expresso

-module(expresso@collision).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch, inline]).
-define(FILEPATH, "src/expresso/collision.gleam").
-export([build_bvh/1, detect_collisions_with_bvh/2, detect_collisions/1, detect_collisions_with_index/2, bodies_to_bvh_items/1, extract_bodies_from_results/2, filter_by_radius/3, filter_by_region/3, find_nearest/2, analyze_distribution/1, calculate_world_bounds/1, raycast/6]).
-export_type([spatial_index/1, contact/1, raycast_hit/1]).

-if(?OTP_RELEASE >= 27).
-define(MODULEDOC(Str), -moduledoc(Str)).
-define(DOC(Str), -doc(Str)).
-else.
-define(MODULEDOC(Str), -compile([])).
-define(DOC(Str), -compile([])).
-endif.

?MODULEDOC(
    " Collision detection with spatial acceleration.\n"
    "\n"
    " This module provides efficient collision detection using spatial partitioning\n"
    " data structures from the `spatial` library.\n"
    "\n"
    " ## Features\n"
    "\n"
    " - **Multi-shape support**: Sphere, Box, Capsule, and Cylinder colliders\n"
    " - **Spatial acceleration**: BVH (O(n log n)) and Grid (O(c + k))\n"
    " - **Adaptive selection**: Auto-choose BVH or Grid based on distribution\n"
    " - **Accurate detection**: Uses `spatial` library's collision algorithms\n"
    "\n"
    " ## Collision Detection Strategies\n"
    "\n"
    " ### Brute Force (< 10 bodies)\n"
    " - Complexity: O(n²)\n"
    " - Used automatically for small scenes\n"
    " - No spatial index overhead\n"
    "\n"
    " ### BVH (10-1000+ bodies, dynamic)\n"
    " - Complexity: O(n log n + k) where k = collision pairs\n"
    " - Best for dynamic scenes with moving objects\n"
    " - Handles non-uniform distributions well\n"
    "\n"
    " ### Grid (100-1000+ bodies, uniform)\n"
    " - Complexity: O(c + k) where c = cells checked, k = collision pairs\n"
    " - Best for particle systems and uniformly distributed bodies\n"
    " - Excellent for 1000s of particles\n"
    "\n"
    " ## Usage\n"
    "\n"
    " Most users won't call this module directly - the `world` module handles\n"
    " collision detection automatically. However, advanced users can use these\n"
    " functions for custom collision detection:\n"
    "\n"
    " ```gleam\n"
    " import expresso/collision\n"
    " import gleam/dict\n"
    "\n"
    " // Simple collision detection (builds BVH internally)\n"
    " let contacts = collision.detect_collisions(bodies)\n"
    "\n"
    " // With pre-built BVH (more efficient if reusing)\n"
    " let bvh = collision.build_bvh(bodies)\n"
    " let contacts = collision.detect_collisions_with_bvh(bodies, option.Some(bvh))\n"
    " ```\n"
).

-type spatial_index(MAH) :: {b_v_h_index, spatial@bvh:b_v_h(MAH)} |
    {grid_index, spatial@grid:grid(MAH)}.

-type contact(MAI) :: {contact,
        MAI,
        MAI,
        vec@vec3:vec3(float()),
        float(),
        vec@vec3:vec3(float())}.

-type raycast_hit(MAJ) :: {raycast_hit,
        MAJ,
        expresso@body:body(MAJ),
        vec@vec3:vec3(float()),
        vec@vec3:vec3(float()),
        float()}.

-file("src/expresso/collision.gleam", 147).
?DOC(" Internal: Build BVH from body list\n").
-spec build_bvh_internal(list({MBH, expresso@body:body(MBH)})) -> {ok,
        spatial@bvh:b_v_h({MBH, expresso@body:body(MBH)})} |
    {error, nil}.
build_bvh_internal(Body_list) ->
    Bvh_items = gleam@list:map(
        Body_list,
        fun(Pair) ->
            {Id, Body} = Pair,
            Pos_3d = {vec3,
                erlang:element(2, erlang:element(3, Body)),
                erlang:element(3, erlang:element(3, Body)),
                +0.0},
            {Pos_3d, {Id, Body}}
        end
    ),
    spatial@bvh:from_items(Bvh_items, 8).

