%% @private
-module(boto_query).

-export([query/2]).

query(Args, Query) ->
    Graph = boto_server:graph(),
    do_query(Graph, Args, Query).

do_query(Graph, Args, Query) ->
    ArgsKeys = maps:keys(Args),
    {QueryClean, NestedQuery} = extract_nested(Query),
    Plan = planner(Graph, ArgsKeys, QueryClean),
    RawResolved = lists:foldl(fun do_resolve/2, Args, Plan),
    CleanResolved = maps:filter(fun(K, _V) -> lists:member(K, QueryClean) end, RawResolved),
    nested_query(Graph, CleanResolved, NestedQuery).

planner(Graph, ArgsKeys, Query) ->
    Fun = fun(Requested) ->
             FlatFun = fun(Arg) -> boto_graph:path(Graph, Arg, Requested) end,
             case lists:flatmap(FlatFun, ArgsKeys) of
                 [] ->
                     boto_graph:path(Graph, noarg, Requested);
                 Plan ->
                     Plan
             end
          end,
    ResultPlan = lists:flatmap(Fun, Query),
    lists:uniq(ResultPlan).

do_resolve({Mod, Name}, Args) ->
    Resolved = apply(Mod, resolve, [Name, Args]),
    maps:merge(Args, Resolved).

nested_query(Graph, Resolved, NestedQuery) ->
    Fun = fun({ArgKey, Query}, Resolving) ->
             Update =
                 case maps:get(ArgKey, Resolving) of
                     One when is_map(One) ->
                         do_query(Graph, One, Query);
                     Many when is_list(Many) ->
                         lists:map(fun(One) -> do_query(Graph, One, Query) end, Many)
                 end,
             maps:put(ArgKey, Update, Resolving)
          end,
    lists:foldl(Fun, Resolved, NestedQuery).

extract_nested(Query) ->
    NestedQuery = lists:filter(fun is_tuple/1, Query),
    QueryClean = lists:map(fun extract_nested_field/1, Query),
    {QueryClean, NestedQuery}.

extract_nested_field({K, _V}) ->
    K;
extract_nested_field(K) ->
    K.