%% ===================================================================
%% EventHub – infra_mnesia (финальная версия с автоочисткой кластера)
%% ===================================================================
-module(infra_mnesia).
-behaviour(gen_server).

-include("records.hrl").

-export([start_link/0, init_tables/0, wait_for_tables/0]).
-export([add_cluster_nodes/1]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  terminate/2, code_change/3]).

-define(TABLES, [
  user, session, admin, admin_session,
  calendar, calendar_share, calendar_specialist,
  event, recurrence_exception,
  booking,
  review, report, banned_word,
  ticket, subscription,
  admin_audit, notification,
  stats, schema_migration
]).

-define(DISC_TABLES, ?TABLES -- [session, admin_session]).
-define(TABLE_WAIT_TIMEOUT, 5000).
-define(CLEANUP_INTERVAL, 30000). % 30 секунд

%% ===================================================================
%% API
%% ===================================================================

start_link() ->
  gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

init_tables() ->
  gen_server:call(?MODULE, init_tables).

wait_for_tables() ->
  gen_server:call(?MODULE, wait_for_tables).

add_cluster_nodes(Nodes) ->
  gen_server:call(?MODULE, {add_nodes, Nodes}).

%% ===================================================================
%% gen_server callbacks
%% ===================================================================

init([]) ->
  {ok, #{}}.

handle_call(init_tables, _From, State) ->
  ExtraNodes = application:get_env(eventhub, extra_db_nodes, []),
  case ExtraNodes of
    [] ->
      ok = maybe_recreate_schema();
    _ ->
      ok = join_cluster(ExtraNodes)
  end,
  lists:foreach(fun create_table/1, ?TABLES),
  ok = create_indices(),
  ok = stats_collector:subscribe(),
  ok = start_cleanup_timer(),
  ok = migration_engine:init_migrations_table(),
  _ = migration_engine:apply_pending(),
  {reply, ok, State};

handle_call({add_nodes, Nodes}, _From, State) ->
  ok = do_add_nodes(Nodes),
  {reply, ok, State};

handle_call(wait_for_tables, _From, State) ->
  mnesia:wait_for_tables(?TABLES, ?TABLE_WAIT_TIMEOUT),
  {reply, ok, State}.

handle_cast(_Msg, State) -> {noreply, State}.
handle_info({cleanup}, State) ->
  prune_dead_nodes(),
  erlang:send_after(?CLEANUP_INTERVAL, self(), {cleanup}),
  {noreply, State};
handle_info(_Info, State) -> {noreply, State}.

terminate(_Reason, _State) -> ok.
code_change(_OldVsn, State, _Extra) -> {ok, State}.

%% ===================================================================
%% Управление схемой
%% ===================================================================

maybe_recreate_schema() ->
  MnesiaDir = mnesia:system_info(directory),
  case filelib:is_dir(MnesiaDir) of
    false ->
      io:format("Mnesia directory not found. Creating fresh schema...~n"),
      mnesia:stop(),
      mnesia:delete_schema([node()]),
      mnesia:create_schema([node()]),
      mnesia:start(),
      ok;
    true ->
      io:format("Mnesia directory exists (~s). Reusing existing schema.~n", [MnesiaDir]),
      case mnesia:system_info(is_running) of
        yes -> ok;
        _  -> mnesia:start()
      end
  end.

join_cluster(Nodes) ->
  case mnesia:system_info(is_running) of
    yes -> mnesia:stop();
    no -> ok
  end,
  application:set_env(mnesia, extra_db_nodes, Nodes),
  mnesia:start(),
  ensure_schema_disc(),
  wait_for_tables_available(),
  lists:foreach(fun add_local_disc_copy/1, ?DISC_TABLES).

do_add_nodes(Nodes) ->
  ExtraNodes = application:get_env(eventhub, extra_db_nodes, []),
  application:set_env(eventhub, extra_db_nodes, Nodes ++ ExtraNodes),
  {ok, _} = mnesia:change_config(extra_db_nodes, Nodes),
  ensure_schema_disc(),
  wait_for_tables_available(),
  lists:foreach(fun add_local_disc_copy/1, ?DISC_TABLES).

ensure_schema_disc() ->
  case lists:member(node(), mnesia:table_info(schema, disc_copies)) of
    false ->
      io:format("Changing schema copy to disc...~n"),
      case mnesia:change_table_copy_type(schema, node(), disc_copies) of
        {atomic, ok} -> ok;
        {aborted, {already_exists, _, _}} -> ok;
        {aborted, Reason} -> error({failed_schema_disc, Reason})
      end;
    true -> ok
  end.

add_local_disc_copy(Tab) ->
  case lists:member(node(), mnesia:table_info(Tab, disc_copies)) of
    false ->
      io:format("Adding local disc copy of table ~p...~n", [Tab]),
      case mnesia:add_table_copy(Tab, node(), disc_copies) of
        {atomic, ok} -> ok;
        {aborted, {already_exists, _}} -> ok;
        {aborted, Reason} ->
          io:format("Could not add disc copy for ~p: ~p~n", [Tab, Reason])
      end;
    true -> ok
  end.

wait_for_tables_available() ->
  lists:foreach(fun(Tab) -> wait_for_table(Tab) end, ?DISC_TABLES).

wait_for_table(Tab) ->
  case lists:member(Tab, mnesia:system_info(tables)) of
    true -> ok;
    false ->
      timer:sleep(100),
      wait_for_table(Tab)
  end.

