-module(expresso@world).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch, inline]).
-define(FILEPATH, "src/expresso/world.gleam").
-export([new/1, add_body/2, remove_body/2, update_body/3, get_body/2, bodies/1, with_iterations/2, with_restitution/2, with_substeps/2, with_spatial_strategy/2, query_radius/3, query_region/3, query_nearest/2, raycast/5, step/2]).
-export_type([spatial_strategy/0, collision_event/1, collision_pair/1, world/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(
    " 2D physics world management with intelligent spatial acceleration.\n"
    "\n"
    " This module provides the `World` type that manages a collection of rigid bodies\n"
    " and simulates physics each step using position-based dynamics.\n"
    "\n"
    " ## Features\n"
    "\n"
    " - **Dual spatial acceleration**: BVH for dynamic scenes, Grid for particles\n"
    " - **Spatial queries**: Find bodies by radius, region, or nearest neighbor\n"
    " - **Auto-selection**: Intelligently chooses BVH or Grid based on body distribution\n"
    " - **Deterministic**: Same inputs always produce same outputs\n"
    "\n"
    " ## Quick Start\n"
    "\n"
    " ```gleam\n"
    " import expresso/world\n"
    " import expresso/body\n"
    " import vec/vec2\n"
    "\n"
    " // Create a world with gravity\n"
    " let world = world.new(gravity: vec2.Vec2(0.0, -9.8))\n"
    "\n"
    " // Add bodies\n"
    " let world = world\n"
    "   |> world.add_body(body.new_circle(\"ball\", vec2.Vec2(0.0, 5.0), radius: 0.5))\n"
    "   |> world.add_body(body.new_box(\"platform\", vec2.Vec2(0.0, 0.0), 5.0, 0.5))\n"
    "\n"
    " // Configure solver\n"
    " let world = world\n"
    "   |> world.with_iterations(10)\n"
    "   |> world.with_restitution(0.5)\n"
    "\n"
    " // Step physics each frame\n"
    " let world = world.step(world, delta_time: 0.016)\n"
    " ```\n"
    "\n"
    " ## Spatial Acceleration\n"
    "\n"
    " Choose the best strategy for your use case:\n"
    "\n"
    " - **UseBVH** - Best for dynamic scenes with moving objects (default)\n"
    " - **UseGrid** - Best for uniform particle systems (1000s of particles)\n"
    " - **AutoSelect** - Automatically picks BVH or Grid based on distribution\n"
    "\n"
    " ```gleam\n"
    " // Force BVH for dynamic game\n"
    " let world = world.with_spatial_strategy(world, world.UseBVH)\n"
    "\n"
    " // Force Grid for particle system\n"
    " let world = world.with_spatial_strategy(world, world.UseGrid(cell_size: 2.0))\n"
    " ```\n"
    "\n"
    " ## Spatial Queries\n"
    "\n"
    " Find bodies efficiently using spatial queries:\n"
    "\n"
    " ```gleam\n"
    " // Find all bodies near a point (e.g., explosion radius)\n"
    " let nearby = world.query_radius(world, center: pos, radius: 5.0)\n"
    "\n"
    " // Find all bodies in a rectangle (e.g., screen culling)\n"
    " let visible = world.query_region(world, min: vec2.Vec2(-10.0, -10.0), \n"
    "                                          max: vec2.Vec2(10.0, 10.0))\n"
    "\n"
    " // Find nearest body (e.g., target acquisition)\n"
    " let nearest = world.query_nearest(world, point: player_pos)\n"
    " ```\n"
).

-type spatial_strategy() :: use_b_v_h | {use_grid, float()} | auto_select.

-type collision_event(NDE) :: {collision_started, NDE, NDE} |
    {collision_ended, NDE, NDE} |
    {trigger_entered, NDE, NDE} |
    {trigger_exited, NDE, NDE}.

-type collision_pair(NDF) :: {collision_pair, NDF, NDF}.

-opaque world(NDG) :: {world,
        gleam@dict:dict(NDG, expresso@body:body(NDG)),
        vec@vec3:vec3(float()),
        integer(),
        float(),
        integer(),
        spatial_strategy(),
        gleam@option:option(expresso@collision:spatial_index(NDG)),
        list(collision_pair(NDG))}.

-file("src/expresso/world.gleam", 141).
?DOC(
    " Create a new empty physics world\n"
    "\n"
    " ## Example\n"
    " ```gleam\n"
    " let world = world.new(\n"
    "   gravity: vec3.Vec3(0.0, -9.8, 0.0),  // Earth gravity pointing down\n"
    " )\n"
    " ```\n"
).
-spec new(vec@vec3:vec3(float())) -> world(any()).
new(Gravity) ->
    {world, maps:new(), Gravity, 4, +0.0, 2, auto_select, none, []}.

