[position, board] Move castle, movement, and sight modules to the board crate

Nothing about this code depends on Position, so push it down to a lower layer.

board/src/castle.rs

@@ -5,3 +5,232 @@ mod rights;
 
 pub use parameters::Parameters;
 pub use rights::Rights;
+
+use crate::Board;
+use chessfriend_core::{Color, Piece, Square, Wing};
+use thiserror::Error;
+
+#[derive(Clone, Copy, Debug, Error, Eq, PartialEq)]
+pub enum CastleEvaluationError {
+    #[error("{color} does not have the right to castle {wing}")]
+    NoRights { color: Color, wing: Wing },
+    #[error("no king")]
+    NoKing,
+    #[error("no rook")]
+    NoRook,
+    #[error("castling path is not clear")]
+    ObstructingPieces,
+    #[error("opposing pieces check castling path")]
+    CheckingPieces,
+}
+
+impl Board {
+    /// Evaluates whether the active color can castle toward the given wing of the board in the
+    /// current position.
+    ///
+    /// ## Errors
+    ///
+    /// Returns an error indicating why the active color cannot castle.
+    pub fn active_color_can_castle(&self, wing: Wing) -> Result<(), CastleEvaluationError> {
+        // TODO: Cache this result. It's expensive!
+        // TODO: Does this actually need to rely on internal state, i.e. active_color?
+
+        let active_color = self.active_color;
+
+        if !self.castling_rights.color_has_right(active_color, wing) {
+            return Err(CastleEvaluationError::NoRights {
+                color: active_color,
+                wing,
+            });
+        }
+
+        let parameters = self.castling_parameters(wing);
+
+        if self.castling_king(parameters.origin.king).is_none() {
+            return Err(CastleEvaluationError::NoKing);
+        }
+
+        if self.castling_rook(parameters.origin.rook).is_none() {
+            return Err(CastleEvaluationError::NoRook);
+        }
+
+        // All squares must be clear.
+        let has_obstructing_pieces = (self.occupancy() & parameters.clear).is_populated();
+        if has_obstructing_pieces {
+            return Err(CastleEvaluationError::ObstructingPieces);
+        }
+
+        // King cannot pass through check.
+        let opposing_sight = self.opposing_sight();
+        let opposing_pieces_can_see_castling_path =
+            (parameters.check & opposing_sight).is_populated();
+        if opposing_pieces_can_see_castling_path {
+            return Err(CastleEvaluationError::CheckingPieces);
+        }
+
+        Ok(())
+    }
+
+    pub(crate) fn castling_king(&self, square: Square) -> Option<Piece> {
+        let active_color = self.active_color;
+        self.get_piece(square)
+            .filter(|piece| piece.color == active_color && piece.is_king())
+    }
+
+    pub(crate) fn castling_rook(&self, square: Square) -> Option<Piece> {
+        let active_color = self.active_color;
+        self.get_piece(square)
+            .filter(|piece| piece.color == active_color && piece.is_rook())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test_board;
+    use chessfriend_core::{piece, Color, Wing};
+
+    #[test]
+    fn king_on_starting_square_can_castle() {
+        let pos = test_board!(
+            White King on E1,
+            White Rook on A1,
+            White Rook on H1
+        );
+
+        let rights = pos.castling_rights;
+        assert!(rights.color_has_right(Color::White, Wing::KingSide));
+        assert!(rights.color_has_right(Color::White, Wing::QueenSide));
+    }
+
+    #[test]
+    fn king_for_castle() {
+        let pos = test_board![
