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    use {SignedNum, Voxel};
    use steps::Steps;
    use std::cmp::max;

    /// An 3-D implementation of bresenham, sourced from [this site].
    ///
    /// It includes both the start and end point and is asymmetrical.
    ///
    /// Example:
    ///
    /// ```
    /// extern crate line_drawing;
    /// use line_drawing::Bresenham3d;
    ///
    /// fn main() {
    ///     for (x, y, z) in Bresenham3d::new((0, 0, 0), (5, 6, 7)) {
    ///         print!("({}, {}, {}), ", x, y, z);
    ///     }
    /// }
    /// ```
    ///
    /// ```text
    /// (0, 0, 0), (1, 1, 1), (1, 2, 2), (2, 3, 3), (3, 3, 4), (4, 4, 5), (4, 5, 6), (5, 6, 7),
    /// ```
    ///
    /// [this site]: http://members.chello.at/~easyfilter/bresenham.html
    pub struct Bresenham3d<T> {
        sign_x: T,
        sign_y: T,
        sign_z: T,
        err_x: T,
        err_y: T,
        err_z: T,
        len_x: T,
        len_y: T,
        len_z: T,
        longest: T,
        count: T,
        voxel: Voxel<T>,
    }

    impl<T: SignedNum> Bresenham3d<T> {
        #[inline]
        pub fn new(start: Voxel<T>, end: Voxel<T>) -> Self {
            let delta_x = end.0 - start.0;
            let delta_y = end.1 - start.1;
            let delta_z = end.2 - start.2;

            let len_x = delta_x.abs();
            let len_y = delta_y.abs();
            let len_z = delta_z.abs();

            let longest = max(len_x, max(len_y, len_z));

            Self {
                len_x,
                len_y,
                len_z,
                longest,
                count: longest,
                err_x: longest / T::cast(2),
                err_y: longest / T::cast(2),
                err_z: longest / T::cast(2),
                sign_x: delta_x.signum(),
                sign_y: delta_y.signum(),
                sign_z: delta_z.signum(),
                voxel: start,
            }
        }

        #[inline]
        pub fn steps(self) -> Steps<Voxel<T>, Self> {
            Steps::new(self)
        }
    }

    impl<T: SignedNum> Iterator for Bresenham3d<T> {
        type Item = Voxel<T>;

        #[inline]
        fn next(&mut self) -> Option<Self::Item> {
            if self.count >= T::zero() {
                self.count -= T::one();
                self.err_x -= self.len_x;
                self.err_y -= self.len_y;
                self.err_z -= self.len_z;

                let voxel = self.voxel;

                if self.err_x < T::zero() {
                    self.err_x += self.longest;
                    self.voxel.0 += self.sign_x;
                }

                if self.err_y < T::zero() {
                    self.err_y += self.longest;
                    self.voxel.1 += self.sign_y;
                }

                if self.err_z < T::zero() {
                    self.err_z += self.longest;
                    self.voxel.2 += self.sign_z;
                }

                Some(voxel)
            } else {
                None
            }
        }
    }

    #[test]
    fn tests() {
        assert_eq!(
            Bresenham3d::new((0, 0, 0), (5, 5, 5)).collect::<Vec<_>>(),
            [
                (0, 0, 0),
                (1, 1, 1),
                (2, 2, 2),
                (3, 3, 3),
                (4, 4, 4),
                (5, 5, 5)
            ]
        );

        assert_eq!(Bresenham3d::new((0, 0, 0), (500, 678, 1000)).count(), 1001);

        assert_eq!(Bresenham3d::new((500, 678, 1000), (0, 0, 0)).count(), 1001);
    }

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