%%%------------------------------------------------------------------------
%% Copyright 2020, OpenTelemetry Authors
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%% http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% @doc An `Observer' is a callback based instrument with a `LastValue' aggregator.
%% On each collection cycle each Observer callback is run and passed an
%% `ObserverInstrument' variable to use when `observe'ing the new value, passing
%% the `ObserverInstrument', the new value and a list of attributes, key/value pairs.
%% @end
%%%-------------------------------------------------------------------------
-module(otel_observer).

%% value containing all information needed by the SDK to record an update
-type instrument() :: term().

-type callback() :: fun((observer_instrument()) -> ok).

%% value containing all information needed by the SDK to record an update
-type observer_instrument() :: term().
-type observer_result() :: {module(), observer_instrument()}.

-export_type([callback/0,
              instrument/0,
              observer_result/0,
              observer_instrument/0]).

-callback set_callback(opentelemetry:meter(), otel_meter:name(), callback()) -> ok.
-callback observe(instrument(), number(), otel_meter:labels()) -> ok.