chessfriend/board/src/position.rs

// 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 {
    const WHITE: u8 = 0;
    const BLACK: u8 = 1;
}

mod piece {
    const PAWN: u8 = 0;
    const KNIGHT: u8 = 1;
    const BISHOP: u8 = 2;
    const ROOK: u8 = 3;
    const QUEEN: u8 = 4;
    const KING: u8 = 5;
}

#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub struct Position {
    /// Composite bitboards for all the pieces of a particular color.
    pieces_per_color: [BitBoard; 2],

    /// Bitboards representing positions of particular piece types per color.
    pieces_per_type: [[BitBoard; 6]; 2],
}

impl Position {
    fn empty() -> Position {
        Position {
            pieces_per_color: [BitBoard::empty(), BitBoard::empty()],
            pieces_per_type: [
                [
                    BitBoard::empty(),
                    BitBoard::empty(),
                    BitBoard::empty(),
                    BitBoard::empty(),
                    BitBoard::empty(),
                    BitBoard::empty(),
                ],
                [
                    BitBoard::empty(),
                    BitBoard::empty(),
                    BitBoard::empty(),
                    BitBoard::empty(),
                    BitBoard::empty(),
                    BitBoard::empty(),
                ],
            ],
        }
    }

    /// Return a starting position.
    fn starting() -> Position {
        let white_pieces = [
            BitBoard::from_bit_field(0x00FF000000000000),
            BitBoard::from_bit_field(0x4200000000000000),
            BitBoard::from_bit_field(0x2400000000000000),
            BitBoard::from_bit_field(0x8100000000000000),
            BitBoard::from_bit_field(0x1000000000000000),
            BitBoard::from_bit_field(0x8000000000000000),
        ];

        let black_pieces = [
            BitBoard::from_bit_field(0xFF00),
            BitBoard::from_bit_field(0x0042),
            BitBoard::from_bit_field(0x0024),
            BitBoard::from_bit_field(0x0081),
            BitBoard::from_bit_field(0x0010),
            BitBoard::from_bit_field(0x0080),
        ];

        Position {
            pieces_per_color: [
                white_pieces.iter().fold(BitBoard::empty(), |a, b| a | b),
                black_pieces.iter().fold(BitBoard::empty(), |a, b| a | b),
            ],
            pieces_per_type: [white_pieces, black_pieces],
        }
    }

    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);
    }
}