-file("src/expresso/collision.gleam", 140).
?DOC(" Build a BVH spatial index from bodies\n").
-spec build_bvh(gleam@dict:dict(MAZ, expresso@body:body(MAZ))) -> {ok,
        spatial@bvh:b_v_h({MAZ, expresso@body:body(MAZ)})} |
    {error, nil}.
build_bvh(Bodies) ->
    build_bvh_internal(maps:to_list(Bodies)).

-file("src/expresso/collision.gleam", 298).
?DOC(
    " Check if two bodies are colliding using their colliders\n"
    "\n"
    " Uses the spatial library's collider.intersects() for accurate collision detection.\n"
    " Respects collision layers - bodies only collide if their layers match.\n"
).
-spec check_collision(expresso@body:body(MCZ), expresso@body:body(MCZ)) -> {ok,
        contact(MCZ)} |
    {error, nil}.
check_collision(Body_a, Body_b) ->
    case expresso@body:should_collide(Body_a, Body_b) of
        false ->
            {error, nil};

        true ->
            Collider_a = expresso@body:world_collider(Body_a),
            Collider_b = expresso@body:world_collider(Body_b),
            case spatial@collider:intersects(Collider_a, Collider_b) of
                false ->
                    {error, nil};

                true ->
                    Center_a = spatial@collider:center(Collider_a),
                    Center_b = spatial@collider:center(Collider_b),
                    Delta = vec@vec3f:subtract(Center_b, Center_a),
                    Distance_3d = vec@vec3f:length(Delta),
                    Size_a = spatial@collider:size(Collider_a),
                    Size_b = spatial@collider:size(Collider_b),
                    Radius_a = gleam@float:max(
                        erlang:element(2, Size_a),
                        erlang:element(3, Size_a)
                    )
                    / 2.0,
                    Radius_b = gleam@float:max(
                        erlang:element(2, Size_b),
                        erlang:element(3, Size_b)
                    )
                    / 2.0,
                    Penetration = (Radius_a + Radius_b) - Distance_3d,
                    Normal = case Distance_3d > 0.0001 of
                        true ->
                            vec@vec3f:scale(Delta, case Distance_3d of
                                    +0.0 -> +0.0;
                                    -0.0 -> -0.0;
                                    Gleam@denominator -> 1.0 / Gleam@denominator
                                end);

                        false ->
                            {vec3, 1.0, +0.0, +0.0}
                    end,
                    Contact_point = vec@vec3f:add(
                        Center_a,
                        vec@vec3f:scale(Delta, 0.5)
                    ),
                    {ok,
                        {contact,
                            erlang:element(2, Body_a),
                            erlang:element(2, Body_b),
                            Normal,
                            Penetration,
                            Contact_point}}
            end
    end.

-file("src/expresso/collision.gleam", 161).
?DOC(" Brute force collision detection for small body counts\n").
-spec detect_collisions_brute_force(list({MBO, expresso@body:body(MBO)})) -> list(contact(MBO)).
detect_collisions_brute_force(Body_list) ->
    gleam@list:flat_map(
        Body_list,
        fun(Pair_a) ->
            {Id_a, Body_a} = Pair_a,
            gleam@list:filter_map(
                Body_list,
                fun(Pair_b) ->
                    {Id_b, Body_b} = Pair_b,
                    case Id_a =:= Id_b of
                        false ->
                            check_collision(Body_a, Body_b);

                        _ ->
                            {error, nil}
                    end
                end
            )
        end
    ).

-file("src/expresso/collision.gleam", 349).
?DOC(" Calculate the maximum bounding radius among all bodies\n").
-spec calculate_max_radius(list({MDF, expresso@body:body(MDF)})) -> float().
calculate_max_radius(Body_list) ->
    gleam@list:fold(
        Body_list,
        +0.0,
        fun(Max_r, Pair) ->
            {_, Body} = Pair,
            gleam@float:max(Max_r, expresso@body:bounding_radius(Body))
        end
    ).

