//! This library contains useful helper functions that may be useful in several problems.

use glam::IVec2;
use std::{
    fmt::{Debug, Display},
    ops::{Div, Mul, Rem},
    str::FromStr,
};

/// Parse a whitespace separated list of things.
///
/// This works with any type that implements [`FromStr`].
///
/// Panics on parse error to keep things simple.
///
/// ```rust
/// # use aoc::parse_ws_separated;
/// let mut nums = parse_ws_separated("1 2 3");
/// assert_eq!(nums.next(), Some(1));
/// assert_eq!(nums.next(), Some(2));
/// assert_eq!(nums.next(), Some(3));
/// assert_eq!(nums.next(), None);
/// ```
///
/// ```rust
/// # use aoc::parse_ws_separated;
/// # use std::net::Ipv4Addr;
/// let mut ips = parse_ws_separated("127.0.0.1      10.0.0.1");
/// assert_eq!(ips.next(), Some(Ipv4Addr::new(127, 0, 0, 1)));
/// assert_eq!(ips.next(), Some(Ipv4Addr::new(10, 0, 0, 1)));
/// assert_eq!(ips.next(), None);
/// ```
pub fn parse_ws_separated<T>(s: &str) -> impl DoubleEndedIterator<Item = T> + '_
where
    T: FromStr,
    <T as FromStr>::Err: Debug,
{
    s.split_ascii_whitespace().map(|s| s.parse().unwrap())
}

/// Concatenate two things.
///
/// Panics if the concatenation is not be parseable to keep things simple.
///
/// ```rust
/// # use aoc::concat;
/// assert_eq!(concat(123, 456), 123456);
/// ```
pub fn concat<T>(a: T, b: T) -> T
where
    T: Display + FromStr,
    <T as FromStr>::Err: Debug,
{
    format!("{a}{b}").parse().unwrap()
}

/// Return the greatest common divisor.
///
/// <https://en.wikipedia.org/wiki/Euclidean_algorithm>
///
/// ```rust
/// # use aoc::gcd;
/// assert_eq!(gcd(12, 8), 4);
/// # assert_eq!(gcd(105, 252), 21);
/// # assert_eq!(gcd(252, 105), 21);
/// ```
pub fn gcd<T>(mut a: T, mut b: T) -> T
where
    T: PartialEq + Default + Rem<Output = T> + Copy,
{
    let zero = T::default();
    while b != zero {
        (a, b) = (b, a % b);
    }

    a
}

/// Return the least common multiple.
///
/// <https://en.wikipedia.org/wiki/Least_common_multiple>
///
/// ```rust
/// # use aoc::lcm;
/// assert_eq!(lcm(4, 6), 12);
/// # assert_eq!(lcm(6, 4), 12);
/// ```
pub fn lcm<T>(a: T, b: T) -> T
where
    T: PartialEq + Default + Rem<Output = T> + Div<Output = T> + Mul<Output = T> + Copy,
{
    let gcd = gcd(a, b);
    a / gcd * b
}

/// Given a function and a name of a file in the `input` directory,
/// assert that the function applied to the contents of the file returns the expected result.
#[macro_export]
macro_rules! assert_example {
    ($solve:ident, $file:expr, $expected:expr) => {
        assert_eq!(
            $solve(include_str!(concat!("../../input/", $file))),
            $expected,
            "{}, {}",
            stringify!($solve),
            $file,
        )
    };
}

/// 4 directions. Start pointing right and go CCW.
pub const DIRECTIONS4: [IVec2; 4] = [
    IVec2::new(1, 0),
    IVec2::new(0, 1),
    IVec2::new(-1, 0),
    IVec2::new(0, -1),
];

/// 8 directions. Start pointing right and go CCW.
pub const DIRECTIONS8: [IVec2; 8] = [
    IVec2::new(1, 0),
    IVec2::new(1, 1),
    IVec2::new(0, 1),
    IVec2::new(-1, 1),
    IVec2::new(-1, 0),
    IVec2::new(-1, -1),
    IVec2::new(0, -1),
    IVec2::new(1, -1),
];

/// Transposes a Vec of Vecs.
///
/// ```rust
/// # use aoc::transpose;
/// let input = vec![vec![1, 2, 3], vec![4, 5, 6]];
/// let expected = vec![vec![1, 4], vec![2, 5], vec![3, 6]];
/// assert_eq!(transpose(input), expected);
/// ```
///
/// https://stackoverflow.com/a/64499219
pub fn transpose<T>(v: Vec<Vec<T>>) -> Vec<Vec<T>> {
    if v.is_empty() {
        return v;
    }

    let len = v[0].len();
    let mut iters: Vec<_> = v.into_iter().map(|n| n.into_iter()).collect();
    (0..len)
        .map(|_| {
            iters
                .iter_mut()
                .map(|n| n.next().unwrap())
                .collect::<Vec<T>>()
        })
        .collect()
}