#!/usr/bin/env escript
%% -*- erlang -*-
main([File|Additions]) ->
    Settings = case file:consult(File) of
                   {ok, S} -> S;
                   _ -> []
               end,
    Terms = [ begin
                  {ok, Tokens, _} = erl_scan:string(String),
                  {ok, Term} = erl_parse:parse_term(Tokens),
                  Term
              end || String <- Additions ],
    Merged = overlay(lists:flatten(Settings), Terms),
    file:write_file(File, io_lib:format("~p.",[Merged])).

overlay(InputConfig, NewConfig) ->
    lists:foldl(
        fun({ApplicationName, ApplicationConfig}, OuterAcc) ->
            GeneratedApplicationConfig = proplists:get_value(ApplicationName, InputConfig, []),
            Updated = lists:foldl(
                fun({ConfigElementName, ConfigElement}, Acc) ->
                    replace_proplist_value(ConfigElementName, ConfigElement, Acc)
                end,
                GeneratedApplicationConfig,
                ApplicationConfig),
            replace_proplist_value(ApplicationName, Updated, OuterAcc)
        end,
        InputConfig,
        NewConfig).

replace_proplist_value(Key, Value, Proplist) ->
    lists:keystore(Key, 1, Proplist, {Key, Value}).