use std::ops::{Add, AddAssign};

macro_rules! point {
    ( $x:expr, $y:expr ) => { Point2D { x:$x, y:$y } };
}

#[derive(Debug, Copy, Clone, PartialEq)]
pub struct Point2D<T> {
    pub x: T,
    pub y: T,
}

impl Point2D<f64> {
    pub fn length(self) -> f64 {
        ((self.x * self.x) + (self.y * self.y)).sqrt()
    }
}

impl<T: Add<Output=T>> Add for Point2D<T> {
    type Output = Point2D<T>;

    fn add(self, rhs: Point2D<T>) -> Self::Output {
        Point2D { x: self.x + rhs.x, y: self.y + rhs.y }
    }
}

impl<T: AddAssign> AddAssign for Point2D<T> {
    fn add_assign(&mut self, rhs: Point2D<T>) {
        self.x += rhs.x;
        self.y += rhs.y;
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn immutable_copy_of_point() {
        let a = point!(0, 0);
        let mut b = a; // Copy
        assert_eq!(a, b); // PartialEq
        b.x = 1;
        assert_ne!(a, b); // PartialEq
    }

    #[test]
    fn add_points() {
        let mut a = point!(1, 0);
        assert_eq!(a + point!(2, 2), point!(3, 2)); // Add
        a += point!(2, 2); // AddAssign
        assert_eq!(a, point!(3, 2));
    }
}