+            White King on E1,
+            White Rook on H1,
+            White Rook on A1,
+        ];
+
+        let kingside_parameters = pos.castling_parameters(Wing::KingSide);
+        assert_eq!(
+            pos.castling_king(kingside_parameters.origin.king),
+            Some(piece!(White King))
+        );
+
+        let queenside_parameters = pos.castling_parameters(Wing::QueenSide);
+        assert_eq!(
+            pos.castling_king(queenside_parameters.origin.king),
+            Some(piece!(White King))
+        );
+    }
+
+    #[test]
+    fn rook_for_castle() {
+        let pos = test_board![
+            White King on E1,
+            White Rook on H1,
+        ];
+
+        let kingside_parameters = pos.castling_parameters(Wing::KingSide);
+        assert_eq!(
+            pos.castling_rook(kingside_parameters.origin.rook),
+            Some(piece!(White Rook))
+        );
+
+        let pos = test_board![
+            White King on E1,
+            White Rook on A1,
+        ];
+
+        let queenside_parameters = pos.castling_parameters(Wing::QueenSide);
+        assert_eq!(
+            pos.castling_rook(queenside_parameters.origin.rook),
+            Some(piece!(White Rook))
+        );
+    }
+
+    #[test]
+    fn white_can_castle() {
+        let pos = test_board![
+            White King on E1,
+            White Rook on H1,
+            White Rook on A1,
+        ];
+
+        assert_eq!(pos.active_color_can_castle(Wing::KingSide), Ok(()));
+        assert_eq!(pos.active_color_can_castle(Wing::QueenSide), Ok(()));
+    }
+
+    #[test]
+    fn white_cannot_castle_missing_king() {
+        let pos = test_board![
+            White King on E2,
+            White Rook on H1,
+            White Rook on A1,
+        ];
+
+        assert_eq!(
+            pos.active_color_can_castle(Wing::KingSide),
+            Err(CastleEvaluationError::NoKing)
+        );
+        assert_eq!(
+            pos.active_color_can_castle(Wing::QueenSide),
+            Err(CastleEvaluationError::NoKing)
+        );
+    }
+
+    #[test]
+    fn white_cannot_castle_missing_rook() {
+        let pos = test_board![
+            White King on E1,
+            White Rook on A1,
+        ];
+
+        assert_eq!(
+            pos.active_color_can_castle(Wing::KingSide),
+            Err(CastleEvaluationError::NoRook)
+        );
+
+        let pos = test_board![
+            White King on E1,
+            White Rook on H1,
+        ];
+
+        assert_eq!(
+            pos.active_color_can_castle(Wing::QueenSide),
+            Err(CastleEvaluationError::NoRook)
+        );
+    }
+
+    #[test]
+    fn white_cannot_castle_obstructing_piece() {
+        let pos = test_board![
+            White King on E1,
+            White Bishop on F1,
+            White Rook on H1,
+            White Rook on A1,
+        ];
+
+        assert_eq!(
+            pos.active_color_can_castle(Wing::KingSide),
+            Err(CastleEvaluationError::ObstructingPieces)
+        );
+        assert_eq!(pos.active_color_can_castle(Wing::QueenSide), Ok(()));
+    }
+
+    #[test]
+    fn white_cannot_castle_checking_pieces() {
+        let pos = test_board![
+            White King on E1,
+            White Rook on H1,
+            White Rook on A1,
+            Black Queen on C6,
+        ];
+
+        assert_eq!(pos.active_color_can_castle(Wing::KingSide), Ok(()));
+        assert_eq!(
+            pos.active_color_can_castle(Wing::QueenSide),
+            Err(CastleEvaluationError::CheckingPieces)
+        );
+    }
+}

