From 4eff49f36795e1e2601f69ad73c915e968747ace Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sat, 16 Jul 2022 14:05:49 +0200
Subject: [PATCH] Add 'Rank' enum

---
 src/board/mod.rs  |  3 ++
 src/board/rank.rs | 85 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 88 insertions(+)
 create mode 100644 src/board/rank.rs

diff --git a/src/board/mod.rs b/src/board/mod.rs
index 06a7d91..ef264e1 100644
--- a/src/board/mod.rs
+++ b/src/board/mod.rs
@@ -1,5 +1,8 @@
 pub mod bitboard;
 pub use bitboard::*;
 
+pub mod rank;
+pub use rank::*;
+
 pub mod square;
 pub use square::*;
diff --git a/src/board/rank.rs b/src/board/rank.rs
new file mode 100644
index 0000000..fab3cdd
--- /dev/null
+++ b/src/board/rank.rs
@@ -0,0 +1,85 @@
+use super::Bitboard;
+
+/// An enum representing a singular rank on a chess board (i.e: the rows).
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum Rank {
+    First,
+    Second,
+    Third,
+    Fourth,
+    Fifth,
+    Sixth,
+    Seventh,
+    Eighth,
+}
+
+impl Rank {
+    const ALL: [Rank; 8] = [
+        Rank::First,
+        Rank::Second,
+        Rank::Third,
+        Rank::Fourth,
+        Rank::Fifth,
+        Rank::Sixth,
+        Rank::Seventh,
+        Rank::Eighth,
+    ];
+
+    /// Iterate over all ranks in order.
+    pub fn iter() -> impl Iterator<Item = Rank> {
+        Self::ALL.iter().cloned()
+    }
+
+    /// Convert from a rank index into a [Rank] type.
+    #[inline(always)]
+    pub fn from_index(index: usize) -> Self {
+        assert!(index < 8);
+        // SAFETY: we know the value is in-bounds
+        unsafe { Self::from_index_unchecked(index) }
+    }
+
+    /// Convert from a rank index into a [Rank] type, no bounds checking.
+    #[inline(always)]
+    pub unsafe fn from_index_unchecked(index: usize) -> Self {
+        std::mem::transmute(index as u8)
+    }
+
+    /// Return the index of a given [Rank].
+    #[inline(always)]
+    pub fn index(self) -> usize {
+        self as usize
+    }
+
+    /// Turn a [Rank] into a [Bitboard] of all squares in that rank.
+    #[inline(always)]
+    pub fn into_bitboard(self) -> Bitboard {
+        // SAFETY: we know the value is in-bounds
+        unsafe { *Bitboard::RANKS.get_unchecked(self.index()) }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn from_index() {
+        assert_eq!(Rank::from_index(0), Rank::First);
+        assert_eq!(Rank::from_index(1), Rank::Second);
+        assert_eq!(Rank::from_index(7), Rank::Eighth);
+    }
+
+    #[test]
+    fn index() {
+        assert_eq!(Rank::First.index(), 0);
+        assert_eq!(Rank::Second.index(), 1);
+        assert_eq!(Rank::Eighth.index(), 7);
+    }
+
+    #[test]
+    fn into_bitboard() {
+        assert_eq!(Rank::First.into_bitboard(), Bitboard::RANKS[0]);
+        assert_eq!(Rank::Second.into_bitboard(), Bitboard::RANKS[1]);
+        assert_eq!(Rank::Eighth.into_bitboard(), Bitboard::RANKS[7]);
+    }
+}