From 3b5b2f16a3b5b17b259acefc5ecfcc75d40660ea Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Fri, 16 May 2025 07:47:28 -0700
Subject: [PATCH] [board] Add occupancy methods that return BitBoards

---
 board/src/board.rs      | 19 ++++++++++++++++++-
 board/src/piece_sets.rs | 26 +++++++++++++++++++-------
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/board/src/board.rs b/board/src/board.rs
index ed719a5..3922511 100644
--- a/board/src/board.rs
+++ b/board/src/board.rs
@@ -82,7 +82,24 @@ impl Board {
 }
 
 impl Board {
-    #[must_use]
+    pub fn occupancy(&self) -> BitBoard {
+        self.pieces.occpuancy()
+    }
+
+    pub fn vacancy(&self) -> BitBoard {
+        !self.occupancy()
+    }
+
+    pub fn friendly_occupancy(&self, color: Color) -> BitBoard {
+        self.pieces.friendly_occupancy(color)
+    }
+
+    pub fn opposing_occupancy(&self, color: Color) -> BitBoard {
+        self.pieces.opposing_occupancy(color)
+    }
+}
+
+impl Board {
     pub fn display(&self) -> DiagramFormatter<'_> {
         DiagramFormatter::new(self)
     }
diff --git a/board/src/piece_sets.rs b/board/src/piece_sets.rs
index 8096100..ff66b98 100644
--- a/board/src/piece_sets.rs
+++ b/board/src/piece_sets.rs
@@ -4,7 +4,7 @@ mod mailbox;
 
 use self::mailbox::Mailbox;
 use chessfriend_bitboard::{BitBoard, IterationDirection};
-use chessfriend_core::{Color, Piece, PlacedPiece, Shape, Square};
+use chessfriend_core::{Color, Piece, Shape, Square};
 use std::ops::BitOr;
 
 #[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
@@ -55,16 +55,28 @@ impl PieceSet {
         }
     }
 
-    /// A [`BitBoard`] representing all the pieces currently on the board. Other
-    /// engines might refer to this concept as 'occupancy'.
-    pub fn all_pieces(&self) -> BitBoard {
+    /// A [`BitBoard`] representing all the pieces on the board.
+    pub fn occpuancy(&self) -> BitBoard {
         self.color_occupancy
             .iter()
-            .fold(BitBoard::empty(), BitOr::bitor)
+            .fold(BitBoard::default(), BitOr::bitor)
     }
 
-    pub(crate) fn iter(&self) -> impl Iterator<Item = PlacedPiece> {
-        self.mailbox.iter()
+    pub fn friendly_occupancy(&self, color: Color) -> BitBoard {
+        self.color_occupancy[color as usize]
+    }
+
+    pub fn opposing_occupancy(&self, color: Color) -> BitBoard {
+        self.color_occupancy.iter().enumerate().fold(
+            BitBoard::default(),
+            |acc, (index, occupancy)| {
+                if index == color as usize {
+                    acc | occupancy
+                } else {
+                    acc
+                }
+            },
+        )
     }
 
     pub(crate) fn get(&self, square: Square) -> Option<Piece> {