path: root/src/grossmeister/evaluation.rs

use crate::{board::{piece::Piece, color::Color, CastlingSide}, bitboard::{BitboardFns, Bitboard}, square::Square};

use super::Grossmeister;

static A_FILE: Bitboard = 0x0101010101010101;

const PAWN_BONUS: [f32; 64] = [
  //  A      B      C      D      E      F      G      H
     0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,
     0.50,  0.50,  0.50,  0.50,  0.50,  0.50,  0.50,  0.50,
     0.10,  0.10,  0.20,  0.30,  0.30,  0.20,  0.10,  0.10,
     0.05,  0.05,  0.10,  0.25,  0.25,  0.10,  0.05,  0.05,
     0.00,  0.00,  0.00,  0.20,  0.20,  0.00,  0.00,  0.00,
     0.05, -0.05, -0.10,  0.00,  0.00, -0.10, -0.05,  0.05,
     0.05,  0.10,  0.10, -0.20, -0.20,  0.10,  0.10,  0.05,
     0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00
];

const KNIGHT_BONUS: [f32; 64] = [
  //  A      B      C      D      E      F      G      H
    -0.50, -0.40, -0.30, -0.30, -0.30, -0.30, -0.40, -0.50,
    -0.40, -0.20,  0.00,  0.00,  0.00,  0.00, -0.20, -0.40,
    -0.30,  0.00,  0.10,  0.15,  0.15,  0.10,  0.00, -0.30,
    -0.30,  0.05,  0.15,  0.20,  0.20,  0.15,  0.05, -0.30,
    -0.30,  0.00,  0.15,  0.20,  0.20,  0.15,  0.00, -0.30,
    -0.30,  0.05,  0.10,  0.15,  0.15,  0.10,  0.05, -0.30,
    -0.40, -0.20,  0.00,  0.05,  0.05,  0.00, -0.20, -0.40,
    -0.50, -0.40, -0.30, -0.30, -0.30, -0.30, -0.40, -0.50,
];

const BISHOP_BONUS: [f32; 64] = [
  //  A      B      C      D      E      F      G      H
    -0.20, -0.10, -0.10, -0.10, -0.10, -0.10, -0.10, -0.20,
    -0.10,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00, -0.10,
    -0.10,  0.00,  0.05,  0.10,  0.10,  0.05,  0.00, -0.10,
    -0.10,  0.05,  0.05,  0.10,  0.10,  0.05,  0.05, -0.10,
    -0.10,  0.00,  0.10,  0.10,  0.10,  0.10,  0.00, -0.10,
    -0.10,  0.10,  0.10,  0.10,  0.10,  0.10,  0.10, -0.10,
    -0.10,  0.25,  0.00,  0.00,  0.00,  0.00,  0.25, -0.10,
    -0.20, -0.10, -0.10, -0.10, -0.10, -0.10, -0.10, -0.20,
];

const ROOK_BONUS: [f32; 64] = [
  //  A      B      C      D      E      F      G      H
     0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,
     0.05,  0.30,  0.30,  0.30,  0.30,  0.30,  0.30,  0.05,
    -0.05,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00, -0.05,
    -0.05,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00, -0.05,
    -0.05,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00, -0.05,
    -0.05,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00, -0.05,
    -0.05,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00, -0.05,
     0.00,  0.00,  0.00,  0.05,  0.05,  0.00,  0.00,  0.00
];

const QUEEN_BONUS: [f32; 64] = [
  //  A      B      C      D      E      F      G      H
    -0.20, -0.10, -0.10, -0.05, -0.05, -0.10, -0.10, -0.20,
    -0.10,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00, -0.10,
    -0.10,  0.00,  0.05,  0.05,  0.05,  0.05,  0.00, -0.10,
    -0.05,  0.00,  0.05,  0.05,  0.05,  0.05,  0.00, -0.05,
     0.00,  0.00,  0.05,  0.05,  0.05,  0.05,  0.00, -0.05,
    -0.10,  0.05,  0.05,  0.05,  0.05,  0.05,  0.00, -0.10,
    -0.10,  0.00,  0.05,  0.00,  0.00,  0.00,  0.00, -0.10,
    -0.20, -0.10, -0.10, -0.05, -0.05, -0.10, -0.10, -0.20
];

const KING_BONUS: [f32; 64] = [
  //  A      B      C      D      E      F      G      H
    -0.30, -0.40, -0.40, -0.50, -0.50, -0.40, -0.40, -0.30,
    -0.30, -0.40, -0.40, -0.50, -0.50, -0.40, -0.40, -0.30,
    -0.30, -0.40, -0.40, -0.50, -0.50, -0.40, -0.40, -0.30,
    -0.30, -0.40, -0.40, -0.50, -0.50, -0.40, -0.40, -0.30,
    -0.20, -0.30, -0.30, -0.40, -0.40, -0.30, -0.30, -0.20,
    -0.10, -0.20, -0.20, -0.20, -0.20, -0.20, -0.20, -0.10,
     0.20,  0.20,  0.00, -0.10, -0.10,  0.00,  0.20,  0.20,
     0.20,  0.10,  0.30, -0.20,  0.00,  0.10,  0.30,  0.20
];

