he3d-physics 0.1.0

use alloc::vec::Vec;

use gp3d::{BodyDesc, BodyHandle, Motion};
use he3d_core::{Mesh, ObjectId, Scene, Transform};
use he3d_math::Vec3;

use crate::StepResult;

/// Default gravity, matching the reference engine's `(0, -9.8, 0)`.
/// 默认重力，与参考引擎的 `(0, -9.8, 0)` 一致。
const DEFAULT_GRAVITY: Vec3 = Vec3::new(0.0, -9.8, 0.0);

/// A physics world mapping render objects by stable [`ObjectId`] onto the
/// standalone [`gp3d`] engine's generational body handles.
/// 一个通过稳定的 [`ObjectId`] 将渲染对象映射到独立 [`gp3d`] 引擎代际刚体句柄上的物理世界。
///
/// Bodies and colliders are owned by gp3d.
/// 刚体和碰撞体由 gp3d 持有。
/// After stepping, call [`PhysicsWorld::synchronize`] to write body transforms back into the scene so the renderer sees the physics state.
/// 步进后，调用 [`PhysicsWorld::synchronize`] 将刚体变换写回场景，使渲染器看到物理状态。
///
/// gp3d and `he3d-math` both wrap `glam`, so `Vec3`/`Quat` interoperate directly.
/// gp3d 与 `he3d-math` 都包装 `glam`，因此 `Vec3`/`Quat` 可直接互操作。
pub struct PhysicsWorld {
    scene: gp3d::PhysicsScene,
    bodies: Vec<(ObjectId, BodyHandle)>,
}

impl PhysicsWorld {
    pub fn new() -> Self {
        let mut scene = gp3d::PhysicsScene::new();
        scene.set_gravity(DEFAULT_GRAVITY);
        Self {
            scene,
            bodies: Vec::new(),
        }
    }

    /// Override the world gravity vector. 覆盖世界重力向量。
    pub fn set_gravity(&mut self, gravity: Vec3) {
        self.scene.set_gravity(gravity);
    }

    /// The current world gravity. 当前世界重力。
    pub fn gravity(&self) -> Vec3 {
        self.scene.gravity()
    }

    /// Returns `false` if the object already has a body, leaving the world unchanged.
    /// 若对象已拥有刚体则返回 `false`，世界保持不变。
    pub fn add_dynamic_box(&mut self, object: ObjectId, half_extents: Vec3, transform: Transform) -> bool {
        self.add_box(object, half_extents, transform, Motion::Dynamic)
    }

    /// Returns `false` if the object already has a body, leaving the world unchanged.
    /// 若对象已拥有刚体则返回 `false`，世界保持不变。
    pub fn add_static_box(&mut self, object: ObjectId, half_extents: Vec3, transform: Transform) -> bool {
        self.add_box(object, half_extents, transform, Motion::Static)
    }

    /// Returns `false` if the object already has a body, leaving the world unchanged.
    /// 若对象已拥有刚体则返回 `false`，世界保持不变。
    pub fn add_kinematic_box(&mut self, object: ObjectId, half_extents: Vec3, transform: Transform) -> bool {
        self.add_box(object, half_extents, transform, Motion::Kinematic)
    }

    /// Register a body, rejecting a duplicate `ObjectId` (the reference `AddBody`
    /// also rejects already-registered objects).
    /// 注册刚体；拒绝重复的 `ObjectId`（参考实现 `AddBody` 同样拒绝已注册对象）。
    fn add_box(&mut self, object: ObjectId, half_extents: Vec3, transform: Transform, motion: Motion) -> bool {
        if self.handle(object).is_some() {
            return false;
        }
        let desc = BodyDesc {
            motion,
            collider: gp3d::Collider::Box { half_extents },
            position: transform.position,
            orientation: transform.orientation,
            ..BodyDesc::default()
        };
        match self.scene.add_body(desc) {
            Ok(handle) => {
                self.bodies.push((object, handle));
                true
            }
            Err(_) => false,
        }
    }

