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%% The contents of this file are subject to the Mozilla Public License
%% Version 1.1 (the "License"); you may not use this file except in
%% compliance with the License. You may obtain a copy of the License
%% at https://www.mozilla.org/MPL/
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and
%% limitations under the License.
%%
%% The Original Code is RabbitMQ.
%%
%% The Initial Developer of the Original Code is GoPivotal, Inc.
%% Copyright (c) 2007-2019 Pivotal Software, Inc. All rights reserved.
%%
%% A dual-index tree.
%%
%% Entries have the following shape:
%%
%% +----+--------------------+---+
%% | PK | SK1, SK2, ..., SKN | V |
%% +----+--------------------+---+
%%
%% i.e. a primary key, set of secondary keys, and a value.
%%
%% There can be only one entry per primary key, but secondary keys may
%% appear in multiple entries.
%%
%% The set of secondary keys must be non-empty. Or, to put it another
%% way, entries only exist while their secondary key set is non-empty.
-module(dtree).
-export([empty/0, insert/4, take/3, take/2, take_one/2, take_all/2, drop/2,
is_defined/2, is_empty/1, smallest/1, size/1]).
%%----------------------------------------------------------------------------
-export_type([?MODULE/0]).
-opaque ?MODULE() :: {gb_trees:tree(), gb_trees:tree()}.
-type pk() :: any().
-type sk() :: any().
-type val() :: any().
-type kv() :: {pk(), val()}.
%%----------------------------------------------------------------------------
-spec empty() -> ?MODULE().
empty() -> {gb_trees:empty(), gb_trees:empty()}.
%% Insert an entry. Fails if there already is an entry with the given
%% primary key.
-spec insert(pk(), [sk()], val(), ?MODULE()) -> ?MODULE().
insert(PK, [], V, {P, S}) ->
%% dummy insert to force error if PK exists
_ = gb_trees:insert(PK, {gb_sets:empty(), V}, P),
{P, S};
insert(PK, SKs, V, {P, S}) ->
{gb_trees:insert(PK, {gb_sets:from_list(SKs), V}, P),
lists:foldl(fun (SK, S0) ->
case gb_trees:lookup(SK, S0) of
{value, PKS} -> PKS1 = gb_sets:insert(PK, PKS),
gb_trees:update(SK, PKS1, S0);
none -> PKS = gb_sets:singleton(PK),
gb_trees:insert(SK, PKS, S0)
end
end, S, SKs)}.
%% Remove the given secondary key from the entries of the given
%% primary keys, returning the primary-key/value pairs of any entries
%% that were dropped as the result (i.e. due to their secondary key
%% set becoming empty). It is ok for the given primary keys and/or
%% secondary key to not exist.
-spec take([pk()], sk(), ?MODULE()) -> {[kv()], ?MODULE()}.
take(PKs, SK, {P, S}) ->
case gb_trees:lookup(SK, S) of
none -> {[], {P, S}};
{value, PKS} -> TakenPKS = gb_sets:from_list(PKs),
PKSInter = gb_sets:intersection(PKS, TakenPKS),
PKSDiff = gb_sets_difference (PKS, PKSInter),
{KVs, P1} = take2(PKSInter, SK, P),
{KVs, {P1, case gb_sets:is_empty(PKSDiff) of
true -> gb_trees:delete(SK, S);
false -> gb_trees:update(SK, PKSDiff, S)
end}}
end.
%% Remove the given secondary key from all entries, returning the
%% primary-key/value pairs of any entries that were dropped as the
%% result (i.e. due to their secondary key set becoming empty). It is
%% ok for the given secondary key to not exist.
-spec take(sk(), ?MODULE()) -> {[kv()], ?MODULE()}.
take(SK, {P, S}) ->
case gb_trees:lookup(SK, S) of
none -> {[], {P, S}};
{value, PKS} -> {KVs, P1} = take2(PKS, SK, P),
{KVs, {P1, gb_trees:delete(SK, S)}}
end.
%% Drop an entry with the primary key and clears secondary keys for this key,
%% returning a list with a key-value pair as a result.
%% If the primary key does not exist, returns an empty list.
-spec take_one(pk(), ?MODULE()) -> {[{pk(), val()}], ?MODULE()}.
take_one(PK, {P, S}) ->
case gb_trees:lookup(PK, P) of
{value, {SKS, Value}} ->
P1 = gb_trees:delete(PK, P),
S1 = gb_sets:fold(
fun(SK, Acc) ->
{value, PKS} = gb_trees:lookup(SK, Acc),
PKS1 = gb_sets:delete(PK, PKS),
case gb_sets:is_empty(PKS1) of
true -> gb_trees:delete(SK, Acc);
false -> gb_trees:update(SK, PKS1, Acc)
end
end, S, SKS),
{[{PK, Value}], {P1, S1}};
none -> {[], {P, S}}
end.
%% Drop all entries which contain the given secondary key, returning
%% the primary-key/value pairs of these entries. It is ok for the
%% given secondary key to not exist.
-spec take_all(sk(), ?MODULE()) -> {[kv()], ?MODULE()}.
take_all(SK, {P, S}) ->
case gb_trees:lookup(SK, S) of
none -> {[], {P, S}};
{value, PKS} -> {KVs, SKS, P1} = take_all2(PKS, P),
{KVs, {P1, prune(SKS, PKS, S)}}
end.
%% Drop all entries for the given primary key (which does not have to exist).
-spec drop(pk(), ?MODULE()) -> ?MODULE().
drop(PK, {P, S}) ->
case gb_trees:lookup(PK, P) of
none -> {P, S};
{value, {SKS, _V}} -> {gb_trees:delete(PK, P),
prune(SKS, gb_sets:singleton(PK), S)}
end.
-spec is_defined(sk(), ?MODULE()) -> boolean().
is_defined(SK, {_P, S}) -> gb_trees:is_defined(SK, S).
-spec is_empty(?MODULE()) -> boolean().
is_empty({P, _S}) -> gb_trees:is_empty(P).
-spec smallest(?MODULE()) -> kv().
smallest({P, _S}) -> {K, {_SKS, V}} = gb_trees:smallest(P),
{K, V}.
-spec size(?MODULE()) -> non_neg_integer().
size({P, _S}) -> gb_trees:size(P).
%%----------------------------------------------------------------------------
take2(PKS, SK, P) ->
gb_sets:fold(fun (PK, {KVs, P0}) ->
{SKS, V} = gb_trees:get(PK, P0),
SKS1 = gb_sets:delete(SK, SKS),
case gb_sets:is_empty(SKS1) of
true -> KVs1 = [{PK, V} | KVs],
{KVs1, gb_trees:delete(PK, P0)};
false -> {KVs, gb_trees:update(PK, {SKS1, V}, P0)}
end
end, {[], P}, PKS).
take_all2(PKS, P) ->
gb_sets:fold(fun (PK, {KVs, SKS0, P0}) ->
{SKS, V} = gb_trees:get(PK, P0),
{[{PK, V} | KVs], gb_sets:union(SKS, SKS0),
gb_trees:delete(PK, P0)}
end, {[], gb_sets:empty(), P}, PKS).
prune(SKS, PKS, S) ->
gb_sets:fold(fun (SK0, S0) ->
PKS1 = gb_trees:get(SK0, S0),
PKS2 = gb_sets_difference(PKS1, PKS),
case gb_sets:is_empty(PKS2) of
true -> gb_trees:delete(SK0, S0);
false -> gb_trees:update(SK0, PKS2, S0)
end
end, S, SKS).
gb_sets_difference(S1, S2) ->
gb_sets:fold(fun gb_sets:delete_any/2, S1, S2).
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