macula

%%%-------------------------------------------------------------------
%%% @doc
%%% GenServer managing Kademlia DHT routing table and operations.
%%% Integrates all routing components: table, DHT algorithms, protocol.
%%% @end
%%%-------------------------------------------------------------------
-module(macula_routing_server).
-behaviour(gen_server).

-include_lib("kernel/include/logger.hrl").

%% API
-export([
    start_link/2,
    add_node/2,
    find_closest/3,
    store_local/3,
    store/3,
    get_local/2,
    get_all_keys/1,
    find_value/3,
    get_routing_table/1,
    size/1,
    handle_message/2
]).

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

%% State
-record(state, {
    local_node_id :: binary(),
    routing_table :: macula_routing_table:routing_table(),
    storage :: #{binary() => term()},  % Local key-value storage
    config :: #{
        k => pos_integer(),
        alpha => pos_integer()
    }
}).

%%%===================================================================
%%% API Functions
%%%===================================================================

%% @doc Start routing server with registered name macula_routing_server.
-spec start_link(binary(), map()) -> {ok, pid()} | {error, term()}.
start_link(LocalNodeId, Config) ->
    gen_server:start_link({local, macula_routing_server}, ?MODULE, {LocalNodeId, Config}, []).

%% @doc Add node to routing table (async - does not block caller).
-spec add_node(pid(), macula_routing_bucket:node_info()) -> ok.
add_node(Pid, NodeInfo) ->
    gen_server:cast(Pid, {add_node, NodeInfo}).

%% @doc Find k closest nodes to target.
-spec find_closest(pid(), binary(), pos_integer()) -> [macula_routing_bucket:node_info()].
find_closest(Pid, Target, K) ->
    gen_server:call(Pid, {find_closest, Target, K}).

%% @doc Store value locally.
-spec store_local(pid(), binary(), term()) -> ok.
store_local(Pid, Key, Value) ->
    gen_server:call(Pid, {store_local, Key, Value}).

%% @doc Store value in DHT by propagating to k closest nodes.
%% Stores locally first, then sends STORE messages to k closest peers.
-spec store(pid(), binary(), term()) -> ok.
store(Pid, Key, Value) ->
    gen_server:call(Pid, {store, Key, Value}, 10000).

%% @doc Get value from local storage.
-spec get_local(pid(), binary()) -> {ok, term()} | not_found.
get_local(Pid, Key) ->
    gen_server:call(Pid, {get_local, Key}).

%% @doc Get all keys from local storage.
-spec get_all_keys(pid()) -> {ok, [binary()]} | {error, term()}.
get_all_keys(Pid) ->
    gen_server:call(Pid, get_all_keys).

%% @doc Find value in DHT using iterative lookup.
%% Returns {ok, Value} if found, {nodes, Nodes} if not found.
-spec find_value(pid(), binary(), pos_integer()) ->
    {ok, term()} | {nodes, [macula_routing_bucket:node_info()]} | {error, term()}.
find_value(Pid, Key, K) ->
    gen_server:call(Pid, {find_value, Key, K}, 10000).

%% @doc Get routing table snapshot.
-spec get_routing_table(pid()) -> macula_routing_table:routing_table().
get_routing_table(Pid) ->
    gen_server:call(Pid, get_routing_table).

%% @doc Get number of nodes in routing table.
-spec size(pid()) -> non_neg_integer().
size(Pid) ->
    gen_server:call(Pid, size).

%% @doc Handle incoming DHT message and return reply.
-spec handle_message(pid(), map()) -> map().
handle_message(Pid, Message) ->
    gen_server:call(Pid, {handle_message, Message}).

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

%% @private
init({LocalNodeId, Config}) ->
    K = maps:get(k, Config, 20),
    Alpha = maps:get(alpha, Config, 3),

    State = #state{
        local_node_id = LocalNodeId,
        routing_table = macula_routing_table:new(LocalNodeId, K),
        storage = #{},
        config = #{
            k => K,
            alpha => Alpha
        }
    },

    {ok, State}.

