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% tree storage
-module(ts).
-include_lib("eunit/include/eunit.hrl").
-export_type([tree_store/0]).
-export([new/0, store/3, append/3, truncate/2, retrieve/2, retrieve_hash/2, delete/2]).
%% FIXME: Keep the arrays in an array instead of in a map? Or maybe an
%% array of binaries? Hashes do have fixed lenght.
-record(tree_store, {arrays :: map()}). % Map of arrays, indexed by layer.
-type tree_store() :: #tree_store{}.
new() ->
#tree_store{arrays = #{}}.
-spec store(tree_store(), tuple(), binary()) -> tree_store().
store(S = #tree_store{arrays = Arrays}, {I, R}, Hash) ->
{A, NewArrays} = get_array(R, Arrays),
Index = case I of
append -> array:size(A);
N -> N
end,
S#tree_store{arrays = maps:put(R, array:set(Index, Hash, A), NewArrays)}.
-spec retrieve(tree_store(), tuple()) -> {tuple(), binary()}.
retrieve(#tree_store{arrays = Arrays}, {I, R}) ->
{{I, R},
case maps:get(R, Arrays, undefined) of
undefined -> undefined;
A -> array:get(I, A)
end}.
-spec retrieve_hash(tree_store(), tuple()) -> binary().
retrieve_hash(S, IR) ->
element(2, retrieve(S, IR)).
-spec delete(tree_store(), tuple()) -> tree_store().
delete(S, {I, R}) ->
{A, NewArrays} = get_array(R, S#tree_store.arrays),
Index = case I of
last -> array:size(A) - 1;
N -> N
end,
S#tree_store{arrays = maps:put(R,
array:reset(Index, A),
NewArrays)}.
append(S, R, Hash) ->
store(S, {append, R}, Hash).
truncate(S, R) ->
delete(S, {last, R}).
%% Private
get_array(Layer, Arrays) ->
case maps:is_key(Layer, Arrays) of
true -> {maps:get(Layer, Arrays), Arrays} ;
false ->
NewArray = array:new(),
{NewArray, maps:put(Layer, NewArray, Arrays)}
end.
%%%%%%%%%%%%%%%%%%%%
%% Testing ts.
-define(TEST_VECTOR, {{{0,0}, <<00>>},
{{0,1}, <<01>>},
{{1,0}, <<10>>}}).
store_test_() ->
T = ?TEST_VECTOR,
S = new(),
S0 = store(S, {0,0}, <<00>>),
S1 = store(S0, {0,1}, <<01>>),
S2 = store(S1, {1,0}, <<10>>),
[?_assertEqual(retrieve(S2, {1,0}), element(3, T)),
?_assertEqual(retrieve(S2, {0,1}), element(2, T)),
?_assertEqual(retrieve(S2, {0,0}), element(1, T)),
?_assertEqual(retrieve_hash(S2, {3,0}), undefined),
?_assertEqual(retrieve_hash(S1, {1,0}), undefined)
].
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