%% -*- erlang -*-
%%
%% cre
%%
%% Copyright 2015-2018 Jörgen Brandt
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% -------------------------------------------------------------------
%% @author Jörgen Brandt <joergen.brandt@onlinehome.de>
%% @version 0.1.8
%% @copyright 2015-2018 Jörgen Brandt
%%
%%
%%
%%
%%
%% @end
%% -------------------------------------------------------------------

-module( cre_client ).
-behavior( gen_server ).


%%====================================================================
%% Exports
%%====================================================================

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

-export( [start_link/3, start_link/4, eval/2, cre_reply/4, stop/1] ).


%%====================================================================
%% Constant definitions
%%====================================================================

-define( INTERVAL, 250 ).

%%====================================================================
%% Callback definitions
%%====================================================================

-callback init( InitArg :: _ ) -> UsrInfo :: _.

-callback is_value( E :: _, UsrInfo :: _ ) -> boolean().

-callback step( E :: _, UsrInfo :: _ ) -> {ok, _, [_]}.

-callback recv( E :: _, ReplyLst :: [{_, _}], UsrInfo :: _ ) -> _.


%%====================================================================
%% Record definitions
%%====================================================================

-record( client_state, { cre_name,
                         client_mod,
                         usr_info,
                         request_map = #{},
                         reply_map   = #{},
                         state_map   = #{} } ).


%%====================================================================
%% API functions
%%====================================================================

start_link( CreName, ClientMod, ClientArg ) ->
  gen_server:start_link( ?MODULE, {CreName, ClientMod, ClientArg}, [] ).

start_link( ClientName, CreName, ClientMod, ClientArg ) ->
  gen_server:start_link( ClientName,
                        ?MODULE,
                        {CreName, ClientMod, ClientArg},
                        [] ).

eval( ClientName, E ) ->
  gen_server:call( ClientName, {eval, E}, infinity ).

cre_reply( ClientName, I, A, Delta ) ->
  gen_server:cast( ClientName, {cre_reply, I, A, Delta} ).

stop( ClientName ) ->
  gen_server:stop( ClientName ).


%%====================================================================
%% gen_server callback functions
%%====================================================================

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

terminate( _Reason, _ClientState ) ->
  ok.


init( {CreName, ClientMod, ClientArg} ) ->
  
  UsrInfo = ClientMod:init( ClientArg ),

  ClientState = #client_state{ cre_name   = CreName,
                               client_mod = ClientMod,
                               usr_info   = UsrInfo },

  _MonitorRef = monitor( process, CreName ),

  {ok, ClientState}.


handle_call( {eval, E}, From, ClientState ) ->

  #client_state{ cre_name    = CreName,
                 client_mod  = ClientMod,
                 usr_info    = UsrInfo,
                 request_map = RequestMap,
                 reply_map   = ReplyMap,
                 state_map   = StateMap } = ClientState,

  Self = self(),

  Send =
    fun( A ) ->
      cre_master:cre_request( CreName, Self, From, A )
    end,

  % evaluate
  {ok, E1, ALst} = ClientMod:step( E, UsrInfo ),

  % send new tasks
  lists:foreach( Send, ALst ),

  % check if a value resulted
  ClientState1 =
    case ClientMod:is_value( E1, UsrInfo ) of

      true  ->
        gen_server:reply( From, E1 ),
        ClientState;

      false ->
        ClientState#client_state{ request_map = RequestMap#{ From => E1 },
                                  reply_map   = ReplyMap#{ From => [] },
                                  state_map   = StateMap#{ From => idle } }
    end,

  {noreply, ClientState1};


handle_call( _Request, _From, ClientState ) ->
  {reply, {error, bad_msg}, ClientState}.


handle_cast( {cre_reply, From, A, Delta}, ClientState ) ->

  #client_state{ reply_map = ReplyMap,
                 state_map = StateMap } = ClientState,

  ClientState1 =
    case StateMap of
      #{ From := State } ->
        case State of
          idle -> start_timer( From );
          _    -> ok
        end,

        #{ From := ReplyLst } = ReplyMap,

        ClientState#client_state{ reply_map = ReplyMap#{ From => [{A, Delta}|ReplyLst] },
                                  state_map = #{ From => primed } };

      _ -> ClientState
    end,

  {noreply, ClientState1};


handle_cast( {continue, From}, ClientState ) ->

  #client_state{ cre_name    = CreName,
                 client_mod  = ClientMod,
                 usr_info    = UsrInfo,
                 request_map = RequestMap,
                 reply_map   = ReplyMap,
                 state_map   = StateMap } = ClientState,

  #{ From := E } = RequestMap,
  #{ From := ReplyLst } = ReplyMap,

  Self = self(),

  Send =
    fun( A ) ->
      cre_master:cre_request( CreName, Self, From, A )
    end,

  % receive new result pairs
  E1 =
    case ReplyLst of
      []    -> E;
      [_|_] -> ClientMod:recv( E, ReplyLst, UsrInfo )
    end,

  % evaluate
  {ok, E2, ALst} = ClientMod:step( E1, UsrInfo ),

  % send new tasks
  lists:foreach( Send, ALst ),

  % check if a value resulted
  ClientState1 =
    case ClientMod:is_value( E2, UsrInfo ) of

      true  ->
        gen_server:reply( From, E2 ),
        ClientState#client_state{ request_map = maps:remove( From, RequestMap ),
                                  reply_map   = maps:remove( From, ReplyMap ),
                                  state_map   = maps:remove( From, StateMap ) };

      false ->
        ClientState#client_state{ request_map = RequestMap#{ From => E2 },
                                  reply_map   = ReplyMap#{ From => [] },
                                  state_map   = StateMap#{ From => idle } }
    end,

  {noreply, ClientState1};


handle_cast( _Request, ClientState ) ->
  {noreply, ClientState}.


handle_info( {'DOWN', _MonitorRef, process, _Object, _Info}, ClientState ) ->
  {stop, cre_down, ClientState};

handle_info( _Info, ClientState ) ->
  {noreply, ClientState}.


-spec start_timer( From :: _ ) -> ok.

start_timer( From ) ->

  Self = self(),

  F =
    fun() ->
      timer:sleep( ?INTERVAL ),
      gen_server:cast( Self, {continue, From} )
    end,

  _Pid = spawn_link( F ),

  ok.