%% @private
handle_call({find_closest, Target, K}, _From, #state{routing_table = Table} = State) ->
    Closest = macula_routing_table:find_closest(Table, Target, K),
    {reply, Closest, State};

handle_call({store_local, Key, Value}, _From, #state{storage = Storage} = State) ->
    ExistingProviders = maps:get(Key, Storage, []),
    ProviderList = ensure_provider_list(ExistingProviders),
    NodeId = maps:get(node_id, Value, undefined),
    UpdatedProviders = upsert_provider(NodeId, Value, ProviderList),
    NewStorage = Storage#{Key => UpdatedProviders},
    {reply, ok, State#state{storage = NewStorage}};

handle_call({store, Key, Value}, _From, #state{routing_table = Table, config = Config} = State) ->
    %% 1. Store locally first
    NewState = case handle_call({store_local, Key, Value}, _From, State) of
        {reply, ok, S} -> S;
        _ -> State  %% Shouldn't happen but be safe
    end,

    %% 2. Find k closest nodes to Key
    K = maps:get(k, Config, 20),
    ClosestNodes = macula_routing_table:find_closest(Table, Key, K),

    %% 3. Send STORE message to each node (fire-and-forget)
    StoreMsg = macula_routing_protocol:encode_store(Key, Value),
    case ClosestNodes of
        [] ->
            %% No nodes in routing table - this is an embedded gateway connected to bootstrap
            %% Forward the STORE to bootstrap gateway via RPC instead
            forward_store_to_bootstrap(Key, Value);
        _ ->
            lists:foreach(fun(NodeInfo) ->
                %% Best effort - don't fail if send fails
                _ = macula_gateway_dht:send_to_peer(NodeInfo, store, StoreMsg)
            end, ClosestNodes)
    end,

    {reply, ok, NewState};

handle_call({get_local, Key}, _From, #state{storage = Storage} = State) ->
    Reply = format_storage_value(maps:get(Key, Storage, undefined)),
    {reply, Reply, State};

handle_call(get_all_keys, _From, #state{storage = Storage} = State) ->
    Keys = maps:keys(Storage),
    {reply, {ok, Keys}, State};

handle_call(get_routing_table, _From, #state{routing_table = Table} = State) ->
    {reply, Table, State};

handle_call(size, _From, #state{routing_table = Table} = State) ->
    Size = macula_routing_table:size(Table),
    {reply, Size, State};

handle_call({delete_local, Key, NodeId}, _From, #state{storage = Storage} = State) ->
    NewStorage = delete_provider_from_storage(Key, NodeId, Storage),
    {reply, ok, State#state{storage = NewStorage}};

handle_call({find_value, Key, K}, _From, #state{routing_table = Table, storage = Storage} = State) ->
    ?LOG_DEBUG("find_value: key=~p, storage_size=~p", [Key, maps:size(Storage)]),
    ?LOG_DEBUG("find_value: storage keys=~p", [maps:keys(Storage)]),
    Reply = find_value_in_storage(Key, K, Storage, Table),
    {reply, Reply, State};

handle_call({handle_message, Message}, _From, State) ->
    {Reply, NewState} = process_dht_message(Message, State),
    {reply, Reply, NewState};

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

%% @private
%% Add node to routing table (async operation)
handle_cast({add_node, NodeInfo}, #state{routing_table = Table} = State) ->
    NewTable = macula_routing_table:add_node(Table, NodeInfo),
    {noreply, State#state{routing_table = NewTable}};

%% @private
%% Handle async store (from _dht.store RPC) - stores locally only without propagation
%% This is used by bootstrap gateway when receiving store requests from peers
handle_cast({store, Key, Value}, #state{storage = Storage} = State) when is_binary(Key) ->
    ?LOG_DEBUG("Async STORE received - key hash prefix: ~p, value: ~p",
              [binary:part(Key, 0, min(8, byte_size(Key))), Value]),
    ExistingProviders = maps:get(Key, Storage, []),
    ProviderList = ensure_provider_list(ExistingProviders),
    NodeId = get_node_id_from_value(Value),
    UpdatedProviders = upsert_provider(NodeId, Value, ProviderList),
    NewStorage = Storage#{Key => UpdatedProviders},
    ?LOG_DEBUG("Stored value for key, now have ~p provider(s)", [length(UpdatedProviders)]),
    {noreply, State#state{storage = NewStorage}};

handle_cast({store, Key, _Value}, State) ->
    ?LOG_ERROR("Async STORE received with non-binary key: ~p", [Key]),
    {noreply, State};

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

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

%% @private
terminate(_Reason, _State) ->
    ok.

