%%%-------------------------------------------------------------------
%%% Автомодерация: сканирование бан-слов, политики, soft-hide, очередь.
%%%-------------------------------------------------------------------
-module(logic_automoderation).
-include("records.hrl").

-export([
  scan_text/1,
  scan_texts/1,
  evaluate_texts/1,
  apply_after_save/4,
  soft_hide/3,
  restore_entity/2,
  censor_text/2,
  get_settings/0,
  update_settings/2,
  list_hits/2,
  resolve_hit/3,
  settings_to_json/1,
  hit_to_json/1,
  record_report_threshold_hit/2,
  reason_reports/0
]).

-define(SYSTEM_ID, <<"system">>).
-define(SYSTEM_EMAIL, <<"system@eventhub">>).
-define(REASON_KEYWORD, <<"auto:keyword">>).
-define(REASON_REPORTS, <<"auto:report_threshold">>).

%%%===================================================================
%%% Scan / evaluate
%%%===================================================================

-spec scan_text(binary()) -> clean | {hit, [binary()]}.
scan_text(Text) when is_binary(Text) ->
  Settings = core_automod_settings:get(),
  Words = case catch core_banned_words:list_banned_words() of
            List when is_list(List) ->
              [W#banned_word.word || W <- List];
            _ ->
              []
          end,
  Hits = [W || W <- Words, word_matches(Text, W, Settings#automod_settings.match_mode)],
  case Hits of
    [] -> clean;
    _ -> {hit, lists:usort(Hits)}
  end;
scan_text(_) ->
  clean.

-spec scan_texts([binary()]) -> clean | {hit, [binary()]}.
scan_texts(Texts) ->
  lists:foldl(fun(Text, Acc) ->
    case scan_text(Text) of
      clean -> Acc;
      {hit, Words} ->
        case Acc of
          clean -> {hit, Words};
          {hit, Prev} -> {hit, lists:usort(Prev ++ Words)}
        end
    end
  end, clean, Texts).

%% @doc До сохранения: reject | {ok, Action, TextsOut, Words}.
%% Action = none | flag | censor. TextsOut — возможно с цензурой.
-spec evaluate_texts([binary()]) ->
  {reject, [binary()]} |
  {ok, none | flag | censor, [binary()], [binary()]}.
evaluate_texts(Texts) ->
  case scan_texts(Texts) of
    clean ->
      {ok, none, Texts, []};
    {hit, Words} ->
      Settings = core_automod_settings:get(),
      case Settings#automod_settings.keyword_action of
        reject ->
          {reject, Words};
        censor ->
          Censored = [censor_text(T, Words) || T <- Texts],
          {ok, censor, Censored, Words};
        flag ->
          {ok, flag, Texts, Words}
      end
  end.

%%%===================================================================
%%% After save
%%%===================================================================

-spec apply_after_save(calendar | event | review, binary(),
    none | flag | censor, [binary()]) -> ok.
apply_after_save(_Type, _Id, none, _) ->
  ok;
apply_after_save(EntityType, EntityId, Action, Words)
  when Action =:= flag; Action =:= censor ->
  case Action of
    flag -> soft_hide(EntityType, EntityId, ?REASON_KEYWORD);
    censor -> ok
  end,
  {ok, Hit} = core_automod_hit:create(EntityType, EntityId, keyword, Words, Action),
  log_system(<<"automod_keyword">>, entity_type_bin(EntityType), EntityId, ?REASON_KEYWORD),
  logic_notification:notify_admin(automod_hit, #{
    hit_id => Hit#automod_hit.id,
    entity_type => entity_type_bin(EntityType),
    entity_id => EntityId,
    trigger => <<"keyword">>,
    action => atom_to_binary(Action, utf8),
    matched_words => Words
  }),
  ok.

-spec soft_hide(calendar | event | review, binary(), binary()) -> ok.
soft_hide(event, Id, Reason) ->
  case core_event:get_by_id(Id) of
    {ok, #event{status = active}} ->
      _ = core_event:freeze(Id, Reason),
      ok;
    _ -> ok
  end;
soft_hide(calendar, Id, Reason) ->
  case core_calendar:get_by_id(Id) of
    {ok, #calendar{status = active}} ->
      _ = core_calendar:freeze(Id, Reason),
      ok;
    _ -> ok
  end;
soft_hide(review, Id, Reason) ->
  case core_review:get_by_id(Id) of
    {ok, #review{status = visible}} ->
      _ = core_review:hide(Id, Reason),
      ok;
    _ -> ok
  end.