-file("src/expresso/world.gleam", 159).
?DOC(" Add a body to the world\n").
-spec add_body(world(NDK), expresso@body:body(NDK)) -> world(NDK).
add_body(World, Body) ->
    New_bodies = gleam@dict:insert(
        erlang:element(2, World),
        erlang:element(2, Body),
        Body
    ),
    New_spatial_index = case erlang:element(8, World) of
        none ->
            none;

        {some, {b_v_h_index, Tree}} ->
            Pos_3d = {vec3,
                erlang:element(2, erlang:element(3, Body)),
                erlang:element(3, erlang:element(3, Body)),
                +0.0},
            Updated_tree = spatial@bvh:insert(
                Tree,
                Pos_3d,
                erlang:element(2, Body),
                8
            ),
            {some, {b_v_h_index, Updated_tree}};

        {some, {grid_index, Grid}} ->
            Pos_3d@1 = {vec3,
                erlang:element(2, erlang:element(3, Body)),
                erlang:element(3, erlang:element(3, Body)),
                +0.0},
            Updated_grid = spatial@grid:insert(
                Grid,
                Pos_3d@1,
                erlang:element(2, Body)
            ),
            {some, {grid_index, Updated_grid}}
    end,
    {world,
        New_bodies,
        erlang:element(3, World),
        erlang:element(4, World),
        erlang:element(5, World),
        erlang:element(6, World),
        erlang:element(7, World),
        New_spatial_index,
        erlang:element(9, World)}.

-file("src/expresso/world.gleam", 182).
?DOC(" Remove a body from the world\n").
-spec remove_body(world(NDO), NDO) -> world(NDO).
remove_body(World, Id) ->
    New_bodies = gleam@dict:delete(erlang:element(2, World), Id),
    New_spatial_index = case erlang:element(8, World) of
        none ->
            none;

        {some, {b_v_h_index, Tree}} ->
            case spatial@bvh:remove(Tree, fun(Body_id) -> Body_id =:= Id end) of
                {ok, Updated_tree} ->
                    {some, {b_v_h_index, Updated_tree}};

                {error, _} ->
                    none
            end;

        {some, {grid_index, _}} ->
            none
    end,
    {world,
        New_bodies,
        erlang:element(3, World),
        erlang:element(4, World),
        erlang:element(5, World),
        erlang:element(6, World),
        erlang:element(7, World),
        New_spatial_index,
        erlang:element(9, World)}.

-file("src/expresso/world.gleam", 207).
?DOC(" Update a body in the world\n").
-spec update_body(
    world(NDR),
    NDR,
    fun((expresso@body:body(NDR)) -> expresso@body:body(NDR))
) -> world(NDR).
update_body(World, Id, Update) ->
    case gleam_stdlib:map_get(erlang:element(2, World), Id) of
        {ok, Body} ->
            Updated_body = Update(Body),
            New_bodies = gleam@dict:insert(
                erlang:element(2, World),
                Id,
                Updated_body
            ),
            New_spatial_index = case erlang:element(8, World) of
                none ->
                    none;

                {some, {b_v_h_index, Tree}} ->
                    New_pos = {vec3,
                        erlang:element(2, erlang:element(3, Updated_body)),
                        erlang:element(3, erlang:element(3, Updated_body)),
                        +0.0},
                    case spatial@bvh:update(
                        Tree,
                        fun(Body_id) -> Body_id =:= Id end,
                        New_pos,
                        Id,
                        8
                    ) of
                        {ok, Updated_tree} ->
                            {some, {b_v_h_index, Updated_tree}};

                        {error, _} ->
                            none
                    end;

                {some, {grid_index, _}} ->
                    none
            end,
            {world,
                New_bodies,
                erlang:element(3, World),
                erlang:element(4, World),
                erlang:element(5, World),
                erlang:element(6, World),
                erlang:element(7, World),
                New_spatial_index,
                erlang:element(9, World)};

        {error, _} ->
            World
    end.

-file("src/expresso/world.gleam", 249).
?DOC(" Get a body from the world\n").
-spec get_body(world(NDW), NDW) -> {ok, expresso@body:body(NDW)} | {error, nil}.
get_body(World, Id) ->
    gleam_stdlib:map_get(erlang:element(2, World), Id).

-file("src/expresso/world.gleam", 254).
?DOC(" Get all bodies in the world\n").
-spec bodies(world(NEB)) -> gleam@dict:dict(NEB, expresso@body:body(NEB)).
bodies(World) ->
    erlang:element(2, World).

