%% Copyright (C) 2026 Fluxer Contributors
%%
%% This file is part of Fluxer.
%%
%% Fluxer is free software: you can redistribute it and/or modify
%% it under the terms of the GNU Affero General Public License as published by
%% the Free Software Foundation, either version 3 of the License, or
%% (at your option) any later version.
%%
%% Fluxer is distributed in the hope that it will be useful,
%% but WITHOUT ANY WARRANTY; without even the implied warranty of
%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
%% GNU Affero General Public License for more details.
%%
%% You should have received a copy of the GNU Affero General Public License
%% along with Fluxer. If not, see <https://www.gnu.org/licenses/>.

-module(presence_targets).

-export([
    friend_ids_from_state/1,
    group_dm_recipients_from_state/1
]).

-type user_id() :: integer().
-type channel_id() :: integer().
-type relationship_type() :: integer().
-type state() :: #{
    user_id := user_id(),
    relationships => #{user_id() => relationship_type()},
    channels => #{channel_id() => map()},
    _ => _
}.

-spec friend_ids_from_state(state()) -> [user_id()].
friend_ids_from_state(State) ->
    Relationships = maps:get(relationships, State, #{}),
    [
        UserId
     || {UserId, Type} <- maps:to_list(Relationships),
        Type =:= 1 orelse Type =:= 3
    ].

-spec group_dm_recipients_from_state(state()) -> #{channel_id() => #{user_id() => true}}.
group_dm_recipients_from_state(State) ->
    UserId = maps:get(user_id, State),
    Channels = maps:get(channels, State, #{}),
    maps:from_list(
        [
            {ChannelId, map_from_ids([Rid || Rid <- RecipientIds, Rid =/= UserId])}
         || {ChannelId, Channel} <- maps:to_list(Channels),
            maps:get(<<"type">>, Channel, 0) =:= 3,
            RecipientIds <- [extract_recipient_ids(Channel)]
        ]
    ).

-spec extract_recipient_ids(map()) -> [user_id()].
extract_recipient_ids(Channel) ->
    Recipients = maps:get(<<"recipients">>, Channel, maps:get(<<"recipient_ids">>, Channel, [])),
    Unique =
        lists:foldl(
            fun(Entry, Acc) ->
                case extract_recipient_id(Entry) of
                    undefined ->
                        Acc;
                    Value ->
                        case lists:member(Value, Acc) of
                            true -> Acc;
                            false -> [Value | Acc]
                        end
                end
            end,
            [],
            Recipients
        ),
    lists:reverse(Unique).

-spec extract_recipient_id(term()) -> user_id() | undefined.
extract_recipient_id(Entry) when is_map(Entry) ->
    type_conv:extract_id(Entry, <<"id">>);
extract_recipient_id(Entry) ->
    case Entry of
        Bin when is_binary(Bin) ->
            type_conv:extract_id(#{<<"id">> => Bin}, <<"id">>);
        Int when is_integer(Int) ->
            Int;
        _ ->
            undefined
    end.

-spec map_from_ids([user_id()]) -> #{user_id() => true}.
map_from_ids(Ids) when is_list(Ids) ->
    maps:from_list([{Id, true} || Id <- Ids]).

-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").

friend_ids_from_state_filters_relationship_types_test() ->
    State = #{
        relationships =>
            #{
                10 => 1,
                11 => 3,
                12 => 4,
                13 => 2
            }
    },
    Ids = lists:sort(friend_ids_from_state(State)),
    ?assertEqual([10, 11], Ids).

friend_ids_from_state_empty_test() ->
    State = #{relationships => #{}},
    ?assertEqual([], friend_ids_from_state(State)).

friend_ids_from_state_missing_key_test() ->
    State = #{},
    ?assertEqual([], friend_ids_from_state(State)).

group_dm_recipients_from_state_test() ->
    State = #{
        user_id => 1,
        channels => #{
            100 => #{
                <<"type">> => 3,
                <<"recipients">> => [
                    #{<<"id">> => <<"2">>},
                    #{<<"id">> => <<"3">>}
                ]
            },
            200 => #{
                <<"type">> => 0,
                <<"recipients">> => [#{<<"id">> => <<"4">>}]
            }
        }
    },
    Result = group_dm_recipients_from_state(State),
    ?assertEqual(#{100 => #{2 => true, 3 => true}}, Result).

group_dm_recipients_excludes_self_test() ->
    State = #{
        user_id => 2,
        channels => #{
            100 => #{
                <<"type">> => 3,
                <<"recipients">> => [
                    #{<<"id">> => <<"2">>},
                    #{<<"id">> => <<"3">>}
                ]
            }
        }
    },
    Result = group_dm_recipients_from_state(State),
    ?assertEqual(#{100 => #{3 => true}}, Result).

extract_recipient_id_map_test() ->
    ?assertEqual(123, extract_recipient_id(#{<<"id">> => <<"123">>})),
    ?assertEqual(undefined, extract_recipient_id(#{})).

extract_recipient_id_binary_test() ->
    ?assertEqual(456, extract_recipient_id(<<"456">>)).

extract_recipient_id_integer_test() ->
    ?assertEqual(789, extract_recipient_id(789)).

extract_recipient_id_invalid_test() ->
    ?assertEqual(undefined, extract_recipient_id(undefined)),
    ?assertEqual(undefined, extract_recipient_id([1, 2, 3])).

extract_recipient_ids_deduplicates_test() ->
    Channel = #{
        <<"recipients">> => [
            #{<<"id">> => <<"1">>},
            #{<<"id">> => <<"1">>},
            #{<<"id">> => <<"2">>}
        ]
    },
    Ids = extract_recipient_ids(Channel),
    ?assertEqual([1, 2], Ids).

map_from_ids_test() ->
    ?assertEqual(#{}, map_from_ids([])),
    ?assertEqual(#{1 => true, 2 => true}, map_from_ids([1, 2])).
-endif.