%%%===================================================================
%%% Internal Functions
%%%===================================================================

%% @doc Forward DHT STORE to bootstrap gateway via RPC when routing table is empty.
%% This allows embedded gateways to propagate subscriptions to the central bootstrap DHT.
-spec forward_store_to_bootstrap(binary(), term()) -> ok.
forward_store_to_bootstrap(Key, Value) ->
    %% Call the _dht.store RPC procedure on the bootstrap gateway
    %% This is a fire-and-forget operation - we don't wait for response
    case whereis(macula_rpc_handler) of
        undefined ->
            ok;
        _RpcHandler ->
            %% Call _dht.store(Key, Value) on the bootstrap gateway
            %% Using cast (fire-and-forget) since we don't need the response
            try
                Procedure = <<"_dht.store">>,
                Args = #{
                    <<"key">> => Key,
                    <<"value">> => Value
                },
                %% Use macula module's call function which handles bootstrap routing
                spawn(fun() ->
                    case whereis(macula_local_client) of
                        undefined ->
                            ok;
                        LocalClient ->
                            _ = macula:call(LocalClient, Procedure, Args, #{timeout => 5000}),
                            ok
                    end
                end),
                ok
            catch
                _:_Error ->
                    ok
            end
    end.

%% @doc Extract node_id from value map, handling both atom and binary keys.
-spec get_node_id_from_value(map()) -> binary() | undefined.
get_node_id_from_value(#{node_id := NodeId}) -> NodeId;
get_node_id_from_value(#{<<"node_id">> := NodeId}) -> NodeId;
get_node_id_from_value(_Value) -> undefined.

%% @doc Find index of provider with matching node_id in provider list.
-spec find_provider_index(binary(), [map()]) -> pos_integer() | not_found.
find_provider_index(NodeId, ProviderList) ->
    find_provider_index(NodeId, ProviderList, 1).

find_provider_index(_NodeId, [], _Index) ->
    not_found;
find_provider_index(NodeId, [Provider | Rest], Index) ->
    ProviderNodeId = get_node_id_from_value(Provider),
    check_provider_match(NodeId, ProviderNodeId, Rest, Index).

check_provider_match(NodeId, NodeId, _Rest, Index) -> Index;
check_provider_match(NodeId, _Other, Rest, Index) ->
    find_provider_index(NodeId, Rest, Index + 1).

%% @doc Ensure value is a list for multi-provider storage.
-spec ensure_provider_list(term()) -> [term()].
ensure_provider_list(List) when is_list(List) -> List;
ensure_provider_list(Value) -> [Value].

%% @doc Insert or update a provider in the list.
-spec upsert_provider(binary() | undefined, map(), [map()]) -> [map()].
upsert_provider(undefined, Value, ProviderList) ->
    [Value | ProviderList];
upsert_provider(NodeId, Value, ProviderList) ->
    upsert_by_index(find_provider_index(NodeId, ProviderList), Value, ProviderList).

upsert_by_index(not_found, Value, ProviderList) ->
    [Value | ProviderList];
upsert_by_index(Index, Value, ProviderList) ->
    lists:sublist(ProviderList, Index - 1) ++ [Value] ++ lists:nthtail(Index, ProviderList).

%% @doc Format storage value for get_local response.
-spec format_storage_value(undefined | term()) -> not_found | {ok, [term()]}.
format_storage_value(undefined) -> not_found;
format_storage_value(Value) when is_list(Value) -> {ok, Value};
format_storage_value(Value) -> {ok, [Value]}.

%% @doc Delete a specific provider from storage by node_id.
-spec delete_provider_from_storage(binary(), binary(), map()) -> map().
delete_provider_from_storage(Key, NodeId, Storage) ->
    case maps:get(Key, Storage, undefined) of
        undefined -> Storage;
        Providers when is_list(Providers) ->
            delete_provider_by_node_id(Key, NodeId, Providers, Storage);
        _SingleValue -> maps:remove(Key, Storage)
    end.

delete_provider_by_node_id(Key, NodeId, Providers, Storage) ->
    FilterFn = fun(P) -> get_node_id_from_value(P) =/= NodeId end,
    UpdatedProviders = lists:filter(FilterFn, Providers),
    update_or_remove_key(Key, UpdatedProviders, Storage).

update_or_remove_key(Key, [], Storage) -> maps:remove(Key, Storage);
update_or_remove_key(Key, Providers, Storage) -> Storage#{Key => Providers}.

