%% Copyright © 2018 Pierre Fenoll ‹pierrefenoll@gmail.com›
%% See LICENSE for licensing information.
%% -*- coding: utf-8 -*-
begin
    %% From https://github.com/erlang/rebar3/blob/c48435a/src/rebar_utils.erl#L489-L526
    OTP_VSN = {X,Y,Z} =
      case erlang:system_info(otp_release) of
          %% If OTP <= R16, otp_release is already what we want.
          "R16B01" -> {"16", "1", "0"};
          "R16B02" -> {"16", "2", "0"};
          "R16B03" -> {"16", "3", "0"};
          "R16B03-1" -> {"16", "3", "1"};

          %% If OTP >= 17.x, erlang:system_info(otp_release) returns just the
          %% major version number, we have to read the full version from
          %% a file. See http://www.erlang.org/doc/system_principles/versions.html
          %% Read vsn string from the 'OTP_VERSION' file and return as list without
          %% the "\n".
          Rel ->
              Split = fun (Bin) -> binary:split(Bin, [<<$.>>,<<$->>], [global]) end,
              ToXYZ = fun ([X,Y]) -> {X, Y, "0"};
                          ([X,Y,<<"rc",_/binary>>]) -> {X, Y, "0"};
                          ([X,Y,Z|_]) -> {X, Y, Z}
                      end,

              File = filename:join([code:root_dir(), "releases", Rel, "OTP_VERSION"]),
              {ok,Vsn} = file:read_file(File),
              Size = byte_size(Vsn),
              %% The shortest vsn string consists of at least two digits
              %% followed by "\n". Therefore, it's safe to assume Size >= 3.
              {SizeMinus1,SizeMinus3} = {Size - 1, Size - 3},
              case Vsn of
                  <<VSN:SizeMinus3/binary, "**\n">> ->
                      %% The OTP documentation mentions that a system patched
                      %% using the otp_patch_apply tool available to licensed
                      %% customers will leave a '**' suffix in the version as a
                      %% flag saying the system consists of application versions
                      %% from multiple OTP versions. We ignore this flag and
                      %% drop the suffix, given for all intents and purposes, we
                      %% cannot obtain relevant information from it as far as
                      %% tooling is concerned.
                      ToXYZ(Split(VSN));
                  <<VSN:SizeMinus1/binary, "\n">> ->
                      ToXYZ(Split(VSN))
              end
      end,

  Data = ["-define(_internal_otp_vsn_", X,$_,Y,$_,Z, ", true).", $\n],

  DefaultBuildLibDir = "_build/default/lib",

  %% get all possible otp_vsn lib dirs
  %% _build/default/lib/otp_vsn --> if no REBAR_LIB_DEPS env specified, or
  %%    no custom rebar.config.script specified
  %% REBAR_LIB_DEPS --> if env exists
  DepsDirs = case os:getenv("REBAR_LIB_DEPS") of
	      false -> [DefaultBuildLibDir];
	      [] -> [DefaultBuildLibDir];
	      Dir -> [Dir,DefaultBuildLibDir]
	    end,

  %% generate internal_otp_vsn.hrl at all possible dirs
  Dsts = case filelib:is_regular(filename:join("src","otp_vsn.app.src")) of
            false ->
                [ filename:join(
                    [LibDir,"otp_vsn","include","internal_otp_vsn.hrl"])
                    || LibDir <- DepsDirs
                ];
            true ->
                %% Current app is this app itself
                [filename:join("include", "internal_otp_vsn.hrl")]
        end,
  %ok = file:write_file(Dst, Data),
  %% ignore write_file error if dir is not exist
  [ file:write_file(Dst,Data) || Dst <- Dsts ] ,

  CONFIG
end.