[core] Rewrite Direction as a coordinate_enum!

- Order the values of Direction in a clockwise fashion
- Implement Direction::opposite() to return the opposing direction
- Make some small changes to the macros in this file to improve readability, maybe.

core/src/coordinates.rs

@@ -1,28 +1,7 @@
 // Eryn Wells <eryn@erynwells.me>
 
 use crate::Color;
-use std::fmt;
-use std::str::FromStr;
-
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-#[repr(u8)]
-pub enum Direction {
-    North,
-    NorthWest,
-    West,
-    SouthWest,
-    South,
-    SouthEast,
-    East,
-    NorthEast,
-}
-
-impl Direction {
-    pub fn to_offset(&self) -> i8 {
-        const OFFSETS: [i8; 8] = [8, 7, -1, -9, -8, -7, 1, 9];
-        OFFSETS[*self as usize]
-    }
-}
+use std::{fmt, str::FromStr};
 
 macro_rules! try_from_integer {
     ($type:ident, $int_type:ident) => {
@@ -30,14 +9,14 @@ macro_rules! try_from_integer {
             type Error = ();
 
             fn try_from(value: $int_type) -> Result<Self, Self::Error> {
-                Square::try_from(value as u8)
+                Self::try_from(value as u8)
             }
         }
     };
 }
 
 macro_rules! coordinate_enum {
-    ($name: ident, $($variant:ident),*) => {
+    ($name: ident, [ $($variant:ident),* ]) => {
         #[repr(u8)]
         #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
         pub enum $name {
@@ -69,7 +48,7 @@ macro_rules! coordinate_enum {
 }
 
 macro_rules! range_bound_struct {
-    ($vis:vis, $type:ident, $repr:ty, $max:expr) => {
+    ($vis:vis $type:ident, $repr:ty, $max:expr) => {
         #[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
         $vis struct $type($repr);
 
@@ -113,7 +92,34 @@ macro_rules! range_bound_struct {
     }
 }
 
-range_bound_struct!(pub, File, u8, 8);
+coordinate_enum!(
+    Direction,
+    [North, NorthEast, East, SouthEast, South, SouthWest, West, NorthWest]
+);
+
+impl Direction {
+    pub fn to_offset(&self) -> i8 {
+        const OFFSETS: [i8; 8] = [8, 9, 1, -7, -8, -9, -1, 7];
+        OFFSETS[*self as usize]
+    }
+
+    pub fn opposite(&self) -> Direction {
+        const OPPOSITES: [Direction; 8] = [
+            Direction::South,
+            Direction::SouthEast,
+            Direction::East,
+            Direction::NorthEast,
+            Direction::North,
+            Direction::NorthWest,
+            Direction::West,
+            Direction::SouthWest,
+        ];
+
+        OPPOSITES[*self as usize]
+    }
+}
+
+range_bound_struct!(pub File, u8, 8);
 
 impl File {
     pub const A: File = File(0);
@@ -137,7 +143,7 @@ impl File {
     ];
 }
 
-range_bound_struct!(pub, Rank, u8, 8);
+range_bound_struct!(pub Rank, u8, 8);
 
 #[allow(dead_code)]
 impl Rank {
@@ -182,7 +188,7 @@ impl Rank {
 }
 
 #[rustfmt::skip]
-coordinate_enum!(Square,
+coordinate_enum!(Square, [
     A1, B1, C1, D1, E1, F1, G1, H1,
     A2, B2, C2, D2, E2, F2, G2, H2,
     A3, B3, C3, D3, E3, F3, G3, H3,
@@ -191,7 +197,7 @@ coordinate_enum!(Square,
     A6, B6, C6, D6, E6, F6, G6, H6,
     A7, B7, C7, D7, E7, F7, G7, H7,
     A8, B8, C8, D8, E8, F8, G8, H8
-);
+]);
 
 impl Square {
     pub unsafe fn from_index(x: u8) -> Square {
@@ -357,6 +363,18 @@ impl TryFrom<char> for Rank {
 mod tests {
     use super::*;
 
+    #[test]
+    fn direction_offsets() {
+        assert_eq!(Direction::North.to_offset(), 8);
+        assert_eq!(Direction::NorthEast.to_offset(), 9);
+        assert_eq!(Direction::East.to_offset(), 1);
+        assert_eq!(Direction::SouthEast.to_offset(), -7);
+        assert_eq!(Direction::South.to_offset(), -8);
+        assert_eq!(Direction::SouthWest.to_offset(), -9);
+        assert_eq!(Direction::West.to_offset(), -1);
+        assert_eq!(Direction::NorthWest.to_offset(), 7);
+    }
+
     #[test]
     fn good_algebraic_input() {
         let sq = Square::from_algebraic_str("a4").expect("Failed to parse 'a4' square");