%%%-------------------------------------------------------------------
%%% @doc Административный обработчик подписок.
%%% GET – список с пагинацией и фильтрацией.
%%% @end
%%%-------------------------------------------------------------------
-module(admin_handler_subscriptions).
-behaviour(cowboy_handler).
-export([init/2]).
-export([trails/0]).

-include("records.hrl").

-spec init(cowboy_req:req(), any()) -> {ok, cowboy_req:req(), any()}.
init(Req, _Opts) ->
  case cowboy_req:method(Req) of
    <<"GET">> -> list_subscriptions(Req);
    _ -> handler_utils:send_error(Req, 405, <<"Method not allowed">>)
  end.

-spec trails() -> [map()].
trails() ->
  [
    #{
      path => <<"/v1/admin/subscriptions">>,
      method => <<"GET">>,
      description => <<"List all subscriptions (admin)">>,
      tags => [<<"Subscriptions">>],
      parameters => [
        #{name => <<"plan">>, in => <<"query">>, schema => #{type => string, enum => [<<"monthly">>, <<"quarterly">>, <<"biannual">>, <<"annual">>]}, description => <<"Filter by plan">>},
        #{name => <<"status">>, in => <<"query">>, schema => #{type => string, enum => [<<"active">>, <<"expired">>, <<"cancelled">>]}, description => <<"Filter by status">>},
        #{name => <<"limit">>, in => <<"query">>, schema => #{type => integer}, description => <<"Page size">>},
        #{name => <<"offset">>, in => <<"query">>, schema => #{type => integer}, description => <<"Offset">>}
      ],
      responses => #{
        200 => #{
          description => <<"Array of subscriptions">>,
          content => #{<<"application/json">> => #{schema => #{
            type => array,
            items => subscription_schema()
          }}}
        }
      }
    }
  ].

subscription_schema() ->
  #{
    type => object,
    properties => #{
      id => #{type => string},
      user_id => #{type => string},
      plan => #{type => string, enum => [<<"monthly">>, <<"quarterly">>, <<"biannual">>, <<"annual">>]},
      status => #{type => string, enum => [<<"active">>, <<"expired">>, <<"cancelled">>]},
      trial_used => #{type => boolean},
      started_at => #{type => string, format => <<"date-time">>},
      expires_at => #{type => string, format => <<"date-time">>},
      created_at => #{type => string, format => <<"date-time">>},
      updated_at => #{type => string, format => <<"date-time">>}
    }
  }.

%%% Internal functions

list_subscriptions(Req) ->
  case handler_utils:auth_admin(Req) of
    {ok, _AdminId, Req1} ->
      Filters = parse_subscription_filters(Req1),
      Pagination = handler_utils:parse_pagination_params(Req1),
      {ok, AllSubscriptions} = core_subscription:list_all(),
      Filtered = apply_filters(AllSubscriptions, Filters),
      Sorted = sort_subscriptions(Filtered, Pagination),
      Total = length(Sorted),
      Page = lists:sublist(Sorted, maps:get(offset, Pagination) + 1, maps:get(limit, Pagination)),
      Json = [handler_utils:subscription_to_json(S) || S <- Page],
      ExtraHeaders = handler_utils:pagination_headers(Pagination, Total),
      handler_utils:send_json(Req1, 200, Json, ExtraHeaders);
    {error, Code, Msg, Req1} ->
      handler_utils:send_error(Req1, Code, Msg)
  end.

parse_subscription_filters(Req) ->
  Qs = cowboy_req:parse_qs(Req),
  #{
    plan => proplists:get_value(<<"plan">>, Qs),
    status => proplists:get_value(<<"status">>, Qs)
  }.

apply_filters(Subs, Filters) ->
  PlanBin = maps:get(plan, Filters, undefined),
  StatusBin = maps:get(status, Filters, undefined),
  F1 = case PlanBin of
         undefined -> Subs;
         _ ->
           Plan = try binary_to_existing_atom(PlanBin, utf8)
                  catch error:badarg -> PlanBin end,
           [S || S <- Subs, S#subscription.plan =:= Plan]
       end,
  case StatusBin of
    undefined -> F1;
    _ ->
      Status = try binary_to_existing_atom(StatusBin, utf8)
               catch error:badarg -> StatusBin end,
      [S || S <- F1, S#subscription.status =:= Status]
  end.

sort_subscriptions(Subs, #{sort := Sort, order := Order}) ->
  Field = binary_to_existing_atom(Sort, utf8),
  lists:sort(
    fun(A, B) ->
      ValA = sub_field(A, Field),
      ValB = sub_field(B, Field),
      if Order == <<"asc">> -> ValA =< ValB;
        true -> ValA >= ValB
      end
    end, Subs).

sub_field(#subscription{created_at = V}, created_at) -> V;
sub_field(#subscription{expires_at = V}, expires_at) -> V;
sub_field(_, _) -> undefined.