-module(robin_handoff).

-export([start/0,start/1,start/2,stop/0]).
-export([step/0]).


%% see if a handoff is in progress

active_count(Node) when is_atom(Node) ->
	Receivers=rpc:call(Node,supervisor,count_children,[riak_core_handoff_receiver_sup]),
	Senders=rpc:call(Node,supervisor,count_children,[riak_core_handoff_sender_sup]),
	lager:log(debug,self(),"Check Active: ~p~n~p~n~p",[Node,Receivers,Senders]),
	case is_list(Receivers) andalso proplists:is_defined(active,Receivers) andalso is_list(Senders) andalso proplists:is_defined(active,Senders) of
		true ->
			ActiveReceivers=proplists:get_value(active,Receivers),
			ActiveSenders=proplists:get_value(active,Senders),
			ActiveReceivers + ActiveSenders;
		false ->
			lager:log(info,self(),"invalid response from ~p",Node),
			reload
	end;
active_count([Node | Rest]) ->
	active_count(Node) + active_count(Rest);
active_count([]) -> 0;
active_count(Node) ->
	lager:log(info,self(),"Handoff rotation enountered invalid node: ~p.",[Node]),
	0.

%% advance to next pair
loop(Delay,[{Node1,Node2}|Rest], NodeList,Concurrency) ->
    receive
        tick ->
			%% disable any new handoffs starting
			rpc:multicall(NodeList,application,set_env,[riak_core,disable_inbound_handoff,true]),
			rpc:multicall(NodeList,application,set_env,[riak_core,disable_outbound_handoff,true]),
			case active_count(NodeList) of
				0 ->
					%% if no handoffs active, move on to the next pair
					rpc:multicall(NodeList,riak_core_handoff_manager,set_concurrency,[0]),
					rpc:multicall([Node1,Node2],application,set_env,[riak_core,disable_inbound_handoff,false]),
					rpc:multicall([Node1,Node2],application,set_env,[riak_core,disable_outbound_handoff,false]),
					rpc:multicall([Node1,Node2],riak_core_handoff_manager,set_concurrency,[Concurrency]),
					lager:log(info,self(),"handoff_concurrency changed: ~p",[[{Node,rpc:call(Node,application,get_env,[riak_core,handoff_concurrency])} || Node <- NodeList]]),
					erlang:send_after(Delay,self(),tick),
					loop(Delay,Rest ++ [{Node1,Node2}],NodeList,Concurrency);
				reload ->
					lager:log(info,self(),"Reloading member list"),
					{ok,Ring} = riak_core_ring_manager:get_my_ring(),
					Members = riak_core_ring:all_members(Ring),
					case length(Members) >= 2 of
						true ->
							{Left,Right} = lists:splitwith(fun(A) -> A =/= {Node1,Node2} end, buildpairs(Members)),
							%%immediate tick to try again
							erlang:send_after(1000,self(),tick),
							loop(Delay, Right ++ Left, Members, Concurrency);
						false ->
							lager:log(info,self(),"Stopping round-robin handoff: Need at least 2 cluster members to handoff")
					end;
				_ ->
					%% don't interrupt handoff in progess, wait 1 minute
					erlang:send_after(60000,self(),tick)
			end;
        _ ->
            lager:log(info,self(),"Stopping round-robin handoff."),
			rpc:multicall(NodeList,application,set_env,[riak_core,disable_inbound_handoff,true]),
			rpc:multicall(NodeList,application,set_env,[riak_core,disable_outbound_handoff,true]),
			rpc:multicall(NodeList,riak_core_handoff_manager,set_concurrency,[0]),
            unregister(?MODULE)
    end.

%% build list of all possible 2-node combinations
buildpairs([ Node1, Node2 ]) ->
    [{Node1, Node2}];
buildpairs([Node | Rest]) ->
    [{Node,Node2} || Node2 <- Rest] ++ buildpairs(Rest).

%% start(Delay) begin round-robin concurrency, advance after Delay
%% minutes - default 1 hour
start() ->
    start(60,2).

start(N) ->
    start(N,2).

start(Delay,Concurrency) ->
    case whereis(?MODULE) of
        undefined ->
            lager:log(info,self(),"Starting round-robin handoff_concurrency of ~p every ~p minutes.",[Concurrency, Delay]),
            {ok,Ring} = riak_core_ring_manager:get_my_ring(),
            Members = riak_core_ring:all_members(Ring),
            if 
                length(Members) > 1 ->
                    register(?MODULE,
                        spawn(fun() -> loop(Delay * 60000,
                                        buildpairs(Members),Members,Concurrency)
                            end)),
                    erlang:send_after(Delay,?MODULE,tick);
                true -> {error, "Need at least 2 cluster members to handoff"}
            end;
        _ -> {error, "Already Started"}
    end.

stop() ->
    case whereis(?MODULE) of
        undefined ->
            {error, "Not running"};
        Pid ->
            Pid ! stop
    end.

step() ->
	whereis(?MODULE) ! tick.