-module(ierl_cmd_kernel).

-export([
         exec/4,
         opt_spec/0
        ]).


opt_spec() ->
    {
     "Start a kernel for the given connection file",
     [
      {conn_file, $f, "conn-file", string, "Connection file provided by"
                                           " Jupyter"},
      {node, undefined, "node", string, "Node to run this kernel on"},
      {sname, undefined, "sname", string, "Short name for this node "
       "(defaults to the backend name"},
      {cookie, undefined, "cookie", string, "Cookie"}
     ]
    }.


exec({BName, Backend}, ParsedArgs, BackendArgs, _BackendSpec) ->
    {ok, _} = application:ensure_all_started(lager),
    lager:set_loglevel(lager_console_backend, error),

    {ok, _Deps} = application:ensure_all_started(ierl),

    JsonFile = maps:get(conn_file, ParsedArgs, undefined),
    case JsonFile of
        undefined -> error(must_specify_conn_file);
        _ -> ok
    end,

    SName = maps:get(sname, ParsedArgs, atom_to_list(BName)),

    Suffix = binary:replace(
               base64:encode(crypto:strong_rand_bytes(6)),
               [<<"+">>, <<"/">>], <<"_">>,
               [global]
              ),

    SName1 = binary_to_atom(iolist_to_binary([SName, "_", Suffix]), utf8),

    net_kernel:start([SName1, shortnames]),
    lager:info("Set node name to ~p", [SName1]),

    case os:getenv("IERL_COOKIE") of
        false -> ok;
        "" -> ok;
        Value ->
            erlang:set_cookie(node(), list_to_atom(Value))
    end,

    Node = case maps:get(node, ParsedArgs, undefined) of
               undefined ->
                   node();
               Val ->
                   list_to_atom(Val)
           end,

    lager:info("Starting Erlang kernel with connection file ~s against ~p",
               [JsonFile, Node]),

    process_flag(trap_exit, true),
    % TODO Parse rest of the args

    Args = #{ node => Node, backend_args => BackendArgs },
    {ok, _Pid} = jupyter:start_kernel(ierlang, JsonFile, Backend, Args),

    receive
        Msg ->
            io:format("Kernel supervisor is down, stopping. (~p)~n", [Msg]),
            application:stop(jupyter),
            init:stop(0)
    end.