-module(nx_kernel).
-behaviour(gen_server).

%% Pure-functional API
-export([new/0, new/3,
         add_actor/4, has_actor/2, actors/1, actor_count/1,
         publish/2, publish/3,
         bootstrap_actor/4,
         actor_id/1, log_state/1, log_tip/1,
         key_spec/1, actor_state/1, projections/1, next_published/1,
         actor_log_state/2, actor_log_tip/2,
         actor_inbox_state/2, actor_inbox_tip/2,
         append_to_actor_inbox/3,
         actor_key_spec/2, actor_state/2, actor_projections/2,
         actor_next_published/2, actor_bucket/2,
         with_projections/2, with_actor_projections/3,
         next_actor_seq/1]).

%% gen_server API
-export([start_link/3, publish/1, query/0, log_tip/0,
         with_projections/1, stop/0,
         add_actor/3, publish_to/2, log_tip_for/1, log_state_for/1,
         inbox_tip_for/1, inbox_state_for/1, append_inbox/2,
         actors/0, state_for/1, bucket_for/1,
         with_projections_for/2,
         bootstrap_actor/3]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2]).

%% Kernel orchestrator — the long-lived runtime state held by the
%% running fed-sx instance. Step 1 (m2) refactor: state is now
%% per-actor bucketed so one kernel hosts any number of actors.
%%
%% New state shape (property list):
%%   [{actors, [{ActorId, ActorBucket}, ...]},
%%    {next_actor_seq, NextN}]
%%
%% ActorBucket = [{key_spec, KS},
%%                {actor_state, AS},
%%                {log, L},
%%                {projections, [Name]},
%%                {next_published, NextSeq}]
%%
%% Legacy single-actor accessors (actor_id/1, key_spec/1, etc.)
%% continue to read from the first registered actor — keeps every
%% pre-m2 test passing through bootstrap:start/3.
%%
%% next_actor_seq is a monotonic counter handed out to add_actor for
%% future use (e.g. per-actor URL paths in Step 4). It's not yet
%% read by the rest of the kernel.

%% ── Pure-functional API ──────────────────────────────────────────

new() ->
    [{actors, []}, {next_actor_seq, 1}].

new(ActorId, KeySpec, ActorStateProplist) ->
    {ok, S} = add_actor(ActorId, KeySpec, ActorStateProplist, new()),
    S.

add_actor(ActorId, KeySpec, AS, State) ->
    Actors = field(actors, State),
    case has_keyed(ActorId, Actors) of
        true ->
            {error, already_present};
        false ->
            {ok, L0} = log:open(ActorId, base_stub()),
            {ok, I0} = log:open(ActorId, inbox_base_stub()),
            Bucket = [{key_spec, KeySpec},
                      {actor_state, AS},
                      {log, L0},
                      {actor_inbox, I0},
                      {projections, []},
                      {next_published, 1}],
            Seq = field(next_actor_seq, State),
            State1 = set(actors, Actors ++ [{ActorId, Bucket}], State),
            State2 = set(next_actor_seq, Seq + 1, State1),
            {ok, State2}
    end.

has_actor(ActorId, State) ->
    has_keyed(ActorId, field(actors, State)).

actors(State) ->
    [Id || {Id, _Bucket} <- field(actors, State)].

actor_count(State) ->
    length(field(actors, State)).

next_actor_seq(State) ->
    field(next_actor_seq, State).

actor_bucket(ActorId, State) ->
    find_keyed(ActorId, field(actors, State)).

%% publish/3 — per-actor publish.
publish(ActorId, Request, State) ->
    case actor_bucket(ActorId, State) of
        {error, no_actor} ->
            {error, no_actor, State};
        {ok, Bucket} ->
            P = field(next_published, Bucket),
            Ctx = [{actor_id,    ActorId},
                   {published,   P},
                   {key_spec,    field(key_spec, Bucket)},
                   {actor_state, field(actor_state, Bucket)},
                   {log,         field(log, Bucket)},
                   {projections, field(projections, Bucket)}],
            case outbox:publish(Request, Ctx) of
                {ok, Result, NewLog} ->
                    B1 = set(log, NewLog, Bucket),
                    B2 = set(next_published, P + 1, B1),
                    NewState = set_bucket(ActorId, B2, State),
                    {ok, Result, NewState};
                {error, Reason, _} ->
                    {error, Reason, State}
            end
    end.