-file("src/expresso/world.gleam", 262).
?DOC(
    " Set the number of solver iterations\n"
    "\n"
    " More iterations = more stable but slower.\n"
    " 3-5 is typical, 10+ for very stable stacks.\n"
).
-spec with_iterations(world(NEG), integer()) -> world(NEG).
with_iterations(World, Iterations) ->
    {world,
        erlang:element(2, World),
        erlang:element(3, World),
        Iterations,
        erlang:element(5, World),
        erlang:element(6, World),
        erlang:element(7, World),
        erlang:element(8, World),
        erlang:element(9, World)}.

-file("src/expresso/world.gleam", 270).
?DOC(
    " Set the coefficient of restitution (bounciness)\n"
    "\n"
    " 0.0 = perfectly inelastic (no bounce)\n"
    " 1.0 = perfectly elastic (full bounce)\n"
).
-spec with_restitution(world(NEJ), float()) -> world(NEJ).
with_restitution(World, Restitution) ->
    {world,
        erlang:element(2, World),
        erlang:element(3, World),
        erlang:element(4, World),
        Restitution,
        erlang:element(6, World),
        erlang:element(7, World),
        erlang:element(8, World),
        erlang:element(9, World)}.

-file("src/expresso/world.gleam", 289).
?DOC(
    " Set the number of substeps per physics step\n"
    "\n"
    " Substeps divide each physics step into smaller timesteps,\n"
    " re-detecting collisions between each substep. This fixes chain\n"
    " collisions where forces need to propagate through multiple bodies.\n"
    "\n"
    " More substeps = more accurate but slower.\n"
    " Typical values: 2-3 for games, 4+ for complex chains.\n"
    "\n"
    " ## Example\n"
    " ```gleam\n"
    " // Handle chains of 10+ enemies pushing each other\n"
    " let world = world.new(gravity: vec2.Vec2(0.0, 0.0))\n"
    "   |> world.with_substeps(3)\n"
    " ```\n"
).
-spec with_substeps(world(NEM), integer()) -> world(NEM).
with_substeps(World, Substeps) ->
    {world,
        erlang:element(2, World),
        erlang:element(3, World),
        erlang:element(4, World),
        erlang:element(5, World),
        Substeps,
        erlang:element(7, World),
        erlang:element(8, World),
        erlang:element(9, World)}.

-file("src/expresso/world.gleam", 307).
?DOC(
    " Set the spatial partitioning strategy\n"
    "\n"
    " - `UseBVH`: Best for dynamic scenes with moving objects (default)\n"
    " - `UseGrid(cell_size)`: Best for uniform distributions (particles, crowds)\n"
    " - `AutoSelect`: Automatically choose based on body count\n"
    "\n"
    " ## Example\n"
    " ```gleam\n"
    " // Force BVH for dynamic game\n"
    " let world = world.with_spatial_strategy(world, UseBVH)\n"
    " \n"
    " // Use grid for particle system\n"
    " let world = world.with_spatial_strategy(world, UseGrid(cell_size: 2.0))\n"
    " ```\n"
).
-spec with_spatial_strategy(world(NEP), spatial_strategy()) -> world(NEP).
with_spatial_strategy(World, Strategy) ->
    {world,
        erlang:element(2, World),
        erlang:element(3, World),
        erlang:element(4, World),
        erlang:element(5, World),
        erlang:element(6, World),
        Strategy,
        none,
        erlang:element(9, World)}.

-file("src/expresso/world.gleam", 322).
?DOC(
    " Query bodies within a radius of a point\n"
    "\n"
    " Uses spatial acceleration when available.\n"
    "\n"
    " ## Example\n"
    " ```gleam\n"
    " let nearby = world.query_radius(world, center: vec3.Vec3(0.0, 0.0, 0.0), radius: 5.0)\n"
    " ```\n"
).
-spec query_radius(world(NES), vec@vec3:vec3(float()), float()) -> list({NES,
    expresso@body:body(NES)}).
query_radius(World, Center, Radius) ->
    case erlang:element(8, World) of
        none ->
            _pipe = maps:to_list(erlang:element(2, World)),
            expresso@collision:filter_by_radius(_pipe, Center, Radius);

        {some, {b_v_h_index, Tree}} ->
            _pipe@1 = spatial@bvh:query_radius(Tree, Center, Radius),
            expresso@collision:extract_bodies_from_results(
                _pipe@1,
                erlang:element(2, World)
            );

        {some, {grid_index, Grid}} ->
            _pipe@2 = spatial@grid:query_radius(Grid, Center, Radius),
            expresso@collision:extract_bodies_from_results(
                _pipe@2,
                erlang:element(2, World)
            )
    end.

