chessfriend/board/src/sight.rs

// Eryn Wells <eryn@erynwells.me>

use crate::{
    piece::{Color, PlacedPiece, Shape},
    BitBoard, Position,
};
use chessfriend_core::Direction;

pub(crate) trait Sight {
    fn sight_in_position(&self, position: &Position) -> BitBoard;
}

impl Sight for PlacedPiece {
    fn sight_in_position(&self, position: &Position) -> BitBoard {
        match self.shape() {
            Shape::Pawn => match self.color() {
                Color::White => self.white_pawn_sight_in_position(position),
                Color::Black => self.black_pawn_sight_in_position(position),
            },
            Shape::Knight => self.knight_sight_in_position(position),
            Shape::Bishop => self.bishop_sight_in_position(position),
            Shape::Rook => self.rook_sight_in_position(position),
            Shape::Queen => self.queen_sight_in_position(position),
            Shape::King => self.king_sight_in_position(position),
        }
    }
}

impl PlacedPiece {
    fn white_pawn_sight_in_position(&self, position: &Position) -> BitBoard {
        let pawn: BitBoard = self.square().into();
        let pawn = pawn.shift_north_west_one() | pawn.shift_north_east_one();

        let mut possible_squares = position.empty_squares() | position.opposing_pieces();
        if let Some(en_passant) = position.en_passant_square() {
            let en_passant_bitboard: BitBoard = en_passant.into();
            possible_squares |= en_passant_bitboard;
        }

        pawn & possible_squares
    }

    fn black_pawn_sight_in_position(&self, position: &Position) -> BitBoard {
        let pawn: BitBoard = self.square().into();
        let pawn = pawn.shift_south_west_one() | pawn.shift_south_east_one();

        let mut possible_squares = position.empty_squares() | position.opposing_pieces();
        if let Some(en_passant) = position.en_passant_square() {
            possible_squares |= &en_passant.into();
        }

        pawn & possible_squares
    }

    fn knight_sight_in_position(&self, position: &Position) -> BitBoard {
        BitBoard::knight_moves(self.square()) & !position.friendly_pieces()
    }

    fn bishop_sight_in_position(&self, position: &Position) -> BitBoard {
        let square = self.square();

        let mut sight = BitBoard::empty();

        let blockers = position.occupied_squares();

        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;
                    sight |= attack_ray;
                } else {
                    sight |= 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);

        sight
    }

    fn rook_sight_in_position(&self, position: &Position) -> BitBoard {
        let square = self.square();

        let mut sight = BitBoard::empty();

        let blockers = position.occupied_squares();

        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;
                    sight |= attack_ray;
                } else {
                    sight |= ray;
                }
            };
        }

        update_moves_with_ray!(North, occupied_squares_trailing);
        update_moves_with_ray!(East, occupied_squares_trailing);
        update_moves_with_ray!(South, occupied_squares);
        update_moves_with_ray!(West, occupied_squares);

        sight
    }

    fn queen_sight_in_position(&self, position: &Position) -> BitBoard {
        let square = self.square();

        let mut sight = BitBoard::empty();

        let blockers = position.occupied_squares();

        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;
                    sight |= attack_ray;
                } else {
                    sight |= ray;
                }
            };
        }

        update_moves_with_ray!(NorthWest, occupied_squares_trailing);
        update_moves_with_ray!(North, occupied_squares_trailing);
        update_moves_with_ray!(NorthEast, occupied_squares_trailing);
        update_moves_with_ray!(East, occupied_squares_trailing);
        update_moves_with_ray!(SouthEast, occupied_squares);
        update_moves_with_ray!(South, occupied_squares);
        update_moves_with_ray!(SouthWest, occupied_squares);
        update_moves_with_ray!(West, occupied_squares);

        sight
    }

    fn king_sight_in_position(&self, position: &Position) -> BitBoard {
        BitBoard::king_moves(self.square()) & !position.friendly_pieces()
    }
}

#[cfg(test)]
mod tests {
    macro_rules! sight_test {
        ($test_name:ident, $position:expr, $piece:expr, $bitboard:expr) => {
            #[test]
            fn $test_name() {
                let pos = $position;
                let pp = $piece;
                let sight = pp.sight_in_position(&pos);

                assert_eq!(sight, $bitboard);
            }
        };
        ($test_name:ident, $piece:expr, $bitboard:expr) => {
            sight_test! {$test_name, $crate::Position::empty(), $piece, $bitboard}
        };
    }

    mod pawn {
        use crate::{sight::Sight, BitBoard};
        use chessfriend_core::Square;

        sight_test!(e4_pawn, piece!(White Pawn on E4), bitboard!(D5, F5));

        sight_test!(
            e4_pawn_one_blocker,
            test_position![
                White Bishop on D5,
                White Pawn on E4,
            ],
            piece!(White Pawn on E4),
            bitboard!(F5)
        );

        #[test]
        fn e4_pawn_two_blocker() {
            let pos = test_position!(
                White Bishop on D5,
                White Queen on F5,
                White Pawn on E4,
            );

            let pp = piece!(White Pawn on E4);
            let sight = pp.sight_in_position(&pos);

            assert_eq!(sight, BitBoard::empty());
        }

        #[test]
        fn e4_pawn_capturable() {
            let pos = test_position!(
                Black Bishop on D5,
                White Queen on F5,
                White Pawn on E4,
            );

            let pp = piece!(White Pawn on E4);
            let sight = pp.sight_in_position(&pos);

            assert_eq!(sight, bitboard!(D5));
        }

        #[test]
        fn e5_en_passant() {
            let mut pos = test_position!(
                White Pawn on E5,
                Black Pawn on D5,
            );
            pos.test_set_en_passant_square(Square::D6);
            let pp = piece!(White Pawn on E5);
            let sight = pp.sight_in_position(&pos);

            assert_eq!(sight, bitboard!(D6, F6));
        }
    }

    #[macro_use]
    mod knight {
        use crate::sight::Sight;

        sight_test!(
            f6_knight,
            piece!(Black Knight on F6),
            bitboard!(H7, G8, E8, D7, D5, E4, G4, H5)
        );
    }

    mod bishop {
        use crate::sight::Sight;

        sight_test!(
            c2_bishop,
            piece!(Black Bishop on C2),
            bitboard!(D1, B3, A4, B1, D3, E4, F5, G6, H7)
        );
    }

    mod rook {
        use crate::sight::Sight;

        sight_test!(
            g3_rook,
            piece!(White Rook on G3),
            bitboard!(G1, G2, G4, G5, G6, G7, G8, A3, B3, C3, D3, E3, F3, H3)
        );
    }
}