From 0ce1e8f7af54cc4dabe187384463723da3d05c1a Mon Sep 17 00:00:00 2001
From: Bill Thiede <git@xinu.tv>
Date: Fri, 16 Jul 2021 21:06:57 -0700
Subject: [PATCH] intersections: create inters module and initial
 functionality.

---
 rtchallenge/src/intersections.rs | 64 ++++++++++++++++++++++++++++++++
 rtchallenge/src/lib.rs           |  2 +
 rtchallenge/src/spheres.rs       |  5 +--
 3 files changed, 68 insertions(+), 3 deletions(-)
 create mode 100644 rtchallenge/src/intersections.rs

diff --git a/rtchallenge/src/intersections.rs b/rtchallenge/src/intersections.rs
new file mode 100644
index 0000000..9e8bba6
--- /dev/null
+++ b/rtchallenge/src/intersections.rs
@@ -0,0 +1,64 @@
+use std::ops::Index;
+
+use crate::spheres::Sphere;
+
+pub struct Intersection<'i> {
+    pub t: f32,
+    pub object: &'i Sphere,
+}
+
+impl<'i> Intersection<'i> {
+    /// Create new `Intersection` at the given `t` that hits the given `object`.
+    ///
+    /// # Examples
+    /// ```
+    /// use rtchallenge::{intersections::Intersection, spheres::Sphere};
+    ///
+    /// // An intersection ecapsulates t and object.
+    /// let s = Sphere::default();
+    /// let i = Intersection::new(3.5, &s);
+    /// assert_eq!(i.t, 3.5);
+    /// assert_eq!(i.object, &s);
+    /// ```
+    pub fn new(t: f32, object: &Sphere) -> Intersection {
+        Intersection { t, object }
+    }
+}
+
+/// Aggregates `Intersection`s.
+///
+/// # Examples
+/// ```
+/// use rtchallenge::{
+///     intersections::{Intersection, Intersections},
+///     spheres::Sphere,
+/// };
+///
+/// let s = Sphere::default();
+/// let i1 = Intersection::new(1., &s);
+/// let i2 = Intersection::new(2., &s);
+/// let xs = Intersections::new(vec![i1, i2]);
+/// assert_eq!(xs.len(), 2);
+/// assert_eq!(xs[0].t, 1.);
+/// assert_eq!(xs[1].t, 2.);
+/// ```
+pub struct Intersections<'i>(Vec<Intersection<'i>>);
+
+impl<'i> Intersections<'i> {
+    pub fn new(xs: Vec<Intersection<'i>>) -> Intersections {
+        Intersections(xs)
+    }
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+    pub fn hit(&self) -> Option<&Intersection> {
+        todo!("Intersections::hit")
+    }
+}
+
+impl<'i> Index<usize> for Intersections<'i> {
+    type Output = Intersection<'i>;
+    fn index(&self, idx: usize) -> &Self::Output {
+        &self.0[idx]
+    }
+}
diff --git a/rtchallenge/src/lib.rs b/rtchallenge/src/lib.rs
index b443f53..5f57a92 100644
--- a/rtchallenge/src/lib.rs
+++ b/rtchallenge/src/lib.rs
@@ -1,6 +1,8 @@
 pub mod canvas;
+pub mod intersections;
 pub mod matrices;
 pub mod rays;
+pub mod spheres;
 pub mod tuples;
 
 /// Value considered close enough for PartialEq implementations.
diff --git a/rtchallenge/src/spheres.rs b/rtchallenge/src/spheres.rs
index 6ed4b58..7568ebd 100644
--- a/rtchallenge/src/spheres.rs
+++ b/rtchallenge/src/spheres.rs
@@ -3,9 +3,9 @@ use crate::{
     tuples::{dot, Tuple},
 };
 
-#[derive(Default)]
+#[derive(Default, Debug, PartialEq)]
+/// Sphere represents the unit-sphere (radius of unit 1.) at the origin 0., 0., 0.
 pub struct Sphere {}
-pub struct Intersection {}
 
 /// Intersect a ray with a sphere.
 ///
@@ -41,7 +41,6 @@ pub struct Intersection {}
 /// let xs = intersect(&s, &r);
 /// assert_eq!(xs, vec![-6., -4.]);
 /// ```
-
 pub fn intersect(_sphere: &Sphere, ray: &Ray) -> Vec<f32> {
     let sphere_to_ray = ray.origin - Tuple::point(0., 0., 0.);
     let a = dot(ray.direction, ray.direction);