brepkit_math/

surfaces.rs

//! Analytic surface types for exact geometric computations.
//!
//! These surfaces complement NURBS surfaces by providing exact parameterizations
//! for common shapes (cylinder, cone, sphere, torus). This enables exact
//! intersection algorithms (e.g., plane-cylinder = ellipse) without sampling.

use crate::MathError;
use crate::aabb::Aabb3;
use crate::frame::Frame3;
use crate::nurbs::surface::NurbsSurface;
use crate::vec::{Point3, Vec3};

/// An infinite cylindrical surface.
///
/// Parameterized as `P(u, v) = origin + radius*(cos(u)*x_axis + sin(u)*y_axis) + v*axis`
/// where `u ∈ [0, 2π)` and `v ∈ (-∞, +∞)`.
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct CylindricalSurface {
    origin: Point3,
    axis: Vec3,
    radius: f64,
    x_axis: Vec3,
    y_axis: Vec3,
}

impl CylindricalSurface {
    /// Creates a new cylindrical surface.
    ///
    /// # Errors
    /// Returns an error if radius is not positive or axis is zero.
    pub fn new(origin: Point3, axis: Vec3, radius: f64) -> Result<Self, MathError> {
        if radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        let f = Frame3::from_normal(origin, axis)?;
        Ok(Self {
            origin,
            axis: f.z,
            radius,
            x_axis: f.x,
            y_axis: f.y,
        })
    }

    /// Evaluates the surface at parameters `(u, v)`.
    #[must_use]
    pub fn evaluate(&self, u: f64, v: f64) -> Point3 {
        let (sin_u, cos_u) = u.sin_cos();
        self.origin
            + self.x_axis * (self.radius * cos_u)
            + self.y_axis * (self.radius * sin_u)
            + self.axis * v
    }

    /// Returns the surface normal at parameters `(u, v)`.
    #[must_use]
    pub fn normal(&self, u: f64, _v: f64) -> Vec3 {
        let (sin_u, cos_u) = u.sin_cos();
        self.x_axis * cos_u + self.y_axis * sin_u
    }

    /// Returns the origin.
    #[must_use]
    pub const fn origin(&self) -> Point3 {
        self.origin
    }

    /// Returns the axis direction.
    #[must_use]
    pub const fn axis(&self) -> Vec3 {
        self.axis
    }

    /// Returns the radius.
    #[must_use]
    pub const fn radius(&self) -> f64 {
        self.radius
    }

    /// Returns the local X axis (first radial direction in the parametric frame).
    #[must_use]
    pub const fn x_axis(&self) -> Vec3 {
        self.x_axis
    }

    /// Returns the local Y axis (second radial direction in the parametric frame).
    #[must_use]
    pub const fn y_axis(&self) -> Vec3 {
        self.y_axis
    }

    /// Creates a cylindrical surface with a specified reference direction.
    ///
    /// `ref_dir` defines the x-axis of the parametric frame (projected
    /// perpendicular to `axis`). This preserves the parametric orientation
    /// from STEP `AXIS2_PLACEMENT_3D` or BREP round-trips.
    ///
    /// # Errors
    /// Returns an error if radius is not positive or axis is zero.
    pub fn with_ref_dir(
        origin: Point3,
        axis: Vec3,
        radius: f64,
        ref_dir: Vec3,
    ) -> Result<Self, MathError> {
        if radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        let f = Frame3::from_normal_and_ref(origin, axis, ref_dir)?;
        Ok(Self {
            origin,
            axis: f.z,
            radius,
            x_axis: f.x,
            y_axis: f.y,
        })
    }

    /// Returns a copy of this cylinder with its origin translated by `offset`.
    #[must_use]
    pub fn translated(&self, offset: Vec3) -> Self {
        Self {
            origin: self.origin + offset,
            ..self.clone()
        }
    }

    /// Project a 3D point onto the cylinder surface, returning (u, v) parameters.
    ///
    /// `u` is the angular parameter [0, 2π), `v` is the axial parameter.
    #[must_use]
    pub fn project_point(&self, point: Point3) -> (f64, f64) {
        let to_pt = Vec3::new(
            point.x() - self.origin.x(),
            point.y() - self.origin.y(),
            point.z() - self.origin.z(),
        );
        let v = self.axis.dot(to_pt);
        let radial = to_pt - self.axis * v;
        let x = self.x_axis.dot(radial);
        let y = self.y_axis.dot(radial);
        let u = y.atan2(x).rem_euclid(std::f64::consts::TAU);
        (u, v)
    }