    /// Add a static triangle-mesh collider from a [`Mesh`]. The mesh vertices are
    /// copied; the reference `MeshCollider` reads live mesh geometry, and gp3d
    /// stores its own copy, so re-adding after the mesh changes is the norm.
    /// 从 [`Mesh`] 添加静态三角网格碰撞体。网格顶点会被复制；参考 `MeshCollider`
    /// 读取实时网格几何，而 gp3d 保存自己的副本，因此网格变化后重新添加是常态。
    pub fn add_static_mesh(&mut self, object: ObjectId, mesh: &Mesh, transform: Transform) -> bool {
        if self.handle(object).is_some() {
            return false;
        }
        let vertices = mesh.vertices().to_vec();
        if vertices.is_empty() || vertices.len() % 3 != 0 {
            return false;
        }
        match self
            .scene
            .add_static_mesh(vertices, transform.position, transform.orientation)
        {
            Ok(handle) => {
                self.bodies.push((object, handle));
                true
            }
            Err(_) => false,
        }
    }

    /// Teleport a body, keeping its velocity. Returns `false` for unknown objects.
    /// 瞬移刚体并保持其速度。对未知对象返回 `false`。
    pub fn set_transform(&mut self, object: ObjectId, transform: Transform) -> bool {
        match self.handle(object) {
            Some(handle) => {
                self.scene
                    .set_transform(handle, transform.position, transform.orientation)
            }
            None => false,
        }
    }

    /// Read the current body transform. Returns `None` for unknown objects.
    /// 读取当前刚体变换。对未知对象返回 `None`。
    pub fn transform(&self, object: ObjectId) -> Option<Transform> {
        let handle = self.handle(object)?;
        let position = self.scene.position(handle)?;
        let orientation = self.scene.orientation(handle)?;
        Some(Transform::from_position_orientation(position, orientation))
    }

    /// Override the body's friction and restitution coefficients.
    /// 覆盖刚体的摩擦系数和恢复系数。
    pub fn set_material(&mut self, object: ObjectId, friction: f32, restitution: f32) -> bool {
        match self.handle(object) {
            Some(handle) => self.scene.set_material(handle, friction, restitution),
            None => false,
        }
    }

    /// Override the body's linear and angular damping. 覆盖刚体的线性和角向阻尼。
    pub fn set_damping(&mut self, object: ObjectId, linear: f32, angular: f32) -> bool {
        let Some(handle) = self.handle(object) else {
            return false;
        };
        self.scene.set_linear_damping(handle, linear);
        self.scene.set_angular_damping(handle, angular);
        true
    }

    /// Whether the body is currently touching another collider.
    /// 刚体当前是否与另一碰撞体接触。
    pub fn has_contacts(&self, object: ObjectId) -> bool {
        match self.handle(object) {
            Some(handle) => self.scene.has_contacts(handle),
            None => false,
        }
    }

    pub fn remove_body(&mut self, object: ObjectId) -> bool {
        let Some(position) = self.bodies.iter().position(|(id, _)| *id == object) else {
            return false;
        };
        let (_, handle) = self.bodies.swap_remove(position);
        self.scene.remove_body(handle)
    }

    pub fn has_body(&self, object: ObjectId) -> bool {
        self.handle(object).is_some()
    }

    /// Override the body's linear velocity. 覆盖刚体线速度。
    pub fn set_velocity(&mut self, object: ObjectId, velocity: Vec3) -> bool {
        match self.handle(object) {
            Some(handle) => self.scene.set_velocity(handle, velocity),
            None => false,
        }
    }

    pub fn velocity(&self, object: ObjectId) -> Vec3 {
        match self.handle(object) {
            Some(handle) => self.scene.velocity(handle),
            None => Vec3::ZERO,
        }
    }

    /// Override the body's angular velocity. 覆盖刚体角速度。
    pub fn set_angular_velocity(&mut self, object: ObjectId, velocity: Vec3) -> bool {
        match self.handle(object) {
            Some(handle) => self.scene.set_angular_velocity(handle, velocity),
            None => false,
        }
    }

    pub fn angular_velocity(&self, object: ObjectId) -> Vec3 {
        match self.handle(object) {
            Some(handle) => self.scene.angular_velocity(handle),
            None => Vec3::ZERO,
        }
    }

    pub fn add_force(&mut self, object: ObjectId, force: Vec3) -> bool {
        match self.handle(object) {
            Some(handle) => self.scene.add_force(handle, force),
            None => false,
        }
    }

    pub fn add_torque(&mut self, object: ObjectId, torque: Vec3) -> bool {
        match self.handle(object) {
            Some(handle) => self.scene.add_torque(handle, torque),
            None => false,
        }
    }

    pub fn add_impulse(&mut self, object: ObjectId, impulse: Vec3) -> bool {
        match self.handle(object) {
            Some(handle) => self.scene.add_impulse(handle, impulse),
            None => false,
        }
    }

    pub fn add_angular_impulse(&mut self, object: ObjectId, impulse: Vec3) -> bool {
        match self.handle(object) {
            Some(handle) => self.scene.add_angular_impulse(handle, impulse),
            None => false,
        }
    }

