class ActiveRecord::Encryption::Cipher::Aes256Gcm

def decrypt(encrypted_message)
  encrypted_data = encrypted_message.payload
  iv = encrypted_message.headers.iv
  auth_tag = encrypted_message.headers.auth_tag
  # Currently the OpenSSL bindings do not raise an error if auth_tag is
  # truncated, which would allow an attacker to easily forge it. See
  # https://github.com/ruby/openssl/issues/63
  raise ActiveRecord::Encryption::Errors::EncryptedContentIntegrity if auth_tag.nil? || auth_tag.bytes.length != 16
  cipher = OpenSSL::Cipher.new(CIPHER_TYPE)
  cipher.decrypt
  cipher.key = @secret
  cipher.iv = iv
  cipher.auth_tag = auth_tag
  cipher.auth_data = ""
  decrypted_data = encrypted_data.empty? ? encrypted_data : cipher.update(encrypted_data)
  decrypted_data << cipher.final
  decrypted_data
rescue OpenSSL::Cipher::CipherError, TypeError, ArgumentError
  raise ActiveRecord::Encryption::Errors::Decryption
end

def encrypt(clear_text)
  # This code is extracted from +ActiveSupport::MessageEncryptor+. Not using it directly because we want to control
  # the message format and only serialize things once at the +ActiveRecord::Encryption::Message+ level. Also, this
  # cipher is prepared to deal with deterministic/non deterministic encryption modes.
  cipher = OpenSSL::Cipher.new(CIPHER_TYPE)
  cipher.encrypt
  cipher.key = @secret
  iv = generate_iv(cipher, clear_text)
  cipher.iv = iv
  encrypted_data = clear_text.empty? ? clear_text.dup : cipher.update(clear_text)
  encrypted_data << cipher.final
  ActiveRecord::Encryption::Message.new(payload: encrypted_data).tap do |message|
    message.headers.iv = iv
    message.headers.auth_tag = cipher.auth_tag
  end
end

def generate_deterministic_iv(clear_text)
  OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, @secret, clear_text)[0, ActiveRecord::Encryption.cipher.iv_length]
end

def generate_iv(cipher, clear_text)
  if @deterministic
    generate_deterministic_iv(clear_text)
  else
    cipher.random_iv
  end
end

def initialize(secret, deterministic: false)
  @secret = secret
  @deterministic = deterministic
end

def iv_length
  OpenSSL::Cipher.new(CIPHER_TYPE).iv_len
end

def key_length
  OpenSSL::Cipher.new(CIPHER_TYPE).key_len
end