%% publish/2 — legacy single-actor publish; routes to first actor.
publish(Request, State) ->
    case actors(State) of
        [] -> {error, no_actor, State};
        [First | _] -> publish(First, Request, State)
    end.

%% bootstrap_actor/4 — register an actor bucket and immediately
%% publish a Create{Person|Service|Group} as that actor's first
%% activity. Profile carries the object fields plus :public_keys.
%% Returns {ok, Result, NewState} where Result has the published
%% Create's CID, or {error, Reason, State} on validation halt.

bootstrap_actor(ActorId, Profile, KeySpec, State) ->
    PublicKeys = case field(public_keys, Profile) of
        nil -> [];
        KS  -> KS
    end,
    AS = [{public_keys, PublicKeys}],
    case add_actor(ActorId, KeySpec, AS, State) of
        {ok, State1} ->
            ActorType = case field(type, Profile) of
                nil -> person;
                T   -> T
            end,
            Object = [{type, ActorType}] ++ collect_profile_fields(
                [name, preferredUsername, summary, icon, public_keys],
                Profile),
            Request = [{type, create}, {object, Object}],
            publish(ActorId, Request, State1);
        {error, Reason} ->
            {error, Reason, State}
    end.

collect_profile_fields([], _) -> [];
collect_profile_fields([F | Rest], Profile) ->
    case field(F, Profile) of
        nil -> collect_profile_fields(Rest, Profile);
        V   -> [{F, V} | collect_profile_fields(Rest, Profile)]
    end.

with_actor_projections(ActorId, Names, State) ->
    case actor_bucket(ActorId, State) of
        {error, no_actor} ->
            {error, no_actor};
        {ok, Bucket} ->
            B1 = set(projections, Names, Bucket),
            {ok, set_bucket(ActorId, B1, State)}
    end.

with_projections(Names, State) ->
    case actors(State) of
        [] -> State;
        [First | _] ->
            {ok, NewState} = with_actor_projections(First, Names, State),
            NewState
    end.

%% Per-actor accessors

actor_log_state(ActorId, State) ->
    case actor_bucket(ActorId, State) of
        {ok, B}     -> {ok, field(log, B)};
        {error, _}  -> {error, no_actor}
    end.

actor_log_tip(ActorId, State) ->
    case actor_log_state(ActorId, State) of
        {ok, L}     -> log:tip(L);
        {error, _}  -> nil
    end.

actor_inbox_state(ActorId, State) ->
    case actor_bucket(ActorId, State) of
        {ok, B}     -> {ok, field(actor_inbox, B)};
        {error, _}  -> {error, no_actor}
    end.

actor_inbox_tip(ActorId, State) ->
    case actor_inbox_state(ActorId, State) of
        {ok, I}     -> log:tip(I);
        {error, _}  -> nil
    end.

%% append_to_actor_inbox/3 — pure-functional inbox append. Mirrors
%% publish/3's bucket-update shape; the activity is already signed
%% + validated by the time it lands here (Step 5's pipeline handles
%% sig verify + replay before this call).

append_to_actor_inbox(ActorId, Activity, State) ->
    case actor_bucket(ActorId, State) of
        {error, no_actor} ->
            {error, no_actor, State};
        {ok, Bucket} ->
            Inbox = field(actor_inbox, Bucket),
            {ok, NewInbox, _Seq} = log:append(Inbox, Activity),
            B1 = set(actor_inbox, NewInbox, Bucket),
            {ok, log:tip(NewInbox), set_bucket(ActorId, B1, State)}
    end.

actor_key_spec(ActorId, State) ->
    case actor_bucket(ActorId, State) of
        {ok, B}     -> {ok, field(key_spec, B)};
        {error, _}  -> {error, no_actor}
    end.

actor_state(ActorId, State) when is_list(State), is_atom(ActorId) ->
    case actor_bucket(ActorId, State) of
        {ok, B}     -> {ok, field(actor_state, B)};
        {error, _}  -> {error, no_actor}
    end.

actor_projections(ActorId, State) ->
    case actor_bucket(ActorId, State) of
        {ok, B}     -> {ok, field(projections, B)};
        {error, _}  -> {error, no_actor}
    end.

actor_next_published(ActorId, State) ->
    case actor_bucket(ActorId, State) of
        {ok, B}     -> {ok, field(next_published, B)};
        {error, _}  -> {error, no_actor}
    end.

