Check if epgsql database connections are on the same timezone

on_same_timezone.erl

% If we have some amount of PostgreSQL instances and want to transfer data between them,
% in case when model has 'timeatamp' fields, we should check that both instances configured with the
% same timezone

on_same_timezone(Connections) ->
    Tests =
        [%% Check using TimeZone connection parameter
         {fun(Conn) ->
                  {ok, TZ} = pgsql:get_parameter(Conn, <<"TimeZone">>),
                  TZ
          end,
          fun(A, B) ->
                  FixTZ = fun (<<"GMT">>) -> <<"UTC">>;
                              (TZ) -> TZ
                          end,
                  ((A =/= undefined)
                   and (B =/= undefined)
                   and (FixTZ(A) == FixTZ(B)))
          end},
         %% Check using now() call
         {fun(Conn) ->
                  {ok, _, [{DT}]} = pgsql:equery(Conn, <<"SELECT now()::timestamp">>),
                  calendar:datetime_to_gregorian_seconds(db_dtime_fix_seconds(DT))
          end,
          fun(A, B) ->
                  %% time differs not more than 60 sec
                  (max(A, B) - min(A, B)) < 60
          end}],
    %% If any test succeed - return true
    lists:any(fun({Extract, Compare}) ->
                      %% compare each value with first one
                      [V1 | Rest] = [Extract(C) || C <- Connections],
                      lists:all(fun(V2) ->
                                        Res = Compare(V1, V2),
                                        lager:debug("TimezoneCmp(~p, ~p) -> ~p", [V1, V2, Res]),
                                        Res
                                end, Rest)
              end, Tests).