%-*-Mode:erlang;coding:utf-8;tab-width:4;c-basic-offset:4;indent-tabs-mode:()-*-
% ex: set ft=erlang fenc=utf-8 sts=4 ts=4 sw=4 et nomod:
%%%
%%%------------------------------------------------------------------------
%%% @doc
%%% ==A Large Priority Queue.==
%%% This priority queue implementation depends on layered tuples, so that tuple
%%% access times can be exploited for quick in/out priority queue operations
%%% when using 64 or more total priorities. This implementation was created
%%% to avoid the slowness within the priority queue used by
%%% both RabbitMQ and Riak
%%% (https://github.com/basho/riak_core/blob/master/src/priority_queue.erl).
%%% @end
%%%
%%% MIT License
%%%
%%% Copyright (c) 2011-2020 Michael Truog <mjtruog at protonmail dot com>
%%%
%%% 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.
%%%
%%% @author Michael Truog <mjtruog at protonmail dot com>
%%% @copyright 2011-2020 Michael Truog
%%% @version 2.0.1 {@date} {@time}
%%%------------------------------------------------------------------------

-module(pqueue3).
-author('mjtruog at protonmail dot com').

%% external interface
-export([in/2,         % O(1)
         in/3,         % O(1)
         is_empty/1,   % O(1)
         is_queue/1,   % O(1)
         len/1,        % O(N)
         new/0,        % O(1)
         new/1,        % O(1)
         out/1,        % O(1) amortized, O(N) worst case
         out/2,        % O(1) amortized, O(N) worst case
         pout/1,       % O(1) amortized, O(N) worst case
         to_list/1]).  % O(N)

%%%------------------------------------------------------------------------
%%% External interface functions
%%%------------------------------------------------------------------------

-type pqueue3() :: {integer(), integer(), empty | integer(), tuple()}.
-type pqueue3_empty() :: {integer(), integer(), empty, tuple()}.

%%-------------------------------------------------------------------------
%% @doc
%% ===Append an item to the tail of the 0 priority queue.===
%% O(1)
%% @end
%%-------------------------------------------------------------------------

-spec in(term(), pqueue3()) -> pqueue3().

in(Value, Q) ->
    in(Value, 0, Q).

%%-------------------------------------------------------------------------
%% @doc
%% ===Append an item to the tail of a specific priority queue.===
%% O(1)
%% @end
%%-------------------------------------------------------------------------

-spec in(term(), integer(), pqueue3()) -> pqueue3().

in(_, P, {Size, Offset, _, _})
    when (P + Offset) < 0; (P + Offset) > Size ->
    erlang:exit(badarg);
in(Value, P, {Size, Offset, empty, Bins}) ->
    PriorityIndex = P + Offset,
    {Size, Offset, PriorityIndex,
     in_queue(layer_indexes(Size, PriorityIndex), Value, Bins)};
in(Value, P, {Size, Offset, I, Bins})
    when (P + Offset) < I ->
    PriorityIndex = P + Offset,
    {Size, Offset, PriorityIndex,
     in_queue(layer_indexes(Size, PriorityIndex), Value, Bins)};
in(Value, P, {Size, Offset, I, Bins}) ->
    {Size, Offset, I,
     in_queue(layer_indexes(Size, P + Offset), Value, Bins)}.

%%-------------------------------------------------------------------------
%% @doc
%% ===Check if the priority queue is empty.===
%% O(1)
%% @end
%%-------------------------------------------------------------------------

-spec is_empty(pqueue3()) -> 'true' | 'false'.

is_empty({_, _, empty, _}) ->
    true;
is_empty({_, _, _, _} = Q) ->
    case out(Q) of
        {empty, _} ->
            true;
        {{value, _}, _} ->
            false
    end.

%%-------------------------------------------------------------------------
%% @doc
%% ===Check if the priority queue type is as expected.===
%% O(1)
%% @end
%%-------------------------------------------------------------------------

-spec is_queue(pqueue3()) -> 'true' | 'false'.

is_queue({Size, Offset, I, Bins})
    when is_integer(Size), is_integer(Offset), is_tuple(Bins) ->
    (I =:= empty) or is_integer(I);
is_queue(_) ->
    false.

%%-------------------------------------------------------------------------
%% @doc
%% ===Determine the length of a priority queue.===
%% O(N)
%% @end
%%-------------------------------------------------------------------------

-spec len(pqueue3()) -> non_neg_integer().

len(Q) ->
    len(0, out(Q)).
len(I, {empty, _}) ->
    I;
len(I, {{value, _}, Q}) ->
    len(I + 1, out(Q)).

%%-------------------------------------------------------------------------
%% @doc
%% ===Create a new priority queue.===
%% O(1)
%% @end
%%-------------------------------------------------------------------------

-spec new() -> pqueue3_empty().

new() ->
    new([]).

