-module(mc_cursor).

-behaviour(gen_server).

-include("mongo_protocol.hrl").

-export([
  next/1, next/2,
  rest/1, rest/2,
  take/2, take/3,
  foldl/4, foldl/5,
  map/3,
  next_batch/1, next_batch/2,
  close/1
]).

-export([
  start_link/5
]).

-export([
  init/1,
  handle_call/3,
  handle_cast/2,
  handle_info/2,
  terminate/2,
  code_change/3
]).

-record(state, {
  connection :: mc_worker:connection(),
  collection :: atom(),
  cursor :: integer(),
  batchsize :: integer(),
  batch :: [bson:document()],
  monitor :: reference()
}).


-spec next(pid()) -> error | {bson:document()}.
next(Cursor) ->
  next(Cursor, cursor_default_timeout()).

-spec next(pid(), timeout()) -> error | {} | {bson:document()}.
next(Cursor, Timeout) ->
  try gen_server:call(Cursor, {next, Timeout}, Timeout)
  catch
    exit:{noproc, _} -> error
  end.

-spec next_batch(pid()) -> error | {bson:document()}.
next_batch(Cursor) ->
  next_batch(Cursor, cursor_default_timeout()).

-spec next_batch(pid(), timeout()) -> error | {} | {bson:document()}.
next_batch(Cursor, Timeout) ->
  try gen_server:call(Cursor, {next_batch, Timeout}, Timeout)
  catch
    exit:{noproc, _} -> error
  end.

-spec rest(pid()) -> [bson:document()] | error.
rest(Cursor) ->
  rest(Cursor, cursor_default_timeout()).

-spec rest(pid(), timeout()) -> [bson:document()] | error.
rest(Cursor, Timeout) ->
  try gen_server:call(Cursor, {rest, infinity, Timeout}, Timeout)
  catch
    exit:{noproc, _} -> error
  end.

-spec take(pid(), non_neg_integer()) -> [bson:document()] | error.
take(Cursor, Limit) ->
  take(Cursor, Limit, cursor_default_timeout()).

-spec take(pid(), non_neg_integer(), timeout()) -> [bson:document()] | error.
take(Cursor, Limit, Timeout) ->
  try gen_server:call(Cursor, {rest, Limit, Timeout}, Timeout)
  catch
    exit:{noproc, _} -> error
  end.

cursor_default_timeout() ->
  application:get_env(mongodb, cursor_timeout, infinity).

-spec foldl(fun((bson:document(), term()) -> term()), term(), pid(), non_neg_integer() | infinity) -> term().
foldl(Fun, Acc, Cursor, Max) ->
  foldl(Fun, Acc, Cursor, Max, cursor_default_timeout()).

-spec foldl(fun((bson:document(), term()) -> term()), term(), pid(), non_neg_integer() | infinity, timeout()) -> term().
foldl(_Fun, Acc, _Cursor, 0, _Timeout) ->
  Acc;
foldl(Fun, Acc, Cursor, infinity, Timeout) ->
  lists:foldl(Fun, Acc, rest(Cursor, Timeout));
foldl(Fun, Acc, Cursor, Max, Timeout) ->
  case next(Cursor, Timeout) of
    error -> Acc;
    {} -> Acc;
    {Doc} -> foldl(Fun, Fun(Doc, Acc), Cursor, Max - 1, Timeout)
  end.

-spec map(fun((bson:document()) -> term()), pid(), non_neg_integer()) -> [term()].
map(Fun, Cursor, Max) ->
  lists:reverse(foldl(fun(Doc, Acc) ->
    [Fun(Doc) | Acc]
                      end, [], Cursor, Max)).

-spec close(pid()) -> ok.
close(Cursor) ->
  gen_server:cast(Cursor, halt).

start_link(Connection, Collection, Cursor, BatchSize, Batch) ->
  gen_server:start_link(?MODULE, [self(), Connection, Collection, Cursor, BatchSize, Batch], []).


%% @hidden
init([Owner, Connection, Collection, Cursor, BatchSize, Batch]) ->
  Monitor = erlang:monitor(process, Owner),
  {ok, #state{
          connection = Connection,
          collection = Collection,
          cursor = Cursor,
          batchsize = BatchSize,
          batch = Batch,
          monitor = Monitor
         }}.

%% @hidden
handle_call({next, Timeout}, _From, State) ->
  case next_i(State, Timeout) of
    {Reply, #state{cursor = 0, batch = []} = UpdatedState} ->
      {stop, normal, Reply, UpdatedState};
    {Reply, UpdatedState} ->
      {reply, Reply, UpdatedState}
  end;
handle_call({rest, Limit, Timeout}, _From, State) ->
  case rest_i(State, Limit, Timeout) of
    {Reply, #state{cursor = 0} = UpdatedState} ->
      {stop, normal, Reply, UpdatedState};
    {Reply, UpdatedState} ->
      {reply, Reply, UpdatedState}
  end;
handle_call({next_batch, Timeout}, _From, State = #state{batchsize = Limit}) ->
  case rest_i(State, Limit, Timeout) of
    {Reply, #state{cursor = 0} = UpdatedState} ->
      {stop, normal, Reply, UpdatedState};
    {Reply, UpdatedState} ->
      {reply, Reply, UpdatedState}
  end.

%% @hidden
handle_cast(halt, State) ->
  {stop, normal, State};
handle_cast(_, State) ->
  {noreply, State}.

%% @hidden
handle_info({'DOWN', Monitor, process, _, _}, #state{monitor = Monitor} = State) ->
  {stop, normal, State};
handle_info(_, State) ->
  {noreply, State}.

%% @hidden
terminate(_, #state{cursor = 0}) -> ok;
terminate(_, State) ->
  gen_server:call(State#state.connection, #killcursor{cursorids = [State#state.cursor]}).

%% @hidden
code_change(_Old, State, _Extra) ->
  {ok, State}.

%% @private
next_i(#state{batch = [Doc | Rest]} = State, _Timeout) ->
  {{Doc}, State#state{batch = Rest}};
next_i(#state{batch = [], cursor = 0} = State, _Timeout) ->
  {{}, State};
next_i(#state{batch = []} = State, Timeout) ->
  Reply = gen_server:call(
    State#state.connection,
    #getmore{
      collection = State#state.collection,
      batchsize = State#state.batchsize,
      cursorid = State#state.cursor
    },
    Timeout),
  Cursor = Reply#reply.cursorid,
  Batch = Reply#reply.documents,
  next_i(State#state{cursor = Cursor, batch = Batch}, Timeout).

%% @private
rest_i(State, infinity, Timeout) ->
  rest_i(State, -1, Timeout);
rest_i(State, Limit, Timeout) when is_integer(Limit) ->
  {Docs, UpdatedState} = rest_i(State, [], Limit, Timeout),
  {lists:reverse(Docs), UpdatedState}.

%% @private
rest_i(State, Acc, 0, _Timeout) ->
  {Acc, State};
rest_i(State, Acc, Limit, Timeout) ->
  case next_i(State, Timeout) of
    {{}, UpdatedState} -> {Acc, UpdatedState};
    {{Doc}, UpdatedState} ->
      rest_i(UpdatedState, [Doc | Acc], Limit - 1, Timeout)
  end.