ram

%% ==========================================================================================================
%% Ram - A distributed KV store for Erlang and Elixir.
%%
%% The MIT License (MIT)
%%
%% Copyright (c) 2021-2022 Roberto Ostinelli <roberto@ostinelli.net>.
%%
%% Permission is hereby granted, free of charge, to any person obtaining a copy
%% of this software and associated documentation files (the "Software"), to deal
%% in the Software without restriction, including without limitation the rights
%% to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
%% copies of the Software, and to permit persons to whom the Software is
%% furnished to do so, subject to the following conditions:
%%
%% The above copyright notice and this permission notice shall be included in
%% all copies or substantial portions of the Software.
%%
%% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
%% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
%% FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
%% AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
%% LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
%% OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
%% THE SOFTWARE.
%% ==========================================================================================================
%% @private
-module(ram_kv).
-behaviour(ra_machine).

%% API
-export([get/2, fetch/1]).
-export([put/2]).
-export([update/3]).
-export([delete/1]).

%% callbacks
-export([init/1, apply/3]).

-type ram_kv_command() ::
{fetch, Key :: term()} |
{put, Key :: term(), Value :: term()} |
{update, Key :: term(), Default :: term(), UpdateFun :: function()} |
{delete, Key :: term()}.

%% ===================================================================
%% API
%% ===================================================================
-spec get(Key :: term(), Default :: term()) -> Value :: term().
get(Key, Default) ->
    case fetch(Key) of
        error -> Default;
        {ok, Value} -> Value
    end.

-spec fetch(Key :: term()) -> {ok, Value :: term()} | error.
fetch(Key) ->
    case ram_backbone:process_query(fun(State) -> maps:find(Key, State) end) of
        {error, Reason} -> error(Reason);
        Ret -> Ret
    end.

-spec put(Key :: term(), Value :: term()) -> ok.
put(Key, Value) ->
    case ram_backbone:process_command({put, Key, Value}) of
        {error, Reason} -> error(Reason);
        Ret -> Ret
    end.

-spec update(Key :: term(), Default :: term(), function()) -> ok.
update(Key, Default, Fun) ->
    case ram_backbone:process_command({update, Key, Default, Fun}) of
        {error, Reason} -> error(Reason);
        Ret -> Ret
    end.

-spec delete(Key :: term()) -> ok.
delete(Key) ->
    case ram_backbone:process_command({delete, Key}) of
        {error, Reason} -> error(Reason);
        Ret -> Ret
    end.

%% ===================================================================
%% Callbacks
%% ===================================================================

%% ----------------------------------------------------------------------------------------------------------
%% Init
%% ----------------------------------------------------------------------------------------------------------
-spec init(Conf :: ra:machine_init_args()) -> map().
init(_Config) ->
    #{}.

%% ----------------------------------------------------------------------------------------------------------
%% Apply messages
%% ----------------------------------------------------------------------------------------------------------
-spec apply(ra:command_meta_data(), ram_kv_command(), map()) ->
    {map(), term(), ra_machine:effects()} | {map(), term()}.
apply(#{index := Index} = _Meta, {put, Key, Value}, State) ->
    State1 = maps:put(Key, Value, State),
    Effects = side_effects(Index, State1),
    {State1, ok, Effects};
apply(#{index := Index} =_Meta, {fetch, Key}, State) ->
    Effects = side_effects(Index, State),
    {State, maps:find(Key, State), Effects};
apply(#{index := Index} =_Meta, {update, Key, Default, Fun}, State) ->
    Value = case maps:find(Key, State) of
        error -> Default;
        {ok, V} -> Fun(V)
    end,
    State1 = maps:put(Key, Value, State),
    Effects = side_effects(Index, State1),
    {State1, ok, Effects};
apply(#{index := Index} =_Meta, {delete, Key}, State) ->
    State1 = maps:remove(Key, State),
    Effects = side_effects(Index, State1),
    {State1, ok, Effects}.

%% ===================================================================
%% Internals
%% ===================================================================
-spec side_effects(ra:index(), map()) -> ra_machine:effects().
side_effects(Index, State) ->
    ApplyResetCount = application:get_env(ram, release_cursor_count, 1000),
    case Index rem ApplyResetCount of
        0 -> [{release_cursor, Index, State}];
        _ -> []
    end.