immutable_lru

-module(immutable_lru).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([new/1, get/2, get_exn/2, set/3, has/2, clear/1]).
-export_type([lru_cache/2]).

-opaque lru_cache(FWG, FWH) :: {lru_cache,
        gleam@dict:dict(FWG, FWH),
        gleam@dict:dict(FWG, FWH),
        integer(),
        integer()}.

-spec new(integer()) -> lru_cache(any(), any()).
new(Max) ->
    Active = gleam@dict:new(),
    Stale = gleam@dict:new(),
    {lru_cache, Active, Stale, Max, 0}.

-spec keep(lru_cache(FXA, FXB), FXA, FXB) -> lru_cache(FXA, FXB).
keep(Cache, Key, Value) ->
    Key_count = erlang:element(5, Cache) + 1,
    {Active, Stale, Key_count@1} = case Key_count > erlang:element(4, Cache) of
        true ->
            {gleam@dict:new(), erlang:element(2, Cache), 1};

        false ->
            {erlang:element(2, Cache), erlang:element(3, Cache), Key_count}
    end,
    Active@1 = gleam@dict:insert(Active, Key, Value),
    erlang:setelement(
        5,
        erlang:setelement(3, erlang:setelement(2, Cache, Active@1), Stale),
        Key_count@1
    ).

-spec get(lru_cache(FWM, FWN), FWM) -> {ok, {lru_cache(FWM, FWN), FWN}} |
    {error, nil}.
get(Cache, Key) ->
    _pipe = erlang:element(2, Cache),
    _pipe@1 = gleam@dict:get(_pipe, Key),
    _pipe@2 = gleam@result:map(_pipe@1, fun(Val) -> {Cache, Val} end),
    gleam@result:lazy_or(_pipe@2, fun() -> _pipe@3 = erlang:element(3, Cache),
            _pipe@4 = gleam@dict:get(_pipe@3, Key),
            gleam@result:map(
                _pipe@4,
                fun(Val@1) -> {keep(Cache, Key, Val@1), Val@1} end
            ) end).

-spec get_exn(lru_cache(FWU, FWV), FWU) -> {lru_cache(FWU, FWV), FWV}.
get_exn(C, Key) ->
    case get(C, Key) of
        {ok, Pair} ->
            Pair;

        _ ->
            erlang:error(#{gleam_error => panic,
                    message => <<"key not found in cache"/utf8>>,
                    module => <<"immutable_lru"/utf8>>,
                    function => <<"get_exn"/utf8>>,
                    line => 103})
    end.

-spec set(lru_cache(FXG, FXH), FXG, FXH) -> lru_cache(FXG, FXH).
set(Cache, Key, Value) ->
    case gleam@dict:has_key(erlang:element(2, Cache), Key) of
        true ->
            Active = gleam@dict:insert(erlang:element(2, Cache), Key, Value),
            erlang:setelement(2, Cache, Active);

        false ->
            keep(Cache, Key, Value)
    end.

-spec has(lru_cache(FXM, any()), FXM) -> boolean().
has(Cache, Key) ->
    _pipe = erlang:element(2, Cache),
    _pipe@1 = gleam@dict:get(_pipe, Key),
    _pipe@3 = gleam@result:lazy_or(
        _pipe@1,
        fun() -> _pipe@2 = erlang:element(3, Cache),
            gleam@dict:get(_pipe@2, Key) end
    ),
    gleam@result:is_ok(_pipe@3).

-spec clear(lru_cache(FXQ, FXR)) -> lru_cache(FXQ, FXR).
clear(Cache) ->
    new(erlang:element(4, Cache)).