laddu-core 0.19.2

use std::fmt::Display;

use approx::{AbsDiffEq, RelativeEq};
use auto_ops::{impl_op_ex, impl_op_ex_commutative};
use nalgebra::Vector4;
use serde::{Deserialize, Serialize};

use super::vec3::Vec3;

/// A four-vector (Lorentz vector) whose last component stores the energy.
///
/// # Examples
/// ```rust
/// use laddu_core::vectors::{Vec3, Vec4};
///
/// let momentum = Vec3::new(1.0, 0.0, 0.0);
/// let four_vector = momentum.with_mass(2.0);
/// assert!((four_vector.m2() - 4.0).abs() < 1e-12);
/// ```
#[derive(Copy, Clone, Debug, PartialEq, Serialize, Deserialize)]
pub struct Vec4 {
    /// The x-component of the vector
    pub x: f64,
    /// The y-component of the vector
    pub y: f64,
    /// The z-component of the vector
    pub z: f64,
    /// The t-component of the vector
    pub t: f64,
}

impl Display for Vec4 {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "[{:6.3}, {:6.3}, {:6.3}; {:6.3}]",
            self.x, self.y, self.z, self.t
        )
    }
}

impl AbsDiffEq for Vec4 {
    type Epsilon = <f64 as approx::AbsDiffEq>::Epsilon;

    fn default_epsilon() -> Self::Epsilon {
        f64::default_epsilon()
    }

    fn abs_diff_eq(&self, other: &Self, epsilon: Self::Epsilon) -> bool {
        f64::abs_diff_eq(&self.x, &other.x, epsilon)
            && f64::abs_diff_eq(&self.y, &other.y, epsilon)
            && f64::abs_diff_eq(&self.z, &other.z, epsilon)
            && f64::abs_diff_eq(&self.t, &other.t, epsilon)
    }
}
impl RelativeEq for Vec4 {
    fn default_max_relative() -> Self::Epsilon {
        f64::default_max_relative()
    }

    fn relative_eq(
        &self,
        other: &Self,
        epsilon: Self::Epsilon,
        max_relative: Self::Epsilon,
    ) -> bool {
        f64::relative_eq(&self.x, &other.x, epsilon, max_relative)
            && f64::relative_eq(&self.y, &other.y, epsilon, max_relative)
            && f64::relative_eq(&self.z, &other.z, epsilon, max_relative)
            && f64::relative_eq(&self.t, &other.t, epsilon, max_relative)
    }
}

impl From<Vec4> for Vector4<f64> {
    fn from(value: Vec4) -> Self {
        Vector4::new(value.x, value.y, value.z, value.t)
    }
}

impl From<Vector4<f64>> for Vec4 {
    fn from(value: Vector4<f64>) -> Self {
        Vec4::new(value.x, value.y, value.z, value.w)
    }
}

impl From<Vec<f64>> for Vec4 {
    fn from(value: Vec<f64>) -> Self {
        Self {
            x: value[0],
            y: value[1],
            z: value[2],
            t: value[3],
        }
    }
}

impl From<Vec4> for Vec<f64> {
    fn from(value: Vec4) -> Self {
        vec![value.x, value.y, value.z, value.t]
    }
}

impl From<[f64; 4]> for Vec4 {
    fn from(value: [f64; 4]) -> Self {
        Self {
            x: value[0],
            y: value[1],
            z: value[2],
            t: value[3],
        }
    }
}

impl From<Vec4> for [f64; 4] {
    fn from(value: Vec4) -> Self {
        [value.x, value.y, value.z, value.t]
    }
}

impl Vec4 {
    /// Create a new 4-vector from its components
    pub fn new(x: f64, y: f64, z: f64, t: f64) -> Self {
        Vec4 { x, y, z, t }
    }

    /// Momentum in the x-direction
    pub fn px(&self) -> f64 {
        self.x
    }

    /// Momentum in the y-direction
    pub fn py(&self) -> f64 {
        self.y
    }

    /// Momentum in the z-direction
    pub fn pz(&self) -> f64 {
        self.z
    }

    /// The energy of the 4-vector
    pub fn e(&self) -> f64 {
        self.t
    }

    /// The 3-momentum
    pub fn momentum(&self) -> Vec3 {
        self.vec3()
    }

    /// The $`\gamma`$ factor $`\frac{1}{\sqrt{1 - \beta^2}}`$.
    pub fn gamma(&self) -> f64 {
        let beta = self.beta();
        let b2 = beta.dot(&beta);
        1.0 / f64::sqrt(1.0 - b2)
    }