-file("src/expresso/collision.gleam", 180).
?DOC(" BVH-accelerated collision detection\n").
-spec detect_collisions_with_bvh_internal(
    list({MBT, expresso@body:body(MBT)}),
    spatial@bvh:b_v_h({MBT, expresso@body:body(MBT)})
) -> list(contact(MBT)).
detect_collisions_with_bvh_internal(Body_list, Bvh_tree) ->
    gleam@list:flat_map(
        Body_list,
        fun(Pair_a) ->
            {Id_a, Body_a} = Pair_a,
            Max_radius = calculate_max_radius(Body_list),
            Query_radius = expresso@body:bounding_radius(Body_a) + Max_radius,
            Pos_3d = {vec3,
                erlang:element(2, erlang:element(3, Body_a)),
                erlang:element(3, erlang:element(3, Body_a)),
                +0.0},
            Nearby = spatial@bvh:query_radius(Bvh_tree, Pos_3d, Query_radius),
            gleam@list:filter_map(
                Nearby,
                fun(Candidate) ->
                    {_, {Id_b, Body_b}} = Candidate,
                    case Id_a =:= Id_b of
                        true ->
                            {error, nil};

                        false ->
                            case Id_a =:= Id_b of
                                false ->
                                    check_collision(Body_a, Body_b);

                                _ ->
                                    {error, nil}
                            end
                    end
                end
            )
        end
    ).

-file("src/expresso/collision.gleam", 112).
?DOC(
    " Detect collisions using an optional pre-built BVH for acceleration\n"
    "\n"
    " This is the recommended API for performance-critical code.\n"
).
-spec detect_collisions_with_bvh(
    gleam@dict:dict(MAQ, expresso@body:body(MAQ)),
    gleam@option:option(spatial@bvh:b_v_h({MAQ, expresso@body:body(MAQ)}))
) -> list(contact(MAQ)).
detect_collisions_with_bvh(Bodies, Bvh_option) ->
    Body_list = maps:to_list(Bodies),
    case Bvh_option of
        {some, Bvh_tree} ->
            detect_collisions_with_bvh_internal(Body_list, Bvh_tree);

        none ->
            case erlang:length(Body_list) < 10 of
                true ->
                    detect_collisions_brute_force(Body_list);

                false ->
                    Bvh_tree@1 = build_bvh_internal(Body_list),
                    case Bvh_tree@1 of
                        {error, nil} ->
                            [];

                        {ok, Tree} ->
                            detect_collisions_with_bvh_internal(Body_list, Tree)
                    end
            end
    end.

-file("src/expresso/collision.gleam", 105).
?DOC(
    " Detect all collisions between bodies\n"
    "\n"
    " Returns a list of contacts for all overlapping pairs.\n"
    " \n"
    " **Performance:**\n"
    " - For best performance, use `detect_collisions_with_index()` with a pre-built spatial index\n"
    " - This function uses brute force or builds a BVH internally\n"
).
-spec detect_collisions(gleam@dict:dict(MAK, expresso@body:body(MAK))) -> list(contact(MAK)).
detect_collisions(Bodies) ->
    detect_collisions_with_bvh(Bodies, none).

-file("src/expresso/collision.gleam", 231).
?DOC(" Detect collisions using BVH (optimized version with ID-based storage)\n").
-spec detect_collisions_with_bvh_new(
    gleam@dict:dict(MCH, expresso@body:body(MCH)),
    list({MCH, expresso@body:body(MCH)}),
    spatial@bvh:b_v_h(MCH)
) -> list(contact(MCH)).
detect_collisions_with_bvh_new(Bodies, Body_list, Bvh_tree) ->
    gleam@list:flat_map(
        Body_list,
        fun(Pair_a) ->
            {Id_a, Body_a} = Pair_a,
            Max_radius = calculate_max_radius(Body_list),
            Query_radius = expresso@body:bounding_radius(Body_a) + Max_radius,
            Pos_3d = {vec3,
                erlang:element(2, erlang:element(3, Body_a)),
                erlang:element(3, erlang:element(3, Body_a)),
                +0.0},
            Nearby = spatial@bvh:query_radius(Bvh_tree, Pos_3d, Query_radius),
            gleam@list:filter_map(
                Nearby,
                fun(Candidate) ->
                    {_, Id_b} = Candidate,
                    case Id_a =:= Id_b of
                        true ->
                            {error, nil};

                        false ->
                            case gleam_stdlib:map_get(Bodies, Id_b) of
                                {ok, Body_b} ->
                                    check_collision(Body_a, Body_b);

                                {error, _} ->
                                    {error, nil}
                            end
                    end
                end
            )
        end
    ).