%% Legacy single-actor accessors — read from first bucket. Keeps
%% every M1 test (smoke_app_pure, bootstrap_start, http_publish,
%% nx_kernel_server, http_post_format) passing.

actor_id(State) ->
    case field(actors, State) of
        []                        -> nil;
        [{First, _Bucket} | _]    -> First
    end.

key_spec(State) ->
    bucket_field(key_spec, State).

actor_state(State) ->
    bucket_field(actor_state, State).

log_state(State) ->
    bucket_field(log, State).

log_tip(State) ->
    log:tip(log_state(State)).

projections(State) ->
    case bucket_field(projections, State) of
        nil -> [];
        Ps  -> Ps
    end.

next_published(State) ->
    bucket_field(next_published, State).

%% ── Internal helpers ──────────────────────────────────────────────

base_stub() ->
    <<98,97,115,101,95,115,116,117,98>>.

%% "inbox_base_stub" — distinct path stub so the in-memory log
%% module's open/2 returns a fresh log state for the per-actor
%% inbox bucket. Disk paths will namespace on this once Step 3b
%% on-disk persistence is reactivated for inbox buckets.
inbox_base_stub() ->
    <<105,110,98,111,120,95,115,116,117,98>>.

bucket_field(Key, State) ->
    case field(actors, State) of
        []                        -> nil;
        [{_First, Bucket} | _]    -> field(Key, Bucket)
    end.

set_bucket(ActorId, NewBucket, State) ->
    Actors = field(actors, State),
    NewActors = set_keyed(ActorId, NewBucket, Actors),
    set(actors, NewActors, State).

set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)];
set_keyed(_, _, []) -> [].

has_keyed(_, []) -> false;
has_keyed(K, [{K, _} | _]) -> true;
has_keyed(K, [_ | Rest]) -> has_keyed(K, Rest).

find_keyed(_, []) -> {error, no_actor};
find_keyed(K, [{K, V} | _]) -> {ok, V};
find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).

field(K, [{K, V} | _]) -> V;
field(K, [_ | Rest]) -> field(K, Rest);
field(_, []) -> nil.

set(K, V, []) -> [{K, V}];
set(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
set(K, V, [P | Rest]) -> [P | set(K, V, Rest)].

%% ── gen_server wrapper ──────────────────────────────────────────
%%
%% Mirrors the registry / projection gen_server patterns from
%% Steps 5b and 7b. Same port quirks: raw Pid return, no `?MODULE`
%% macro, spawned processes don't persist across separate
%% erlang-eval-ast calls — tests inline start_link with operations.
%%
%% Step 1b (m2) adds multi-actor gen_server calls:
%% add_actor/3, publish_to/2, log_tip_for/1, actors/0, state_for/1,
%% with_projections_for/2 — all delegating to the pure-functional
%% bucket APIs. Existing single-actor calls (publish/1, log_tip/0,
%% with_projections/1) continue to route through bucket 0.

start_link(ActorId, KeySpec, ActorStateProplist) ->
    Pid = gen_server:start_link(nx_kernel,
            [ActorId, KeySpec, ActorStateProplist]),
    erlang:register(nx_kernel, Pid),
    Pid.

stop() ->
    R = gen_server:call(nx_kernel, '$gen_stop'),
    erlang:unregister(nx_kernel),
    R.

publish(Request) ->
    gen_server:call(nx_kernel, {publish, Request}).

query() ->
    gen_server:call(nx_kernel, get_state).

log_tip() ->
    gen_server:call(nx_kernel, get_log_tip).

with_projections(Names) ->
    gen_server:call(nx_kernel, {set_projections, Names}).