    /// The $`\vec{\beta}`$ vector $`\frac{\vec{p}}{E}`$.
    pub fn beta(&self) -> Vec3 {
        self.momentum() / self.e()
    }

    /// The invariant mass corresponding to this 4-momentum
    pub fn m(&self) -> f64 {
        self.mag()
    }

    /// The squared invariant mass corresponding to this 4-momentum
    pub fn m2(&self) -> f64 {
        self.mag2()
    }

    /// Pretty-prints the four-momentum.
    pub fn to_p4_string(&self) -> String {
        format!(
            "[e = {:.5}; p = ({:.5}, {:.5}, {:.5}); m = {:.5}]",
            self.e(),
            self.px(),
            self.py(),
            self.pz(),
            self.m()
        )
    }

    /// The magnitude of the vector (with $`---+`$ signature).
    pub fn mag(&self) -> f64 {
        f64::sqrt(self.mag2())
    }

    /// The squared magnitude of the vector (with $`---+`$ signature).
    pub fn mag2(&self) -> f64 {
        self.t * self.t - (self.x * self.x + self.y * self.y + self.z * self.z)
    }

    /// Gives the vector boosted along a $`\vec{\beta}`$ vector.
    pub fn boost(&self, beta: &Vec3) -> Self {
        let b2 = beta.dot(beta);
        if b2 == 0.0 {
            return *self;
        }
        let gamma = 1.0 / f64::sqrt(1.0 - b2);
        let p3 = self.vec3() + beta * ((gamma - 1.0) * self.vec3().dot(beta) / b2 + gamma * self.t);
        Vec4::new(p3.x, p3.y, p3.z, gamma * (self.t + beta.dot(&self.vec3())))
    }

    /// The 3-vector contained in this 4-vector
    pub fn vec3(&self) -> Vec3 {
        Vec3 {
            x: self.x,
            y: self.y,
            z: self.z,
        }
    }
}

impl_op_ex!(+ |a: &Vec4, b: &Vec4| -> Vec4 { Vec4::new(a.x + b.x, a.y + b.y, a.z + b.z, a.t + b.t) });
impl_op_ex!(-|a: &Vec4, b: &Vec4| -> Vec4 {
    Vec4::new(a.x - b.x, a.y - b.y, a.z - b.z, a.t - b.t)
});
impl_op_ex!(-|a: &Vec4| -> Vec4 { Vec4::new(-a.x, -a.y, -a.z, a.t) });
impl_op_ex_commutative!(+ |a: &Vec4, b: &f64| -> Vec4 { Vec4::new(a.x + b, a.y + b, a.z + b, a.t) });
impl_op_ex_commutative!(-|a: &Vec4, b: &f64| -> Vec4 { Vec4::new(a.x - b, a.y - b, a.z - b, a.t) });
impl_op_ex_commutative!(*|a: &Vec4, b: &f64| -> Vec4 { Vec4::new(a.x * b, a.y * b, a.z * b, a.t) });
impl_op_ex!(/ |a: &Vec4, b: &f64| -> Vec4 { Vec4::new(a.x / b, a.y / b, a.z / b, a.t) });

impl<'a> std::iter::Sum<&'a Vec4> for Vec4 {
    fn sum<I: Iterator<Item = &'a Self>>(iter: I) -> Self {
        iter.fold(Self::new(0.0, 0.0, 0.0, 0.0), |a, b| a + b)
    }
}

impl std::iter::Sum<Vec4> for Vec4 {
    fn sum<I: Iterator<Item = Self>>(iter: I) -> Self {
        iter.fold(Self::new(0.0, 0.0, 0.0, 0.0), |a, b| a + b)
    }
}

#[cfg(test)]
mod tests {
    use approx::{assert_abs_diff_eq, assert_relative_eq};
    use nalgebra::{Vector3, Vector4};

    use super::*;

    #[test]
    fn test_display() {
        let v3 = Vec3::new(1.2341, -2.3452, 3.4563);
        assert_eq!(format!("{}", v3), "[ 1.234, -2.345,  3.456]");
        let v4 = Vec4::new(1.2341, -2.3452, 3.4563, 4.5674);
        assert_eq!(format!("{}", v4), "[ 1.234, -2.345,  3.456;  4.567]");
    }

