fifocache.erl

-module(fifocache).

-export([new/1, push/3, lookup/2]).

%%-----------------------------------------
%% FIFO cache
%%
%% - Representation
%%
%% {Map, Array, Size, Bottom, Top, NewFlag}
%%
%% - Usage
%%
%% Cache = ffcache:new(10).
%% Cache0 = ffcache:put(key0, value0, Cache).
%% value0 = ffcache:lookup(key0, Cache0).
%% not_found = ffcache:lookup(key1, Cache0).
%%

-type fifocache() :: {array:array(), map(), non_neg_integer(),
                      non_neg_integer(), non_neg_integer(), boolean()}.

-spec new(Size :: non_neg_integer()) -> fifocache().
new(Size) ->
  {maps:new(), array:new(Size), Size, 0, 0, true}.

-spec push(term(), term(), fifocache()) -> fifocache(). 
push(Key, Value, {Map, Array, Size, Bottom, Top, false}) when Bottom == Top ->
  RemoveKey = array:get(Top, Array),
  Map0 = maps:remove(RemoveKey, Map),
  {maps:put(Key, Value, Map0), array:set(Top, Key, Array),
   Size, (Bottom + 1) rem Size, (Top + 1) rem Size, false};
push(Key, Value, {Map, Array, Size, Bottom, Top, _}) ->
  {maps:put(Key, Value, Map), array:set(Top, Key, Array), 
   Size, Bottom, (Top + 1) rem Size, false}.

-spec lookup(term(), fifocache()) -> term() | not_found.
lookup(Key, {Map, _, _, _, _, _}) ->
  case maps:find(Key, Map) of
    {ok, Value} ->
      Value;
    error ->
      not_found
  end.