//! The `pos` module contains structures for representation an
//! entity or objects position and facing direction inside the
//! dungeon grid.

use crate::{MAP_SIZE_USIZE, map::MAP_SIZE};

macro_rules! downcast {
	($usize:expr, $type:ty) => {
		if $usize > <$type>::MAX as usize {
			None
		} else {
			#[expect(clippy::cast_possible_truncation)]
			Some($usize as $type)
		}
	};
}

#[macro_export]
macro_rules! const_pos {
	($name:ident, $x:expr, $y:expr) => {
		const $name: Pos = Pos::new_unchecked($x, $y);
	};
}

/// The `Direction` type represents a direction an entity
/// or any position object is facing inside the dungeon map.
/// Since the dungeon lives on a grid, there are only four
/// possible directions.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum Direction {
	North,
	South,
	East,
	West,
}

/// The `Pos` type represents a 2D position inside the dungeon grid.
///
/// The max size for the dungeon map is set by the `MAP_SIZE` constant
/// and therefore the x and y positions can be between 0 and `MAP_SIZE - 1`.
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Pos(u16, u16);
impl Pos {
	/// Creates a new position from a given x and y position.
	///
	/// Returns `None` if the position goes out of the map.
	///
	/// # Examples
	///
	/// ```
	/// use dungeon::Pos;
	///
	/// let pos = Pos::new(0,0);
	/// assert!(pos.is_some());
	/// ```
	///
	/// ```
	/// use dungeon::{Pos, MAP_SIZE};
	///
	/// let pos = Pos::new(MAP_SIZE, MAP_SIZE);
	/// assert!(pos.is_none())
	/// ```
	#[must_use]
	pub const fn new(x: u16, y: u16) -> Option<Self> {
		if x >= MAP_SIZE || y >= MAP_SIZE {
			None
		} else {
			Some(Self(x, y))
		}
	}

	/// Creates a new position from a given x and y position.
	///
	/// Bounds checks are asserted at runtime and will panic if out of bounds.
	///
	/// # Examples
	///
	/// ```
	/// use dungeon::Pos;
	///
	/// let pos = Pos::new_unchecked(1, 1);
	/// assert_eq!(pos.xy(), (1,1));
	/// ```
	#[must_use]
	pub const fn new_unchecked(x: u16, y: u16) -> Self {
		assert!(x < MAP_SIZE, "Positions must be smaller then MAP_SIZE");
		assert!(y < MAP_SIZE, "Positions must be smaller then MAP_SIZE");
		Self(x, y)
	}

	/// Returns the x and y positions of `Pos`.
	///
	/// # Examples
	///
	/// ```
	/// use dungeon::Pos;
	///
	/// let pos = Pos::new(5,7).unwrap();
	/// let (x,y) = pos.xy();
	/// assert_eq!(x, 5);
	/// assert_eq!(y, 7);
	/// ```
	#[must_use]
	pub const fn xy(self) -> (u16, u16) {
		(self.0, self.1)
	}

	/// Converts the x and y positions into an index of a continous list.
	///
	/// # Examples
	///
	/// ```
	/// use dungeon::{Pos, MAP_SIZE_USIZE};
	///
	/// let pos = Pos::new(1,2).unwrap();
	/// let idx = pos.idx();
	/// assert_eq!(idx, 1 + 2 * MAP_SIZE_USIZE);
	/// ```
	#[must_use]
	pub const fn idx(self) -> usize {
		let (x, y) = self.xy();
		let idx = x + y * MAP_SIZE;
		idx as usize
	}

