-module(ow_collision).
-export([new/4, new/2, add_entity/3, add_entities/3, check_area/3]).

% these aren't eunit tests as such, just some scaffolding toward building those
-export([
    add_entity_test/0,
    add_entities_test/0,
    check_area_test/0,
    check_area_random_test/0,
    generate_random_entities/3
]).

% Generic collision detection module.

%:: {pos_integer(), pos_integer()}
-record(test_entity, {
    pos,
    %:: [{ow_vector:vector(), ...}, ...]
    bbox
}).

-spec new(integer(), integer(), integer(), integer()) ->
    erlquad:erlquad_node().
new(Xmin, Ymin, Xmax, Ymax) ->
    erlquad:new(Xmin, Ymin, Xmax, Ymax, 5).

-spec new(pos_integer(), pos_integer()) -> erlquad:erlquad_node().
new(X, Y) ->
    % Create an empty quadtree with no entities.
    erlquad:new(0, 0, X, Y, 5).
%Random internet stuff suggests the depth of the quadtree should be
%log4(N) where N is number of entities.
% log4(25) -> 2.32
% log4(100) -> 3.32

-spec add_entity(any(), fun(), erlquad:erlquad_node()) ->
    erlquad:erlquad_node().
add_entity(Entity, PosFun, Quadtree) ->
    add_entities([Entity], PosFun, Quadtree).

add_entity_test() ->
    Q = new(1000, 1000),
    % coordinates
    Entity = #test_entity{pos = {10, 20}},
    PositionFun = fun(#test_entity{pos = {X, Y}}) -> {X, Y} end,
    add_entity(Entity, PositionFun, Q).

-spec add_entities(list(), fun(), erlquad:erlquad_node()) ->
    erlquad:erlquad_node().
add_entities(Entities, PositionFun, Quadtree) ->
    erlquad:objects_add(Entities, PositionFun, Quadtree).

add_entities_test() ->
    Q = new(1000, 1000),
    Entities = [
        #test_entity{pos = {10, 20}},
        #test_entity{pos = {15, 35}}
    ],
    PositionFun = fun(#test_entity{pos = {X, Y}}) -> {X, Y} end,
    add_entities(Entities, PositionFun, Q).

check_area(
    {Left, Bottom, Right, Top}, BoundingBoxFun, Quadtree
) ->
    % Query the area to check
    Entities = erlquad:area_query(
        Left, Bottom, Right, Top, Quadtree
    ),
    %io:format("Entities in the queried area: ~p~n", [Entities]),
    % Create a list of all objects in the area of interest to check.
    ObjPairs = [
        [Obj1, Obj2]
     || Obj1 <- Entities,
        Obj2 <- Entities,
        Obj1 =/= Obj2
    ],
    % Sort the inner list pair, then delete duplicates
    UniqObjPairs = lists:usort([lists:sort(X) || X <- ObjPairs]),
    [
        {Obj1, Obj2,
            ow_vector:is_collision(
                BoundingBoxFun(Obj1), BoundingBoxFun(Obj2)
            )}
     || [Obj1, Obj2] <- UniqObjPairs
    ].

generate_random_entities(Number, XRange, YRange) ->
    L = lists:seq(1, Number),
    Bounds = [{-10, -10}, {-10, 10}, {10, -10}, {10, 10}],
    [
        #test_entity{
            pos = {rand:uniform(XRange), rand:uniform(YRange)},
            bbox = Bounds
        }
     || _N <- L
    ].

