From ef15da41ea90d151f30d82199721de6d08eebf3d Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sat, 16 Jul 2022 14:05:56 +0200
Subject: [PATCH] Add 'File' enum

---
 src/board/file.rs | 89 +++++++++++++++++++++++++++++++++++++++++++++++
 src/board/mod.rs  |  3 ++
 2 files changed, 92 insertions(+)
 create mode 100644 src/board/file.rs

diff --git a/src/board/file.rs b/src/board/file.rs
new file mode 100644
index 0000000..b2e87f1
--- /dev/null
+++ b/src/board/file.rs
@@ -0,0 +1,89 @@
+use super::Bitboard;
+
+/// An enum representing a singular file on a chess board (i.e: the columns).
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum File {
+    A,
+    B,
+    C,
+    D,
+    E,
+    F,
+    G,
+    H,
+}
+
+impl File {
+    const ALL: [File; 8] = [
+        File::A,
+        File::B,
+        File::C,
+        File::D,
+        File::E,
+        File::F,
+        File::G,
+        File::H,
+    ];
+
+    /// Iterate over all files in order.
+    pub fn iter() -> impl Iterator<Item = File> {
+        Self::ALL.iter().cloned()
+    }
+
+    /// Convert from a file index into a [File] 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 file index into a [File] type, no bounds checking.
+    ///
+    /// # Safety
+    ///
+    /// Should only be called with values that can be output by [File::index()].
+    #[inline(always)]
+    pub unsafe fn from_index_unchecked(index: usize) -> Self {
+        std::mem::transmute(index as u8)
+    }
+
+    /// Return the index of a given [File].
+    #[inline(always)]
+    pub fn index(self) -> usize {
+        self as usize
+    }
+
+    /// Turn a [File] into a [Bitboard] of all squares in that file.
+    #[inline(always)]
+    pub fn into_bitboard(self) -> Bitboard {
+        // SAFETY: we know the value is in-bounds
+        unsafe { *Bitboard::FILES.get_unchecked(self.index()) }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn from_index() {
+        assert_eq!(File::from_index(0), File::A);
+        assert_eq!(File::from_index(1), File::B);
+        assert_eq!(File::from_index(7), File::H);
+    }
+
+    #[test]
+    fn index() {
+        assert_eq!(File::A.index(), 0);
+        assert_eq!(File::B.index(), 1);
+        assert_eq!(File::H.index(), 7);
+    }
+
+    #[test]
+    fn into_bitboard() {
+        assert_eq!(File::A.into_bitboard(), Bitboard::FILES[0]);
+        assert_eq!(File::B.into_bitboard(), Bitboard::FILES[1]);
+        assert_eq!(File::H.into_bitboard(), Bitboard::FILES[7]);
+    }
+}
diff --git a/src/board/mod.rs b/src/board/mod.rs
index ef264e1..7923cab 100644
--- a/src/board/mod.rs
+++ b/src/board/mod.rs
@@ -1,6 +1,9 @@
 pub mod bitboard;
 pub use bitboard::*;
 
+pub mod file;
+pub use file::*;
+
 pub mod rank;
 pub use rank::*;