-module(prometheus_cowboy).

-behaviour(application).
-export([start/2, stop/1]).
-behaviour(supervisor).
-export([init/1]).

-export([to_cowboy_headers/1]).

%% ===================================================================
%% Application & supervisor callbacks
%% ===================================================================

start(_, _) ->
  case code:ensure_loaded(cowboy_metrics_h) of
    {module, _} -> prometheus_cowboy2_instrumenter:setup();
    _ -> ok
  end,
  supervisor:start_link({local, ?MODULE}, ?MODULE, []).

stop(_) -> ok.

init([]) ->
  {ok, {{one_for_one, 0, 1}, []}}.

%% ===================================================================
%% API
%% ===================================================================

to_cowboy_headers(RespHeaders) ->
  lists:map(fun to_cowboy_headers_/1, RespHeaders).

%% ===================================================================
%% Private functions
%% ===================================================================

to_cowboy_headers_({Name, Value}) ->
  {to_cowboy_name(Name), Value}.

to_cowboy_name(Name) ->
  binary:replace(atom_to_binary(Name, utf8), <<"_">>, <<"-">>).