-file("src/expresso/collision.gleam", 263).
?DOC(" Detect collisions using a Grid spatial index (with ID-based storage)\n").
-spec detect_collisions_with_grid_new(
    gleam@dict:dict(MCQ, expresso@body:body(MCQ)),
    list({MCQ, expresso@body:body(MCQ)}),
    spatial@grid:grid(MCQ)
) -> list(contact(MCQ)).
detect_collisions_with_grid_new(Bodies, Body_list, Grid_index) ->
    gleam@list:flat_map(
        Body_list,
        fun(Pair_a) ->
            {Id_a, Body_a} = Pair_a,
            Max_radius = calculate_max_radius(Body_list),
            Query_radius = expresso@body:bounding_radius(Body_a) + Max_radius,
            Pos_3d = {vec3,
                erlang:element(2, erlang:element(3, Body_a)),
                erlang:element(3, erlang:element(3, Body_a)),
                +0.0},
            Nearby = spatial@grid:query_radius(Grid_index, Pos_3d, Query_radius),
            gleam@list:filter_map(
                Nearby,
                fun(Candidate) ->
                    {_, Id_b} = Candidate,
                    case Id_a =:= Id_b of
                        true ->
                            {error, nil};

                        false ->
                            case gleam_stdlib:map_get(Bodies, Id_b) of
                                {ok, Body_b} ->
                                    check_collision(Body_a, Body_b);

                                {error, _} ->
                                    {error, nil}
                            end
                    end
                end
            )
        end
    ).

-file("src/expresso/collision.gleam", 218).
?DOC(" Detect collisions using a spatial index (BVH or Grid)\n").
-spec detect_collisions_with_index(
    gleam@dict:dict(MCA, expresso@body:body(MCA)),
    spatial_index(MCA)
) -> list(contact(MCA)).
detect_collisions_with_index(Bodies, Spatial_index) ->
    Body_list = maps:to_list(Bodies),
    case Spatial_index of
        {b_v_h_index, Tree} ->
            detect_collisions_with_bvh_new(Bodies, Body_list, Tree);

        {grid_index, Grid} ->
            detect_collisions_with_grid_new(Bodies, Body_list, Grid)
    end.

-file("src/expresso/collision.gleam", 361).
?DOC(" Convert bodies to BVH items\n").
-spec bodies_to_bvh_items(list({binary(), expresso@body:body(MDI)})) -> list({vec@vec3:vec3(float()),
    expresso@body:body(MDI)}).
bodies_to_bvh_items(Body_list) ->
    gleam@list:map(
        Body_list,
        fun(Pair) ->
            {_, Body} = Pair,
            Pos_3d = {vec3,
                erlang:element(2, erlang:element(3, Body)),
                erlang:element(3, erlang:element(3, Body)),
                +0.0},
            {Pos_3d, Body}
        end
    ).

-file("src/expresso/collision.gleam", 372).
?DOC(" Extract body IDs from query results and lookup bodies from dict\n").
-spec extract_bodies_from_results(
    list({vec@vec3:vec3(float()), MDP}),
    gleam@dict:dict(MDP, expresso@body:body(MDP))
) -> list({MDP, expresso@body:body(MDP)}).
extract_bodies_from_results(Results, Bodies) ->
    gleam@list:filter_map(
        Results,
        fun(Result) ->
            {_, Id} = Result,
            case gleam_stdlib:map_get(Bodies, Id) of
                {ok, Body} ->
                    {ok, {Id, Body}};

                {error, _} ->
                    {error, nil}
            end
        end
    ).

-file("src/expresso/collision.gleam", 386).
?DOC(" Filter bodies by radius (brute force)\n").
-spec filter_by_radius(
    list({MDW, expresso@body:body(MDW)}),
    vec@vec3:vec3(float()),
    float()
) -> list({MDW, expresso@body:body(MDW)}).
filter_by_radius(Body_list, Center, Radius) ->
    gleam@list:filter(
        Body_list,
        fun(Pair) ->
            {_, Body} = Pair,
            Distance = vec@vec3f:distance(Center, erlang:element(3, Body)),
            Distance =< (Radius + expresso@body:bounding_radius(Body))
        end
    ).

