[board] Implement bishop::ClassicalMoveGenerator

Implement a bishop move generator using the "classical" approach.
This approach walks each ray to find blockers and then masks out friendly pieces.
This is not efficient compared to other approaches, but it's much easier to implement.

board/src/moves/bishop.rs

@@ -0,0 +1,167 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use super::{move_generator_declaration, MoveGeneratorInternal, MoveSet};
+use crate::{
+    bitboard::BitBoard,
+    piece::{Color, Piece, PlacedPiece},
+    square::Direction,
+    Move, Position,
+};
+
+move_generator_declaration!(ClassicalMoveGenerator);
+
+impl<'pos> MoveGeneratorInternal for ClassicalMoveGenerator<'pos> {
+    fn piece(color: Color) -> Piece {
+        Piece::bishop(color)
+    }
+
+    fn move_set_for_piece(position: &Position, placed_piece: PlacedPiece) -> MoveSet {
+        let piece = placed_piece.piece();
+        let color = piece.color();
+        let square = placed_piece.square();
+
+        let blockers = position.occupied_squares();
+        let empty_squares = !blockers;
+        let friendly_pieces = position.bitboard_for_color(color);
+        let opposing_pieces = position.bitboard_for_color(color.other());
+
+        let mut all_moves = BitBoard::empty();
+
+        macro_rules! update_moves_with_ray {
+            ($direction:ident, $occupied_squares:tt) => {
+                let ray = BitBoard::ray(square, Direction::$direction);
+                if let Some(first_occupied_square) =
+                    BitBoard::$occupied_squares(&(ray & blockers)).next()
+                {
+                    let remainder = BitBoard::ray(first_occupied_square, Direction::$direction);
+                    let attack_ray = ray & !remainder;
+                    all_moves |= attack_ray;
+                } else {
+                    all_moves |= ray;
+                }
+            };
+        }
+
+        update_moves_with_ray!(NorthEast, occupied_squares_trailing);
+        update_moves_with_ray!(NorthWest, occupied_squares_trailing);
+        update_moves_with_ray!(SouthEast, occupied_squares);
+        update_moves_with_ray!(SouthWest, occupied_squares);
+
+        let quiet_moves_bb = all_moves & (empty_squares | !friendly_pieces);
+        let capture_moves_bb = all_moves & opposing_pieces;
+
+        let map_to_move = |sq| Move::new(piece, square, sq);
+        let quiet_moves = quiet_moves_bb.occupied_squares().map(map_to_move);
+        let capture_moves = capture_moves_bb.occupied_squares().map(map_to_move);
+
+        MoveSet::new(placed_piece)
+            .quiet_moves(quiet_moves_bb, quiet_moves)
+            .capture_moves(capture_moves_bb, capture_moves)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{
+        bitboard::BitBoard,
+        piece::{Color, Piece},
+        position::DiagramFormatter,
+        Position, Square,
+    };
+
+    #[test]
+    fn classical_single_bishop_bitboard() {
+        let mut pos = Position::empty();
+        [(Piece::bishop(Color::White), Square::A1)]
+            .into_iter()
+            .for_each(|(p, sq)| {
+                pos.place_piece(p, sq)
+                    .expect(&format!("Unable to place {:?} on {}", &p, &sq))
+            });
+
+        let generator = ClassicalMoveGenerator::new(&pos, Color::White);
+
+        assert_eq!(
+            generator.bitboard(),
+            BitBoard::new(
+                0b10000000_01000000_00100000_00010000_00001000_00000100_00000010_00000000
+            )
+        );
+    }
+
+    /// Test that a bishop can move up to, but not onto, a friendly piece.
+    #[test]
+    fn classical_single_bishop_with_same_color_blocker_bitboard() {
+        let mut pos = Position::empty();
+        [
+            (Piece::bishop(Color::White), Square::A1),
+            (Piece::knight(Color::White), Square::E5),
+        ]
+        .into_iter()
+        .for_each(|(p, sq)| {
+            pos.place_piece(p, sq)
+                .expect(&format!("Unable to place {} on {}", p, sq))
+        });
+
+        println!("{}", DiagramFormatter::new(&pos));
+
+        let generator = ClassicalMoveGenerator::new(&pos, Color::White);
+
+        assert_eq!(
+            generator.bitboard(),
+            BitBoard::new(
+                0b00000000_00000000_00000000_00000000_00001000_00000100_00000010_00000000
+            )
+        );
+    }
+
+    /// Test that a rook can move up to, and then capture, an enemy piece.
+    #[test]
+    fn classical_single_bishop_with_opposing_color_blocker_bitboard() {
+        let mut pos = Position::empty();
+        [
+            (Piece::bishop(Color::White), Square::A1),
+            (Piece::knight(Color::Black), Square::C3),
+        ]
+        .into_iter()
+        .for_each(|(p, sq)| {
+            pos.place_piece(p, sq)
+                .expect(&format!("Unable to place {} on {}", p, sq))
+        });
+
+        let generator = ClassicalMoveGenerator::new(&pos, Color::White);
+
+        assert_eq!(
+            generator.bitboard(),
+            BitBoard::new(
+                0b00000000_00000000_00000000_00000000_00000000_00000100_00000010_00000000
+            )
+        );
+    }
+
+    #[test]
+    fn classical_single_bishop_in_center() {
+        let mut pos = Position::empty();
+        [(Piece::bishop(Color::White), Square::E4)]
+            .into_iter()
+            .for_each(|(p, sq)| {
+                pos.place_piece(p, sq)
+                    .expect(&format!("Unable to place {} on {}", p, sq))
+            });
+
+        println!("{}", DiagramFormatter::new(&pos));
+
+        let generator = ClassicalMoveGenerator::new(&pos, Color::White);
+        let bitboard = generator.bitboard();
+        let expected = BitBoard::new(
+            0b00000001_10000010_01000100_00101000_00000000_00101000_01000100_10000010,
+        );
+
+        assert_eq!(
+            bitboard, expected,
+            "actual:\n{}\nexpected:\n{}",
+            bitboard, expected
+        );
+    }
+}