    /// Convert to an exact rational NURBS surface over the given v-range.
    ///
    /// Uses degree (2, 1) with 9 control points per ring (standard rational
    /// representation of a full circle). The result is geometrically exact.
    ///
    /// # Errors
    ///
    /// Returns an error if `NurbsSurface` construction fails.
    pub fn to_nurbs(&self, v_min: f64, v_max: f64) -> Result<NurbsSurface, MathError> {
        // 9 CPs for a full circle (degree 2, 4 arcs of 90°).
        let w1 = std::f64::consts::FRAC_1_SQRT_2;
        let circle_weights = [1.0, w1, 1.0, w1, 1.0, w1, 1.0, w1, 1.0];
        // Directions at 0°, 45°, 90°, ... 360° in the (x_axis, y_axis) plane.
        let dirs: [(f64, f64); 9] = [
            (1.0, 0.0),
            (1.0, 1.0),
            (0.0, 1.0),
            (-1.0, 1.0),
            (-1.0, 0.0),
            (-1.0, -1.0),
            (0.0, -1.0),
            (1.0, -1.0),
            (1.0, 0.0),
        ];

        let mut cps = Vec::with_capacity(9);
        let mut ws = Vec::with_capacity(9);
        for (i, &(dx, dy)) in dirs.iter().enumerate() {
            let radial = self.x_axis * (self.radius * dx) + self.y_axis * (self.radius * dy);
            let p_bot = self.origin + radial + self.axis * v_min;
            let p_top = self.origin + radial + self.axis * v_max;
            cps.push(vec![p_bot, p_top]);
            ws.push(vec![circle_weights[i], circle_weights[i]]);
        }

        let knots_u = vec![
            0.0, 0.0, 0.0, 0.25, 0.25, 0.5, 0.5, 0.75, 0.75, 1.0, 1.0, 1.0,
        ];
        let knots_v = vec![0.0, 0.0, 1.0, 1.0];
        NurbsSurface::new(2, 1, knots_u, knots_v, cps, ws)
    }
}

/// An infinite conical surface.
///
/// Parameterized as `P(u, v) = apex + v*(cos(half_angle)*(cos(u)*x_axis + sin(u)*y_axis) + sin(half_angle)*axis)`
/// where `u ∈ [0, 2π)` and `v ∈ [0, +∞)`.
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct ConicalSurface {
    apex: Point3,
    axis: Vec3,
    half_angle: f64,
    x_axis: Vec3,
    y_axis: Vec3,
}

impl ConicalSurface {
    /// Creates a new conical surface.
    ///
    /// `half_angle` is the angle from the radial plane to the cone's surface
    /// generator (radians). Small angles produce wide/flat cones; angles near
    /// π/2 produce narrow/spike cones. In the evaluate formula
    /// `P(u,v) = apex + v*(cos(a)*radial + sin(a)*axis)`, `a` is this angle.
    ///
    /// # Errors
    /// Returns an error if half-angle is not in `(0, π/2)` or axis is zero.
    pub fn new(apex: Point3, axis: Vec3, half_angle: f64) -> Result<Self, MathError> {
        if half_angle <= 0.0 || half_angle >= std::f64::consts::FRAC_PI_2 {
            return Err(MathError::ParameterOutOfRange {
                value: half_angle,
                min: f64::EPSILON,
                max: std::f64::consts::FRAC_PI_2,
            });
        }
        let f = Frame3::from_normal(apex, axis)?;
        Ok(Self {
            apex,
            axis: f.z,
            half_angle,
            x_axis: f.x,
            y_axis: f.y,
        })
    }

    /// Evaluates the surface at parameters `(u, v)`.
    #[must_use]
    pub fn evaluate(&self, u: f64, v: f64) -> Point3 {
        let (sin_u, cos_u) = u.sin_cos();
        let (sin_a, cos_a) = self.half_angle.sin_cos();
        let radial = self.x_axis * cos_u + self.y_axis * sin_u;
        self.apex + (radial * cos_a + self.axis * sin_a) * v
    }