check_area_test() ->
    % create a new quadtree
    Q1 = new(10000, 10000),
    % Create some entities in the quadtree
    Entities = [
        #test_entity{
            pos = {10, 20},
            bbox = [{-5, -5}, {-5, 5}, {5, -5}, {5, 5}]
        },
        #test_entity{
            pos = {10, 21},
            bbox = [{-5, -5}, {-5, 5}, {5, -5}, {5, 5}]
        },
        #test_entity{
            pos = {25, 30},
            bbox = [{-5, -5}, {-5, 5}, {5, -5}, {5, 5}]
        }
    ],
    % Function for deriving the position of the entity
    PositionFun = fun(#test_entity{pos = {X, Y}}) -> {X, Y} end,
    % Add entity positions to the quadtree
    Q2 = add_entities(Entities, PositionFun, Q1),
    io:format("New quadtree is ~p~n", [Q2]),
    % Calculate an area of interest from one of the entities
    [H | _T] = Entities,
    io:format("Selecting entity to check for collisions: ~p~n", [H]),
    {POI_X, POI_Y} = H#test_entity.pos,
    % Extend 100 units in all directions around the entity to define the area to check for collisions
    Left = POI_X - 50,
    Bottom = POI_Y - 50,
    Right = POI_X + 50,
    Top = POI_Y + 50,
    BoundingBox = fun(#test_entity{bbox = Box, pos = Pos}) ->
        % translate all coordinates by Pos
        ow_vector:translate(Box, Pos)
    end,
    statistics(runtime),
    statistics(wall_clock),
    Results = check_area({Left, Bottom, Right, Top}, BoundingBox, Q2),
    Collisions = [
        {Obj1, Obj2}
     || {Obj1, Obj2, Collision} <- Results, Collision == true
    ],
    {_, Time1} = statistics(runtime),
    {_, Time2} = statistics(wall_clock),
    U1 = Time1 * 1000,
    U2 = Time2 * 1000,
    io:format("Code time=~p (~p) microseconds~n", [U1, U2]),
    io:format("Collisions at: ~p~n", [Collisions]).

check_area_random_test() ->
    % create a new quadtree
    Q1 = new(10000, 10000),
    % Create some entities in the quadtree
    % Entities = [
    %           #test_entity{
    %              pos={10,20},
    %              bbox=[{-5,-5}, {-5,5}, {5,-5}, {5,5}]
    %              },
    %           #test_entity{
    %              pos={10,21},
    %              bbox=[{-5,-5}, {-5,5}, {5,-5}, {5,5}]
    %             },
    %           #test_entity{
    %              pos={25,30},
    %              bbox=[{-5,-5}, {-5,5}, {5,-5}, {5,5}]
    %             }
    %          ],
    Entities = generate_random_entities(5000, 10000, 10000),
    % Function for deriving the position of the entity
    PositionFun = fun(#test_entity{pos = {X, Y}}) -> {X, Y} end,
    % Add entity positions to the quadtree
    Q2 = add_entities(Entities, PositionFun, Q1),
    io:format("New quadtree is ~p~n", [Q2]),
    % Calculate an area of interest from one of the entities
    [H | _T] = Entities,
    io:format("Selecting entity to check for collisions: ~p~n", [H]),
    {POI_X, POI_Y} = H#test_entity.pos,
    % Extend 100 units in all directions around the entity to define the area to check for collisions
    Left = POI_X - 50,
    Bottom = POI_Y - 50,
    Right = POI_X + 50,
    Top = POI_Y + 50,
    BoundingBox = fun(#test_entity{bbox = Box, pos = Pos}) ->
        % translate all coordinates by Pos
        ow_vector:translate(Box, Pos)
    end,
    statistics(runtime),
    statistics(wall_clock),
    Results = check_area({Left, Bottom, Right, Top}, BoundingBox, Q2),
    Collisions = [
        {Obj1, Obj2}
     || {Obj1, Obj2, Collision} <- Results, Collision == true
    ],
    {_, Time1} = statistics(runtime),
    {_, Time2} = statistics(wall_clock),
    U1 = Time1 * 1000,
    U2 = Time2 * 1000,
    io:format("Code time=~p (~p) microseconds~n", [U1, U2]),
    io:format("Collisions at: ~p~n", [Collisions]).