%%-------------------------------------------------------------------------
%% @doc
%% ===Create a new priority queue with customization options.===
%% O(1)
%% @end
%%-------------------------------------------------------------------------

-spec new(list({atom(), term()})) -> pqueue3().

new(Options) ->
    Size = proplists:get_value(priorities, Options, 256),
    MiddleZero = proplists:get_value(middle_priority_zero, Options, true),
    Offset = if
        MiddleZero =:= true ->
            erlang:round((Size / 2) + 0.5) - 1;
        true ->
            0
    end,
    {Size, Offset, empty, create(layer_sizes(Size))}.

%%-------------------------------------------------------------------------
%% @doc
%% ===Take an item from the head of the priority queue.===
%% O(1) amortized, O(N) worst case
%% @end
%%-------------------------------------------------------------------------

-spec out(pqueue3()) ->
    {{'value', term()}, pqueue3()} | {'empty', pqueue3()}.

out({_, _, empty, _} = Q) ->
    {empty, Q};
out({Size, Offset, I, Bins}) ->
    {Result, NewI, NewBins} = out_check(
        I, Size, out_queue(layer_indexes(Size, I), Bins)
    ),
    {Result, {Size, Offset, NewI, NewBins}}.

%%-------------------------------------------------------------------------
%% @doc
%% ===Take an item of a specific priority from the head of the queue.===
%% O(1) amortized, O(N) worst case
%% @end
%%-------------------------------------------------------------------------

-spec out(integer(), pqueue3()) ->
    {{'value', term()}, pqueue3()} | {'empty', pqueue3()}.

out(P, {Size, Offset, _, _})
    when (P + Offset) < 0; (P + Offset) > Size ->
    erlang:exit(badarg);
out(_, {_, _, empty, _} = Q) ->
    {empty, Q};
out(P, {Size, Offset, I, Bins}) ->
    {Result, NewBins} = out_queue(layer_indexes(Size, P + Offset), Bins),
    {Result, {Size, Offset, I, NewBins}}.

%%-------------------------------------------------------------------------
%% @doc
%% ===Take an item from the head of the priority queue.===
%% Includes the priority in the return value.
%% O(1) amortized, O(N) worst case
%% @end
%%-------------------------------------------------------------------------

-spec pout(pqueue3()) ->
    {{'value', term(), integer()}, pqueue3()} | {'empty', pqueue3()}.

pout({_, _, empty, _} = Q) ->
    {empty, Q};
pout({Size, Offset, I, Bins}) ->
    {Result, NewI, NewBins} = pout_check(
        I, Size, Offset, out_queue(layer_indexes(Size, I), Bins)
    ),
    {Result, {Size, Offset, NewI, NewBins}}.

%%-------------------------------------------------------------------------
%% @doc
%% ===Convert the priority queue to a list.===
%% O(N)
%% @end
%%-------------------------------------------------------------------------

-spec to_list(pqueue3()) -> list(term()).

to_list(Q) ->
    to_list([], out(Q)).
to_list(L, {empty, _}) ->
    lists:reverse(L);
to_list(L, {{value, Value}, Q}) ->
    to_list([Value | L], out(Q)).

%%%------------------------------------------------------------------------
%%% Private functions
%%%------------------------------------------------------------------------

create([]) ->
    queue:new();

create([I | Is]) ->
    erlang:make_tuple(I + 1, create(Is)).

in_queue({I1}, Value, Bins1) ->
    erlang:setelement(I1, Bins1, queue:in(Value, erlang:element(I1, Bins1)));

in_queue({I1, I2}, Value, Bins1) ->
    Bins2 = erlang:element(I1, Bins1),
    erlang:setelement(I1, Bins1,
    erlang:setelement(I2, Bins2, queue:in(Value, erlang:element(I2, Bins2))));

in_queue({I1, I2, I3}, Value, Bins1) ->
    Bins2 = erlang:element(I1, Bins1),
    Bins3 = erlang:element(I2, Bins2),
    erlang:setelement(I1, Bins1,
    erlang:setelement(I2, Bins2,
    erlang:setelement(I3, Bins3, queue:in(Value, erlang:element(I3, Bins3)))));

in_queue({I1, I2, I3, I4}, Value, Bins1) ->
    Bins2 = erlang:element(I1, Bins1),
    Bins3 = erlang:element(I2, Bins2),
    Bins4 = erlang:element(I3, Bins3),
    erlang:setelement(I1, Bins1,
    erlang:setelement(I2, Bins2,
    erlang:setelement(I3, Bins3,
    erlang:setelement(I4, Bins4, queue:in(Value, erlang:element(I4, Bins4)))))).

pout_check(Size, Size, _, {empty, Bins}) ->
    {empty, empty, Bins};
pout_check(I, _, Offset, {{value, Value}, Bins}) ->
    {{value, Value, I - Offset}, I, Bins};
pout_check(I, Size, Offset, {empty, Bins}) ->
    NewI = I + 1,
    pout_check(NewI, Size, Offset, out_queue(layer_indexes(Size, NewI), Bins)).