    /// Returns the surface normal at parameters `(u, v)`.
    #[must_use]
    pub fn normal(&self, u: f64, _v: f64) -> Vec3 {
        let (sin_u, cos_u) = u.sin_cos();
        let (sin_a, cos_a) = self.half_angle.sin_cos();
        let radial = self.x_axis * cos_u + self.y_axis * sin_u;
        // Normal points outward: radial * sin(a) - axis * cos(a)
        radial * sin_a + self.axis * (-cos_a)
    }

    /// Returns the apex point.
    #[must_use]
    pub const fn apex(&self) -> Point3 {
        self.apex
    }

    /// Returns the axis direction.
    #[must_use]
    pub const fn axis(&self) -> Vec3 {
        self.axis
    }

    /// Returns the half-angle in radians.
    #[must_use]
    pub const fn half_angle(&self) -> f64 {
        self.half_angle
    }

    /// Returns the local X axis (first radial direction in the parametric frame).
    #[must_use]
    pub const fn x_axis(&self) -> Vec3 {
        self.x_axis
    }

    /// Returns the local Y axis (second radial direction in the parametric frame).
    #[must_use]
    pub const fn y_axis(&self) -> Vec3 {
        self.y_axis
    }

    /// Creates a conical surface with a specified reference direction.
    ///
    /// `ref_dir` defines the x-axis of the parametric frame (projected
    /// perpendicular to `axis`). This preserves the parametric orientation
    /// from STEP `AXIS2_PLACEMENT_3D` or BREP round-trips.
    ///
    /// # Errors
    /// Returns an error if half-angle is not in `(0, π/2)` or axis is zero.
    pub fn with_ref_dir(
        apex: Point3,
        axis: Vec3,
        half_angle: f64,
        ref_dir: Vec3,
    ) -> Result<Self, MathError> {
        if half_angle <= 0.0 || half_angle >= std::f64::consts::FRAC_PI_2 {
            return Err(MathError::ParameterOutOfRange {
                value: half_angle,
                min: f64::EPSILON,
                max: std::f64::consts::FRAC_PI_2,
            });
        }
        let f = Frame3::from_normal_and_ref(apex, axis, ref_dir)?;
        Ok(Self {
            apex,
            axis: f.z,
            half_angle,
            x_axis: f.x,
            y_axis: f.y,
        })
    }

    /// Returns a copy of this cone with its apex translated by `offset`.
    #[must_use]
    pub fn translated(&self, offset: Vec3) -> Self {
        Self {
            apex: self.apex + offset,
            ..self.clone()
        }
    }

    /// Returns the radius at a given distance `v` along the axis from the apex.
    #[must_use]
    pub fn radius_at(&self, v: f64) -> f64 {
        v * self.half_angle.cos()
    }

    /// Project a 3D point onto the cone surface, returning `(u, v)` parameters.
    ///
    /// `u` is the angular parameter `[0, 2π)`, `v` is the distance from the
    /// apex along the cone surface generator line.
    #[must_use]
    pub fn project_point(&self, point: Point3) -> (f64, f64) {
        let to_pt = Vec3::new(
            point.x() - self.apex.x(),
            point.y() - self.apex.y(),
            point.z() - self.apex.z(),
        );

        let h = self.axis.dot(to_pt);
        let radial = to_pt - self.axis * h;
        let x = self.x_axis.dot(radial);
        let y = self.y_axis.dot(radial);

        let u = y.atan2(x).rem_euclid(std::f64::consts::TAU);

        let sin_a = self.half_angle.sin();
        let v = if sin_a.abs() > 1e-15 {
            h / sin_a
        } else {
            let cos_a = self.half_angle.cos();
            if cos_a.abs() > 1e-15 {
                radial.length() / cos_a
            } else {
                0.0
            }
        };

        (u, v)
    }

    /// Convert to an approximate NURBS surface over the given v-range.
    ///
    /// # Errors
    ///
    /// Returns an error if `NurbsSurface` construction fails.
    pub fn to_nurbs(&self, v_min: f64, v_max: f64) -> Result<NurbsSurface, MathError> {
        analytic_to_nurbs_sampled(
            |u, v| self.evaluate(u, v),
            (0.0, std::f64::consts::TAU),
            (v_min, v_max),
        )
    }
}