-file("src/expresso/world.gleam", 354).
?DOC(
    " Query bodies within a rectangular region\n"
    "\n"
    " ## Example\n"
    " ```gleam\n"
    " let bodies_in_region = world.query_region(\n"
    "   world,\n"
    "   min: vec3.Vec3(-10.0, -10.0, -10.0),\n"
    "   max: vec3.Vec3(10.0, 10.0, 10.0),\n"
    " )\n"
    " ```\n"
).
-spec query_region(world(NEX), vec@vec3:vec3(float()), vec@vec3:vec3(float())) -> list({NEX,
    expresso@body:body(NEX)}).
query_region(World, Min, Max) ->
    Region = spatial@collider:box(Min, Max),
    case erlang:element(8, World) of
        none ->
            _pipe = maps:to_list(erlang:element(2, World)),
            expresso@collision:filter_by_region(_pipe, Min, Max);

        {some, {b_v_h_index, Tree}} ->
            _pipe@1 = spatial@bvh:'query'(Tree, Region),
            expresso@collision:extract_bodies_from_results(
                _pipe@1,
                erlang:element(2, World)
            );

        {some, {grid_index, Grid}} ->
            _pipe@2 = spatial@grid:'query'(Grid, Region),
            expresso@collision:extract_bodies_from_results(
                _pipe@2,
                erlang:element(2, World)
            )
    end.

-file("src/expresso/world.gleam", 387).
?DOC(
    " Find the nearest body to a point\n"
    "\n"
    " ## Example\n"
    " ```gleam\n"
    " case world.query_nearest(world, point: vec3.Vec3(5.0, 5.0, 5.0)) {\n"
    "   Some(#(id, body, distance)) -> // Use nearest body\n"
    "   None -> // No bodies in world\n"
    " }\n"
    " ```\n"
).
-spec query_nearest(world(NFD), vec@vec3:vec3(float())) -> gleam@option:option({NFD,
    expresso@body:body(NFD),
    float()}).
query_nearest(World, Point) ->
    Max_radius = 1000.0,
    _pipe = query_radius(World, Point, Max_radius),
    expresso@collision:find_nearest(_pipe, Point).

-file("src/expresso/world.gleam", 438).
?DOC(
    " Cast a ray and find the first body it hits\n"
    "\n"
    " Returns detailed information about the hit including:\n"
    " - The body that was hit\n"
    " - The exact hit point\n"
    " - The surface normal at the hit point\n"
    " - The distance from the ray origin\n"
    "\n"
    " Optionally filter by collision layers using the layer_mask parameter.\n"
    "\n"
    " ## Example\n"
    " ```gleam\n"
    " // Shoot a laser forward\n"
    " case world.raycast(\n"
    "   world,\n"
    "   origin: player_pos,\n"
    "   direction: vec3.Vec3(1.0, 0.0, 0.0),\n"
    "   max_distance: 100.0,\n"
    "   layer_mask: option.None,  // Hit all layers\n"
    " ) {\n"
    "   Some(hit) -> {\n"
    "     // Hit something!\n"
    "     io.println(\"Hit \" <> hit.body.id <> \" at distance \" <> float.to_string(hit.distance))\n"
    "   }\n"
    "   None -> {\n"
    "     // No hit\n"
    "   }\n"
    " }\n"
    "\n"
    " // Only hit enemies\n"
    " case world.raycast(\n"
    "   world,\n"
    "   origin: player_pos,\n"
    "   direction: aim_direction,\n"
    "   max_distance: 50.0,\n"
    "   layer_mask: option.Some(body.layer_enemy),\n"
    " ) {\n"
    "   Some(hit) -> damage_enemy(hit.body_id)\n"
    "   None -> {}\n"
    " }\n"
    " ```\n"
).
-spec raycast(
    world(NFI),
    vec@vec3:vec3(float()),
    vec@vec3:vec3(float()),
    float(),
    gleam@option:option(integer())
) -> gleam@option:option(expresso@collision:raycast_hit(NFI)).
raycast(World, Origin, Direction, Max_distance, Layer_mask) ->
    expresso@collision:raycast(
        erlang:element(2, World),
        erlang:element(8, World),
        Origin,
        Direction,
        Max_distance,
        Layer_mask
    ).

-file("src/expresso/world.gleam", 514).
?DOC(" Check if world has fast-moving CCD bodies that need extra substeps\n").
-spec has_fast_ccd_bodies(world(any()), float()) -> boolean().
has_fast_ccd_bodies(World, Delta_time) ->
    _pipe = maps:to_list(erlang:element(2, World)),
    gleam@list:any(
        _pipe,
        fun(Pair) ->
            {_, Body_val} = Pair,
            case erlang:element(13, Body_val) of
                false ->
                    false;

                true ->
                    Speed = vec@vec3f:length(erlang:element(4, Body_val)),
                    Distance_per_frame = Speed * Delta_time,
                    Bounding_radius = expresso@body:bounding_radius(Body_val),
                    Distance_per_frame > (Bounding_radius * 0.5)
            end
        end
    ).

