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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);
}