board/src/lib.rs

@@ -5,6 +5,8 @@ pub mod display;
 pub mod en_passant;
 pub mod fen;
 pub mod macros;
+pub mod movement;
+pub mod sight;
 
 mod board;
 mod piece_sets;

board/src/movement.rs

@@ -4,17 +4,26 @@
 //! of squares a piece can move to. For all pieces except pawns, the Movement
 //! set is equal to the Sight set.
 
-use crate::{sight::Sight, Position};
+use crate::{sight::Sight, Board};
 use chessfriend_bitboard::BitBoard;
 use chessfriend_core::{Color, Piece, Rank, Shape, Square, Wing};
 
+impl Board {
+    pub fn movement(&self, square: Square) -> BitBoard {
+        if let Some(piece) = self.get_piece(square) {
+            piece.movement(square, self)
+        } else {
+            BitBoard::empty()
+        }
+    }
+}
+
 pub trait Movement {
-    fn movement(&self, square: Square, position: &Position) -> BitBoard;
+    fn movement(&self, square: Square, board: &Board) -> BitBoard;
 }
 
 impl Movement for Piece {
-    fn movement(&self, square: Square, position: &Position) -> BitBoard {
-        let board = &position.board;
+    fn movement(&self, square: Square, board: &Board) -> BitBoard {
         let opposing_occupancy = board.opposing_occupancy(self.color);
 
         match self.shape {
@@ -27,7 +36,7 @@ impl Movement for Piece {
             }
             Shape::King => {
                 let kingside_target_square =
-                    if position.active_color_can_castle(Wing::KingSide).is_ok() {
+                    if board.active_color_can_castle(Wing::KingSide).is_ok() {
                         let parameters = board.castling_parameters(Wing::KingSide);
                         parameters.target.king.into()
                     } else {
@@ -35,7 +44,7 @@ impl Movement for Piece {
                     };
 
                 let queenside_target_square =
-                    if position.active_color_can_castle(Wing::QueenSide).is_ok() {
+                    if board.active_color_can_castle(Wing::QueenSide).is_ok() {
                         let parameters = board.castling_parameters(Wing::QueenSide);
                         parameters.target.king.into()
                     } else {

board/src/sight.rs

@@ -16,9 +16,50 @@
 //! : The set of squares occupied by friendly pieces that block moves to that
 //! square and beyond.
 
-use chessfriend_bitboard::BitBoard;
-use chessfriend_board::Board;
+use crate::Board;
+use chessfriend_bitboard::{BitBoard, IterationDirection};
 use chessfriend_core::{Color, Direction, Piece, Shape, Square};
+use std::ops::BitOr;
+
+impl Board {
+    /// Compute sight of the piece on the given square.
+    pub fn sight(&self, square: Square) -> BitBoard {
+        if let Some(piece) = self.get_piece(square) {
+            piece.sight(square, self)
+        } else {
+            BitBoard::empty()
+        }
+    }
+
+    pub fn active_sight(&self) -> BitBoard {
+        self.friendly_sight(self.active_color)
+    }
+
+    /// A [`BitBoard`] of all squares the given color can see.
+    pub fn friendly_sight(&self, color: Color) -> BitBoard {
+        // TODO: Probably want to implement a caching layer here.
+        self.friendly_occupancy(color)
+            .occupied_squares(&IterationDirection::default())
+            .map(|square| self.sight(square))
+            .fold(BitBoard::empty(), BitOr::bitor)
+    }
+
+    /// A [`BitBoard`] of all squares visible by colors that oppose the given color.
+    pub fn opposing_sight(&self) -> BitBoard {
+        // TODO: Probably want to implement a caching layer here.
+        let active_color = self.active_color;
+        Color::ALL
+            .into_iter()
+            .filter_map(|c| {
+                if c == active_color {
+                    None
+                } else {
+                    Some(self.friendly_sight(c))
+                }
+            })
+            .fold(BitBoard::empty(), BitOr::bitor)
+    }
+}
 
 pub trait Sight {
     fn sight(&self, square: Square, board: &Board) -> BitBoard;
@@ -142,6 +183,7 @@ fn king_sight(info: &SightInfo) -> BitBoard {
 
 #[cfg(test)]
 mod tests {
+    use crate::test_board;
     use chessfriend_bitboard::bitboard;
     use chessfriend_core::piece;
 
@@ -154,16 +196,37 @@ mod tests {
 
                 let pos = $position;
                 let piece = $piece;
-                let sight = piece.sight($square, &pos.board);
+                let sight = piece.sight($square, &pos);
 
                 assert_eq!(sight, $bitboard);
             }
         };
         ($test_name:ident, $piece:expr, $square:expr, $bitboard:expr) => {
-            sight_test! {$test_name, $crate::Position::empty(), $piece, $square, $bitboard}
+            sight_test! {$test_name, $crate::Board::empty(), $piece, $square, $bitboard}
         };
     }
 
