bikoret/sanhedrin/src/panel.erl

%%%-------------------------------------------------------------------
%%% @doc Panel — manage a deliberation panel.
%%%
%%% Architecture §3.2:
%%% convene/3 spawns judges, deliberate/2 collects votes.
%%%
%%% THE CRITICAL CHECK: unanimous conviction on capital case
%%% triggers suspicion of consensus — acquit.
%%%
%%% Minority opinions are ALWAYS preserved.
%%% @end
%%%-------------------------------------------------------------------
-module(panel).

-behaviour(gen_server).

-include("sanhedrin.hrl").

%% API
-export([start_link/2, deliberate_async/2, get_state/1]).
%% Exported for testing
-export([check_unanimous/2, compute_majority_minority/1, determine_outcome/3]).

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

-record(state, {
    panel        :: #panel{},
    case_data    :: #sanhedrin_case{},
    timeout      :: pos_integer(),
    escalation   :: pid() | undefined,
    timer_ref    :: reference() | undefined
}).

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

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

%% @doc Start deliberation asynchronously.
%% The panel will collect votes and send the result
%% back to escalation when done.
-spec deliberate_async(pid(), pos_integer()) -> ok.
deliberate_async(PanelPid, Timeout) ->
    gen_server:cast(PanelPid, {deliberate, Timeout}).

%% @doc Get current panel state (for testing/inspection).
-spec get_state(pid()) -> map().
get_state(PanelPid) ->
    gen_server:call(PanelPid, get_state).

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

init({Case, Size}) ->
    PanelId = generate_id(),
    Now = erlang:system_time(millisecond),

    %% Spawn judges
    Judges = convene_judges(Case, Size),

    Panel = #panel{
        panel_id    = PanelId,
        case_ref    = Case#sanhedrin_case.case_ref,
        size        = Size,
        judges      = Judges,
        votes       = [],
        status      = convened,
        convened_at = Now,
        decided_at  = undefined
    },

    {ok, #state{
        panel     = Panel,
        case_data = Case,
        timeout   = ?TIMEOUT_MONETARY,
        escalation = whereis(escalation)
    }}.

handle_call(get_state, _From, State) ->
    P = State#state.panel,
    Reply = #{
        panel_id   => P#panel.panel_id,
        case_ref   => P#panel.case_ref,
        size       => P#panel.size,
        status     => P#panel.status,
        vote_count => length(P#panel.votes)
    },
    {reply, Reply, State};

handle_call(_Request, _From, State) ->
    {reply, {error, unknown_request}, State}.

handle_cast({deliberate, Timeout}, State) ->
    Panel = State#state.panel,

    %% Instruct all judges to deliberate
    lists:foreach(
        fun(JudgePid) ->
            judge:deliberate(JudgePid, self())
        end,
        Panel#panel.judges
    ),

    %% Set timeout for deliberation
    TimerRef = erlang:send_after(Timeout, self(), deliberation_timeout),

    NewPanel = Panel#panel{status = deliberating},
    {noreply, State#state{
        panel = NewPanel,
        timeout = Timeout,
        timer_ref = TimerRef
    }};

handle_cast(_Msg, State) ->
    {noreply, State}.

handle_info({vote, Vote}, State) ->
    Panel = State#state.panel,
    NewVotes = [Vote | Panel#panel.votes],
    NewPanel = Panel#panel{votes = NewVotes},
    NewState = State#state{panel = NewPanel},

    %% Check if all votes are in
    case length(NewVotes) >= Panel#panel.size of
        true ->
            %% All votes collected — decide
            maybe_cancel_timer(State#state.timer_ref),
            decide(NewState);
        false ->
            {noreply, NewState}
    end;

handle_info(deliberation_timeout, State) ->
    %% Timeout — decide with whatever votes we have
    decide(State);

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

terminate(_Reason, State) ->
    %% Ensure all judges are stopped
    Panel = State#state.panel,
    lists:foreach(
        fun(JudgePid) ->
            case is_process_alive(JudgePid) of
                true -> judge:stop(JudgePid);
                false -> ok
            end
        end,
        Panel#panel.judges
    ),
    ok.

%%====================================================================
%% Internal — Deliberation logic
%%====================================================================

%% @doc Decide based on collected votes.
%% THE CRITICAL CHECK: unanimous guilty on capital case → suspicion → acquit.
decide(State) ->
    Panel = State#state.panel,
    Votes = Panel#panel.votes,
    Now = erlang:system_time(millisecond),

    {Majority, Minority} = compute_majority_minority(Votes),
    UnanimousCheck = check_unanimous(Panel#panel.size, Votes),

    Decision = #decision{
        case_ref            = Panel#panel.case_ref,
        outcome             = determine_outcome(Majority, Minority, UnanimousCheck),
        majority            = Majority,
        minority            = Minority,
        panel_size          = Panel#panel.size,
        deliberation_time_ms = Now - Panel#panel.convened_at,
        unanimous_check     = UnanimousCheck
    },

    %% Store all opinions via clerk (majority AND minority)
    store_all_opinions(Panel#panel.case_ref, Votes, Majority),

    %% Notify escalation
    case State#state.escalation of
        undefined -> ok;
        EscPid when is_pid(EscPid) ->
            EscPid ! {panel_decided, Panel#panel.case_ref, Decision}
    end,

    FinalPanel = Panel#panel{
        status = decided,
        decided_at = Now
    },

    {stop, normal, State#state{panel = FinalPanel}}.

