// Triangle mesh model — produced by the kernel Shell/Solid tessellation.
//
// Stored alongside WireModels in the scene; rendered by the mesh pipeline
// (wgpu TriangleList with depth test, flat normals).

/// A tessellated triangle mesh ready to upload to the GPU.
#[derive(Clone, Debug)]
#[allow(dead_code)]
pub struct MeshModel {
    /// Unique identifier (entity handle value as decimal string).
    pub name: String,
    /// World-space vertex positions (high half of the double-single pair).
    pub verts: Vec<[f32; 3]>,
    /// Low residual paired with `verts` so meshes stay precise at UTM scale.
    /// Empty = all-zero (legacy / interactive meshes near the origin).
    pub verts_low: Vec<[f32; 3]>,
    /// Per-vertex normals (may be empty if not available).
    pub normals: Vec<[f32; 3]>,
    /// Triangle indices into `verts` (every 3 values = one triangle).
    pub indices: Vec<u32>,
    /// Optional AcDbMaterial handle per triangle. Empty means the whole mesh
    /// uses `MeshLodSet::material`; otherwise each entry aligns with one
    /// `indices` triplet and overrides the entity material for that face.
    pub triangle_material_handles: Vec<Option<acadrust::Handle>>,
    /// Optional ACIS face colour per triangle, aligned with `indices` triplets.
    pub triangle_colors: Vec<Option<[f32; 4]>>,
    /// RGBA colour in [0, 1].
    pub color: [f32; 4],
    /// Whether this mesh is currently selected.
    pub selected: bool,
}

/// Bundle of mesh tessellations at different sampling densities, picked
/// per frame by the render pipeline based on the projected pixel size of
/// `world_aabb`. Phase 3.4 LOD ladder:
///
/// | LOD | Source     | Use when projected diagonal |
/// |-----|------------|------------------------------|
/// | 0   | HIGH       | > 200 px                     |
/// | 1   | MID (½)    | 50–200 px                    |
/// | 2   | LOW (¼)    | < 50 px                      |
///
/// `lods` holds up to one MeshModel per LOD level (high → low). Empty
/// slots fall back to the nearest available LOD at render time.
/// Kernel-owned source for a view-dependent silhouette.
#[derive(Clone, Debug)]
pub struct CurvedGen {
    pub source: cadkernel::brep::mesh::SilhouetteSource,
}

#[derive(Clone, Copy, Debug, Default)]
pub struct MeshMetrics {
    pub vertices: usize,
    pub triangles: usize,
    pub surface_area: f64,
    pub volume: f64,
    pub centroid: [f64; 3],
    pub moment_of_inertia: [f64; 3],
    pub principal_directions: [f64; 9],
    pub principal_moments: [f64; 3],
    pub product_of_inertia: [f64; 3],
    pub radii_of_gyration: [f64; 3],
}

impl MeshMetrics {
    fn apply_mass_properties(&mut self, properties: cadkernel::brep::MassProperties) {
        self.volume = properties.volume;
        self.centroid = properties.centroid;
        self.moment_of_inertia = properties.moment_of_inertia;
        self.principal_directions = properties.principal_directions;
        self.principal_moments = properties.principal_moments;
        self.product_of_inertia = properties.product_of_inertia;
        self.radii_of_gyration = properties.radii_of_gyration;
    }

    pub fn translate(&mut self, delta: [f64; 3]) {
        if self.volume > 1e-18 {
            self.apply_mass_properties(
                cadkernel::brep::MassProperties {
                    volume: self.volume,
                    centroid: self.centroid,
                    moment_of_inertia: self.moment_of_inertia,
                    principal_directions: self.principal_directions,
                    principal_moments: self.principal_moments,
                    product_of_inertia: self.product_of_inertia,
                    radii_of_gyration: self.radii_of_gyration,
                }
                .translated(delta),
            );
        } else {
            for axis in 0..3 {
                self.centroid[axis] += delta[axis];
            }
        }
    }
}

