%%%-------------------------------------------------------------------
%%% @doc Административный обработчик статистики по подпискам.
%%% GET /v1/admin/subscriptions/stats – возвращает общее количество,
%%% распределение по планам, статусам, пробные, заканчивающиеся платные.
%%% @end
%%%-------------------------------------------------------------------
-module(admin_handler_subscription_stats).
-behaviour(cowboy_handler).
-export([init/2]).
-export([trails/0]).

-include("records.hrl").

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

%%% Swagger metadata
-spec trails() -> [map()].
trails() ->
  [
    #{
      path => <<"/v1/admin/subscriptions/stats">>,
      method => <<"GET">>,
      description => <<"Get detailed subscription statistics (total, by plan, by status, trial count, ending paid subscriptions)">>,
      tags => [<<"Statistics">>],
      responses => #{
        200 => #{
          description => <<"Subscription statistics object">>,
          content => #{<<"application/json">> => #{schema => subscription_stats_schema()}}
        },
        403 => #{description => <<"Admin access required">>}
      }
    }
  ].

subscription_stats_schema() ->
  #{
    type => object,
    properties => #{
      <<"total_subscriptions">> => #{type => integer, description => <<"Total number of subscriptions">>},
      <<"subscriptions_by_plan">> => #{
        type => object,
        description => <<"Number of subscriptions grouped by plan">>,
        additionalProperties => #{type => integer}
      },
      <<"subscriptions_by_status">> => #{
        type => object,
        description => <<"Number of subscriptions grouped by status">>,
        additionalProperties => #{type => integer}
      },
      <<"trial_subscriptions">> => #{type => integer, description => <<"Number of subscriptions in trial period (trial_used = false)">>},
      <<"ending_paid_subscriptions">> => #{
        type => array,
        description => <<"Paid subscriptions expiring within 30 days">>,
        items => #{
          type => object,
          properties => #{
            <<"id">> => #{type => string},
            <<"user_id">> => #{type => string},
            <<"plan">> => #{type => string},
            <<"expires_at">> => #{type => string, format => <<"date-time">>}
          }
        }
      }
    }
  }.

%%% Internal functions

%% @doc GET /v1/admin/subscriptions/stats – статистика по подпискам.
-spec get_subscription_stats(cowboy_req:req()) -> {ok, binary(), cowboy_req:req()}.
get_subscription_stats(Req) ->
  case handler_utils:auth_admin(Req) of
    {ok, _AdminId, Req1} ->
      Total = core_subscription:count_subscriptions(),
      ByPlan = core_subscription:count_subscriptions_by_plan(),
      ByStatus = core_subscription:count_subscriptions_by_status(),
      Trial = core_subscription:count_trial_subscriptions(),
      EndingPaid = core_subscription:get_ending_paid_subscriptions(30),
      Stats = #{
        <<"total_subscriptions">> => Total,
        <<"subscriptions_by_plan">> => maps:from_list([{atom_to_binary(Plan, utf8), Count} || {Plan, Count} <- ByPlan]),
        <<"subscriptions_by_status">> => maps:from_list([{atom_to_binary(Status, utf8), Count} || {Status, Count} <- ByStatus]),
        <<"trial_subscriptions">> => Trial,
        <<"ending_paid_subscriptions">> => lists:map(fun(Sub) ->
          #{
            <<"id">> => Sub#subscription.id,
            <<"user_id">> => Sub#subscription.user_id,
            <<"plan">> => atom_to_binary(Sub#subscription.plan, utf8),
            <<"expires_at">> => handler_utils:datetime_to_iso8601(Sub#subscription.expires_at)
          }
                                                     end, EndingPaid)
      },
      handler_utils:send_json(Req1, 200, Stats);
    {error, Code, Msg, Req1} ->
      handler_utils:send_error(Req1, Code, Msg)
  end.