/// An infinite spherical surface (actually a sphere).
///
/// Parameterized as `P(u, v) = center + radius*(cos(v)*cos(u)*x + cos(v)*sin(u)*y + sin(v)*z)`
/// where `u ∈ [0, 2π)` (longitude) and `v ∈ [-π/2, π/2]` (latitude).
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct SphericalSurface {
    center: Point3,
    radius: f64,
    x_axis: Vec3,
    y_axis: Vec3,
    z_axis: Vec3,
}

impl SphericalSurface {
    /// Creates a new spherical surface.
    ///
    /// # Errors
    /// Returns an error if radius is not positive.
    pub fn new(center: Point3, radius: f64) -> Result<Self, MathError> {
        if radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        Ok(Self {
            center,
            radius,
            x_axis: Vec3::new(1.0, 0.0, 0.0),
            y_axis: Vec3::new(0.0, 1.0, 0.0),
            z_axis: Vec3::new(0.0, 0.0, 1.0),
        })
    }

    /// Creates a spherical surface with a custom orientation.
    ///
    /// # Errors
    /// Returns an error if radius is not positive or the z-axis is zero.
    pub fn with_axis(center: Point3, radius: f64, z_axis: Vec3) -> Result<Self, MathError> {
        if radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        let f = Frame3::from_normal(center, z_axis)?;
        Ok(Self {
            center,
            radius,
            x_axis: f.x,
            y_axis: f.y,
            z_axis: f.z,
        })
    }

    /// Evaluates the surface at parameters `(u, v)`.
    #[must_use]
    pub fn evaluate(&self, u: f64, v: f64) -> Point3 {
        let (sin_u, cos_u) = u.sin_cos();
        let (sin_v, cos_v) = v.sin_cos();
        self.center
            + self.x_axis * (self.radius * cos_v * cos_u)
            + self.y_axis * (self.radius * cos_v * sin_u)
            + self.z_axis * (self.radius * sin_v)
    }

    /// Returns the outward normal at parameters `(u, v)`.
    #[must_use]
    pub fn normal(&self, u: f64, v: f64) -> Vec3 {
        let (sin_u, cos_u) = u.sin_cos();
        let (sin_v, cos_v) = v.sin_cos();
        self.x_axis * (cos_v * cos_u) + self.y_axis * (cos_v * sin_u) + self.z_axis * sin_v
    }

    /// Returns the center.
    #[must_use]
    pub const fn center(&self) -> Point3 {
        self.center
    }

    /// Returns the radius.
    #[must_use]
    pub const fn radius(&self) -> f64 {
        self.radius
    }

    /// Returns the local X axis.
    #[must_use]
    pub const fn x_axis(&self) -> Vec3 {
        self.x_axis
    }

    /// Returns the local Y axis.
    #[must_use]
    pub const fn y_axis(&self) -> Vec3 {
        self.y_axis
    }

    /// Returns the local Z axis (pole direction).
    #[must_use]
    pub const fn z_axis(&self) -> Vec3 {
        self.z_axis
    }

    /// Returns a copy of this sphere with its center translated by `offset`.
    #[must_use]
    pub fn translated(&self, offset: Vec3) -> Self {
        Self {
            center: self.center + offset,
            ..self.clone()
        }
    }

    /// Axis-aligned bounding box of the full sphere (`center ± radius` on every
    /// axis). Orientation-independent and a sound superset of any spherical
    /// patch — the boolean broad-phase uses it because a face's boundary-only
    /// bbox misses the surface bulge between its boundary edges (a hemisphere's
    /// only boundary is its equator).
    #[must_use]
    pub fn aabb(&self) -> Aabb3 {
        let r = self.radius;
        Aabb3 {
            min: Point3::new(
                self.center.x() - r,
                self.center.y() - r,
                self.center.z() - r,
            ),
            max: Point3::new(
                self.center.x() + r,
                self.center.y() + r,
                self.center.z() + r,
            ),
        }
    }

