chessfriend/board/src/board.rs

// Eryn Wells <eryn@erynwells.me>

use crate::{display::DiagramFormatter, Castle, EnPassant, Flags, PieceBitBoards, Pieces};
use chessfriend_bitboard::BitBoard;
use chessfriend_core::{Color, Piece, PlacedPiece, Shape, Square};

#[derive(Clone, Debug, Eq)]
pub struct Board {
    player_to_move: Color,
    flags: Flags,
    pieces: PieceBitBoards,
    en_passant: Option<EnPassant>,
    half_move_counter: u16,
    full_move_number: u16,
}

impl Board {
    /// An empty board
    #[must_use]
    pub fn empty() -> Self {
        Board::default()
    }

    /// The starting position
    #[must_use]
    pub fn starting() -> Self {
        const BLACK_PIECES: [BitBoard; Shape::NUM] = [
            BitBoard::new(0b0000_0000_1111_1111 << 48),
            BitBoard::new(0b0100_0010_0000_0000 << 48),
            BitBoard::new(0b0010_0100_0000_0000 << 48),
            BitBoard::new(0b1000_0001_0000_0000 << 48),
            BitBoard::new(0b0000_1000_0000_0000 << 48),
            BitBoard::new(0b0001_0000_0000_0000 << 48),
        ];

        const WHITE_PIECES: [BitBoard; Shape::NUM] = [
            BitBoard::new(0b1111_1111_0000_0000),
            BitBoard::new(0b0000_0000_0100_0010),
            BitBoard::new(0b0000_0000_0010_0100),
            BitBoard::new(0b0000_0000_1000_0001),
            BitBoard::new(0b0000_0000_0000_1000),
            BitBoard::new(0b0000_0000_0001_0000),
        ];

        Self {
            player_to_move: Color::White,
            pieces: PieceBitBoards::new([WHITE_PIECES, BLACK_PIECES]),
            ..Default::default()
        }
    }

    pub(crate) fn new(
        player_to_move: Color,
        flags: Flags,
        pieces: PieceBitBoards,
        en_passant: Option<EnPassant>,
        half_move_counter: u16,
        full_move_number: u16,
    ) -> Self {
        Self {
            player_to_move,
            flags,
            pieces,
            en_passant,
            half_move_counter,
            full_move_number,
        }
    }

    #[must_use]
    pub fn player_to_move(&self) -> Color {
        self.player_to_move
    }

    #[must_use]
    pub fn move_number(&self) -> u16 {
        self.full_move_number
    }

    #[must_use]
    pub fn ply_counter(&self) -> u16 {
        self.half_move_counter
    }

    #[must_use]
    pub(crate) fn flags(&self) -> &Flags {
        &self.flags
    }

    /// Returns `true` if the player has the right to castle on the given side of the board.
    ///
    /// The right to castle on a particular side of the board is retained as long as the player has
    /// not moved their king, or the rook on that side of the board.
    #[must_use]
    pub fn player_has_right_to_castle(&self, color: Color, castle: Castle) -> bool {
        self.flags.player_has_right_to_castle(color, castle)
    }

    /// The rook to use for a castling move.
    #[must_use]
    pub fn rook_for_castle(&self, player: Color, castle: Castle) -> Option<PlacedPiece> {
        let square = castle.parameters(player).rook_origin_square();
        self.piece_on_square(square)
    }

    /// A [`BitBoard`] representing the set of squares containing a piece.
    #[inline]
    #[must_use]
    pub fn occupied_squares(&self) -> &BitBoard {
        self.pieces.all_pieces()
    }

    #[inline]
    #[must_use]
    pub fn friendly_pieces(&self) -> &BitBoard {
        self.pieces.all_pieces_of_color(self.player_to_move)
    }

    #[inline]
    #[must_use]
    pub fn opposing_pieces(&self) -> &BitBoard {
        self.pieces.all_pieces_of_color(self.player_to_move.other())
    }

    #[inline]
    #[must_use]
    pub fn all_pieces(&self) -> (&BitBoard, &BitBoard) {
        (self.friendly_pieces(), self.opposing_pieces())
    }