    #[test]
    fn test_vec_vector_conversion() {
        let v = Vec3::new(1.0, 2.0, 3.0);
        let vector3: Vec<f64> = v.into();
        assert_eq!(vector3[0], 1.0);
        assert_eq!(vector3[1], 2.0);
        assert_eq!(vector3[2], 3.0);

        let v_from_vec: Vec3 = vector3.into();
        assert_eq!(v_from_vec, v);

        let v = Vec4::new(1.0, 2.0, 3.0, 4.0);
        let vector4: Vec<f64> = v.into();
        assert_eq!(vector4[0], 1.0);
        assert_eq!(vector4[1], 2.0);
        assert_eq!(vector4[2], 3.0);
        assert_eq!(vector4[3], 4.0);

        let v_from_vec: Vec4 = vector4.into();
        assert_eq!(v_from_vec, v);
    }

    #[test]
    fn test_vec_array_conversion() {
        let arr = [1.0, 2.0, 3.0];
        let v: Vec3 = arr.into();
        assert_eq!(v, Vec3::new(1.0, 2.0, 3.0));

        let back_to_array: [f64; 3] = v.into();
        assert_eq!(back_to_array, arr);

        let arr = [1.0, 2.0, 3.0, 4.0];
        let v: Vec4 = arr.into();
        assert_eq!(v, Vec4::new(1.0, 2.0, 3.0, 4.0));

        let back_to_array: [f64; 4] = v.into();
        assert_eq!(back_to_array, arr);
    }

    #[test]
    fn test_vec_nalgebra_conversion() {
        let v = Vec3::new(1.0, 2.0, 3.0);
        let vector3: Vector3<f64> = v.into();
        assert_eq!(vector3.x, 1.0);
        assert_eq!(vector3.y, 2.0);
        assert_eq!(vector3.z, 3.0);

        let v_from_vec: Vec3 = vector3.into();
        assert_eq!(v_from_vec, v);

        let v = Vec4::new(1.0, 2.0, 3.0, 4.0);
        let vector4: Vector4<f64> = v.into();
        assert_eq!(vector4.x, 1.0);
        assert_eq!(vector4.y, 2.0);
        assert_eq!(vector4.z, 3.0);
        assert_eq!(vector4.w, 4.0);

        let v_from_vec: Vec4 = vector4.into();
        assert_eq!(v_from_vec, v);
    }

    #[test]
    fn test_vec_sums() {
        let vectors = [Vec3::new(1.0, 2.0, 3.0), Vec3::new(4.0, 5.0, 6.0)];
        let sum: Vec3 = vectors.iter().sum();
        assert_eq!(sum, Vec3::new(5.0, 7.0, 9.0));
        let sum: Vec3 = vectors.into_iter().sum();
        assert_eq!(sum, Vec3::new(5.0, 7.0, 9.0));

        let vectors = [Vec4::new(1.0, 2.0, 3.0, 4.0), Vec4::new(4.0, 5.0, 6.0, 7.0)];
        let sum: Vec4 = vectors.iter().sum();
        assert_eq!(sum, Vec4::new(5.0, 7.0, 9.0, 11.0));
        let sum: Vec4 = vectors.into_iter().sum();
        assert_eq!(sum, Vec4::new(5.0, 7.0, 9.0, 11.0));
    }

    #[test]
    fn test_three_to_four_momentum_conversion() {
        let p3 = Vec3::new(1.0, 2.0, 3.0);
        let target_p4 = Vec4::new(1.0, 2.0, 3.0, 10.0);
        let p4_from_mass = p3.with_mass(target_p4.m());
        assert_eq!(target_p4.e(), p4_from_mass.e());
        assert_eq!(target_p4.px(), p4_from_mass.px());
        assert_eq!(target_p4.py(), p4_from_mass.py());
        assert_eq!(target_p4.pz(), p4_from_mass.pz());
        let p4_from_energy = p3.with_energy(target_p4.e());
        assert_eq!(target_p4.e(), p4_from_energy.e());
        assert_eq!(target_p4.px(), p4_from_energy.px());
        assert_eq!(target_p4.py(), p4_from_energy.py());
        assert_eq!(target_p4.pz(), p4_from_energy.pz());
    }