-spec restore_entity(calendar | event | review, binary()) -> ok | {error, term()}.
restore_entity(event, Id) ->
  case core_event:unfreeze(Id, <<"automod:approved">>) of
    {ok, _} -> ok;
    Err -> Err
  end;
restore_entity(calendar, Id) ->
  case core_calendar:unfreeze(Id, <<"automod:approved">>) of
    {ok, _} -> ok;
    Err -> Err
  end;
restore_entity(review, Id) ->
  case core_review:unhide(Id, <<"automod:approved">>) of
    {ok, _} -> ok;
    Err -> Err
  end.

%%%===================================================================
%%% Settings / hits (admin)
%%%===================================================================

get_settings() ->
  core_automod_settings:ensure_defaults(),
  {ok, core_automod_settings:get()}.

update_settings(AdminId, Updates) ->
  case admin_utils:check_role(AdminId, [superadmin, admin]) of
    true ->
      case core_automod_settings:update(Updates, AdminId) of
        {ok, S} -> {ok, S};
        Error -> Error
      end;
    false ->
      {error, access_denied}
  end.

list_hits(AdminId, Filters) ->
  case admin_utils:check_role(AdminId, [superadmin, admin, moderator]) of
    true -> {ok, core_automod_hit:list(Filters)};
    false -> {error, access_denied}
  end.

resolve_hit(AdminId, HitId, Decision) when Decision =:= approved; Decision =:= rejected ->
  case admin_utils:check_role(AdminId, [superadmin, admin, moderator]) of
    true ->
      case core_automod_hit:resolve(HitId, Decision, AdminId) of
        {ok, Hit} ->
          case Decision of
            approved ->
              _ = restore_entity(Hit#automod_hit.entity_type, Hit#automod_hit.entity_id);
            rejected ->
              soft_hide(Hit#automod_hit.entity_type, Hit#automod_hit.entity_id,
                <<"automod:rejected">>)
          end,
          {ok, Hit};
        Error ->
          Error
      end;
    false ->
      {error, access_denied}
  end.

%%%===================================================================
%%% Text helpers
%%%===================================================================

-spec censor_text(binary(), [binary()]) -> binary().
censor_text(Text, Words) ->
  lists:foldl(fun(Word, Acc) ->
    replace_word(Acc, Word, <<"***">>)
  end, Text, Words).

replace_word(Text, Word, Replacement) ->
  Settings = core_automod_settings:get(),
  case Settings#automod_settings.match_mode of
    substring ->
      replace_substring_ci(Text, Word, Replacement);
    word_boundary ->
      replace_boundary_ci(Text, Word, Replacement)
  end.

word_matches(Text, Word, Mode) ->
  TextL = unicode:characters_to_list(string:lowercase(Text)),
  WordL = unicode:characters_to_list(string:lowercase(Word)),
  case Mode of
    substring -> string:str(TextL, WordL) > 0;
    word_boundary -> find_boundary(TextL, WordL, 1)
  end.

find_boundary(_Text, [], _) -> false;
find_boundary(Text, Word, Start) when Start > length(Text) -> false;
find_boundary(Text, Word, Start) ->
  Tail = lists:nthtail(Start - 1, Text),
  case string:str(Tail, Word) of
    0 -> false;
    Rel ->
      Pos = Start + Rel - 1,
      BeforeOk = Pos =:= 1 orelse not is_word_char(lists:nth(Pos - 1, Text)),
      AfterPos = Pos + length(Word),
      AfterOk = AfterPos > length(Text) orelse not is_word_char(lists:nth(AfterPos, Text)),
      case BeforeOk andalso AfterOk of
        true -> true;
        false -> find_boundary(Text, Word, Pos + 1)
      end
  end.

is_word_char(C) when C >= $a, C =< $z -> true;
is_word_char(C) when C >= $0, C =< $9 -> true;
is_word_char($_) -> true;
is_word_char(C) when C >= 16#0400, C =< 16#04FF -> true; % Cyrillic block
is_word_char(_) -> false.

replace_substring_ci(Text, Word, Replacement) ->
  TextL = string:lowercase(Text),
  WordL = string:lowercase(Word),
  case binary:match(TextL, WordL) of
    nomatch -> Text;
    {Pos, Len} ->
      <<Prefix:Pos/binary, _:Len/binary, Rest/binary>> = Text,
      replace_substring_ci(<<Prefix/binary, Replacement/binary, Rest/binary>>, Word, Replacement)
  end.

