class ActiveSupport::EncryptedFile

def self.expected_key_length # :nodoc:
  @expected_key_length ||= generate_key.length
end

def self.generate_key
  SecureRandom.hex(ActiveSupport::MessageEncryptor.key_len(CIPHER))
end

def change(&block)
  writing read, &block
end

def check_key_length
  raise InvalidKeyLengthError if key&.length != self.class.expected_key_length
end

def decrypt(contents)
  encryptor.decrypt_and_verify contents
end

def encrypt(contents)
  check_key_length
  encryptor.encrypt_and_sign contents
end

def encryptor
  @encryptor ||= ActiveSupport::MessageEncryptor.new([ key ].pack("H*"), cipher: CIPHER)
end

def handle_missing_key
  raise MissingKeyError.new(key_path: key_path, env_key: env_key) if raise_if_missing_key
end

def initialize(content_path:, key_path:, env_key:, raise_if_missing_key:)
  @content_path = Pathname.new(content_path).yield_self { |path| path.symlink? ? path.realpath : path }
  @key_path = Pathname.new(key_path)
  @env_key, @raise_if_missing_key = env_key, raise_if_missing_key
end

def key
  read_env_key || read_key_file || handle_missing_key
end

def read
  if !key.nil? && content_path.exist?
    decrypt content_path.binread
  else
    raise MissingContentError, content_path
  end
end

def read_env_key
  ENV[env_key].presence
end

def read_key_file
  return @key_file_contents if defined?(@key_file_contents)
  @key_file_contents = (key_path.binread.strip if key_path.exist?)
end

def write(contents)
  IO.binwrite "#{content_path}.tmp", encrypt(contents)
  FileUtils.mv "#{content_path}.tmp", content_path
end

def writing(contents)
  tmp_file = "#{Process.pid}.#{content_path.basename.to_s.chomp('.enc')}"
  tmp_path = Pathname.new File.join(Dir.tmpdir, tmp_file)
  tmp_path.binwrite contents
  yield tmp_path
  updated_contents = tmp_path.binread
  write(updated_contents) if updated_contents != contents
ensure
  FileUtils.rm(tmp_path) if tmp_path&.exist?
end