%% @doc Compute majority and minority positions.
compute_majority_minority([]) ->
    {#{position => <<"no votes">>,
       reasoning => <<"no judges voted">>,
       torah_refs => [],
       vote_count => 0},
     #{position => <<"no dissent">>,
       reasoning => <<"no judges voted">>,
       torah_refs => [],
       vote_count => 0}};
compute_majority_minority(Votes) ->
    %% Count accepts vs rejects
    Accepts = [V || V <- Votes, V#vote.verdict == accept],
    Rejects = [V || V <- Votes, V#vote.verdict == reject],
    Abstains = [V || V <- Votes, V#vote.verdict == abstain],

    {MajVotes, MinVotes} =
        case length(Accepts) >= length(Rejects) of
            true  -> {Accepts, Rejects ++ Abstains};
            false -> {Rejects, Accepts ++ Abstains}
        end,

    MajSample = case MajVotes of
        [First | _] -> First;
        [] -> #vote{position = <<"none">>, reasoning = <<"none">>,
                    torah_refs = [], verdict = abstain,
                    judge_id = make_ref(), cast_at = 0}
    end,
    MinSample = case MinVotes of
        [MFirst | _] -> MFirst;
        [] -> #vote{position = <<"no dissent">>,
                    reasoning = <<"unanimous">>,
                    torah_refs = [], verdict = abstain,
                    judge_id = make_ref(), cast_at = 0}
    end,

    Majority = #{
        position   => MajSample#vote.position,
        reasoning  => MajSample#vote.reasoning,
        torah_refs => MajSample#vote.torah_refs,
        vote_count => length(MajVotes),
        verdict    => MajSample#vote.verdict
    },
    Minority = #{
        position   => MinSample#vote.position,
        reasoning  => MinSample#vote.reasoning,
        torah_refs => MinSample#vote.torah_refs,
        vote_count => length(MinVotes),
        verdict    => MinSample#vote.verdict
    },
    {Majority, Minority}.

%% @doc THE CRITICAL CHECK.
%% Architecture §3.2: unanimous conviction on capital case
%% triggers suspicion of malfunction — acquit.
%%
%% "If the Sanhedrin unanimously finds guilty, the accused is acquitted."
%% — Sanhedrin 17a
check_unanimous(Size, Votes) when Size >= ?PANEL_CAPITAL ->
    AllGuilty = lists:all(
        fun(V) -> V#vote.verdict == reject end,
        Votes
    ),
    case AllGuilty andalso length(Votes) > 0 of
        true  -> {failed, suspicion_of_consensus};
        false -> passed
    end;
check_unanimous(_Size, _Votes) ->
    %% Unanimous check only applies to capital+ panels
    passed.

%% @doc Determine the outcome from majority, minority, and unanimous check.
determine_outcome(_Majority, _Minority, {failed, suspicion_of_consensus}) ->
    %% Unanimous guilty on capital → acquit (accepted, not rejected)
    accepted;
determine_outcome(Majority, _Minority, passed) ->
    MajCount = maps:get(vote_count, Majority, 0),
    MajVerdict = maps:get(verdict, Majority, abstain),
    case {MajCount, MajVerdict} of
        {0, _} -> teiku;
        {_, accept} -> accepted;
        {_, reject} -> rejected;
        {_, abstain} -> teiku
    end.

%% @doc Store all opinions via clerk — majority AND minority preserved.
store_all_opinions(CaseRef, Votes, Majority) ->
    MajPosition = maps:get(position, Majority, <<>>),
    lists:foreach(
        fun(Vote) ->
            IsMajority = (Vote#vote.position == MajPosition),
            Opinion = #opinion{
                case_ref   = CaseRef,
                judge_id   = Vote#vote.judge_id,
                position   = Vote#vote.position,
                reasoning  = Vote#vote.reasoning,
                torah_refs = Vote#vote.torah_refs,
                verdict    = Vote#vote.verdict,
                is_majority = IsMajority,
                stored_at  = erlang:system_time(millisecond)
            },
            clerk:store_opinion(Opinion)
        end,
        Votes
    ).

%%====================================================================
%% Internal — Panel setup
%%====================================================================

convene_judges(Case, Size) ->
    lists:map(
        fun(_N) ->
            {ok, Pid} = judge:start_link(Case),
            Pid
        end,
        lists:seq(1, Size)
    ).

generate_id() ->
    Bytes = crypto:strong_rand_bytes(8),
    base64:encode(Bytes).

maybe_cancel_timer(undefined) -> ok;
maybe_cancel_timer(Ref) -> erlang:cancel_timer(Ref).