    #[test]
    fn test_four_momentum_basics() {
        let p = Vec4::new(3.0, 4.0, 5.0, 10.0);
        assert_eq!(p.e(), 10.0);
        assert_eq!(p.px(), 3.0);
        assert_eq!(p.py(), 4.0);
        assert_eq!(p.pz(), 5.0);
        assert_eq!(p.momentum().px(), 3.0);
        assert_eq!(p.momentum().py(), 4.0);
        assert_eq!(p.momentum().pz(), 5.0);
        assert_relative_eq!(p.beta().x, 0.3);
        assert_relative_eq!(p.beta().y, 0.4);
        assert_relative_eq!(p.beta().z, 0.5);
        assert_relative_eq!(p.m2(), 50.0);
        assert_relative_eq!(p.m(), f64::sqrt(50.0));
        assert_eq!(
            format!("{}", p.to_p4_string()),
            "[e = 10.00000; p = (3.00000, 4.00000, 5.00000); m = 7.07107]"
        );
        assert_relative_eq!(Vec3::x().x, 1.0);
        assert_relative_eq!(Vec3::x().y, 0.0);
        assert_relative_eq!(Vec3::x().z, 0.0);
        assert_relative_eq!(Vec3::y().x, 0.0);
        assert_relative_eq!(Vec3::y().y, 1.0);
        assert_relative_eq!(Vec3::y().z, 0.0);
        assert_relative_eq!(Vec3::z().x, 0.0);
        assert_relative_eq!(Vec3::z().y, 0.0);
        assert_relative_eq!(Vec3::z().z, 1.0);
        assert_relative_eq!(Vec3::default().x, 0.0);
        assert_relative_eq!(Vec3::default().y, 0.0);
        assert_relative_eq!(Vec3::default().z, 0.0);
    }

    #[test]
    fn test_three_momentum_basics() {
        let p = Vec4::new(3.0, 4.0, 5.0, 10.0);
        let q = Vec4::new(1.2, -3.4, 7.6, 0.0);
        let p3_view = p.momentum();
        let q3_view = q.momentum();
        assert_eq!(p3_view.px(), 3.0);
        assert_eq!(p3_view.py(), 4.0);
        assert_eq!(p3_view.pz(), 5.0);
        assert_relative_eq!(p3_view.mag2(), 50.0);
        assert_relative_eq!(p3_view.mag(), f64::sqrt(50.0));
        assert_relative_eq!(p3_view.costheta(), 5.0 / f64::sqrt(50.0));
        assert_relative_eq!(p3_view.theta(), f64::acos(5.0 / f64::sqrt(50.0)));
        assert_relative_eq!(p3_view.phi(), f64::atan2(4.0, 3.0));
        assert_relative_eq!(
            p3_view.unit(),
            Vec3::new(
                3.0 / f64::sqrt(50.0),
                4.0 / f64::sqrt(50.0),
                5.0 / f64::sqrt(50.0)
            )
        );
        assert_relative_eq!(p3_view.cross(&q3_view), Vec3::new(47.4, -16.8, -15.0));
    }

    #[test]
    fn test_vec_equality() {
        let p = Vec3::new(1.1, 2.2, 3.3);
        let p2 = Vec3::new(1.1 * 2.0, 2.2 * 2.0, 3.3 * 2.0);
        assert_abs_diff_eq!(p * 2.0, p2);
        assert_relative_eq!(p * 2.0, p2);
        let p = Vec4::new(1.1, 2.2, 3.3, 10.0);
        let p2 = Vec4::new(1.1 * 2.0, 2.2 * 2.0, 3.3 * 2.0, 10.0);
        assert_abs_diff_eq!(p * 2.0, p2);
        assert_relative_eq!(p * 2.0, p2);
    }

    #[test]
    fn test_boost_com() {
        let p = Vec4::new(3.0, 4.0, 5.0, 10.0);
        let zero = p.boost(&-p.beta()).momentum();
        assert_relative_eq!(zero, Vec3::zero());
    }

    #[test]
    fn test_boost() {
        let p0 = Vec4::new(0.0, 0.0, 0.0, 1.0);
        assert_relative_eq!(p0.gamma(), 1.0);
        let p0 = Vec4::new(f64::sqrt(3.0) / 2.0, 0.0, 0.0, 1.0);
        assert_relative_eq!(p0.gamma(), 2.0);
        let p1 = Vec4::new(3.0, 4.0, 5.0, 10.0);
        let p2 = Vec4::new(3.4, 2.3, 1.2, 9.0);
        let p1_boosted = p1.boost(&-p2.beta());
        assert_relative_eq!(p1_boosted.e(), 8.157632144622882);
        assert_relative_eq!(p1_boosted.px(), -0.6489200627053444);
        assert_relative_eq!(p1_boosted.py(), 1.5316128987581492);
        assert_relative_eq!(p1_boosted.pz(), 3.712145860221643);
    }
}