    /// Advance the simulation by one fixed step using the reference default of 4
    /// solver iterations. Forces and torques applied with [`PhysicsWorld::add_force`]
    /// / [`PhysicsWorld::add_torque`] act for one step only and are then cleared.
    /// 以参考默认的 4 次求解器迭代推进模拟。由 [`PhysicsWorld::add_force`] /
    /// [`PhysicsWorld::add_torque`] 施加的力与力矩只作用一步并被清除。
    pub fn step(&mut self, delta_time: f32) -> StepResult {
        self.scene.step(delta_time, 4)
    }

    /// Write body transforms back into the scene's render objects.
    /// 将刚体变换写回场景的渲染对象。
    pub fn synchronize(&mut self, scene: &mut Scene) {
        for &(object, handle) in &self.bodies {
            let Some(render_object) = scene.objects.get_mut(object) else {
                continue;
            };
            let Some(position) = self.scene.position(handle) else {
                continue;
            };
            let Some(orientation) = self.scene.orientation(handle) else {
                continue;
            };
            render_object.transform.position = position;
            render_object.transform.orientation = orientation;
        }
    }

    fn handle(&self, object: ObjectId) -> Option<BodyHandle> {
        self.bodies
            .iter()
            .find(|(id, _)| *id == object)
            .map(|(_, handle)| *handle)
    }
}

impl Default for PhysicsWorld {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod tests {
    use alloc::vec;

    use super::*;
    use he3d_core::{ColorRgba8, Material, Mesh, RenderObject, Rgb, Texture};
    use he3d_math::Quat;

    const DT: f32 = 1.0 / 60.0;

    fn spawn_box(scene: &mut Scene, position: Vec3) -> ObjectId {
        let mesh = scene.meshes.insert(Mesh::cube(1.0, 1.0, 1.0).expect("cube"));
        let solid = scene.textures.insert(Texture::solid(ColorRgba8::WHITE));
        scene.spawn(RenderObject {
            mesh,
            texture: Some(solid),
            transform: Transform::from_position(position),
            material: Material::new(Rgb::WHITE),
            visible: true,
        })
    }

    /// A flat quad mesh floor with a render object; use with `add_static_mesh`.
    /// 一个带渲染对象的平坦四边形网格地面；配合 `add_static_mesh` 使用。
    fn spawn_quad_floor(scene: &mut Scene, half: f32) -> (ObjectId, Mesh) {
        let h = half;
        let quad = Mesh::from_vertices(vec![
            Vec3::new(-h, 0.0, -h),
            Vec3::new(h, 0.0, h),
            Vec3::new(h, 0.0, -h),
            Vec3::new(-h, 0.0, -h),
            Vec3::new(-h, 0.0, h),
            Vec3::new(h, 0.0, h),
        ])
        .expect("quad");
        let mesh_id = scene.meshes.insert(quad.clone());
        let solid = scene.textures.insert(Texture::solid(ColorRgba8::from_rgb(77, 179, 77)));
        let object = scene.spawn(RenderObject {
            mesh: mesh_id,
            texture: Some(solid),
            transform: Transform::default(),
            material: Material::new(Rgb::WHITE),
            visible: true,
        });
        (object, quad)
    }

    fn run(world: &mut PhysicsWorld, steps: usize) {
        for _ in 0..steps {
            assert_eq!(world.step(DT), StepResult::Completed);
        }
    }

    #[test]
    fn registration_and_removal() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::ZERO);
        let mut world = PhysicsWorld::new();

        assert!(world.add_dynamic_box(cube, Vec3::splat(0.5), Transform::default()));
        assert!(world.has_body(cube));
        // Duplicate registration is rejected. 重复注册被拒绝。
        assert!(!world.add_dynamic_box(cube, Vec3::splat(0.5), Transform::default()));
        assert!(!world.add_static_box(cube, Vec3::splat(0.5), Transform::default()));

        assert!(world.remove_body(cube));
        assert!(!world.has_body(cube));
        assert!(!world.remove_body(cube));
        assert!(!world.add_force(cube, Vec3::X));
    }