-file("src/expresso/world.gleam", 534).
?DOC(" Apply gravity to all dynamic bodies\n").
-spec apply_gravity(world(NFW), float()) -> world(NFW).
apply_gravity(World, Delta_time) ->
    New_bodies = gleam@dict:map_values(
        erlang:element(2, World),
        fun(_, Body) -> case erlang:element(9, Body) of
                true ->
                    Body;

                false ->
                    Gravity_velocity = vec@vec3f:scale(
                        erlang:element(3, World),
                        Delta_time
                    ),
                    {body,
                        erlang:element(2, Body),
                        erlang:element(3, Body),
                        vec@vec3f:add(erlang:element(4, Body), Gravity_velocity),
                        erlang:element(5, Body),
                        erlang:element(6, Body),
                        erlang:element(7, Body),
                        erlang:element(8, Body),
                        erlang:element(9, Body),
                        erlang:element(10, Body),
                        erlang:element(11, Body),
                        erlang:element(12, Body),
                        erlang:element(13, Body),
                        erlang:element(14, Body),
                        erlang:element(15, Body),
                        erlang:element(16, Body)}
            end end
    ),
    {world,
        New_bodies,
        erlang:element(3, World),
        erlang:element(4, World),
        erlang:element(5, World),
        erlang:element(6, World),
        erlang:element(7, World),
        erlang:element(8, World),
        erlang:element(9, World)}.

-file("src/expresso/world.gleam", 591).
?DOC(" Integrate angular velocity into rotation using quaternions\n").
-spec integrate_angular_velocity(
    quaternion:quaternion(),
    vec@vec3:vec3(float()),
    float()
) -> quaternion:quaternion().
integrate_angular_velocity(Rotation, Angular_velocity, Delta_time) ->
    Speed_squared = ((erlang:element(2, Angular_velocity) * erlang:element(
        2,
        Angular_velocity
    ))
    + (erlang:element(3, Angular_velocity) * erlang:element(3, Angular_velocity)))
    + (erlang:element(4, Angular_velocity) * erlang:element(4, Angular_velocity)),
    case Speed_squared < 0.000001 of
        true ->
            Rotation;

        false ->
            Speed = case gleam@float:square_root(Speed_squared) of
                {ok, S} ->
                    S;

                {error, _} ->
                    +0.0
            end,
            Angle = Speed * Delta_time,
            Axis = {vec3, case Speed of
                    +0.0 -> +0.0;
                    -0.0 -> -0.0;
                    Gleam@denominator -> erlang:element(2, Angular_velocity) / Gleam@denominator
                end, case Speed of
                    +0.0 -> +0.0;
                    -0.0 -> -0.0;
                    Gleam@denominator@1 -> erlang:element(3, Angular_velocity) / Gleam@denominator@1
                end, case Speed of
                    +0.0 -> +0.0;
                    -0.0 -> -0.0;
                    Gleam@denominator@2 -> erlang:element(4, Angular_velocity) / Gleam@denominator@2
                end},
            Delta_rotation = quaternion:from_axis_angle(Axis, Angle),
            _pipe = quaternion:multiply(Rotation, Delta_rotation),
            quaternion:normalize(_pipe)
    end.

-file("src/expresso/world.gleam", 553).
?DOC(" Integrate velocities to update positions and rotations\n").
-spec integrate_velocities(world(NFZ), float()) -> world(NFZ).
integrate_velocities(World, Delta_time) ->
    New_bodies = gleam@dict:map_values(
        erlang:element(2, World),
        fun(_, Body) ->
            Displacement = vec@vec3f:scale(erlang:element(4, Body), Delta_time),
            New_position = vec@vec3f:add(erlang:element(3, Body), Displacement),
            Friction_factor = 1.0 - (erlang:element(10, Body) * Delta_time),
            New_velocity = vec@vec3f:scale(
                erlang:element(4, Body),
                Friction_factor
            ),
            New_rotation = integrate_angular_velocity(
                erlang:element(5, Body),
                erlang:element(6, Body),
                Delta_time
            ),
            Angular_damping = 0.98,
            New_angular_velocity = vec@vec3f:scale(
                erlang:element(6, Body),
                Angular_damping
            ),
            {body,
                erlang:element(2, Body),
                New_position,
                New_velocity,
                New_rotation,
                New_angular_velocity,
                erlang:element(7, Body),
                erlang:element(8, Body),
                erlang:element(9, Body),
                erlang:element(10, Body),
                erlang:element(11, Body),
                erlang:element(12, Body),
                erlang:element(13, Body),
                erlang:element(14, Body),
                erlang:element(15, Body),
                erlang:element(16, Body)}
        end
    ),
    {world,
        New_bodies,
        erlang:element(3, World),
        erlang:element(4, World),
        erlang:element(5, World),
        erlang:element(6, World),
        erlang:element(7, World),
        erlang:element(8, World),
        erlang:element(9, World)}.

