%%%-------------------------------------------------------------------
%%% @doc ETS ordered_set tops для admin stats.
%%% Класс A: denormalized rating на event/calendar.
%%% Класс B: агрегаты целей review/report (+ calendar pos/neg).
%%% @end
%%%-------------------------------------------------------------------
-module(stats_tops).

-include("records.hrl").

-export([
  init_tables/0,
  clear/0,
  rebuild/0,
  on_event/2,
  on_calendar/2,
  on_review/2,
  on_report/2,
  remove_event/1,
  remove_calendar/1,
  remove_review/1,
  remove_report/1,
  get_top_events_by_rating/1,
  get_top_calendars_by_rating/1,
  get_top_calendars_by_reviews/1,
  get_top_calendars_by_positive_reviews/1,
  get_top_calendars_by_negative_reviews/1,
  get_top_targets_by_reviews/1,
  get_top_targets_by_positive_reviews/1,
  get_top_targets_by_negative_reviews/1,
  get_top_targets_by_reports/1
]).

-define(IDX, stats_tops_idx).
-define(ORD_EVENT_RATING, stats_top_event_rating).
-define(ORD_CAL_RATING, stats_top_calendar_rating).
-define(ORD_CAL_REVIEWS, stats_top_calendar_reviews).
-define(ORD_CAL_POS, stats_top_calendar_pos).
-define(ORD_CAL_NEG, stats_top_calendar_neg).
-define(ORD_REVIEWS_ALL, stats_top_reviews_all).
-define(ORD_REVIEWS_POS, stats_top_reviews_pos).
-define(ORD_REVIEWS_NEG, stats_top_reviews_neg).
-define(ORD_REPORTS_ALL, stats_top_reports_all).

-define(ALL_ORD, [
  ?ORD_EVENT_RATING, ?ORD_CAL_RATING, ?ORD_CAL_REVIEWS,
  ?ORD_CAL_POS, ?ORD_CAL_NEG,
  ?ORD_REVIEWS_ALL, ?ORD_REVIEWS_POS, ?ORD_REVIEWS_NEG, ?ORD_REPORTS_ALL
]).

%%%===================================================================
%%% Lifecycle
%%%===================================================================

init_tables() ->
  ensure_ets(?IDX, [named_table, public, set, {read_concurrency, true}]),
  lists:foreach(fun(T) ->
    ensure_ets(T, [named_table, public, ordered_set, {read_concurrency, true}])
  end, ?ALL_ORD),
  ok.

clear() ->
  case ready() of
    true ->
      ets:delete_all_objects(?IDX),
      lists:foreach(fun(T) -> ets:delete_all_objects(T) end, ?ALL_ORD);
    false -> ok
  end,
  ok.

rebuild() ->
  clear(),
  foreach_table(event, #event{_ = '_'}, fun(E) -> on_event(E, undefined) end),
  foreach_table(calendar, #calendar{_ = '_'}, fun(C) -> on_calendar(C, undefined) end),
  foreach_table(review, #review{_ = '_'}, fun(R) -> on_review(R, undefined) end),
  foreach_table(report, #report{_ = '_'}, fun(R) -> on_report(R, undefined) end),
  ok.

ready() ->
  ets:info(?IDX) =/= undefined.

foreach_table(Table, Pattern, Fun) ->
  case lists:member(Table, mnesia:system_info(tables)) of
    true ->
      try lists:foreach(Fun, mnesia:dirty_match_object(Pattern))
      catch
        exit:{aborted, {no_exists, _}} -> ok;
        error:{aborted, {no_exists, _}} -> ok
      end;
    false -> ok
  end.

%%%===================================================================
%%% Entity rating updates (class A)
%%%===================================================================

on_event(undefined, _) -> ok;
on_event(#event{id = Id, rating_avg = Avg}, Old) ->
  when_ready(fun() ->
    OldAvg = case Old of #event{rating_avg = A} -> A; _ -> undefined end,
    set_score(?ORD_EVENT_RATING, {event_rating, Id}, Id, OldAvg, Avg)
  end);
on_event(_, _) -> ok.