	/// Converse an index into a possible x and y position
	///
	/// # Examples
	///
	/// ```
	/// use dungeon::{Pos};
	///
	/// let idx_pos = Pos::from_idx(17);
	/// let pos = Pos::new(17, 0);
	///
	/// assert_eq!(idx_pos, pos);
	/// ```
	///
	/// ```
	/// use dungeon::{Pos};
	///
	/// let idx_pos = Pos::from_idx(170);
	/// let pos = Pos::new(70, 1);
	///
	/// assert_eq!(idx_pos, pos);
	/// ```
	#[must_use]
	pub const fn from_idx(idx: usize) -> Option<Self> {
		let x = downcast!(idx % MAP_SIZE_USIZE, u16);
		let y = downcast!(idx / MAP_SIZE_USIZE, u16);
		match (x, y) {
			(Some(a), Some(b)) => Self::new(a, b),
			_ => None,
		}
	}

	/// Steps `Pos` one space in the `Direction` `dir`.
	///
	/// Returns `None` if the position goes out of the map.
	///
	/// # Examples
	///
	/// ```
	/// use dungeon::{Direction, Pos};
	///
	/// let pos = Pos::new(0, 1).unwrap();
	/// let new_pos = pos.step(Direction::North);
	/// assert_eq!(new_pos, Pos::new(0, 0));
	/// ```
	///
	/// ```
	/// use dungeon::{Direction, Pos};
	///
	/// let pos = Pos::new(0, 1).unwrap();
	/// let new_pos = pos.step(Direction::West);
	/// assert!(new_pos.is_none());
	/// ```
	#[must_use]
	pub const fn step(self, dir: Direction) -> Option<Self> {
		use Direction as D;
		let (x, y) = self.xy();
		match dir {
			D::North if y > 0 => Self::new(x, y - 1),
			D::South => Self::new(x, y + 1),
			D::East => Self::new(x + 1, y),
			D::West if x > 0 => Self::new(x - 1, y),
			_ => None,
		}
	}

	/// Computes the absolute difference between to positions
	///
	/// Both values are gurenteed to be less than MAP_SIZE
	///
	/// # Examples
	///
	/// ```
	/// use dungeon::Pos;
	///
	/// let pos1 = Pos::new(2,7).unwrap();
	/// let pos2 = Pos::new(1,17).unwrap();
	/// let diff = pos1.abs_diff(pos2);
	/// assert_eq!(diff.xy(), (1, 10));
	/// ```
	///
	#[must_use]
	pub const fn abs_diff(self, other: Self) -> Self {
		let x = self.0.abs_diff(other.0);
		let y = self.1.abs_diff(other.1);
		Self(x, y)
	}

	/// Returns of the given position is on the border of the map
	///
	/// ```
	/// use dungeon::{Pos, MAP_SIZE};
	///
	/// let pos1 = Pos::new(0, 17).unwrap();
	/// let pos2 = Pos::new(1, 17).unwrap();
	/// let pos3 = Pos::new(MAP_SIZE - 1, 17).unwrap();
	/// let pos4 = Pos::new(55, MAP_SIZE - 1).unwrap();
	/// let pos5 = Pos::new(55, 0).unwrap();
	///
	/// assert!(pos1.is_border());
	/// assert!(!pos2.is_border());
	/// assert!(pos3.is_border());
	/// assert!(pos4.is_border());
	/// assert!(pos5.is_border());
	/// ```
	#[must_use]
	pub const fn is_border(&self) -> bool {
		self.0 == 0 || self.0 == MAP_SIZE - 1 || self.1 == 0 || self.1 == MAP_SIZE - 1
	}

	/// Returns an iterator over all possible `Pos`
	pub fn values() -> impl Iterator<Item = Self> {
		(0..MAP_SIZE).flat_map(|y| (0..MAP_SIZE).filter_map(move |x| Self::new(x, y)))
	}
}
impl Default for Pos {
	/// Returns a default postion at the origin (0,0)
	///
	/// ```
	/// use dungeon::Pos;
	///
	/// let pos = Pos::default();
	///
	/// assert_eq!(pos.xy(), (0, 0));
	/// ```
	///
	fn default() -> Self {
		const_pos!(DEFAULT, 0, 0);
		DEFAULT
	}
}