From 3c0ce13781240f52180c9846ed19c486499d4578 Mon Sep 17 00:00:00 2001
From: Freya Murphy <freya@freyacat.org>
Date: Tue, 7 Oct 2025 13:27:13 -0400
Subject: add some functionality to Pos

---
 dungeon/src/map.rs |  5 +++-
 dungeon/src/pos.rs | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 76 insertions(+), 5 deletions(-)

(limited to 'dungeon')

diff --git a/dungeon/src/map.rs b/dungeon/src/map.rs
index cb602e8..bb83ba9 100644
--- a/dungeon/src/map.rs
+++ b/dungeon/src/map.rs
@@ -6,8 +6,11 @@ use crate::pos::{Direction, Pos};
 /// `MAP_SIZE` is the size of the size of the dungeon grid.
 pub const MAP_SIZE: u16 = 100;
 
+/// `MAP_SIZE` as a usize
+pub const MAP_SIZE_USIZE: usize = MAP_SIZE as usize;
+
 /// The number of tiles in the dungeon grid
-pub const TILE_COUNT: usize = MAP_SIZE as usize * MAP_SIZE as usize;
+pub const TILE_COUNT: usize = MAP_SIZE_USIZE * MAP_SIZE_USIZE;
 
 /// The `EntityKind` represents what kind of entity this is.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
diff --git a/dungeon/src/pos.rs b/dungeon/src/pos.rs
index e953ea4..1d4526b 100644
--- a/dungeon/src/pos.rs
+++ b/dungeon/src/pos.rs
@@ -2,7 +2,18 @@
 //! entity or objects position and facing direction inside the
 //! dungeon grid.
 
-use crate::map::MAP_SIZE;
+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)
+		}
+	};
+}
 
 /// The `Direction` type represents a direction an entity
 /// or any position object is facing inside the dungeon map.
@@ -92,11 +103,11 @@ impl Pos {
 	/// # Examples
 	///
 	/// ```
-	/// use dungeon::{Pos, MAP_SIZE};
+	/// use dungeon::{Pos, MAP_SIZE_USIZE};
 	///
 	/// let pos = Pos::new(1,2).unwrap();
 	/// let idx = pos.idx();
-	/// assert_eq!(idx, 1 + 2 * MAP_SIZE as usize);
+	/// assert_eq!(idx, 1 + 2 * MAP_SIZE_USIZE);
 	/// ```
 	#[must_use]
 	pub const fn idx(self) -> usize {
@@ -105,6 +116,37 @@ impl Pos {
 		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.
@@ -140,8 +182,24 @@ impl Pos {
 	}
 
 	/// 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 fn is_border(&self) -> bool {
+	pub const fn is_border(&self) -> bool {
 		self.0 == 0 || self.0 == MAP_SIZE - 1 || self.1 == 0 || self.1 == MAP_SIZE - 1
 	}
 
@@ -151,6 +209,16 @@ impl Pos {
 	}
 }
 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 DEFAULT: Pos = Pos::new_const::<0, 0>();
 		DEFAULT
-- 
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