on_calendar(undefined, _) -> ok;
on_calendar(#calendar{id = Id, rating_avg = Avg, rating_count = Count}, Old) ->
  when_ready(fun() ->
    {OldAvg, OldCount} = case Old of
                           #calendar{rating_avg = A, rating_count = C} -> {A, C};
                           _ -> {undefined, undefined}
                         end,
    set_score(?ORD_CAL_RATING, {calendar_rating, Id}, Id, OldAvg, Avg),
    set_score(?ORD_CAL_REVIEWS, {calendar_reviews, Id}, Id, OldCount, Count)
  end);
on_calendar(_, _) -> ok.

remove_event(#event{id = Id, rating_avg = Avg}) ->
  when_ready(fun() -> clear_score(?ORD_EVENT_RATING, {event_rating, Id}, Id, Avg) end);
remove_event(_) -> ok.

remove_calendar(#calendar{id = Id, rating_avg = Avg, rating_count = Count}) ->
  when_ready(fun() ->
    clear_score(?ORD_CAL_RATING, {calendar_rating, Id}, Id, Avg),
    clear_score(?ORD_CAL_REVIEWS, {calendar_reviews, Id}, Id, Count)
  end);
remove_calendar(_) -> ok.

%%%===================================================================
%%% Review / report target updates (class B)
%%%===================================================================

on_review(undefined, _) -> ok;
on_review(New, undefined) ->
  when_ready(fun() -> apply_review_delta(New, 1) end);
on_review(New, Old) when is_tuple(Old) ->
  when_ready(fun() ->
    apply_review_delta(Old, -1),
    apply_review_delta(New, 1)
  end);
on_review(_, _) -> ok.

remove_review(Review) ->
  when_ready(fun() -> apply_review_delta(Review, -1) end).

on_report(undefined, _) -> ok;
on_report(New, undefined) ->
  when_ready(fun() -> apply_report_delta(New, 1) end);
on_report(New, Old) when is_tuple(Old) ->
  when_ready(fun() ->
    apply_report_delta(Old, -1),
    apply_report_delta(New, 1)
  end);
on_report(_, _) -> ok.

remove_report(Report) ->
  when_ready(fun() -> apply_report_delta(Report, -1) end).

apply_review_delta(#review{target_type = Type, target_id = Id, rating = Rating}, Delta)
    when is_atom(Type), is_binary(Id) ->
  Target = {Type, Id},
  bump(?ORD_REVIEWS_ALL, {reviews_all, Type, Id}, Target, Delta),
  case Rating >= 4 of
    true ->
      bump(?ORD_REVIEWS_POS, {reviews_pos, Type, Id}, Target, Delta),
      case Type of
        calendar -> bump(?ORD_CAL_POS, {calendar_pos, Id}, Id, Delta);
        _ -> ok
      end;
    false -> ok
  end,
  case Rating =< 2 of
    true ->
      bump(?ORD_REVIEWS_NEG, {reviews_neg, Type, Id}, Target, Delta),
      case Type of
        calendar -> bump(?ORD_CAL_NEG, {calendar_neg, Id}, Id, Delta);
        _ -> ok
      end;
    false -> ok
  end;
apply_review_delta(_, _) -> ok.

apply_report_delta(#report{target_type = Type, target_id = Id}, Delta)
    when is_atom(Type), is_binary(Id) ->
  bump(?ORD_REPORTS_ALL, {reports_all, Type, Id}, {Type, Id}, Delta);
apply_report_delta(_, _) -> ok.

%%%===================================================================
%%% Reads
%%%===================================================================

get_top_events_by_rating(N) ->
  get_entities(?ORD_EVENT_RATING, N, fun load_event/1).

get_top_calendars_by_rating(N) ->
  get_entities(?ORD_CAL_RATING, N, fun load_calendar/1).

get_top_calendars_by_reviews(N) ->
  get_entities(?ORD_CAL_REVIEWS, N, fun load_calendar/1).

get_top_calendars_by_positive_reviews(N) ->
  get_entities(?ORD_CAL_POS, N, fun load_calendar/1).

get_top_calendars_by_negative_reviews(N) ->
  get_entities(?ORD_CAL_NEG, N, fun load_calendar/1).

get_top_targets_by_reviews(N) ->
  get_target_triples(?ORD_REVIEWS_ALL, N).

get_top_targets_by_positive_reviews(N) ->
  get_target_triples(?ORD_REVIEWS_POS, N).

get_top_targets_by_negative_reviews(N) ->
  get_target_triples(?ORD_REVIEWS_NEG, N).

get_top_targets_by_reports(N) ->
  get_target_triples(?ORD_REPORTS_ALL, N).