    /// Axis-aligned bounding box of the hemisphere on the `pole`-axis side —
    /// the half-ball `{center + radius·d : d·pole ≥ 0}`. A tight, sound superset
    /// of any spherical patch lying on that side; the boolean broad-phase uses
    /// it so that one hemisphere face's box does not admit the other's sections
    /// (the full-sphere `aabb` would). Falls back to the full sphere when `pole`
    /// is degenerate (side ambiguous).
    #[must_use]
    pub fn aabb_region(&self, pole: Vec3) -> Aabb3 {
        let Ok(n) = pole.normalize() else {
            return self.aabb();
        };
        let c = self.center;
        let r = self.radius;
        // For world axis ê, the extreme of d·ê over {d·n ≥ 0, |d| = 1} is 1 when
        // ê·n ≥ 0 (the axis itself is in the half-space), else the equator-plane
        // projection √(1 − (ê·n)²); the minimum is the mirror image.
        let span = |en: f64| -> (f64, f64) {
            let s = (1.0 - en * en).max(0.0).sqrt();
            let hi = if en >= 0.0 { 1.0 } else { s };
            let lo = if en <= 0.0 { -1.0 } else { -s };
            (lo, hi)
        };
        let (lx, hx) = span(n.x());
        let (ly, hy) = span(n.y());
        let (lz, hz) = span(n.z());
        Aabb3 {
            min: Point3::new(c.x() + r * lx, c.y() + r * ly, c.z() + r * lz),
            max: Point3::new(c.x() + r * hx, c.y() + r * hy, c.z() + r * hz),
        }
    }

    /// Project a 3D point onto the sphere, returning (u, v) parameters.
    ///
    /// `u` is the longitudinal angle [0, 2π), `v` is the latitude [-π/2, π/2].
    #[must_use]
    pub fn project_point(&self, point: Point3) -> (f64, f64) {
        let to_pt = Vec3::new(
            point.x() - self.center.x(),
            point.y() - self.center.y(),
            point.z() - self.center.z(),
        );
        let r = to_pt.length();
        if r < 1e-15 {
            return (0.0, 0.0);
        }
        let x = self.x_axis.dot(to_pt);
        let y = self.y_axis.dot(to_pt);
        let z = self.z_axis.dot(to_pt);
        let u = y.atan2(x).rem_euclid(std::f64::consts::TAU);
        let v = (z / r).clamp(-1.0, 1.0).asin();
        (u, v)
    }

    /// Convert to an approximate NURBS surface.
    ///
    /// # Errors
    ///
    /// Returns an error if `NurbsSurface` construction fails.
    pub fn to_nurbs(&self) -> Result<NurbsSurface, MathError> {
        analytic_to_nurbs_sampled(
            |u, v| self.evaluate(u, v),
            (0.0, std::f64::consts::TAU),
            (-std::f64::consts::FRAC_PI_2, std::f64::consts::FRAC_PI_2),
        )
    }
}

/// A toroidal surface.
///
/// Parameterized as `P(u, v) = center + (R + r*cos(v))*(cos(u)*x + sin(u)*y) + r*sin(v)*z`
/// where `R` is the major radius, `r` is the minor radius,
/// `u ∈ [0, 2π)` (around the tube) and `v ∈ [0, 2π)` (around the cross-section).
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct ToroidalSurface {
    center: Point3,
    major_radius: f64,
    minor_radius: f64,
    x_axis: Vec3,
    y_axis: Vec3,
    z_axis: Vec3,
}

impl ToroidalSurface {
    /// Creates a new toroidal surface.
    ///
    /// # Errors
    /// Returns an error if either radius is not positive or `minor_radius > major_radius`.
    pub fn new(center: Point3, major_radius: f64, minor_radius: f64) -> Result<Self, MathError> {
        if major_radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: major_radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        if minor_radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: minor_radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        Ok(Self {
            center,
            major_radius,
            minor_radius,
            x_axis: Vec3::new(1.0, 0.0, 0.0),
            y_axis: Vec3::new(0.0, 1.0, 0.0),
            z_axis: Vec3::new(0.0, 0.0, 1.0),
        })
    }