#[derive(Clone, Debug)]
pub struct MeshLodSet {
    pub lods: Vec<MeshModel>,
    /// Effective AcDbMaterial resolved from entity/layer/INSERT inheritance.
    /// Geometry remains usable when it is absent; the renderer then keeps the
    /// per-mesh entity colour.
    pub material: Option<super::material_model::MeshMaterial>,
    /// Face-level ACIS material overrides, resolved from each LOD's
    /// `triangle_material_handles`. Only handles actually referenced by the
    /// tessellation are retained.
    pub face_materials:
        rustc_hash::FxHashMap<acadrust::Handle, super::material_model::MeshMaterial>,
    /// Effective AcDbVisualStyle override resolved from the entity's full,
    /// face and edge style handles.
    pub visual_style: Option<super::visual_style_model::MeshVisualStyle>,
    /// True only when every source face produced triangles. False keeps
    /// downstream solid-edit code from treating a display-only partial shell
    /// as a closed, valid solid.
    pub complete: bool,
    /// Feature-edge line list (LOD-independent): pairs of endpoints, high half
    /// of the double-single. Populated for ACIS solids (the B-rep face-boundary
    /// edges) so their wireframe shows real edges rather than the triangulation.
    /// Empty for plain meshes — those fall back to triangle edges at batch time.
    pub edge_verts: Vec<[f32; 3]>,
    /// Low residual paired with `edge_verts`.
    pub edge_verts_low: Vec<[f32; 3]>,
    /// Kernel sources for per-frame silhouettes.
    pub curved_gens: Vec<CurvedGen>,
    /// Geometry measurements calculated once from the highest available LOD.
    /// Properties can read these without re-parsing or re-tessellating ACIS on
    /// the UI thread.
    pub metrics: MeshMetrics,
    /// World XY AABB `[min_x, min_y, max_x, max_y]` of the mesh — used
    /// by the per-frame LOD selector to compute the projected pixel
    /// diagonal.
    pub world_aabb: [f32; 4],
    /// World Z extent `[min_z, max_z]`. With `world_aabb` this is the full 3D
    /// box, which the pick path projects to a screen rect to skip solids whose
    /// footprint isn't under the cursor (O(solids) instead of ray-testing every
    /// triangle). `verts` carry only the high half of the double-single
    /// position, so the bound is f32-precise — fine for a conservative cull.
    pub z_aabb: [f32; 2],
    /// Immutable block-local geometry shared by every INSERT instance of this
    /// block entity. Top-level meshes leave this empty.
    pub instance_source: Option<std::sync::Arc<MeshInstanceSource>>,
    /// Accumulated block-local → world transform for this rendered instance.
    pub instance_transform: Option<acadrust::types::Transform>,
    /// Parent INSERT selected for this rendered block instance.
    pub instance_handle: Option<acadrust::Handle>,
    /// Effective colour after INSERT inheritance, without copying the mesh.
    pub instance_color: Option<[f32; 4]>,
    /// Precise world bounds used by the interaction index.
    pub instance_aabb: Option<[f64; 6]>,
}

#[derive(Clone, Debug)]
pub struct MeshInstanceSource {
    pub handle: acadrust::Handle,
    pub lods: Vec<MeshModel>,
    pub edge_verts: Vec<[f32; 3]>,
    pub edge_verts_low: Vec<[f32; 3]>,
    pub curved_gens: Vec<CurvedGen>,
}

/// 3D bounds of every LOD's vertices: `([min_x, min_y, max_x, max_y], [min_z, max_z])`.
pub fn compute_mesh_aabb(lods: &[MeshModel]) -> ([f32; 4], [f32; 2]) {
    let (mut min_x, mut min_y, mut min_z) = (f32::INFINITY, f32::INFINITY, f32::INFINITY);
    let (mut max_x, mut max_y, mut max_z) =
        (f32::NEG_INFINITY, f32::NEG_INFINITY, f32::NEG_INFINITY);
    for lod in lods {
        for &[x, y, z] in &lod.verts {
            if !x.is_finite() || !y.is_finite() || !z.is_finite() {
                continue;
            }
            min_x = min_x.min(x);
            min_y = min_y.min(y);
            min_z = min_z.min(z);
            max_x = max_x.max(x);
            max_y = max_y.max(y);
            max_z = max_z.max(z);
        }
    }
    ([min_x, min_y, max_x, max_y], [min_z, max_z])
}