%%%===================================================================
%%% Internal
%%%===================================================================

when_ready(Fun) ->
  case ready() of
    true -> Fun();
    false -> ok
  end.

ensure_ets(Name, Opts) ->
  case ets:info(Name) of
    undefined -> ets:new(Name, Opts);
    _ -> Name
  end.

set_score(_Ord, _IdxKey, _Entity, Same, Same) ->
  ok;
set_score(Ord, IdxKey, Entity, _OldScore, NewScore) ->
  case ets:lookup(?IDX, IdxKey) of
    [{IdxKey, Prev}] -> ets:delete(Ord, ord_key(Prev, Entity));
    [] -> ok
  end,
  ets:insert(Ord, {ord_key(NewScore, Entity), Entity}),
  ets:insert(?IDX, {IdxKey, NewScore}),
  ok.

clear_score(Ord, IdxKey, Entity, Score) ->
  case ets:lookup(?IDX, IdxKey) of
    [{IdxKey, Prev}] ->
      ets:delete(Ord, ord_key(Prev, Entity)),
      ets:delete(?IDX, IdxKey);
    [] ->
      ets:delete(Ord, ord_key(Score, Entity))
  end,
  ok.

bump(_Ord, _IdxKey, _Entity, 0) ->
  ok;
bump(Ord, IdxKey, Entity, Delta) ->
  Old = case ets:lookup(?IDX, IdxKey) of
          [{IdxKey, C}] -> C;
          [] -> 0
        end,
  case Old > 0 of
    true -> ets:delete(Ord, ord_key(Old, Entity));
    false -> ok
  end,
  New = max(0, Old + Delta),
  case New > 0 of
    true ->
      ets:insert(Ord, {ord_key(New, Entity), Entity}),
      ets:insert(?IDX, {IdxKey, New});
    false ->
      ets:delete(?IDX, IdxKey)
  end,
  ok.

ord_key(Score, Entity) when is_number(Score) ->
  {-Score, Entity};
ord_key(_, Entity) ->
  {0, Entity}.

get_entities(Ord, N, LoadFun) ->
  case ready() of
    false -> {error, not_ready};
    true ->
      Keys = take_entities(Ord, ets:first(Ord), N, []),
      {ok, lists:filtermap(LoadFun, Keys)}
  end.

get_target_triples(Ord, N) ->
  case ready() of
    false -> {error, not_ready};
    true ->
      Items = take_entities(Ord, ets:first(Ord), N, []),
      Triples = lists:filtermap(fun
        ({Type, Id}) ->
          case ets:lookup(?IDX, idx_for_ord(Ord, Type, Id)) of
            [{_, Count}] when Count > 0 -> {true, {Type, Id, Count}};
            _ -> false
          end;
        (_) -> false
      end, Items),
      {ok, Triples}
  end.

idx_for_ord(?ORD_REVIEWS_ALL, Type, Id) -> {reviews_all, Type, Id};
idx_for_ord(?ORD_REVIEWS_POS, Type, Id) -> {reviews_pos, Type, Id};
idx_for_ord(?ORD_REVIEWS_NEG, Type, Id) -> {reviews_neg, Type, Id};
idx_for_ord(?ORD_REPORTS_ALL, Type, Id) -> {reports_all, Type, Id}.

take_entities(_Ord, '$end_of_table', _N, Acc) ->
  lists:reverse(Acc);
take_entities(_Ord, _Key, 0, Acc) ->
  lists:reverse(Acc);
take_entities(Ord, Key, N, Acc) ->
  case ets:lookup(Ord, Key) of
    [{Key, Entity}] ->
      take_entities(Ord, ets:next(Ord, Key), N - 1, [Entity | Acc]);
    [] ->
      take_entities(Ord, ets:next(Ord, Key), N, Acc)
  end.

load_event(Id) when is_binary(Id) ->
  case mnesia:dirty_read({event, Id}) of
    [E] -> {true, E};
    _ -> false
  end;
load_event(_) -> false.

load_calendar(Id) when is_binary(Id) ->
  case mnesia:dirty_read({calendar, Id}) of
    [C] -> {true, C};
    _ -> false
  end;
load_calendar(_) -> false.