    /// Creates a toroidal surface with a specified axis direction.
    ///
    /// The axis is the central symmetry axis of the torus. The local
    /// coordinate frame is derived from it.
    ///
    /// # Errors
    /// Returns an error if either radius is not positive or axis is zero.
    pub fn with_axis(
        center: Point3,
        major_radius: f64,
        minor_radius: f64,
        z_axis: Vec3,
    ) -> Result<Self, MathError> {
        if major_radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: major_radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        if minor_radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: minor_radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        let f = Frame3::from_normal(center, z_axis)?;
        Ok(Self {
            center,
            major_radius,
            minor_radius,
            x_axis: f.x,
            y_axis: f.y,
            z_axis: f.z,
        })
    }

    /// Create a torus with explicit axis and reference direction.
    ///
    /// `ref_dir` defines the x-axis of the local frame (projected
    /// perpendicular to `z_axis`). This preserves the parametric
    /// orientation from STEP `AXIS2_PLACEMENT_3D`.
    ///
    /// # Errors
    ///
    /// Returns [`MathError::ParameterOutOfRange`] if either radius is
    /// non-positive, or [`MathError::ZeroVector`] if `z_axis` is zero.
    ///
    /// # Panics
    ///
    /// Panics if the fallback perpendicular vector cannot be normalized
    /// (should not occur for any valid unit `z_axis`).
    pub fn with_axis_and_ref_dir(
        center: Point3,
        major_radius: f64,
        minor_radius: f64,
        z_axis: Vec3,
        ref_dir: Vec3,
    ) -> Result<Self, MathError> {
        if major_radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: major_radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        if minor_radius <= 0.0 {
            return Err(MathError::ParameterOutOfRange {
                value: minor_radius,
                min: f64::EPSILON,
                max: f64::MAX,
            });
        }
        let f = Frame3::from_normal_and_ref(center, z_axis, ref_dir)?;
        Ok(Self {
            center,
            major_radius,
            minor_radius,
            x_axis: f.x,
            y_axis: f.y,
            z_axis: f.z,
        })
    }

    /// Evaluates the surface at parameters `(u, v)`.
    #[must_use]
    pub fn evaluate(&self, u: f64, v: f64) -> Point3 {
        let (sin_u, cos_u) = u.sin_cos();
        let (sin_v, cos_v) = v.sin_cos();
        let tube_radius = self.minor_radius.mul_add(cos_v, self.major_radius);
        self.center
            + self.x_axis * (tube_radius * cos_u)
            + self.y_axis * (tube_radius * sin_u)
            + self.z_axis * (self.minor_radius * sin_v)
    }

    /// Returns the outward surface normal at parameters `(u, v)`.
    #[must_use]
    pub fn normal(&self, u: f64, v: f64) -> Vec3 {
        let (sin_u, cos_u) = u.sin_cos();
        let (sin_v, cos_v) = v.sin_cos();
        let radial = self.x_axis * cos_u + self.y_axis * sin_u;
        radial * cos_v + self.z_axis * sin_v
    }

    /// Returns the center.
    #[must_use]
    pub const fn center(&self) -> Point3 {
        self.center
    }

    /// Returns a copy of this torus with its center translated by `offset`.
    #[must_use]
    pub fn translated(&self, offset: Vec3) -> Self {
        Self {
            center: self.center + offset,
            ..self.clone()
        }
    }

    /// Axis-aligned bounding box of the full torus. The half-extent along each
    /// world axis sums the ring's projection onto the plane perpendicular to the
    /// torus axis (`(major+minor)·‖(x·ê, y·ê)‖`) and the tube's projection onto
    /// the axis (`minor·|z·ê|`); `x/y/z_axis` are orthonormal. A sound superset
    /// used by the boolean broad-phase — a full torus's boundary is degenerate
    /// seam points, so a boundary-only bbox collapses to a point.
    #[must_use]
    pub fn aabb(&self) -> Aabb3 {
        let rr = self.major_radius + self.minor_radius;
        let r = self.minor_radius;
        let hx = rr * self.x_axis.x().hypot(self.y_axis.x()) + r * self.z_axis.x().abs();
        let hy = rr * self.x_axis.y().hypot(self.y_axis.y()) + r * self.z_axis.y().abs();
        let hz = rr * self.x_axis.z().hypot(self.y_axis.z()) + r * self.z_axis.z().abs();
        Aabb3 {
            min: Point3::new(
                self.center.x() - hx,
                self.center.y() - hy,
                self.center.z() - hz,
            ),
            max: Point3::new(
                self.center.x() + hx,
                self.center.y() + hy,
                self.center.z() + hz,
            ),
        }
    }

