use parry3d_f64::query::{Ray, RayCast as _};

use crate::Vector;

use super::{Point, Scalar};

/// A triangle
///
/// The dimensionality of the triangle is defined by the const generic `D`
/// parameter.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq, Hash, Ord, PartialOrd)]
#[repr(C)]
pub struct Triangle<const D: usize> {
    points: [Point<D>; 3],
}

impl<const D: usize> Triangle<D> {
    /// Construct a triangle from three points
    ///
    /// Returns an error, if the points don't form a triangle.
    pub fn from_points(
        points: [impl Into<Point<D>>; 3],
    ) -> Result<Self, NotATriangle<D>> {
        let points = points.map(Into::into);

        let area = {
            let [a, b, c] = points.map(Point::to_xyz);
            (b - a).cross(&(c - a)).magnitude()
        };

        // A triangle is not valid if it doesn't span any area
        if area != Scalar::from(0.0) {
            Ok(Self { points })
        } else {
            Err(NotATriangle { points })
        }
    }

    /// Access the triangle's points
    pub fn points(&self) -> [Point<D>; 3] {
        self.points
    }

    /// Normalize the triangle
    ///
    /// Returns a new `Triangle` instance with the same points, but the points
    /// ordered such that they are ordered according to their `Ord`/`PartialOrd`
    /// implementation.
    ///
    /// This is useful for comparing triangles, where the order of points is not
    /// important.
    pub fn normalize(mut self) -> Self {
        self.points.sort();
        self
    }
}

impl Triangle<2> {
    /// Returns the direction of the line through the points of the triangle.
    pub fn winding(&self) -> Winding {
        let [pa, pb, pc] = self.points.map(|point| robust::Coord {
            x: point.u,
            y: point.v,
        });
        let orient2d = robust::orient2d(pa, pb, pc);

        if orient2d < 0. {
            return Winding::Cw;
        }
        if orient2d > 0. {
            return Winding::Ccw;
        }

        unreachable!(
            "Points don't form a triangle, but this was verified in the \
            constructor."
        )
    }
}

impl Triangle<3> {
    /// Convert the triangle to a Parry triangle
    pub fn to_parry(self) -> parry3d_f64::shape::Triangle {
        self.points().map(|vertex| vertex.to_na()).into()
    }

    /// Cast a ray against the Triangle
    pub fn cast_local_ray(
        &self,
        origin: Point<3>,
        dir: Vector<3>,
        max_toi: f64,
        solid: bool,
    ) -> Option<Scalar> {
        let ray = Ray {
            origin: origin.to_na(),
            dir: dir.to_na(),
        };

        self.to_parry()
            .cast_local_ray(&ray, max_toi, solid)
            .map(Into::into)
    }

    /// Compute the triangle's normal
    pub fn normal(&self) -> Vector<3> {
        self.to_parry()
            .normal()
            .expect("triangle is valid (validated on construction)")
            .into_inner()
            .into()
    }
}

impl<P, const D: usize> From<[P; 3]> for Triangle<D>
where
    P: Into<Point<D>>,
{
    fn from(points: [P; 3]) -> Self {
        Self::from_points(points).expect("invalid triangle")
    }
}

/// Returned by [`Triangle::from_points`], if the points don't form a triangle
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
pub struct NotATriangle<const D: usize> {
    pub points: [Point<D>; 3],
}

/// Winding direction of a triangle.
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
pub enum Winding {
    /// Counter-clockwise
    Ccw,
    /// Clockwise
    Cw,
}

#[cfg(test)]
mod tests {
    use crate::{Point, Vector};

    use super::Triangle;

    #[test]
    fn valid_triangle_2d() {
        let a = Point::from([0.0, 0.0]);
        let b = Point::from([1.0, 1.0]);
        let c = Point::from([1.0, 2.0]);
        let _triangle = Triangle::from([a, b, c]);
    }

    #[test]
    fn valid_triangle_3d() {
        let a = Point::from([0.0, 0.0, 0.0]);
        let b = Point::from([1.0, 1.0, 0.0]);
        let c = Point::from([1.0, 2.0, 0.0]);
        let _triangle = Triangle::from([a, b, c]);
    }

    #[test]
    #[should_panic]
    fn invalid_triangle_2d() {
        let a = Point::from([0.0, 0.0]);
        let b = Point::from([1.0, 1.0]);
        let c = Point::from([2.0, 2.0]);
        let _triangle = Triangle::from([a, b, c]);
    }

    #[test]
    #[should_panic]
    fn invalid_triangle_3d() {
        let a = Point::from([0.0, 0.0, 0.0]);
        let b = Point::from([1.0, 1.0, 1.0]);
        let c = Point::from([2.0, 2.0, 2.0]);
        let _triangle = Triangle::from([a, b, c]);
    }

    #[test]
    fn normal() {
        let triangle =
            Triangle::from([[0.0, 0.0, 0.0], [2.0, 1.0, 0.0], [2.0, 0.0, 0.0]]);
        assert_eq!(triangle.normal(), Vector::from([0.0, 0.0, -1.0]));
    }
}