+    #[test]
+    fn friendly_sight() {
+        let pos = test_board!(
+            White King on E4,
+        );
+
+        let sight = pos.active_sight();
+        assert_eq!(sight, bitboard![E5 F5 F4 F3 E3 D3 D4 D5]);
+    }
+
+    #[test]
+    fn opposing_sight() {
+        let pos = test_board!(
+            White King on E4,
+            Black Rook on E7,
+        );
+
+        let sight = pos.opposing_sight();
+        assert_eq!(sight, bitboard![A7 B7 C7 D7 F7 G7 H7 E8 E6 E5 E4]);
+    }
+
     // #[test]
     // fn pawns_and_knights_cannot_make_rays() {
     //     assert_eq!(Shape::Pawn.ray_to_square(Square::F7, Square::E8), None);
@@ -171,7 +234,7 @@ mod tests {
     // }
 
     mod pawn {
-        use crate::{sight::Sight, test_position};
+        use crate::{sight::Sight, test_board};
         use chessfriend_bitboard::{bitboard, BitBoard};
         use chessfriend_core::{piece, Square};
 
@@ -179,7 +242,7 @@ mod tests {
 
         sight_test!(
             e4_pawn_one_blocker,
-            test_position![
+            test_board![
                 White Bishop on D5,
                 White Pawn on E4,
             ],
@@ -190,40 +253,40 @@ mod tests {
 
         #[test]
         fn e4_pawn_two_blocker() {
-            let pos = test_position!(
+            let pos = test_board!(
                 White Bishop on D5,
                 White Queen on F5,
                 White Pawn on E4,
             );
 
             let piece = piece!(White Pawn);
-            let sight = piece.sight(Square::E4, &pos.board);
+            let sight = piece.sight(Square::E4, &pos);
 
             assert_eq!(sight, BitBoard::empty());
         }
 
         #[test]
         fn e4_pawn_capturable() {
-            let pos = test_position!(
+            let pos = test_board!(
                 Black Bishop on D5,
                 White Queen on F5,
                 White Pawn on E4,
             );
 
             let piece = piece!(White Pawn);
-            let sight = piece.sight(Square::E4, &pos.board);
+            let sight = piece.sight(Square::E4, &pos);
 
             assert_eq!(sight, bitboard![D5]);
         }
 
         #[test]
         fn e5_en_passant() {
-            let pos = test_position!(White, [
+            let pos = test_board!(White, [
                 White Pawn on E5,
                 Black Pawn on D5,
             ], D6);
             let piece = piece!(White Pawn);
-            let sight = piece.sight(Square::E5, &pos.board);
+            let sight = piece.sight(Square::E5, &pos);
 
             assert_eq!(sight, bitboard!(D6 F6));
         }
@@ -262,7 +325,7 @@ mod tests {
 
     mod rook {
         use super::*;
-        use crate::test_position;
+        use crate::test_board;
 
         sight_test!(
             g3_rook,
@@ -273,7 +336,7 @@ mod tests {
 
         sight_test!(
             e4_rook_with_e1_white_king_e7_black_king,
-            test_position![
+            test_board![
                 White Rook on E4,
                 White King on E2,
                 Black King on E7,

position/src/lib.rs

@@ -1,8 +1,6 @@
 // Eryn Wells <eryn@erynwells.me>
 
-mod movement;
 mod position;
-mod sight;
 
