use std::{
    fmt,
    ops::{Add, AddAssign, Mul, Sub, SubAssign},
    str::FromStr,
};

#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Vec2 {
    x: i32, // increases toward right
    y: i32, // increases toward top
}

impl Vec2 {
    #[must_use]
    pub const fn new(x: i32, y: i32) -> Self {
        Self { x, y }
    }

    #[must_use]
    pub fn map(self, mut f: impl FnMut(i32) -> i32) -> Self {
        Self {
            x: f(self.x),
            y: f(self.y),
        }
    }

    #[must_use]
    pub fn len(self) -> f64 {
        (f64::from(self.x).powi(2) + f64::from(self.y).powi(2)).sqrt()
    }
}

impl fmt::Display for Vec2 {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{:?}", (self.x, self.y))
    }
}

impl Add for Vec2 {
    type Output = Self;

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

impl AddAssign for Vec2 {
    fn add_assign(&mut self, rhs: Self) {
        self.x += rhs.x;
        self.y += rhs.y;
    }
}

impl Sub for Vec2 {
    type Output = Self;

    fn sub(self, rhs: Self) -> Self::Output {
        Self {
            x: self.x - rhs.x,
            y: self.y - rhs.y,
        }
    }
}

impl SubAssign for Vec2 {
    fn sub_assign(&mut self, rhs: Self) {
        self.x -= rhs.x;
        self.y -= rhs.y;
    }
}

impl Mul<i32> for Vec2 {
    type Output = Self;

    fn mul(self, n: i32) -> Self::Output {
        Vec2 {
            x: self.x * n,
            y: self.y * n,
        }
    }
}

impl Mul<Vec2> for i32 {
    type Output = Vec2;

    fn mul(self, Vec2 { x, y }: Vec2) -> Self::Output {
        Vec2 {
            x: x * self,
            y: y * self,
        }
    }
}

impl From<(i32, i32)> for Vec2 {
    fn from((x, y): (i32, i32)) -> Self {
        Self { x, y }
    }
}

impl From<Vec2> for (i32, i32) {
    fn from(v: Vec2) -> Self {
        (v.x, v.y)
    }
}

impl From<Direction> for Vec2 {
    /// Creates a unit vector in the given direction.
    fn from(dir: Direction) -> Self {
        match dir {
            Direction::Up => (0, 1),
            Direction::Down => (0, -1),
            Direction::Left => (-1, 0),
            Direction::Right => (1, 0),
        }
        .into()
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum Direction {
    Up,
    Down,
    Left,
    Right,
}

impl FromStr for Direction {
    type Err = ();

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "U" => Ok(Direction::Up),
            "D" => Ok(Direction::Down),
            "L" => Ok(Direction::Left),
            "R" => Ok(Direction::Right),
            _ => Err(()),
        }
    }
}