From 366f15ca1273eab7d16a7b6dd3fcc377dc439501 Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Sat, 23 Dec 2023 09:31:41 -0700
Subject: [PATCH] [board] Implement placing a piece in a mutable position

---
 board/src/bitboard.rs |  4 +--
 board/src/position.rs | 71 ++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 72 insertions(+), 3 deletions(-)

diff --git a/board/src/bitboard.rs b/board/src/bitboard.rs
index 9b8580d..e5e126c 100644
--- a/board/src/bitboard.rs
+++ b/board/src/bitboard.rs
@@ -19,11 +19,11 @@ impl BitBoard {
         self.0 == 0
     }
 
-    fn has_piece_at(&self, sq: &Square) -> bool {
+    pub fn has_piece_at(&self, sq: &Square) -> bool {
         (self.0 & (1 << sq.index)) > 0
     }
 
-    fn place_piece_at(&mut self, sq: &Square) {
+    pub fn place_piece_at(&mut self, sq: &Square) {
         self.0 |= 1 << sq.index
     }
 
diff --git a/board/src/position.rs b/board/src/position.rs
index 6279c16..c9f33b0 100644
--- a/board/src/position.rs
+++ b/board/src/position.rs
@@ -1,6 +1,8 @@
 // Eryn Wells <eryn@erynwells.me>
 
 use crate::bitboard::BitBoard;
+use crate::piece::{Color, Piece, PiecePlacementError, PieceShape};
+use crate::square::Square;
 use std::fmt;
 
 mod color {
@@ -80,11 +82,78 @@ impl Position {
         }
     }
 
-    fn piece_at_square(&self, sq: &str) {}
+    fn place_piece(&mut self, piece: &Piece, square: &Square) -> Result<(), PiecePlacementError> {
+        let mut bitboard = self.bitboard_for_piece_mut(piece);
+
+        if bitboard.has_piece_at(&square) {
+            return Err(PiecePlacementError::PieceExistsOnSquare);
+        }
+
+        bitboard.place_piece_at(&square);
+
+        Ok(())
+    }
+
+    fn bitboard_for_piece(&self, piece: &Piece) -> &BitBoard {
+        let color_index: usize = match piece.color {
+            Color::White => 0,
+            Color::Black => 1,
+        };
+
+        let piece_index: usize = match piece.piece {
+            PieceShape::Pawn => 0,
+            PieceShape::Knight => 1,
+            PieceShape::Bishop => 2,
+            PieceShape::Rook => 3,
+            PieceShape::Queen => 4,
+            PieceShape::King => 5,
+        };
+
+        &self.pieces_per_type[color_index][piece_index]
+    }
+
+    fn bitboard_for_piece_mut(&mut self, piece: &Piece) -> &mut BitBoard {
+        let color_index: usize = match piece.color {
+            Color::White => 0,
+            Color::Black => 1,
+        };
+
+        let piece_index: usize = match piece.piece {
+            PieceShape::Pawn => 0,
+            PieceShape::Knight => 1,
+            PieceShape::Bishop => 2,
+            PieceShape::Rook => 3,
+            PieceShape::Queen => 4,
+            PieceShape::King => 5,
+        };
+
+        &mut self.pieces_per_type[color_index][piece_index]
+    }
 }
 
 impl fmt::Display for Position {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "abcdefg")
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn place_piece_at() {
+        let mut position = Position::empty();
+
+        let piece = Piece::new(Color::White, PieceShape::Queen);
+        let square = Square::from_algebraic_string("e4").expect("Unable to get e4 square");
+
+        position
+            .place_piece(&piece, &square)
+            .expect("Unable to place white queen on e4");
+
+        position
+            .place_piece(&piece, &square)
+            .expect_err("Placed white queen on e4 a second time?!");
+
+        println!("{:?}", position);
     }
 }