fn compute_mesh_metrics(lods: &[MeshModel]) -> MeshMetrics {
    let Some(mesh) = lods.iter().find(|mesh| !mesh.indices.is_empty()) else {
        return MeshMetrics::default();
    };
    let kernel_mesh = cadkernel::brep::Mesh {
        positions: mesh
            .verts
            .iter()
            .enumerate()
            .map(|(index, high)| {
                let low = mesh.verts_low.get(index).copied().unwrap_or([0.0; 3]);
                [
                    high[0] as f64 + low[0] as f64,
                    high[1] as f64 + low[1] as f64,
                    high[2] as f64 + low[2] as f64,
                ]
            })
            .collect(),
        normals: Vec::new(),
        triangles: mesh
            .indices
            .chunks_exact(3)
            .map(|triangle| {
                [
                    triangle[0] as usize,
                    triangle[1] as usize,
                    triangle[2] as usize,
                ]
            })
            .collect(),
    };
    let surface = kernel_mesh.surface_properties();
    let mut metrics = MeshMetrics {
        vertices: mesh.verts.len(),
        triangles: mesh.indices.len() / 3,
        surface_area: surface.map_or(0.0, |value| value.0),
        centroid: surface.map_or([0.0; 3], |value| value.1),
        ..MeshMetrics::default()
    };
    if let Some(properties) = kernel_mesh.inertial_properties() {
        metrics.apply_mass_properties(properties);
    }
    metrics
}

impl MeshLodSet {
    pub fn apply_mass_properties(&mut self, properties: cadkernel::brep::MassProperties) {
        self.metrics.apply_mass_properties(properties);
    }

    /// Build a set from its LODs, computing the 3D AABB.
    pub fn from_lods(lods: Vec<MeshModel>) -> Self {
        let (world_aabb, z_aabb) = compute_mesh_aabb(&lods);
        let metrics = compute_mesh_metrics(&lods);
        Self {
            lods,
            material: None,
            face_materials: rustc_hash::FxHashMap::default(),
            visual_style: None,
            complete: true,
            edge_verts: Vec::new(),
            edge_verts_low: Vec::new(),
            curved_gens: Vec::new(),
            metrics,
            world_aabb,
            z_aabb,
            instance_source: None,
            instance_transform: None,
            instance_handle: None,
            instance_color: None,
            instance_aabb: None,
        }
    }

    /// Wrap a single MeshModel as a one-LOD set. Used by interactive
    /// commands that only produce one tessellation (e.g. the kernel-based
    /// BOX/CYLINDER creation). The LOD selector will pick slot 0 for
    /// every zoom level.
    pub fn from_single(mesh: MeshModel) -> Self {
        Self::from_lods(vec![mesh])
    }

    /// Recompute `world_aabb` / `z_aabb` after the LODs' vertices were rewritten
    /// (relative-to-eye re-split, INSERT transform).
    pub fn recompute_aabb(&mut self) {
        let (xy, z) = compute_mesh_aabb(&self.lods);
        self.world_aabb = xy;
        self.z_aabb = z;
    }

    pub fn prepare_instance_source(&mut self, handle: acadrust::Handle) {
        self.instance_source = Some(std::sync::Arc::new(MeshInstanceSource {
            handle,
            lods: self.lods.clone(),
            edge_verts: self.edge_verts.clone(),
            edge_verts_low: self.edge_verts_low.clone(),
            curved_gens: self.curved_gens.clone(),
        }));
        self.instance_transform = None;
        self.instance_handle = None;
        self.instance_color = None;
        self.instance_aabb = None;
    }

    pub fn geometry_lods(&self) -> &[MeshModel] {
        self.instance_source
            .as_ref()
            .map_or(self.lods.as_slice(), |source| source.lods.as_slice())
    }

    pub fn geometry_edges(&self) -> (&[[f32; 3]], &[[f32; 3]]) {
        self.instance_source.as_ref().map_or(
            (self.edge_verts.as_slice(), self.edge_verts_low.as_slice()),
            |source| (
                source.edge_verts.as_slice(),
                source.edge_verts_low.as_slice(),
            ),
        )
    }

    pub fn entity_handle(&self) -> Option<acadrust::Handle> {
        self.instance_handle.or_else(|| {
            self.lods
                .first()
                .and_then(|mesh| mesh.name.parse::<u64>().ok())
                .map(acadrust::Handle::new)
        })
    }

    pub fn display_color(&self) -> Option<[f32; 4]> {
        self.instance_color.or_else(|| {
            self.geometry_lods()
                .iter()
                .find(|mesh| !mesh.indices.is_empty())
                .map(|mesh| mesh.color)
        })
    }
}