-file("src/expresso/world.gleam", 724).
?DOC(" Auto-select the best spatial strategy based on body count and distribution\n").
-spec auto_select_strategy(
    gleam@dict:dict(NGL, expresso@body:body(NGL)),
    integer()
) -> spatial_strategy().
auto_select_strategy(Bodies, Body_count) ->
    case Body_count of
        N when N < 100 ->
            use_b_v_h;

        _ ->
            {Is_uniform, Avg_radius} = expresso@collision:analyze_distribution(
                Bodies
            ),
            case Is_uniform of
                true ->
                    {use_grid, Avg_radius * 4.0};

                false ->
                    use_b_v_h
            end
    end.

-file("src/expresso/world.gleam", 742).
?DOC(
    " Build a BVH spatial index from bodies (stores IDs for efficient updates)\n"
    " Optimized: Single pass with dict.fold instead of dict.to_list + list.map\n"
).
-spec build_bvh_index(gleam@dict:dict(NGP, expresso@body:body(NGP))) -> expresso@collision:spatial_index(NGP).
build_bvh_index(Bodies) ->
    Items = gleam@dict:fold(
        Bodies,
        [],
        fun(Acc, Id, Body) ->
            Pos_3d = {vec3,
                erlang:element(2, erlang:element(3, Body)),
                erlang:element(3, erlang:element(3, Body)),
                +0.0},
            [{Pos_3d, Id} | Acc]
        end
    ),
    Tree@1 = case spatial@bvh:from_items(Items, 8) of
        {ok, Tree} -> Tree;
        _assert_fail ->
            erlang:error(#{gleam_error => let_assert,
                        message => <<"Expected body count to be always nonzero"/utf8>>,
                        file => <<?FILEPATH/utf8>>,
                        module => <<"expresso/world"/utf8>>,
                        function => <<"build_bvh_index"/utf8>>,
                        line => 749,
                        value => _assert_fail,
                        start => 22764,
                        'end' => 22825,
                        pattern_start => 22775,
                        pattern_end => 22783})
    end,
    {b_v_h_index, Tree@1}.

-file("src/expresso/world.gleam", 756).
?DOC(" Build a Grid spatial index from bodies (stores IDs for efficient updates)\n").
-spec build_grid_index(gleam@dict:dict(NGU, expresso@body:body(NGU)), float()) -> expresso@collision:spatial_index(NGU).
build_grid_index(Bodies, Cell_size) ->
    Bounds = expresso@collision:calculate_world_bounds(Bodies),
    Grid_empty = spatial@grid:new(Cell_size, Bounds),
    Grid_filled = gleam@dict:fold(
        Bodies,
        Grid_empty,
        fun(G, Id, Body) ->
            Pos_3d = {vec3,
                erlang:element(2, erlang:element(3, Body)),
                erlang:element(3, erlang:element(3, Body)),
                +0.0},
            spatial@grid:insert(G, Pos_3d, Id)
        end
    ),
    {grid_index, Grid_filled}.

-file("src/expresso/world.gleam", 700).
?DOC(" Build or rebuild the spatial index based on current bodies\n").
-spec rebuild_spatial_index(world(NGI)) -> world(NGI).
rebuild_spatial_index(World) ->
    Body_count = maps:size(erlang:element(2, World)),
    case Body_count of
        0 ->
            {world,
                erlang:element(2, World),
                erlang:element(3, World),
                erlang:element(4, World),
                erlang:element(5, World),
                erlang:element(6, World),
                erlang:element(7, World),
                none,
                erlang:element(9, World)};

        _ ->
            Strategy = case erlang:element(7, World) of
                use_b_v_h ->
                    use_b_v_h;

                {use_grid, Cell_size} ->
                    {use_grid, Cell_size};

                auto_select ->
                    auto_select_strategy(erlang:element(2, World), Body_count)
            end,
            Spatial_index = case Strategy of
                use_b_v_h ->
                    build_bvh_index(erlang:element(2, World));

                {use_grid, Cell_size@1} ->
                    build_grid_index(erlang:element(2, World), Cell_size@1);

                auto_select ->
                    build_bvh_index(erlang:element(2, World))
            end,
            {world,
                erlang:element(2, World),
                erlang:element(3, World),
                erlang:element(4, World),
                erlang:element(5, World),
                erlang:element(6, World),
                erlang:element(7, World),
                {some, Spatial_index},
                erlang:element(9, World)}
    end.

-file("src/expresso/world.gleam", 778).
?DOC(" Check if a collision pair exists in a list (order-independent)\n").
-spec contains_collision(list(collision_pair(NGZ)), NGZ, NGZ) -> boolean().
contains_collision(Collisions, A, B) ->
    gleam@list:any(
        Collisions,
        fun(Pair) ->
            ((erlang:element(2, Pair) =:= A) andalso (erlang:element(3, Pair)
            =:= B))
            orelse ((erlang:element(2, Pair) =:= B) andalso (erlang:element(
                3,
                Pair
            )
            =:= A))
        end
    ).