    /// A [`BitBoard`] representing the set of squares containing a piece. This set is the inverse of
    /// `Board::occupied_squares`.
    #[inline]
    #[must_use]
    pub fn empty_squares(&self) -> BitBoard {
        !self.occupied_squares()
    }

    #[must_use]
    pub fn piece_on_square(&self, sq: Square) -> Option<PlacedPiece> {
        for color in Color::iter() {
            for shape in Shape::iter() {
                let piece = Piece::new(*color, *shape);
                if self.pieces.bitboard_for_piece(&piece).is_set(sq) {
                    return Some(PlacedPiece::new(piece, sq));
                }
            }
        }

        None
    }

    #[must_use]
    pub fn pieces(&self, color: Color) -> Pieces {
        Pieces::new(self, color)
    }

    #[must_use]
    pub fn has_en_passant_square(&self) -> bool {
        self.en_passant.is_some()
    }

    #[must_use]
    pub fn en_passant(&self) -> Option<EnPassant> {
        self.en_passant
    }

    fn king_bitboard(&self, player: Color) -> &BitBoard {
        self.pieces.bitboard_for_piece(&Piece::king(player))
    }

    pub(crate) fn king_square(&self, player: Color) -> Square {
        self.king_bitboard(player)
            .occupied_squares()
            .next()
            .unwrap()
    }

    #[must_use]
    pub fn display(&self) -> DiagramFormatter<'_> {
        DiagramFormatter::new(self)
    }

    #[must_use]
    pub fn bitboard_for_color(&self, color: Color) -> &BitBoard {
        self.pieces.bitboard_for_color(color)
    }

    #[must_use]
    pub fn bitboard_for_piece(&self, piece: Piece) -> &BitBoard {
        self.pieces.bitboard_for_piece(&piece)
    }
}

#[cfg(test)]
impl Board {
    pub(crate) fn test_set_en_passant(&mut self, en_passant: EnPassant) {
        self.en_passant = Some(en_passant);
    }
}

impl Default for Board {
    fn default() -> Self {
        Self {
            player_to_move: Color::White,
            flags: Flags::default(),
            pieces: PieceBitBoards::default(),
            en_passant: None,
            half_move_counter: 0,
            full_move_number: 1,
        }
    }
}

impl PartialEq for Board {
    fn eq(&self, other: &Self) -> bool {
        self.pieces == other.pieces
            && self.player_to_move == other.player_to_move
            && self.flags == other.flags
            && self.en_passant == other.en_passant
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::test_board;
    use chessfriend_core::piece;

    #[test]
    fn piece_on_square() {
        let pos = test_board![
            Black Bishop on F7,
        ];

        let piece = pos.piece_on_square(Square::F7);
        assert_eq!(piece, Some(piece!(Black Bishop on F7)));
    }

    #[test]
    fn piece_in_starting_position() {
        let board = test_board!(starting);

        assert_eq!(
            board.piece_on_square(Square::H1),
            Some(piece!(White Rook on H1))
        );
        assert_eq!(
            board.piece_on_square(Square::A8),
            Some(piece!(Black Rook on A8))
        );
    }

    #[test]
    fn king_not_on_starting_square_cannot_castle() {
        let board = test_board!(White King on E4);
        assert!(!board.player_has_right_to_castle(Color::White, Castle::KingSide));
        assert!(!board.player_has_right_to_castle(Color::White, Castle::QueenSide));
    }

    #[test]
    fn king_on_starting_square_can_castle() {
        let board = test_board!(
            White King on E1,
            White Rook on A1,
            White Rook on H1
        );

        assert!(board.player_has_right_to_castle(Color::White, Castle::KingSide));
        assert!(board.player_has_right_to_castle(Color::White, Castle::QueenSide));
    }

    #[test]
    fn rook_for_castle() {
        let board = test_board![
            White King on E1,
            White Rook on H1,
            White Rook on A1,
        ];

        assert_eq!(
            board.rook_for_castle(Color::White, Castle::KingSide),
            Some(piece!(White Rook on H1))
        );
        assert_eq!(
            board.rook_for_castle(Color::White, Castle::QueenSide),
            Some(piece!(White Rook on A1))
        );
    }
}