-file("src/expresso/collision.gleam", 399).
?DOC(" Filter bodies by rectangular region (brute force)\n").
-spec filter_by_region(
    list({MEC, expresso@body:body(MEC)}),
    vec@vec3:vec3(float()),
    vec@vec3:vec3(float())
) -> list({MEC, expresso@body:body(MEC)}).
filter_by_region(Body_list, Min, Max) ->
    gleam@list:filter(
        Body_list,
        fun(Pair) ->
            {_, Body} = Pair,
            (((((erlang:element(2, erlang:element(3, Body)) >= erlang:element(
                2,
                Min
            ))
            andalso (erlang:element(2, erlang:element(3, Body)) =< erlang:element(
                2,
                Max
            )))
            andalso (erlang:element(3, erlang:element(3, Body)) >= erlang:element(
                3,
                Min
            )))
            andalso (erlang:element(3, erlang:element(3, Body)) =< erlang:element(
                3,
                Max
            )))
            andalso (erlang:element(4, erlang:element(3, Body)) >= erlang:element(
                4,
                Min
            )))
            andalso (erlang:element(4, erlang:element(3, Body)) =< erlang:element(
                4,
                Max
            ))
        end
    ).

-file("src/expresso/collision.gleam", 416).
?DOC(" Find the nearest body to a point\n").
-spec find_nearest(list({MEJ, expresso@body:body(MEJ)}), vec@vec3:vec3(float())) -> gleam@option:option({MEJ,
    expresso@body:body(MEJ),
    float()}).
find_nearest(Candidates, Point) ->
    gleam@list:fold(
        Candidates,
        none,
        fun(Best, Pair) ->
            {Id, Body} = Pair,
            Distance = vec@vec3f:distance(Point, erlang:element(3, Body)),
            case Best of
                none ->
                    {some, {Id, Body, Distance}};

                {some, {_, _, Best_dist}} ->
                    case Distance < Best_dist of
                        true ->
                            {some, {Id, Body, Distance}};

                        false ->
                            Best
                    end
            end
        end
    ).

-file("src/expresso/collision.gleam", 471).
?DOC(" Calculate variance in positions (simplified)\n").
-spec calculate_position_variance(list(vec@vec3:vec3(float()))) -> float().
calculate_position_variance(Positions) ->
    case erlang:length(Positions) of
        0 ->
            +0.0;

        N ->
            Sum = gleam@list:fold(
                Positions,
                {vec3, +0.0, +0.0, +0.0},
                fun(Acc, Pos) -> vec@vec3f:add(Acc, Pos) end
            ),
            Centroid = vec@vec3f:scale(Sum, case erlang:float(N) of
                    +0.0 -> +0.0;
                    -0.0 -> -0.0;
                    Gleam@denominator -> 1.0 / Gleam@denominator
                end),
            Total_sq_dist = gleam@list:fold(
                Positions,
                +0.0,
                fun(Acc@1, Pos@1) ->
                    Dist = vec@vec3f:distance(Centroid, Pos@1),
                    Acc@1 + (Dist * Dist)
                end
            ),
            case erlang:float(N) of
                +0.0 -> +0.0;
                -0.0 -> -0.0;
                Gleam@denominator@1 -> Total_sq_dist / Gleam@denominator@1
            end
    end.

-file("src/expresso/collision.gleam", 438).
?DOC(
    " Analyze body distribution to determine if uniform\n"
    "\n"
    " Returns #(is_uniform, average_bounding_radius)\n"
).
-spec analyze_distribution(gleam@dict:dict(MEP, expresso@body:body(MEP))) -> {boolean(),
    float()}.
analyze_distribution(Bodies) ->
    Body_list = maps:to_list(Bodies),
    Count = erlang:length(Body_list),
    case Count of
        0 ->
            {false, 1.0};

        _ ->
            Total_radius = gleam@list:fold(
                Body_list,
                +0.0,
                fun(Sum, Pair) ->
                    {_, Body} = Pair,
                    Sum + expresso@body:bounding_radius(Body)
                end
            ),
            Avg_radius = case erlang:float(Count) of
                +0.0 -> +0.0;
                -0.0 -> -0.0;
                Gleam@denominator -> Total_radius / Gleam@denominator
            end,
            Positions = gleam@list:map(
                Body_list,
                fun(Pair@1) ->
                    {_, Body@1} = Pair@1,
                    erlang:element(3, Body@1)
                end
            ),
            Variance = calculate_position_variance(Positions),
            Is_uniform = Variance < 100.0,
            {Is_uniform, Avg_radius}
    end.