    /// Returns the major radius (distance from center to tube center).
    #[must_use]
    pub const fn major_radius(&self) -> f64 {
        self.major_radius
    }

    /// Returns the minor radius (tube cross-section radius).
    #[must_use]
    pub const fn minor_radius(&self) -> f64 {
        self.minor_radius
    }

    /// Returns the local X axis.
    #[must_use]
    pub const fn x_axis(&self) -> Vec3 {
        self.x_axis
    }

    /// Returns the local Y axis.
    #[must_use]
    pub const fn y_axis(&self) -> Vec3 {
        self.y_axis
    }

    /// Returns the torus axis direction (perpendicular to the ring plane).
    #[must_use]
    pub const fn z_axis(&self) -> Vec3 {
        self.z_axis
    }

    /// Project a 3D point onto the torus surface, returning `(u, v)` parameters.
    ///
    /// `u ∈ [0, 2π)` is the angle around the major circle.
    /// `v ∈ [0, 2π)` is the angle around the tube cross-section.
    #[must_use]
    pub fn project_point(&self, point: Point3) -> (f64, f64) {
        let to_pt = Vec3::new(
            point.x() - self.center.x(),
            point.y() - self.center.y(),
            point.z() - self.center.z(),
        );

        let x_comp = self.x_axis.dot(to_pt);
        let y_comp = self.y_axis.dot(to_pt);
        let u = y_comp.atan2(x_comp).rem_euclid(std::f64::consts::TAU);

        let (sin_u, cos_u) = u.sin_cos();
        let tube_center = self.center
            + self.x_axis * (self.major_radius * cos_u)
            + self.y_axis * (self.major_radius * sin_u);

        let to_tube = Vec3::new(
            point.x() - tube_center.x(),
            point.y() - tube_center.y(),
            point.z() - tube_center.z(),
        );

        let radial_dir = self.x_axis * cos_u + self.y_axis * sin_u;
        let r_comp = radial_dir.dot(to_tube);
        let z_comp = self.z_axis.dot(to_tube);

        let v = z_comp.atan2(r_comp).rem_euclid(std::f64::consts::TAU);
        (u, v)
    }

    /// Convert to an approximate NURBS surface.
    ///
    /// # Errors
    ///
    /// Returns an error if `NurbsSurface` construction fails.
    pub fn to_nurbs(&self) -> Result<NurbsSurface, MathError> {
        analytic_to_nurbs_sampled(
            |u, v| self.evaluate(u, v),
            (0.0, std::f64::consts::TAU),
            (0.0, std::f64::consts::TAU),
        )
    }
}

/// A surface of revolution created by revolving a curve around an axis.
///
/// Parameterized as `P(u, v) = origin + (curve(v) ⊗ rotation(u, axis))`
/// where `u ∈ [0, 2π)` is the revolution angle and `v` parameterizes
/// the generatrix curve.
#[derive(Debug, Clone)]
pub struct RevolutionSurface {
    origin: Point3,
    axis: Vec3,
    x_axis: Vec3,
    y_axis: Vec3,
    /// The generatrix (meridian) curve in the `(distance_from_axis, height)` plane.
    generatrix_radii: Vec<f64>,
    generatrix_heights: Vec<f64>,
}

impl RevolutionSurface {
    /// Creates a surface of revolution from a set of meridian profile points.
    ///
    /// Each point `(radius, height)` defines the generatrix in the rotation plane.
    ///
    /// # Errors
    /// Returns an error if the profile is empty or the axis is zero.
    pub fn new(
        origin: Point3,
        axis: Vec3,
        radii: Vec<f64>,
        heights: Vec<f64>,
    ) -> Result<Self, MathError> {
        if radii.is_empty() || heights.is_empty() {
            return Err(MathError::EmptyInput);
        }
        if radii.len() != heights.len() {
            return Err(MathError::InvalidWeights {
                expected: radii.len(),
                got: heights.len(),
            });
        }
        let f = Frame3::from_normal(origin, axis)?;
        Ok(Self {
            origin,
            axis: f.z,
            x_axis: f.x,
            y_axis: f.y,
            generatrix_radii: radii,
            generatrix_heights: heights,
        })
    }

