geo-offset 0.4.0

use geo_types::CoordFloat;

type Point<F> = geo_types::Coord<F>;

/// This enumeration contains error cases for edges manipulation.
#[derive(Debug, Copy, Clone, PartialEq)]
pub enum EdgeError {
    /// This error can be produced if normals of an edge of null length are computed.
    VerticesOverlap,
}

#[derive(Debug, Copy, Clone, PartialEq)]
pub struct Edge<F: CoordFloat> {
    pub current: Point<F>,
    pub next: Point<F>,
}

impl<F: CoordFloat> Edge<F> {
    pub fn new(current: &Point<F>, next: &Point<F>) -> Self {
        Self {
            current: *current,
            next: *next,
        }
    }

    pub fn new_with_offset(current: &Point<F>, next: &Point<F>, dx: F, dy: F) -> Self {
        Self {
            current: (current.x + dx, current.y + dy).into(),
            next: (next.x + dx, next.y + dy).into(),
        }
    }

    pub fn inwards_normal(&self) -> Result<Point<F>, EdgeError> {
        let dx = self.next.x - self.current.x;
        let dy = self.next.y - self.current.y;
        let edge_length = (dx * dx + dy * dy).sqrt();
        let x = -dy / edge_length;
        let y = dx / edge_length;

        if x.is_finite() && y.is_finite() {
            Ok((x, y).into())
        } else {
            Err(EdgeError::VerticesOverlap)
        }
    }

    pub fn outwards_normal(&self) -> Result<Point<F>, EdgeError> {
        let inwards = self.inwards_normal()?;
        Ok((-inwards.x, -inwards.y).into())
    }

    pub fn with_offset(&self, dx: F, dy: F) -> Self {
        Self::new_with_offset(&self.current, &self.next, dx, dy)
    }

    pub fn inverse_with_offset(&self, dx: F, dy: F) -> Self {
        Self::new_with_offset(&self.next, &self.current, dx, dy)
    }

    pub fn inverse(&self) -> Self {
        Self::new(&self.next, &self.current)
    }
}