-file("src/expresso/collision.gleam", 495).
?DOC(" Calculate world bounds for Grid creation\n").
-spec calculate_world_bounds(gleam@dict:dict(MEV, expresso@body:body(MEV))) -> spatial@collider:internal_collider().
calculate_world_bounds(Bodies) ->
    Body_list = maps:to_list(Bodies),
    case Body_list of
        [] ->
            spatial@collider:box(
                {vec3, -100.0, -100.0, -1.0},
                {vec3, 100.0, 100.0, 1.0}
            );

        _ ->
            Init_min = {vec3, 1.0e10, 1.0e10, 1.0e10},
            Init_max = {vec3, -1.0e10, -1.0e10, -1.0e10},
            {Min_3d, Max_3d} = gleam@list:fold(
                Body_list,
                {Init_min, Init_max},
                fun(Acc, Pair) ->
                    {Current_min, Current_max} = Acc,
                    {_, Body} = Pair,
                    Radius = expresso@body:bounding_radius(Body),
                    Body_min = {vec3,
                        erlang:element(2, erlang:element(3, Body)) - Radius,
                        erlang:element(3, erlang:element(3, Body)) - Radius,
                        erlang:element(4, erlang:element(3, Body)) - Radius},
                    Body_max = {vec3,
                        erlang:element(2, erlang:element(3, Body)) + Radius,
                        erlang:element(3, erlang:element(3, Body)) + Radius,
                        erlang:element(4, erlang:element(3, Body)) + Radius},
                    {{vec3,
                            gleam@float:min(
                                erlang:element(2, Current_min),
                                erlang:element(2, Body_min)
                            ),
                            gleam@float:min(
                                erlang:element(3, Current_min),
                                erlang:element(3, Body_min)
                            ),
                            gleam@float:min(
                                erlang:element(4, Current_min),
                                erlang:element(4, Body_min)
                            )},
                        {vec3,
                            gleam@float:max(
                                erlang:element(2, Current_max),
                                erlang:element(2, Body_max)
                            ),
                            gleam@float:max(
                                erlang:element(3, Current_max),
                                erlang:element(3, Body_max)
                            ),
                            gleam@float:max(
                                erlang:element(4, Current_max),
                                erlang:element(4, Body_max)
                            )}}
                end
            ),
            Padding = 10.0,
            spatial@collider:box(
                {vec3,
                    erlang:element(2, Min_3d) - Padding,
                    erlang:element(3, Min_3d) - Padding,
                    erlang:element(4, Min_3d) - Padding},
                {vec3,
                    erlang:element(2, Max_3d) + Padding,
                    erlang:element(3, Max_3d) + Padding,
                    erlang:element(4, Max_3d) + Padding}
            )
    end.

-file("src/expresso/collision.gleam", 659).
?DOC(" Test ray against a single body's collider\n").
-spec raycast_body(
    vec@vec3:vec3(float()),
    vec@vec3:vec3(float()),
    float(),
    MFM,
    expresso@body:body(MFM)
) -> {ok, raycast_hit(MFM)} | {error, nil}.
raycast_body(Origin, Direction, Max_distance, Body_id, Body_data) ->
    Collider_center = erlang:element(3, Body_data),
    Radius = expresso@body:bounding_radius(Body_data),
    To_center = vec@vec3f:subtract(Collider_center, Origin),
    Projection = vec@vec3f:dot(To_center, Direction),
    case Projection < +0.0 of
        true ->
            {error, nil};

        false ->
            Closest_point = vec@vec3f:add(
                Origin,
                vec@vec3f:scale(Direction, Projection)
            ),
            Distance_to_center = vec@vec3f:distance(
                Closest_point,
                Collider_center
            ),
            case Distance_to_center =< Radius of
                false ->
                    {error, nil};

                true ->
                    Offset_sq = (Radius * Radius) - (Distance_to_center * Distance_to_center),
                    Offset = case Offset_sq of
                        +0.0 ->
                            +0.0;

                        _ ->
                            case begin
                                _pipe = Offset_sq,
                                gleam@float:square_root(_pipe)
                            end of
                                {ok, O} ->
                                    O;

                                {error, _} ->
                                    +0.0
                            end
                    end,
                    Hit_distance = Projection - Offset,
                    case (Hit_distance >= +0.0) andalso (Hit_distance =< Max_distance) of
                        false ->
                            {error, nil};