board/src/moves/mod.rs

@@ -1,5 +1,6 @@
 // Eryn Wells <eryn@erynwells.me>
 
+mod bishop;
 mod king;
 mod knight;
 mod r#move;

board/src/moves/move_generator.rs

@@ -1,7 +1,8 @@
 // Eryn Wells <eryn@erynwells.me>
 
 use super::{
-    king::KingMoveGenerator, knight::KnightMoveGenerator, pawn::PawnMoveGenerator,
+    bishop::ClassicalMoveGenerator as BishopMoveGenerator, king::KingMoveGenerator,
+    knight::KnightMoveGenerator, pawn::PawnMoveGenerator,
     rook::ClassicalMoveGenerator as RookMoveGenerator, Move,
 };
 use crate::piece::Color;
@@ -10,6 +11,7 @@ use crate::Position;
 pub struct Moves<'pos> {
     pawn_moves: PawnMoveGenerator<'pos>,
     knight_moves: KnightMoveGenerator<'pos>,
+    bishop_moves: BishopMoveGenerator<'pos>,
     rook_moves: RookMoveGenerator<'pos>,
     king_moves: KingMoveGenerator<'pos>,
 }
@@ -19,6 +21,7 @@ impl<'a> Moves<'a> {
         Moves {
             pawn_moves: PawnMoveGenerator::new(position, color),
             knight_moves: KnightMoveGenerator::new(position, color),
+            bishop_moves: BishopMoveGenerator::new(position, color),
             rook_moves: RookMoveGenerator::new(position, color),
             king_moves: KingMoveGenerator::new(position, color),
         }
@@ -28,6 +31,7 @@ impl<'a> Moves<'a> {
         self.pawn_moves
             .iter()
             .chain(self.knight_moves.iter())
+            .chain(self.bishop_moves.iter())
             .chain(self.rook_moves.iter())
             .chain(self.king_moves.iter())
             .cloned()