replace_boundary_ci(Text, Word, Replacement) ->
  TextList = unicode:characters_to_list(Text),
  WordList = unicode:characters_to_list(Word),
  TextLower = unicode:characters_to_list(string:lowercase(Text)),
  WordLower = unicode:characters_to_list(string:lowercase(Word)),
  case find_boundary(TextLower, WordLower, 1) of
    false -> Text;
    true ->
      case string:str(TextLower, WordLower) of
        0 -> Text;
        Pos ->
          %% may be false positive on first substring; walk like find_boundary
          case find_boundary_pos(TextLower, WordLower, 1) of
            undefined -> Text;
            RealPos ->
              Prefix = lists:sublist(TextList, RealPos - 1),
              Rest = lists:nthtail(RealPos - 1 + length(WordList), TextList),
              New = unicode:characters_to_binary(Prefix ++ unicode:characters_to_list(Replacement) ++ Rest),
              replace_boundary_ci(New, Word, Replacement)
          end
      end
  end.

find_boundary_pos(_Text, [], _) -> undefined;
find_boundary_pos(Text, Word, Start) when Start > length(Text) -> undefined;
find_boundary_pos(Text, Word, Start) ->
  Tail = lists:nthtail(Start - 1, Text),
  case string:str(Tail, Word) of
    0 -> undefined;
    Rel ->
      Pos = Start + Rel - 1,
      BeforeOk = Pos =:= 1 orelse not is_word_char(lists:nth(Pos - 1, Text)),
      AfterPos = Pos + length(Word),
      AfterOk = AfterPos > length(Text) orelse not is_word_char(lists:nth(AfterPos, Text)),
      case BeforeOk andalso AfterOk of
        true -> Pos;
        false -> find_boundary_pos(Text, Word, Pos + 1)
      end
  end.

%%%===================================================================
%%% JSON / audit helpers
%%%===================================================================

settings_to_json(#automod_settings{} = S) ->
  #{
    keyword_action => atom_to_binary(S#automod_settings.keyword_action, utf8),
    match_mode => atom_to_binary(S#automod_settings.match_mode, utf8),
    report_threshold => S#automod_settings.report_threshold,
    updated_at => handler_utils:datetime_to_iso8601(S#automod_settings.updated_at),
    updated_by => S#automod_settings.updated_by
  }.

hit_to_json(#automod_hit{} = H) ->
  #{
    id => H#automod_hit.id,
    entity_type => atom_to_binary(H#automod_hit.entity_type, utf8),
    entity_id => H#automod_hit.entity_id,
    trigger => atom_to_binary(H#automod_hit.trigger, utf8),
    matched_words => H#automod_hit.matched_words,
    action_taken => atom_to_binary(H#automod_hit.action_taken, utf8),
    status => atom_to_binary(H#automod_hit.status, utf8),
    created_at => handler_utils:datetime_to_iso8601(H#automod_hit.created_at),
    resolved_at => case H#automod_hit.resolved_at of
                     undefined -> null;
                     Dt -> handler_utils:datetime_to_iso8601(Dt)
                   end,
    resolved_by => H#automod_hit.resolved_by
  }.

log_system(Action, EntityType, EntityId, Reason) ->
  core_admin_audit:log(?SYSTEM_ID, ?SYSTEM_EMAIL, system, Action,
    EntityType, EntityId, <<"127.0.0.1">>, Reason).

entity_type_bin(calendar) -> <<"calendar">>;
entity_type_bin(event) -> <<"event">>;
entity_type_bin(review) -> <<"review">>.

record_report_threshold_hit(EntityType, EntityId) ->
  Action = case EntityType of
             review -> hide;
             _ -> freeze
           end,
  soft_hide(EntityType, EntityId, ?REASON_REPORTS),
  {ok, Hit} = core_automod_hit:create(EntityType, EntityId, report_threshold, [], Action),
  log_system(<<"automod_report_threshold">>, entity_type_bin(EntityType), EntityId, ?REASON_REPORTS),
  logic_notification:notify_admin(automod_hit, #{
    hit_id => Hit#automod_hit.id,
    entity_type => entity_type_bin(EntityType),
    entity_id => EntityId,
    trigger => <<"report_threshold">>,
    action => atom_to_binary(Action, utf8)
  }),
  ok.

reason_reports() -> ?REASON_REPORTS.