                        true ->
                            Hit_point = vec@vec3f:add(
                                Origin,
                                vec@vec3f:scale(Direction, Hit_distance)
                            ),
                            Normal_vec = vec@vec3f:subtract(
                                Hit_point,
                                Collider_center
                            ),
                            Normal_length = vec@vec3f:length(Normal_vec),
                            Normal = case Normal_length > 0.0001 of
                                true ->
                                    vec@vec3f:scale(
                                        Normal_vec,
                                        case Normal_length of
                                            +0.0 -> +0.0;
                                            -0.0 -> -0.0;
                                            Gleam@denominator -> 1.0 / Gleam@denominator
                                        end
                                    );

                                false ->
                                    {vec3, 1.0, +0.0, +0.0}
                            end,
                            {ok,
                                {raycast_hit,
                                    Body_id,
                                    Body_data,
                                    Hit_point,
                                    Normal,
                                    Hit_distance}}
                    end
            end
    end.

-file("src/expresso/collision.gleam", 569).
?DOC(
    " Cast a ray and find the first body it hits\n"
    "\n"
    " Returns the closest hit along the ray, or None if no hit.\n"
).
-spec raycast(
    gleam@dict:dict(MEZ, expresso@body:body(MEZ)),
    gleam@option:option(spatial_index(MEZ)),
    vec@vec3:vec3(float()),
    vec@vec3:vec3(float()),
    float(),
    gleam@option:option(integer())
) -> gleam@option:option(raycast_hit(MEZ)).
raycast(Bodies, Spatial_index, Origin, Direction, Max_distance, Layer_mask) ->
    Dir_length = vec@vec3f:length(Direction),
    Dir_normalized = case Dir_length > 0.0001 of
        true ->
            vec@vec3f:scale(Direction, case Dir_length of
                    +0.0 -> +0.0;
                    -0.0 -> -0.0;
                    Gleam@denominator -> 1.0 / Gleam@denominator
                end);

        false ->
            {vec3, 1.0, +0.0, +0.0}
    end,
    Candidates = case Spatial_index of
        none ->
            maps:to_list(Bodies);

        {some, {b_v_h_index, Tree}} ->
            Endpoint = vec@vec3f:add(
                Origin,
                vec@vec3f:scale(Dir_normalized, Max_distance)
            ),
            Center_3d = {vec3,
                (erlang:element(2, Origin) + erlang:element(2, Endpoint)) / 2.0,
                (erlang:element(3, Origin) + erlang:element(3, Endpoint)) / 2.0,
                (erlang:element(4, Origin) + erlang:element(4, Endpoint)) / 2.0},
            Radius = (Max_distance / 2.0) + 10.0,
            Results = spatial@bvh:query_radius(Tree, Center_3d, Radius),
            extract_bodies_from_results(Results, Bodies);

        {some, {grid_index, Grid}} ->
            Endpoint@1 = vec@vec3f:add(
                Origin,
                vec@vec3f:scale(Dir_normalized, Max_distance)
            ),
            Center_3d@1 = {vec3,
                (erlang:element(2, Origin) + erlang:element(2, Endpoint@1)) / 2.0,
                (erlang:element(3, Origin) + erlang:element(3, Endpoint@1)) / 2.0,
                (erlang:element(4, Origin) + erlang:element(4, Endpoint@1)) / 2.0},
            Radius@1 = (Max_distance / 2.0) + 10.0,
            Results@1 = spatial@grid:query_radius(Grid, Center_3d@1, Radius@1),
            extract_bodies_from_results(Results@1, Bodies)
    end,
    Hits = gleam@list:filter_map(
        Candidates,
        fun(Pair) ->
            {Id, Candidate_body} = Pair,
            case Layer_mask of
                {some, Mask} ->
                    case erlang:'band'(erlang:element(14, Candidate_body), Mask)
                    =:= 0 of
                        true ->
                            {error, nil};

                        false ->
                            raycast_body(
                                Origin,
                                Dir_normalized,
                                Max_distance,
                                Id,
                                Candidate_body
                            )
                    end;

                none ->
                    raycast_body(
                        Origin,
                        Dir_normalized,
                        Max_distance,
                        Id,
                        Candidate_body
                    )
            end
        end
    ),
    gleam@list:fold(Hits, none, fun(Closest, Hit) -> case Closest of
                none ->
                    {some, Hit};

                {some, Closest_hit} ->
                    case erlang:element(6, Hit) < erlang:element(6, Closest_hit) of
                        true ->
                            {some, Hit};

                        false ->
                            Closest
                    end
            end end).