    #[test]
    fn transform_and_velocity_passthrough() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::new(0.0, 1.0, 0.0));
        let mut world = PhysicsWorld::new();
        world.add_dynamic_box(cube, Vec3::splat(0.5), Transform::from_position(Vec3::new(0.0, 1.0, 0.0)));

        assert!(world.set_velocity(cube, Vec3::new(2.0, 0.0, 0.0)));
        assert_eq!(world.velocity(cube), Vec3::new(2.0, 0.0, 0.0));

        // Teleport keeps velocity. 瞬移保持速度。
        let teleport = Transform::from_position_orientation(
            Vec3::new(3.0, 4.0, 5.0),
            Quat::from_rotation_y(1.0),
        );
        assert!(world.set_transform(cube, teleport));
        assert_eq!(world.transform(cube), Some(teleport));
        assert_eq!(world.velocity(cube), Vec3::new(2.0, 0.0, 0.0));

        assert!(world.set_angular_velocity(cube, Vec3::new(0.0, 0.0, 1.0)));
        assert_eq!(world.angular_velocity(cube), Vec3::new(0.0, 0.0, 1.0));

        // Unknown objects are no-ops. 未知对象为无操作。
        let stale = spawn_box(&mut scene, Vec3::ZERO);
        scene.objects.remove(stale);
        assert!(!world.set_transform(stale, Transform::default()));
        assert_eq!(world.transform(stale), None);
    }

    #[test]
    fn gravity_pulls_dynamic_body_down() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::new(0.0, 10.0, 0.0));
        let mut world = PhysicsWorld::new();
        world.add_dynamic_box(
            cube,
            Vec3::splat(0.5),
            Transform::from_position(Vec3::new(0.0, 10.0, 0.0)),
        );
        run(&mut world, 60);
        world.synchronize(&mut scene);
        let y = scene.objects.get(cube).unwrap().transform.position.y;
        assert!(y < 9.0, "body should have fallen, got y={y}");
        assert!(y > 0.0, "body should not have fallen through, got y={y}");
    }

    #[test]
    fn cube_rests_on_static_mesh_ground() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::new(0.0, 5.0, 0.0));
        let (floor, floor_mesh) = spawn_quad_floor(&mut scene, 3.0);
        let mut world = PhysicsWorld::new();
        world.add_dynamic_box(
            cube,
            Vec3::splat(0.5),
            Transform::from_position(Vec3::new(0.0, 5.0, 0.0)),
        );
        assert!(world.add_static_mesh(
            floor,
            &floor_mesh,
            Transform::from_position(Vec3::new(0.0, -0.4, 0.0)),
        ));

        run(&mut world, 300);
        world.synchronize(&mut scene);
        let y = scene.objects.get(cube).unwrap().transform.position.y;
        assert!((y - 0.1).abs() < 0.05, "cube should rest near y=0.1, got y={y}");
    }

    #[test]
    fn restitution_bounces_on_fast_impact() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::new(0.0, 5.0, 0.0));
        let (floor, floor_mesh) = spawn_quad_floor(&mut scene, 6.0);
        let mut world = PhysicsWorld::new();
        world.add_dynamic_box(
            cube,
            Vec3::splat(0.5),
            Transform::from_position(Vec3::new(0.0, 5.0, 0.0)),
        );
        world.set_material(cube, 0.5, 0.5);
        world.add_static_mesh(floor, &floor_mesh, Transform::from_position(Vec3::new(0.0, -0.4, 0.0)));

        let mut max_vy = 0.0f32;
        for _ in 0..120 {
            world.step(DT);
            max_vy = max_vy.max(world.velocity(cube).y);
        }
        assert!(max_vy > 0.5, "fast impact must bounce, got max_vy={max_vy}");
    }

    #[test]
    fn force_acts_for_one_step_then_is_cleared() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::ZERO);
        let mut world = PhysicsWorld::new();
        world.set_gravity(Vec3::ZERO);
        world.add_dynamic_box(cube, Vec3::splat(0.5), Transform::default());

        assert!(world.add_force(cube, Vec3::new(60.0, 0.0, 0.0)));
        assert_eq!(world.step(DT), StepResult::Completed);
        let after_force = world.velocity(cube).x;
        assert!(after_force > 0.9, "got {after_force}");

        assert_eq!(world.step(DT), StepResult::Completed);
        let after_idle = world.velocity(cube).x;
        assert!(after_idle < after_force);
        assert!(after_idle > after_force * 0.99);
    }

