey = undefined
}