% @doc spy: knows constraints {recipient, amount, payload}
%
% spies the chain for transactions that satisfy that constraint
%
-module(fd_spy).
-vsn("0.2.0").

% MVP: register search patterns
% simply print to console when one of them is found

-behavior(gen_server).

-export_type([
]).

-export([
    %% caller context
    reg/3,

    %% api
    start_link/0,

    %% process context
    init/1, handle_call/3, handle_cast/2, handle_info/2,
    code_change/3, terminate/2
]).

% recipient is a string
-type pubkey32() :: <<_:256>>.

-record(sp,
        {recipient  :: pubkey32(),
         amount     :: pos_integer(),
         payload    :: binary()}).
-type search_pattern() :: #sp{}.

-record(s,
        {last_height_seen = none :: none | integer(),
         searching_for    = []   :: [search_pattern()]}).

-type state() :: #s{}.

-include("$zx_include/zx_logger.hrl").

%%-----------------------------------------------------------------------------
%% caller context
%%-----------------------------------------------------------------------------

-spec reg(Recipient, Amount, Payload) -> ok | {error, Reason}
    when Recipient :: pubkey32(),
         Amount    :: pos_integer(),
         Payload   :: binary(),
         Reason    :: any().

reg(R, A, P) when is_binary(R), byte_size(R) =:= 32,
                  is_integer(A), A >= 0,
                  is_binary(P) ->
    gen_server:call(?MODULE, {reg, R, A, P}).



%% gen_server callbacks
start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, none, []).


%%-----------------------------------------------------------------------------
%% process context below this line
%%-----------------------------------------------------------------------------

%% gen_server callbacks

-spec init(none) -> {ok, state()}.

init(none) ->
    tell("starting fd_spy"),
    hz:chain_nodes(fewd:chain_nodes()),
    erlang:send_after(1000, self(), check_chain),
    InitState = #s{},
    {ok, InitState}.



-spec handle_call(Msg, From, State) -> Result
    when Msg      :: any(),
         From     :: {pid(), reference()},
         State    :: state(),
         Result   :: {reply, Reply, NewState}
                   | {noreply, NewState},
         Reply    :: any(),
         NewState :: state().

handle_call({reg, Recipient, Amount, Payload}, _From, State) ->
    {Reply, NewState} = do_reg(Recipient, Amount, Payload, State),
    {reply, Reply, NewState};
handle_call(Unexpected, From, State) ->
    tell("~tp: unexpected call from ~tp: ~tp", [?MODULE, Unexpected, From]),
    {noreply, State}.



handle_cast(Unexpected, State) ->
    tell("~tp: unexpected cast: ~tp", [?MODULE, Unexpected]),
    {noreply, State}.



handle_info(check_chain, State) ->
    NewState = do_check_chain(State),
    erlang:send_after(1000, self(), check_chain),
    {noreply, NewState};
handle_info(Unexpected, State) ->
    tell("~tp: unexpected info: ~tp", [?MODULE, Unexpected]),
    {noreply, State}.



code_change(_, State, _) ->
    {ok, State}.



terminate(_, _) ->
    ok.



%%-----------------------------------------------------------------------------
%% internals
%%-----------------------------------------------------------------------------

do_check_chain(State = #s{last_height_seen = none}) ->
    case hz:kb_current_height() of
        {ok, Max} ->
            hh(Max-1, Max, State);
        Error     ->
            tell("~tp hz error: ~tp", [?MODULE, Error]),
            State
    end;
do_check_chain(State = #s{last_height_seen = Min}) ->
    case hz:kb_current_height() of
        {ok, Max} ->
            hh(Min, Max, State);
        Error     ->
            tell("~tp hz error: ~tp", [?MODULE, Error]),
            State
    end.

% handle height
hh(PrevHeight, NewHeight, State) when PrevHeight < NewHeight ->
    tell("~tp cool: PrevHeight=~tp, NewHeight=~tp", [?MODULE, PrevHeight, NewHeight]),
    Spends = fd_hz:filter_spends(fd_hz:txs_from_to(PrevHeight + 1, NewHeight)),
    tell("~tp spends: ~tp", [?MODULE, Spends]),
    NewState = State#s{last_height_seen = NewHeight},
    NewState;
hh(PrevHeight, NewHeight, State) when PrevHeight >= NewHeight ->
    log(info, "~tp lame: PrevHeight=~tp, NewHeight=~tp", [?MODULE, PrevHeight, NewHeight]),
    State.


-spec do_reg(Recipient, Amount, Payload, State) -> {Reply, NewState}
    when Recipient :: pubkey32(),
         Amount    :: pos_integer(),
         Payload   :: binary(),
         State     :: state(),
         Reply     :: ok
                    | {error, Reason},
         Reason    :: any(),
         NewState  :: state().

do_reg(Recipient, Amount, Payload, State) ->
    case already_registered(Recipient, Payload, State) of
        true  -> {error, already_registered};
        false -> really_register(Recipient, Amount, Payload, State)
    end.



-spec already_registered(Recipient, Payload, State) -> boolean()
    when Recipient :: pubkey32(),
         Payload   :: binary(),
         State     :: state().

already_registered(Recipient, Payload, _State = #s{searching_for = SPs}) ->
    ar(Recipient, Payload, SPs).

ar(Recipient, Payload, [#sp{recipient=Recipient, payload=Payload} | _]) ->
    true;
ar(Recipient, Payload, [_ | Rest]) ->
    ar(Recipient, Payload, Rest);
ar(_, _, []) ->
    false.



-spec really_register(Recipient, Amount, Payload, State) -> {Reply, NewState}
    when Recipient :: pubkey32(),
         Amount    :: pos_integer(),
         Payload   :: binary(),
         State     :: state(),
         Reply     :: ok
                    | {error, Reason},
         Reason    :: any(),
         NewState  :: state().

really_register(R, A, P, State = #s{searching_for = SPs}) ->
    NewSearchPattern = #sp{recipient = R,
                           amount    = A,
                           payload   = P},
    tell("~tp: really_register(~tp,~tp,~tp)", [?MODULE, R, A, P]),
    NewSearchPatterns = [NewSearchPattern | SPs],
    NewState = State#s{searching_for = NewSearchPatterns},
    {reply, ok, NewState}.