%% @doc A
%% @end
-module(boto_server).

-behaviour(gen_server).

-vsn(1).

-export([child_spec/1, graph/0, start_link/1, init/1, handle_call/3, handle_cast/2,
         handle_info/2, terminate/2, code_change/3, format_status/1]).


%% @doc A
%% @end
child_spec(args) ->
    #{id => boto_server,
      start => {boto_server, start_link, [args]},
      shutdown => brutal_kil,
      restart => permanent,
      type => worker}.

%% @private
graph() ->
    gen_server:call(boto_server, graph).

%% @doc A
%% @end
start_link(Args) ->
    gen_server:start_link({local, boto_server}, boto_server, Args, []).

%% @private
init(Args) ->
    Graph = boto_graph:start(),
    Table = ets:new(boto_resolvers_config, [set, protected]),
    State = #{graph => Graph, resolvers => Table},
    ResolverList = proplists:get_value(resolvers, Args),
    Resolvers = lists:flatmap(fun get_resolver/1, ResolverList),
    boto_graph:add_vertex(Graph, noarg),
    [create_vertices(R, Graph) || R <- Resolvers],
    [create_edges(R, Graph) || R <- Resolvers],
    [store_resolvers(R, Table) || R <- Resolvers],
    {ok, State}.

%% @private
handle_call(graph, _Ref, State) ->
    {reply, maps:get(graph, State), State}.

%% @private
handle_cast(_M, State) ->
    {noreply, State}.

%% @private
handle_info(_M, State) ->
    {noreply, State}.

%% @private
terminate(_R, _S) ->
    normal.

%% @private
code_change(_Vsn, State, _Extra) ->
    {ok, State}.

%% @private
format_status(Status) ->
    Status.

get_resolver(Mod) when is_atom(Mod) ->
    Exports = apply(Mod, module_info, [exports]),
    case lists:member({resolver_init, 0}, Exports) of
        true ->
            ModConfig = apply(Mod, resolver_init, []),
            [{{Mod, Name}, Config} || {Name, Config} <- list_wrap(ModConfig)];
        false ->
            %TODO: prepare error message
            []
    end;
get_resolver(_Mod) ->
    %TODO: prepare error message
    [].

create_vertices({_Resolver, Config}, Graph) ->
    Input = proplists:get_value(input, Config),
    [add_vertex(I, Graph) || I <- list_wrap(Input)],
    Output = proplists:get_value(output, Config),
    [add_vertex(O, Graph) || O <- list_wrap(Output)].

add_vertex({Vertex, Nested}, Graph) ->
    boto_graph:add_vertex(Graph, Vertex),
    lists:foreach(fun(I) -> add_vertex(I, Graph) end, Nested);
add_vertex(Vertex, Graph) ->
    boto_graph:add_vertex(Graph, Vertex).

create_edges({Resolver, Config}, Graph) ->
    Outputs = proplists:get_value(output, Config),
    case proplists:get_value(input, Config) of
        nil ->
            ok;
        [] ->
            lists:foreach(fun(O) -> add_edge(O, noarg, Resolver, Graph) end, Outputs);
        Inputs ->
            [add_edge(O, I, Resolver, Graph) || O <- Outputs, I <- Inputs]
    end.

add_edge({Output, Nested}, Input, Resolver, Graph) ->
    boto_graph:add_edge(Graph, Input, Output, Resolver),
    [add_edge(N, Output, Resolver, Graph) || N <- Nested];
add_edge(Output, Input, Resolver, Graph) ->
    boto_graph:add_edge(Graph, Input, Output, Resolver).

store_resolvers({Resolver, Config}, Table) ->
    ets:insert(Table, {Resolver, Config}).

list_wrap(nil) ->
    [];
list_wrap(List) when is_list(List) ->
    List;
list_wrap(Other) ->
    [Other].