%% @doc Find value in local storage or DHT.
-spec find_value_in_storage(binary(), pos_integer(), map(), macula_routing_table:routing_table()) ->
    {ok, term()} | {error, term()}.
find_value_in_storage(Key, K, Storage, Table) ->
    case maps:get(Key, Storage, undefined) of
        undefined -> find_value_via_dht(Key, K, Table);
        Value when is_list(Value) -> {ok, Value};
        Value -> {ok, [Value]}
    end.

find_value_via_dht(Key, K, Table) ->
    QueryFn = fun(_NodeInfo, _QueryKey) -> {nodes, [_NodeInfo]} end,
    case macula_routing_dht:find_value(Table, Key, K, QueryFn) of
        {ok, Value} -> {ok, Value};
        {nodes, _Nodes} -> {ok, []};
        {error, Reason} -> {error, Reason}
    end.

%% @doc Process incoming DHT message and generate reply.
-spec process_dht_message(map(), #state{}) -> {map(), #state{}}.
process_dht_message(Message, State) ->
    MessageType = classify_dht_message(Message),
    dispatch_dht_message(MessageType, Message, State).

classify_dht_message(Message) ->
    case macula_routing_protocol:is_find_node(Message) of
        true -> find_node;
        false -> classify_non_find_node(Message)
    end.

classify_non_find_node(Message) ->
    case macula_routing_protocol:is_store(Message) of
        true -> store;
        false -> classify_find_value(Message)
    end.

classify_find_value(Message) ->
    case macula_routing_protocol:is_find_value(Message) of
        true -> find_value;
        false -> unknown
    end.

dispatch_dht_message(find_node, Message, State) ->
    handle_find_node(Message, State);
dispatch_dht_message(store, Message, State) ->
    handle_store(Message, State);
dispatch_dht_message(find_value, Message, State) ->
    handle_find_value(Message, State);
dispatch_dht_message(unknown, _Message, State) ->
    {#{type => error, reason => unknown_message}, State}.

%% @doc Handle FIND_NODE request.
-spec handle_find_node(map(), #state{}) -> {map(), #state{}}.
handle_find_node(Message, #state{routing_table = Table, config = Config} = State) ->
    {ok, Target} = macula_routing_protocol:decode_find_node(Message),
    K = maps:get(k, Config, 20),

    %% Find k closest nodes
    Closest = macula_routing_table:find_closest(Table, Target, K),

    %% Encode reply
    Reply = macula_routing_protocol:encode_find_node_reply(Closest),

    {Reply, State}.

%% @doc Handle STORE request.
-spec handle_store(map(), #state{}) -> {map(), #state{}}.
handle_store(Message, #state{storage = Storage} = State) ->
    {ok, Key, Value} = macula_routing_protocol:decode_store(Message),
    ?LOG_DEBUG("STORE: key=~p, value=~p", [Key, Value]),
    ExistingProviders = maps:get(Key, Storage, []),
    ProviderList = ensure_provider_list(ExistingProviders),
    NodeId = get_node_id_from_value(Value),
    UpdatedProviders = upsert_provider(NodeId, Value, ProviderList),
    NewStorage = Storage#{Key => UpdatedProviders},
    ?LOG_DEBUG("STORE complete: new_storage_size=~p, key_prefix=~p",
              [maps:size(NewStorage), binary:part(Key, 0, min(8, byte_size(Key)))]),
    Reply = #{type => store_reply, result => ok},
    {Reply, State#state{storage = NewStorage}}.

%% @doc Handle FIND_VALUE request.
-spec handle_find_value(map(), #state{}) -> {map(), #state{}}.
handle_find_value(Message, #state{storage = Storage, routing_table = Table, config = Config} = State) ->
    {ok, Key} = macula_routing_protocol:decode_find_value(Message),
    StorageValue = maps:get(Key, Storage, undefined),
    K = maps:get(k, Config, 20),
    Reply = encode_find_value_result(StorageValue, Key, K, Table),
    {Reply, State}.

encode_find_value_result(undefined, Key, K, Table) ->
    Closest = macula_routing_table:find_closest(Table, Key, K),
    macula_routing_protocol:encode_find_value_reply({nodes, Closest});
encode_find_value_result(Value, _Key, _K, _Table) when is_list(Value) ->
    macula_routing_protocol:encode_find_value_reply({value, Value});
encode_find_value_result(Value, _Key, _K, _Table) ->
    macula_routing_protocol:encode_find_value_reply({value, Value}).