 #[macro_use]
 mod macros;

position/src/position/make_move.rs

@@ -1,7 +1,7 @@
 // Eryn Wells <eryn@erynwells.me>
 
-use crate::{movement::Movement, Position};
-use chessfriend_board::{PlacePieceError, PlacePieceStrategy};
+use crate::Position;
+use chessfriend_board::{movement::Movement, PlacePieceError, PlacePieceStrategy};
 use chessfriend_core::{Color, Piece, Rank, Square, Wing};
 use chessfriend_moves::Move;
 use thiserror::Error;
@@ -276,7 +276,7 @@ impl Position {
         // Pawns can see squares they can't move to. So, calculating valid
         // squares requires a concept that includes Sight, but adds pawn pushes.
         // In ChessFriend, that concept is Movement.
-        let movement = active_piece.movement(origin_square, self);
+        let movement = active_piece.movement(origin_square, &self.board);
         if !movement.contains(target_square) {
             return Err(MakeMoveError::NoMove {
                 piece: active_piece,

position/src/position/position.rs

@@ -1,13 +1,11 @@
 // Eryn Wells <eryn@erynwells.me>
 
-use crate::{movement::Movement, sight::Sight};
-use chessfriend_bitboard::{BitBoard, IterationDirection};
+use chessfriend_bitboard::BitBoard;
 use chessfriend_board::{
-    display::DiagramFormatter, en_passant::EnPassant, fen::ToFenStr, Board, PlacePieceError,
-    PlacePieceStrategy,
+    display::DiagramFormatter, fen::ToFenStr, Board, PlacePieceError, PlacePieceStrategy,
 };
 use chessfriend_core::{Color, Piece, Square};
-use std::{cell::OnceCell, fmt, ops::BitOr};
+use std::{cell::OnceCell, fmt};
 
 #[must_use]
 #[derive(Clone, Debug, Eq)]
@@ -64,51 +62,27 @@ impl Position {
 
 impl Position {
     pub fn sight(&self, square: Square) -> BitBoard {
-        if let Some(piece) = self.get_piece(square) {
-            piece.sight(square, &self.board)
-        } else {
-            BitBoard::empty()
-        }
+        self.board.sight(square)
     }
 
     pub fn movement(&self, square: Square) -> BitBoard {
-        if let Some(piece) = self.get_piece(square) {
-            piece.movement(square, self)
-        } else {
-            BitBoard::empty()
-        }
+        self.board.movement(square)
     }
 }
 
 impl Position {
     pub fn active_sight(&self) -> BitBoard {
-        self.friendly_sight(self.board.active_color)
+        self.board.active_sight()
     }
 
     /// A [`BitBoard`] of all squares the given color can see.
     pub fn friendly_sight(&self, color: Color) -> BitBoard {
-        // TODO: Probably want to implement a caching layer here.
-        self.board
-            .friendly_occupancy(color)
-            .occupied_squares(&IterationDirection::default())
-            .map(|square| self.sight(square))
-            .fold(BitBoard::empty(), BitOr::bitor)
+        self.board.friendly_sight(color)
     }
 
     /// A [`BitBoard`] of all squares visible by colors that oppose the given color.
     pub fn opposing_sight(&self) -> BitBoard {
-        // TODO: Probably want to implement a caching layer here.
-        let active_color = self.board.active_color;
-        Color::ALL
-            .into_iter()
-            .filter_map(|c| {
-                if c == active_color {
-                    None
-                } else {
-                    Some(self.friendly_sight(c))
-                }
-            })
-            .fold(BitBoard::empty(), BitOr::bitor)
+        self.board.opposing_sight()
     }
 }
 
@@ -292,27 +266,6 @@ mod tests {
     //     assert!(!rights.color_has_right(Color::White, Castle::QueenSide));
     // }
 
-    #[test]
-    fn friendly_sight() {
-        let pos = test_position!(
-            White King on E4,
-        );
-
-        let sight = pos.active_sight();
-        assert_eq!(sight, bitboard![E5 F5 F4 F3 E3 D3 D4 D5]);
-    }
-
-    #[test]
-    fn opposing_sight() {
-        let pos = test_position!(
-            White King on E4,
-            Black Rook on E7,
-        );
-
-        let sight = pos.opposing_sight();
-        assert_eq!(sight, bitboard![A7 B7 C7 D7 F7 G7 H7 E8 E6 E5 E4]);
-    }
-
     // #[test]
     // fn danger_squares() {
     //     let pos = test_position!(Black, [