%% Step 1b — multi-actor gen_server calls.

add_actor(ActorId, KeySpec, AS) ->
    gen_server:call(nx_kernel, {add_actor, ActorId, KeySpec, AS}).

publish_to(ActorId, Request) ->
    gen_server:call(nx_kernel, {publish_to, ActorId, Request}).

log_tip_for(ActorId) ->
    gen_server:call(nx_kernel, {log_tip_for, ActorId}).

log_state_for(ActorId) ->
    gen_server:call(nx_kernel, {log_state_for, ActorId}).

inbox_tip_for(ActorId) ->
    gen_server:call(nx_kernel, {inbox_tip_for, ActorId}).

inbox_state_for(ActorId) ->
    gen_server:call(nx_kernel, {inbox_state_for, ActorId}).

append_inbox(ActorId, Activity) ->
    gen_server:call(nx_kernel, {append_inbox, ActorId, Activity}).

actors() ->
    gen_server:call(nx_kernel, get_actors).

state_for(ActorId) ->
    gen_server:call(nx_kernel, {state_for, ActorId}).

bucket_for(ActorId) ->
    gen_server:call(nx_kernel, {bucket_for, ActorId}).

with_projections_for(ActorId, Names) ->
    gen_server:call(nx_kernel, {set_projections_for, ActorId, Names}).

bootstrap_actor(ActorId, Profile, KeySpec) ->
    gen_server:call(nx_kernel, {bootstrap_actor, ActorId, Profile, KeySpec}).

%% gen_server callbacks

init([ActorId, KeySpec, AS]) ->
    {ok, new(ActorId, KeySpec, AS)}.

handle_call({publish, Request}, _From, State) ->
    case publish(Request, State) of
        {ok, Result, NewState} ->
            {reply, {ok, Result}, NewState};
        {error, Reason, SameState} ->
            {reply, {error, Reason}, SameState}
    end;
handle_call(get_state, _From, State) ->
    {reply, State, State};
handle_call(get_log_tip, _From, State) ->
    {reply, log_tip(State), State};
handle_call({set_projections, Names}, _From, State) ->
    {reply, ok, with_projections(Names, State)};
handle_call({add_actor, ActorId, KeySpec, AS}, _From, State) ->
    case add_actor(ActorId, KeySpec, AS, State) of
        {ok, NewState}      -> {reply, ok, NewState};
        {error, Reason}     -> {reply, {error, Reason}, State}
    end;
handle_call({publish_to, ActorId, Request}, _From, State) ->
    case publish(ActorId, Request, State) of
        {ok, Result, NewState}      -> {reply, {ok, Result}, NewState};
        {error, Reason, SameState}  -> {reply, {error, Reason}, SameState}
    end;
handle_call({log_tip_for, ActorId}, _From, State) ->
    {reply, actor_log_tip(ActorId, State), State};
handle_call({log_state_for, ActorId}, _From, State) ->
    {reply, actor_log_state(ActorId, State), State};
handle_call({inbox_tip_for, ActorId}, _From, State) ->
    {reply, actor_inbox_tip(ActorId, State), State};
handle_call({inbox_state_for, ActorId}, _From, State) ->
    {reply, actor_inbox_state(ActorId, State), State};
handle_call({append_inbox, ActorId, Activity}, _From, State) ->
    case append_to_actor_inbox(ActorId, Activity, State) of
        {ok, Tip, NewState}     -> {reply, {ok, Tip}, NewState};
        {error, Reason, Same}   -> {reply, {error, Reason}, Same}
    end;
handle_call(get_actors, _From, State) ->
    {reply, actors(State), State};
handle_call({state_for, ActorId}, _From, State) ->
    {reply, actor_state(ActorId, State), State};
handle_call({bucket_for, ActorId}, _From, State) ->
    {reply, actor_bucket(ActorId, State), State};
handle_call({set_projections_for, ActorId, Names}, _From, State) ->
    case with_actor_projections(ActorId, Names, State) of
        {ok, NewState}      -> {reply, ok, NewState};
        {error, Reason}     -> {reply, {error, Reason}, State}
    end;
handle_call({bootstrap_actor, ActorId, Profile, KeySpec}, _From, State) ->
    case bootstrap_actor(ActorId, Profile, KeySpec, State) of
        {ok, Result, NewState}      -> {reply, {ok, Result}, NewState};
        {error, Reason, SameState}  -> {reply, {error, Reason}, SameState}
    end.

handle_cast(_, S) -> {noreply, S}.

handle_info(_, S) -> {noreply, S}.