import crypto from 'node:crypto'

const ALGORITHM = 'chacha20-poly1305'
const NONCE_LENGTH = 12
const TAG_LENGTH = 16

function getKey(): Buffer {
  const hex = process.env.ENCRYPTION_KEY
  if (!hex || hex.length !== 64) {
    throw new Error('ENCRYPTION_KEY must be a 64-character hex string (32 bytes)')
  }
  return Buffer.from(hex, 'hex')
}

export function encrypt(plaintext: string): string {
  const key = getKey()
  const nonce = crypto.randomBytes(NONCE_LENGTH)
  const cipher = crypto.createCipheriv(ALGORITHM, key, nonce, { authTagLength: TAG_LENGTH })
  const encrypted = Buffer.concat([cipher.update(plaintext, 'utf8'), cipher.final()])
  const tag = cipher.getAuthTag()
  return Buffer.concat([nonce, tag, encrypted]).toString('hex')
}

export function decrypt(ciphertext: string): string {
  const key = getKey()
  const buf = Buffer.from(ciphertext, 'hex')
  const nonce = buf.subarray(0, NONCE_LENGTH)
  const tag = buf.subarray(NONCE_LENGTH, NONCE_LENGTH + TAG_LENGTH)
  const encrypted = buf.subarray(NONCE_LENGTH + TAG_LENGTH)
  const decipher = crypto.createDecipheriv(ALGORITHM, key, nonce, { authTagLength: TAG_LENGTH })
  decipher.setAuthTag(tag)
  return decipher.update(encrypted) + decipher.final('utf8')
}