%% ===================================================================
%% Автоматическая очистка мёртвых узлов
%% ===================================================================

start_cleanup_timer() ->
  erlang:send_after(?CLEANUP_INTERVAL, self(), {cleanup}),
  ok.

prune_dead_nodes() ->
  AliveNodes = lists:filter(fun(Node) ->
    Node =/= node() andalso net_adm:ping(Node) =:= pong
                            end, mnesia:system_info(db_nodes)),
  DeadNodes = mnesia:system_info(db_nodes) -- [node() | AliveNodes],
  lists:foreach(fun(Node) ->
    io:format("Removing dead node ~p from Mnesia schema...~n", [Node]),
    lists:foreach(fun(Tab) ->
      case lists:member(Node, mnesia:table_info(Tab, disc_copies)) of
        true -> catch mnesia:del_table_copy(Tab, Node);
        false -> ok
      end
                  end, ?DISC_TABLES),
    catch mnesia:del_table_copy(schema, Node)
                end, DeadNodes).

%% ===================================================================
%% Создание / открытие таблиц
%% ===================================================================

create_table(Table) ->
  Opts = table_opts(Table),
  case mnesia:create_table(Table, Opts) of
    {atomic, ok} -> ok;
    {aborted, {already_exists, _}} -> ok;
    {aborted, Reason} ->
      error({table_creation_failed, Table, Reason})
  end.

%% ===================================================================
%% Опции хранения таблиц
%% ===================================================================

table_opts(user) -> [{disc_copies, [node()]}, {attributes, record_info(fields, user)}];
table_opts(admin) -> [{disc_copies, [node()]}, {attributes, record_info(fields, admin)}];
table_opts(calendar) -> [{disc_copies, [node()]}, {attributes, record_info(fields, calendar)}];
table_opts(calendar_share) -> [{disc_copies, [node()]}, {attributes, record_info(fields, calendar_share)}];
table_opts(calendar_specialist) -> [{disc_copies, [node()]}, {attributes, record_info(fields, calendar_specialist)}];
table_opts(event) -> [{disc_copies, [node()]}, {attributes, record_info(fields, event)}];
table_opts(recurrence_exception) -> [{disc_copies, [node()]}, {attributes, record_info(fields, recurrence_exception)}];
table_opts(booking) -> [{disc_copies, [node()]}, {attributes, record_info(fields, booking)}];
table_opts(review) -> [{disc_copies, [node()]}, {attributes, record_info(fields, review)}];
table_opts(report) -> [{disc_copies, [node()]}, {attributes, record_info(fields, report)}];
table_opts(banned_word) -> [{disc_copies, [node()]}, {attributes, record_info(fields, banned_word)}];
table_opts(ticket) -> [{disc_copies, [node()]}, {attributes, record_info(fields, ticket)}];
table_opts(subscription) -> [{disc_copies, [node()]}, {attributes, record_info(fields, subscription)}];
table_opts(admin_audit) -> [{disc_copies, [node()]}, {attributes, record_info(fields, admin_audit)}];
table_opts(notification) -> [{disc_copies, [node()]}, {attributes, record_info(fields, notification)}];
table_opts(stats) -> [{disc_copies, [node()]}, {attributes, record_info(fields, stats)}];
table_opts(schema_migration) -> [{disc_copies, [node()]}, {attributes, record_info(fields, schema_migration)}];
table_opts(session) -> [{ram_copies, [node()]}, {attributes, record_info(fields, session)}];
table_opts(admin_session) -> [{ram_copies, [node()]}, {attributes, record_info(fields, admin_session)}].

%% ===================================================================
%% Индексы
%% ===================================================================

create_indices() ->
  mnesia:add_table_index(event, calendar_id),
  mnesia:add_table_index(event, start_time),
  mnesia:add_table_index(event, event_type),
  mnesia:add_table_index(event, master_id),
  mnesia:add_table_index(event, specialist_id),
  mnesia:add_table_index(event, status),
  mnesia:add_table_index(booking, event_id),
  mnesia:add_table_index(booking, user_id),
  mnesia:add_table_index(booking, status),
  mnesia:add_table_index(calendar, owner_id),
  mnesia:add_table_index(calendar, status),
  mnesia:add_table_index(calendar, short_name),
  mnesia:add_table_index(calendar, category),
  mnesia:add_table_index(calendar_specialist, calendar_id),
  mnesia:add_table_index(calendar_specialist, user_id),
  mnesia:add_table_index(user, nickname),
  mnesia:add_table_index(user, email),
  mnesia:add_table_index(notification, user_id),
  mnesia:add_table_index(notification, is_read),
  ok.