use glam::{IVec2, Vec2};

// Amanatides and Woo's fast Voxel Traversal
pub struct AwDda {
    next: IVec2,
    step_sign: IVec2,
    step_delta: Vec2,
    t_max: Vec2,
}

impl AwDda {
    pub fn new(from: Vec2, to: Vec2) -> Self {
        let first = from.round().as_ivec2();
        // direction we step for each component on each iteration
        let from_to_delta = to - from;
        let step_sign = from_to_delta.signum().as_ivec2();

        let step_delta = 1.0 / from_to_delta.abs();

        let frac = Vec2::new(
            if step_sign.x > 0 {
                (first.x as f32 + 0.5) - from.x
            } else {
                from.x - (first.x as f32 - 0.5)
            },
            if step_sign.y > 0 {
                (first.y as f32 + 0.5) - from.y
            } else {
                from.y - (first.y as f32 - 0.5)
            },
        );

        let t_max = frac * step_delta;

        AwDda {
            next: first,
            step_sign,
            step_delta,
            t_max,
        }
    }
}

impl Iterator for AwDda {
    type Item = IVec2;
    fn next(&mut self) -> Option<Self::Item> {
        if self.t_max.min_element() >= 1.0 {
            return None;
        }

        let cur = self.next;

        if self.t_max.x < self.t_max.y {
            self.next.x += self.step_sign.x;
            self.t_max.x += self.step_delta.x;
        } else {
            self.next.y += self.step_sign.y;
            self.t_max.y += self.step_delta.y;
        }

        Some(cur)
    }
}