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-module(nats_hd).
%% -compile([bin_opt_info]).

-export([header/2, header/1, headers/1]).
-export([parse_headers/1]).

-type status() :: 100..999.
-export_type([status/0]).

-type headers() :: [{binary(), iodata()}].
-export_type([headers/0]).

-define(NL, ~"\r\n").

-spec header(status() | binary(), headers()) -> iolist().
header(Status, Headers) ->
    [version(), ~" ", status(Status), ?NL, headers(Headers)].

-spec header(headers()) -> iolist().
header(Headers) ->
    [version(), ?NL, headers(Headers)].

-spec headers(headers()) -> iolist().
headers(Headers) ->
    [[N, ~": ", V, ?NL] || {N, V} <- Headers].

version() ->
    ~"NATS/1.0".

status(X) when is_integer(X) ->
    integer_to_binary(X);
status(X) when is_binary(X) ->
    X.

%% @doc Parse the list of headers.
%% copied from cowlib

-spec parse_headers(binary()) -> [{binary(), binary()}].
parse_headers(Data) ->
    parse_header(Data, []).

parse_header(<<>>, Acc) ->
    lists:reverse(Acc);
parse_header(<<Data/binary>>, Acc) ->
    parse_hd_name(Data, Acc, <<>>).

parse_hd_name(<<>>, Acc, << $\r, $\n>>) ->
    parse_header(<<>>, Acc);
parse_hd_name(<< C, Rest/binary >>, Acc, SoFar) ->
    case C of
        $: -> parse_hd_before_value(Rest, Acc, SoFar);
        $\s -> parse_hd_name_ws(Rest, Acc, SoFar);
        $\t -> parse_hd_name_ws(Rest, Acc, SoFar);
        _ -> parse_hd_name(Rest, Acc, <<SoFar/binary, C>>)
    end.

parse_hd_name_ws(<< C, Rest/binary >>, Acc, Name) ->
    case C of
        $: -> parse_hd_before_value(Rest, Acc, Name);
        $\s -> parse_hd_name_ws(Rest, Acc, Name);
        $\t -> parse_hd_name_ws(Rest, Acc, Name)
    end.

parse_hd_before_value(<< $\s, Rest/binary >>, Acc, Name) ->
    parse_hd_before_value(Rest, Acc, Name);
parse_hd_before_value(<< $\t, Rest/binary >>, Acc, Name) ->
    parse_hd_before_value(Rest, Acc, Name);
parse_hd_before_value(Data, Acc, Name) ->
    parse_hd_value(Data, Acc, Name, <<>>).

parse_hd_value(<< $\r, $\n, Rest/binary >>, Acc, Name, SoFar) ->
    Value = clean_value_ws_end(SoFar, byte_size(SoFar) - 1),
    parse_header(Rest, [{Name, Value}|Acc]);
parse_hd_value(<< C, Rest/binary >>, Acc, Name, SoFar) ->
    parse_hd_value(Rest, Acc, Name, << SoFar/binary, C >>).

%% This function has been copied from cowboy_http.
clean_value_ws_end(_, -1) ->
    <<>>;
clean_value_ws_end(Value, N) ->
    case binary:at(Value, N) of
        $\s -> clean_value_ws_end(Value, N - 1);
        $\t -> clean_value_ws_end(Value, N - 1);
        _ ->
            S = N + 1,
            << Value2:S/binary, _/binary >> = Value,
            Value2
    end.