-file("src/expresso/world.gleam", 785).
?DOC(" Convert contacts to collision pairs\n").
-spec contacts_to_pairs(
    list(expresso@collision:contact(NHC)),
    gleam@dict:dict(NHC, expresso@body:body(NHC))
) -> {list(collision_pair(NHC)), list(collision_pair(NHC))}.
contacts_to_pairs(Contacts, Bodies) ->
    gleam@list:fold(
        Contacts,
        {[], []},
        fun(Acc, Contact) ->
            {Regular, Triggers} = Acc,
            case {gleam_stdlib:map_get(Bodies, erlang:element(2, Contact)),
                gleam_stdlib:map_get(Bodies, erlang:element(3, Contact))} of
                {{ok, Body_a}, {ok, Body_b}} ->
                    Pair = {collision_pair,
                        erlang:element(2, Contact),
                        erlang:element(3, Contact)},
                    case erlang:element(16, Body_a) orelse erlang:element(
                        16,
                        Body_b
                    ) of
                        true ->
                            {Regular, [Pair | Triggers]};

                        false ->
                            {[Pair | Regular], Triggers}
                    end;

                {_, _} ->
                    Acc
            end
        end
    ).

-file("src/expresso/world.gleam", 807).
?DOC(" Generate collision events by comparing current and previous collisions\n").
-spec generate_collision_events(
    list(collision_pair(NHM)),
    list(collision_pair(NHM)),
    list(collision_pair(NHM)),
    gleam@dict:dict(NHM, expresso@body:body(NHM))
) -> list(collision_event(NHM)).
generate_collision_events(Current_regular, Current_triggers, Previous, Bodies) ->
    Started_events = gleam@list:filter_map(
        Current_regular,
        fun(Pair) ->
            case contains_collision(
                Previous,
                erlang:element(2, Pair),
                erlang:element(3, Pair)
            ) of
                true ->
                    {error, nil};

                false ->
                    {ok,
                        {collision_started,
                            erlang:element(2, Pair),
                            erlang:element(3, Pair)}}
            end
        end
    ),
    Ended_events = gleam@list:filter_map(
        Previous,
        fun(Pair@1) ->
            case contains_collision(
                Current_regular,
                erlang:element(2, Pair@1),
                erlang:element(3, Pair@1)
            ) of
                true ->
                    {error, nil};

                false ->
                    {ok,
                        {collision_ended,
                            erlang:element(2, Pair@1),
                            erlang:element(3, Pair@1)}}
            end
        end
    ),
    Trigger_events = gleam@list:filter_map(
        Current_triggers,
        fun(Pair@2) ->
            case {gleam_stdlib:map_get(Bodies, erlang:element(2, Pair@2)),
                gleam_stdlib:map_get(Bodies, erlang:element(3, Pair@2))} of
                {{ok, Body_a}, {ok, Body_b}} ->
                    case {erlang:element(16, Body_a),
                        erlang:element(16, Body_b)} of
                        {true, false} ->
                            case contains_collision(
                                Previous,
                                erlang:element(2, Pair@2),
                                erlang:element(3, Pair@2)
                            ) of
                                true ->
                                    {error, nil};

                                false ->
                                    {ok,
                                        {trigger_entered,
                                            erlang:element(3, Pair@2),
                                            erlang:element(2, Pair@2)}}
                            end;

                        {false, true} ->
                            case contains_collision(
                                Previous,
                                erlang:element(2, Pair@2),
                                erlang:element(3, Pair@2)
                            ) of
                                true ->
                                    {error, nil};

                                false ->
                                    {ok,
                                        {trigger_entered,
                                            erlang:element(2, Pair@2),
                                            erlang:element(3, Pair@2)}}
                            end;

                        {_, _} ->
                            {error, nil}
                    end;

                {_, _} ->
                    {error, nil}
            end
        end
    ),
    Trigger_exit_events = gleam@list:filter_map(
        Previous,
        fun(Pair@3) ->
            case {gleam_stdlib:map_get(Bodies, erlang:element(2, Pair@3)),
                gleam_stdlib:map_get(Bodies, erlang:element(3, Pair@3)),
                contains_collision(
                    Current_triggers,
                    erlang:element(2, Pair@3),
                    erlang:element(3, Pair@3)
                )} of
                {{ok, Body_a@1}, {ok, Body_b@1}, false} ->
                    case {erlang:element(16, Body_a@1),
                        erlang:element(16, Body_b@1)} of
                        {true, false} ->
                            {ok,
                                {trigger_exited,
                                    erlang:element(3, Pair@3),
                                    erlang:element(2, Pair@3)}};

                        {false, true} ->
                            {ok,
                                {trigger_exited,
                                    erlang:element(2, Pair@3),
                                    erlang:element(3, Pair@3)}};

                        {_, _} ->
                            {error, nil}
                    end;

                {_, _, _} ->
                    {error, nil}
            end
        end
    ),
    lists:append(
        [Started_events, Ended_events, Trigger_events, Trigger_exit_events]
    ).

