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%% -*- mode: erlang;erlang-indent-level: 2;indent-tabs-mode: nil -*-
%% vim: set ft=erlang ts=2 sw=2:

%% this code is not particularly nice.
%% the idea is to test for the presence of functions, in order to set
%% preprocessor flags, so that we can use the preprocessor to hide new
%% functions from old compilers.
%% "erl_opts" gets passed to the compiler.
%% "CONFIG" is a magic rebar thing.

KeyAppend =
fun(Tag,[],E,_)          -> [{Tag,[E]}];
   (Tag,[{Tag,O}|T],E,_) -> [{Tag,[E|O]}|T];
   (Tag,[H|T],E,G)       -> [H|G(Tag,T,E,G)]
end,

Crypto =
fun(CFG) ->
    code:ensure_loaded(crypto),
    case erlang:function_exported(crypto,block_encrypt,3) of
      true  -> KeyAppend(erl_opts,CFG,{d,'CRYPTO_R16'},KeyAppend);
      false -> CFG
    end
end,

Timestamp =
fun(CFG) ->
    case erlang:is_builtin(erlang,timestamp,0) of
      true  -> KeyAppend(erl_opts,CFG,{d,'HAS_TIMESTAMP'},KeyAppend);
      false -> CFG
    end
end,

lists:foldl(fun(F,Cfg) -> F(Cfg) end,CONFIG,[Crypto,Timestamp]).