    #[test]
    fn damping_decays_velocity() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::ZERO);
        let mut world = PhysicsWorld::new();
        world.set_gravity(Vec3::ZERO);
        world.add_dynamic_box(cube, Vec3::splat(0.5), Transform::default());
        assert!(world.set_damping(cube, 0.5, 0.5));
        assert!(world.set_velocity(cube, Vec3::new(10.0, 0.0, 0.0)));
        assert_eq!(world.step(DT), StepResult::Completed);
        let vx = world.velocity(cube).x;
        assert!(vx > 9.0 && vx < 10.0, "got {vx}");
    }

    #[test]
    fn contacts_detect_overlap_and_separation() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::ZERO);
        let other = spawn_box(&mut scene, Vec3::ZERO);
        let mut world = PhysicsWorld::new();
        world.add_dynamic_box(cube, Vec3::splat(0.5), Transform::default());
        world.add_dynamic_box(other, Vec3::splat(0.5), Transform::default());

        assert!(world.has_contacts(cube));
        assert!(world.has_contacts(other));

        assert!(world.set_transform(
            other,
            Transform::from_position(Vec3::new(10.0, 0.0, 0.0)),
        ));
        assert!(!world.has_contacts(cube));
    }

    #[test]
    fn kinematic_body_moves_and_ignores_gravity() {
        let mut scene = Scene::new();
        let mover = spawn_box(&mut scene, Vec3::ZERO);
        let mut world = PhysicsWorld::new();
        world.add_kinematic_box(mover, Vec3::splat(0.5), Transform::default());
        assert!(world.set_velocity(mover, Vec3::new(1.0, 0.0, 0.0)));
        run(&mut world, 10);
        let position = world.transform(mover).unwrap().position;
        assert!((position.x - 10.0 * DT).abs() < 1e-4, "got x={}", position.x);
        assert_eq!(position.y, 0.0);
    }

    #[test]
    fn step_rejects_invalid_input() {
        let mut world = PhysicsWorld::new();
        assert_eq!(world.step(0.0), StepResult::InvalidInput);
        assert_eq!(world.step(-1.0), StepResult::InvalidInput);
        assert_eq!(world.step(f32::NAN), StepResult::InvalidInput);
    }

    #[test]
    fn synchronize_writes_orientation_and_position() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::new(0.0, 2.0, 0.0));
        let mut world = PhysicsWorld::new();
        world.add_dynamic_box(cube, Vec3::splat(0.5), Transform::from_position(Vec3::new(0.0, 2.0, 0.0)));
        assert!(world.set_angular_velocity(cube, Vec3::new(0.0, 0.0, 2.0)));
        run(&mut world, 30);
        world.synchronize(&mut scene);
        let orientation = scene.objects.get(cube).unwrap().transform.orientation;
        assert_ne!(orientation, Quat::IDENTITY, "cube should have rotated");
        assert!(orientation.is_finite());
    }

    #[test]
    fn add_static_mesh_registers_and_rejects_duplicates() {
        let mut scene = Scene::new();
        let cube = spawn_box(&mut scene, Vec3::new(0.0, 5.0, 0.0));
        let (floor, floor_mesh) = spawn_quad_floor(&mut scene, 3.0);
        let mut world = PhysicsWorld::new();
        assert!(world.add_static_mesh(
            floor,
            &floor_mesh,
            Transform::from_position(Vec3::new(0.0, -0.4, 0.0)),
        ));
        assert!(world.has_body(floor));
        // Duplicate registration for the same object is rejected.
        // 同一对象的重复注册被拒绝。
        assert!(!world.add_static_mesh(
            floor,
            &floor_mesh,
            Transform::from_position(Vec3::new(0.0, -0.4, 0.0)),
        ));
        assert!(world.add_dynamic_box(
            cube,
            Vec3::splat(0.5),
            Transform::from_position(Vec3::new(0.0, 5.0, 0.0)),
        ));
        run(&mut world, 300);
        world.synchronize(&mut scene);
        let y = scene.objects.get(cube).unwrap().transform.position.y;
        assert!((y - 0.1).abs() < 0.05, "cube should rest near y=0.1, got y={y}");
    }
}