@callback identify(user :: map()) :: :ok

@callback initialized(tag :: atom()) :: boolean()

@callback new_user(user :: map()) :: user :: term()

@callback set_value(is_on? :: boolean(), flag :: map()) :: flag_builder :: term()

@callback start_instance(sdk_key :: binary(), opts :: map()) ::
  :ok | {:error, atom(), term()}

@callback stop_all_instances() :: :ok

@callback test_flag(flag_name :: binary()) :: {:ok, flag_builder :: term()}

@callback test_update(flag_builder :: term()) :: :ok

@callback track(event_name :: binary(), context :: map(), data :: map()) :: :ok

@callback track(event_name :: binary(), context :: map(), data :: map(), tag :: atom()) ::
  :ok

@callback value_for_all(value :: term(), flag_builder :: term()) :: flag_builder :: term()

@callback variation(flag_name :: binary(), context :: map(), fallback :: term()) :: term()