From 12cebf1f2bc9593c6bd57eb4f1ac1d5ee6873c8a Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Tue, 17 Jun 2025 16:24:28 -0700
Subject: [PATCH] WIP

---
 board/src/board.rs | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/board/src/board.rs b/board/src/board.rs
index 666488e..1a9cca7 100644
--- a/board/src/board.rs
+++ b/board/src/board.rs
@@ -326,6 +326,45 @@ impl Board {
     }
 }
 
+impl Board {
+    #[must_use]
+    pub fn is_valid(&self) -> bool {
+        true
+    }
+
+    /// Determines whether `self` is a repetition of the given [`Board`]
+    /// according to the standard chess rules. A position is considered
+    /// equal or a repetition of another position if:
+    ///
+    /// 1. The placement of all pieces of all colors is the same, i.e. same
+    ///    pieces on same squares
+    /// 2. Castling rights are equal
+    /// 3. The target position does not have an en passant capture available
+    ///
+    /// ## See Also
+    ///
+    /// * The [Chess Programming][1] wiki page on repetitions
+    ///
+    /// [1]: https://www.chessprogramming.org/Repetitions
+    ///
+    #[must_use]
+    pub fn is_repetition(&self, other: &Board) -> bool {
+        if other.en_passant_target.is_some() {
+            return false;
+        }
+
+        if self.castling_rights != other.castling_rights {
+            return false;
+        }
+
+        if self.pieces != other.pieces {
+            return false;
+        }
+
+        true
+    }
+}
+
 impl Board {
     pub fn display(&self) -> DiagramFormatter<'_> {
         DiagramFormatter::new(self)