    /// Evaluates at `(u, v)` where `u` is the revolution angle and `v ∈ [0, 1]`
    /// parameterizes the generatrix via linear interpolation.
    #[must_use]
    #[allow(
        clippy::cast_precision_loss,
        clippy::cast_possible_truncation,
        clippy::cast_sign_loss
    )]
    pub fn evaluate(&self, u: f64, v: f64) -> Point3 {
        let num_pts = self.generatrix_radii.len();
        let param = v.clamp(0.0, 1.0) * (num_pts - 1) as f64;
        let idx = (param as usize).min(num_pts - 2);
        let frac = param - idx as f64;

        let r = frac.mul_add(
            self.generatrix_radii[idx + 1] - self.generatrix_radii[idx],
            self.generatrix_radii[idx],
        );
        let height = frac.mul_add(
            self.generatrix_heights[idx + 1] - self.generatrix_heights[idx],
            self.generatrix_heights[idx],
        );

        let (sin_u, cos_u) = u.sin_cos();
        self.origin + self.x_axis * (r * cos_u) + self.y_axis * (r * sin_u) + self.axis * height
    }

    /// Returns the origin.
    #[must_use]
    pub const fn origin(&self) -> Point3 {
        self.origin
    }

    /// Returns the axis.
    #[must_use]
    pub const fn axis(&self) -> Vec3 {
        self.axis
    }
}

// ---------------------------------------------------------------------------
// Analytic → NURBS conversion helper
// ---------------------------------------------------------------------------

/// Sample an analytic surface on a grid and build a degree (1,1) NURBS surface.
///
/// APPROXIMATE: piecewise-bilinear interpolation through a 33×9 grid.
/// Max chord-height error ≈ 0.5% of surface radius (R × (1-cos(π/32))).
/// Used only for intersection seed-finding — the output face retains
/// the original analytic `FaceSurface`, so final geometry is exact.
fn analytic_to_nurbs_sampled(
    surface_fn: impl Fn(f64, f64) -> Point3,
    u_range: (f64, f64),
    v_range: (f64, f64),
) -> Result<NurbsSurface, MathError> {
    // Dense sampling reduces chord-height error. For angular coordinates
    // (u on cylinder/sphere), 32 spans → max error R*(1-cos(π/32)) ≈ 0.005*R.
    // For v (latitude/height), 8 spans keeps error under 0.02*R.
    let nu = 33;
    let nv = 9;

    let mut cps = Vec::with_capacity(nu);
    let mut weights = Vec::with_capacity(nu);

    #[allow(clippy::cast_precision_loss)]
    for iu in 0..nu {
        let u = u_range.0 + (u_range.1 - u_range.0) * (iu as f64 / (nu - 1) as f64);
        let mut row = Vec::with_capacity(nv);
        let mut w_row = Vec::with_capacity(nv);
        for iv in 0..nv {
            let v = v_range.0 + (v_range.1 - v_range.0) * (iv as f64 / (nv - 1) as f64);
            row.push(surface_fn(u, v));
            w_row.push(1.0);
        }
        cps.push(row);
        weights.push(w_row);
    }

    // Uniform clamped knot vectors for degree 1 (bilinear interpolation
    // through the sample grid — control points ARE surface points).
    let knots_u = uniform_clamped_knots(nu, 1);
    let knots_v = uniform_clamped_knots(nv, 1);

    NurbsSurface::new(1, 1, knots_u, knots_v, cps, weights)
}

/// Build a uniform clamped knot vector for `n` control points at the given degree.
///
/// Produces `degree+1` zeros, then evenly spaced interior knots, then `degree+1` ones.
/// For degree-1 NURBS this gives bilinear interpolation through all control points.
#[allow(clippy::cast_precision_loss)]
fn uniform_clamped_knots(n: usize, degree: usize) -> Vec<f64> {
    let mut k = vec![0.0; degree + 1];
    for i in 1..n - degree {
        k.push(i as f64 / (n - degree) as f64);
    }
    k.extend(vec![1.0; degree + 1]);
    k
}

#[cfg(test)]
#[allow(clippy::unwrap_used, clippy::expect_used)]
mod tests;