out_check(Size, Size, {empty, Bins}) ->
    {empty, empty, Bins};
out_check(I, _, {{value, _} = Result, Bins}) ->
    {Result, I, Bins};
out_check(I, Size, {empty, Bins}) ->
    NewI = I + 1,
    out_check(NewI, Size, out_queue(layer_indexes(Size, NewI), Bins)).

out_queue({I1}, Bins1) ->
    {Result, NewQueue} = queue:out(erlang:element(I1, Bins1)),
    {Result,
     erlang:setelement(I1, Bins1, NewQueue)};

out_queue({I1, I2}, Bins1) ->
    Bins2 = erlang:element(I1, Bins1),
    {Result, NewQueue} = queue:out(erlang:element(I2, Bins2)),
    {Result,
     erlang:setelement(I1, Bins1,
     erlang:setelement(I2, Bins2, NewQueue))};

out_queue({I1, I2, I3}, Bins1) ->
    Bins2 = erlang:element(I1, Bins1),
    Bins3 = erlang:element(I2, Bins2),
    {Result, NewQueue} = queue:out(erlang:element(I3, Bins3)),
    {Result,
     erlang:setelement(I1, Bins1,
     erlang:setelement(I2, Bins2,
     erlang:setelement(I3, Bins3, NewQueue)))};

out_queue({I1, I2, I3, I4}, Bins1) ->
    Bins2 = erlang:element(I1, Bins1),
    Bins3 = erlang:element(I2, Bins2),
    Bins4 = erlang:element(I3, Bins3),
    {Result, NewQueue} = queue:out(erlang:element(I4, Bins4)),
    {Result,
     erlang:setelement(I1, Bins1,
     erlang:setelement(I2, Bins2,
     erlang:setelement(I3, Bins3,
     erlang:setelement(I4, Bins4, NewQueue))))}.

layer_indexes(Size, PriorityIndex) ->
    if
        Size =< 127 ->
            {PriorityIndex + 1};
        Size =< 255 ->
            <<I1:4, I2:4>> = <<PriorityIndex:8>>,
            {I1 + 1, I2 + 1};
        Size =< 511 ->
            <<I1:4, I2:5>> = <<PriorityIndex:9>>,
            {I1 + 1, I2 + 1};
        Size =< 1023 ->
            <<I1:3, I2:3, I3:4>> = <<PriorityIndex:10>>,
            {I1 + 1, I2 + 1, I3 + 1};
        Size =< 2047 ->
            <<I1:3, I2:4, I3:4>> = <<PriorityIndex:11>>,
            {I1 + 1, I2 + 1, I3 + 1};
        Size =< 4095 ->
            <<I1:4, I2:4, I3:4>> = <<PriorityIndex:12>>,
            {I1 + 1, I2 + 1, I3 + 1};
        Size =< 8191 ->
            <<I1:4, I2:4, I3:5>> = <<PriorityIndex:13>>,
            {I1 + 1, I2 + 1, I3 + 1};
        Size =< 16383 ->
            <<I1:4, I2:5, I3:5>> = <<PriorityIndex:14>>,
            {I1 + 1, I2 + 1, I3 + 1};
        Size =< 32767 ->
            <<I1:3, I2:4, I3:4, I4:4>> = <<PriorityIndex:15>>,
            {I1 + 1, I2 + 1, I3 + 1, I4 + 1};
        Size =< 65535 ->
            <<I1:4, I2:4, I3:4, I4:4>> = <<PriorityIndex:16>>,
            {I1 + 1, I2 + 1, I3 + 1, I4 + 1}
    end.

layer_sizes(Size) ->
    if
        Size =< 127 ->
            <<I1:7>> = <<127:7>>,
            [I1];
        Size =< 255 ->
            <<I1:4, I2:4>> = <<255:8>>,
            [I1, I2];
        Size =< 511 ->
            <<I1:4, I2:5>> = <<511:9>>,
            [I1, I2];
        Size =< 1023 ->
            <<I1:3, I2:3, I3:4>> = <<1023:10>>,
            [I1, I2, I3];
        Size =< 2047 ->
            <<I1:3, I2:4, I3:4>> = <<2047:11>>,
            [I1, I2, I3];
        Size =< 4095 ->
            <<I1:4, I2:4, I3:4>> = <<4095:12>>,
            [I1, I2, I3];
        Size =< 8191 ->
            <<I1:4, I2:4, I3:5>> = <<8191:13>>,
            [I1, I2, I3];
        Size =< 16383 ->
            <<I1:4, I2:5, I3:5>> = <<16383:14>>,
            [I1, I2, I3];
        Size =< 32767 ->
            <<I1:3, I2:4, I3:4, I4:4>> = <<32767:15>>,
            [I1, I2, I3, I4];
        Size =< 65535 ->
            <<I1:4, I2:4, I3:4, I4:4>> = <<65535:16>>,
            [I1, I2, I3, I4]
    end.