-file("src/expresso/world.gleam", 636).
?DOC(
    " Detect collisions and resolve them\n"
    " Returns updated world and collision events (only generated if generate_events is True)\n"
).
-spec detect_and_resolve_collisions(world(NGD), boolean()) -> {world(NGD),
    list(collision_event(NGD))}.
detect_and_resolve_collisions(World, Generate_events) ->
    World@1 = rebuild_spatial_index(World),
    Contacts = case erlang:element(8, World@1) of
        none ->
            expresso@collision:detect_collisions(erlang:element(2, World@1));

        {some, Spatial_index} ->
            expresso@collision:detect_collisions_with_index(
                erlang:element(2, World@1),
                Spatial_index
            )
    end,
    Bodies_after_position = expresso@internal@solver:solve_position_constraints(
        erlang:element(2, World@1),
        Contacts,
        erlang:element(4, World@1)
    ),
    Bodies_after_velocity = expresso@internal@solver:solve_velocity_constraints(
        Bodies_after_position,
        Contacts,
        erlang:element(5, World@1)
    ),
    {Current_regular, Current_triggers} = contacts_to_pairs(
        Contacts,
        erlang:element(2, World@1)
    ),
    All_current = lists:append(Current_regular, Current_triggers),
    Events = case Generate_events of
        false ->
            [];

        true ->
            generate_collision_events(
                Current_regular,
                Current_triggers,
                erlang:element(9, World@1),
                erlang:element(2, World@1)
            )
    end,
    New_previous = case Generate_events of
        true ->
            All_current;

        false ->
            erlang:element(9, World@1)
    end,
    Updated_world = {world,
        Bodies_after_velocity,
        erlang:element(3, World@1),
        erlang:element(4, World@1),
        erlang:element(5, World@1),
        erlang:element(6, World@1),
        erlang:element(7, World@1),
        erlang:element(8, World@1),
        New_previous},
    {Updated_world, Events}.

-file("src/expresso/world.gleam", 477).
?DOC(
    " Simulate one physics timestep using substeps\n"
    "\n"
    " This is the main physics update function. Call it each game tick with delta_time.\n"
    " Returns the updated world and a list of collision events that occurred.\n"
    "\n"
    " The timestep is divided into `world.substeps` smaller steps, with collision\n"
    " detection happening between each substep. This fixes chain collisions where\n"
    " forces need to propagate through multiple bodies (e.g., Enemy1 → Enemy2 → Enemy3).\n"
    "\n"
    " ## Example\n"
    " ```gleam\n"
    " let #(world, events) = world.step(world, delta_time: 1.0 /. 60.0)  // 60 FPS\n"
    "\n"
    " // Handle collision events\n"
    " list.each(events, fn(event) {\n"
    "   case event {\n"
    "     CollisionStarted(a, b) -> io.println(\"Collision started!\")\n"
    "     TriggerEntered(body, trigger) -> io.println(\"Entered trigger zone!\")\n"
    "     _ -> Nil\n"
    "   }\n"
    " })\n"
    " ```\n"
).
-spec step(world(NFP), float()) -> {world(NFP), list(collision_event(NFP))}.
step(World, Delta_time) ->
    Needs_ccd = has_fast_ccd_bodies(World, Delta_time),
    Substeps = case Needs_ccd of
        true ->
            erlang:element(6, World) * 4;

        false ->
            erlang:element(6, World)
    end,
    Substep_dt = case erlang:float(Substeps) of
        +0.0 -> +0.0;
        -0.0 -> -0.0;
        Gleam@denominator -> Delta_time / Gleam@denominator
    end,
    {Final_world, Events} = begin
        _pipe = gleam@list:range(0, Substeps - 1),
        gleam@list:fold(
            _pipe,
            {World, []},
            fun(Acc, Substep_index) ->
                {Current_world, _} = Acc,
                Is_final_substep = Substep_index =:= (Substeps - 1),
                Updated_world = begin
                    _pipe@1 = Current_world,
                    _pipe@2 = apply_gravity(_pipe@1, Substep_dt),
                    integrate_velocities(_pipe@2, Substep_dt)
                end,
                detect_and_resolve_collisions(Updated_world, Is_final_substep)
            end
        )
    end,
    {Final_world, Events}.