impl Grossmeister {
    /// Evaluate a position relative to the current player
    pub fn evaluate(&self) -> f32 {
        let color = self.board.color();
        let opponent_color = color.flip();

        let mobility_advantage = self.mobility(color) - self.mobility(opponent_color);

        let opponent_material = self.material(opponent_color);
        let material_advantage = self.material(color) - opponent_material;

        let pawn_structure_penalty = self.pawn_structure_penalty(color) - self.pawn_structure_penalty(opponent_color);

        let king_tropism_penalty = self.king_tropism(color) - self.king_tropism(opponent_color);

        material_advantage
            + 0.15 * mobility_advantage
            - 0.3 * pawn_structure_penalty
            + king_tropism_penalty * (opponent_material / 40.0) * 0.07
    }

    /// Count player pieces' material, giving bonus for pieces standing well
    pub fn material(&self, color: Color) -> f32 {
        let mut material = 0f32;
        for (piece_index, bitboard) in self.board.pieces_by_color(color).iter().enumerate() {
            let piece_type = Piece::from(piece_index);

            let bonus_table = match piece_type {
                Piece::Pawn => PAWN_BONUS,
                Piece::Knight => KNIGHT_BONUS,
                Piece::Bishop => BISHOP_BONUS,
                Piece::Rook => ROOK_BONUS,
                Piece::King => KING_BONUS,
                Piece::Queen => QUEEN_BONUS,
                _ => panic!("Unreachable")
            };

            material += bitboard.serialize().iter().fold(0., |acc, square| {
                acc + piece_type.static_eval() + bonus_table[
                    match color {
                        Color::White => square.mirror() as usize,
                        Color::Black => *square as usize,
                    }
                ]
            });
        }
        material
    }

    /// Returns sum of the doubled, blocked and isolated pawns
    /// The greater result is, the worse is the pawn structure
    pub fn pawn_structure_penalty(&self, color: Color) -> f32 {
        let mut result = 0.0;

        let pawns = match color {
            Color::White => self.board.piece_sets[Piece::Pawn as usize],
            Color::Black => self.board.piece_sets[Piece::PawnBlack as usize],
        };

        for file in 0..8 {
            let file_mask = A_FILE << file;
            let pawns_on_file = (pawns & file_mask).pop_count() as f32;

            // Doubled pawns (-1 because one pawn on a file is ok)
            result += (pawns_on_file - 1.).max(0.0);

            // Isolated pawns (no pawns on neighbor files)
            if [
                A_FILE << (file - 1).max(0), // File to the left (if any)
                A_FILE << (file + 1).min(7), // File to the right (if any)
            ].iter().all(|file| file & pawns == 0) {
                result += pawns_on_file;
            }
        }

        // Blocked pawns
        let blocked_mask = match color {
            Color::White => self.board.occupancy >> 8,
            Color::Black => self.board.occupancy << 8,
        };
        result += (pawns & blocked_mask).pop_count() as f32;

        result
    }

    /// Returns the weighted sum of distances from attacking pieces to a king
    /// The higher this value, the safer is the king
    pub fn king_tropism(&self, color: Color) -> f32 {
        let mut result = 0.0;

        let king_square = match color {
            Color::White => self.board.piece_sets[Piece::King as usize],
            Color::Black => self.board.piece_sets[Piece::KingBlack as usize],
        }.bitscan();

        for (piece_type, bitboard) in self.board.pieces_by_color(color.flip()).iter().enumerate() {
            if piece_type != Piece::King as usize && piece_type != Piece::Pawn as usize {
                for square in bitboard.serialize() {
                    let distance =
                        (king_square.rank() as f32 - square.rank() as f32).abs() +
                        (king_square.file() as f32 - square.file() as f32).abs();

                    result += distance / Piece::from(piece_type).static_eval();
                }
            }
        }
        result
    }

    /// Count pseudo-legal moves without actually generating them
    /// Also exclude all moves that put a piece under attack of a pawn - so called safe mobility
    pub fn mobility(&self, color: Color) -> f32 {
        let mut mobility = 0.;
        let opponent_occupancy = self.board.color_occupancy(color.flip());
        let player_pieces = self.board.pieces_by_color(color);

        let opponent_pawns = match color {
            Color::Black => self.board.piece_sets[Piece::Pawn as usize],
            Color::White => self.board.piece_sets[Piece::PawnBlack as usize],
        };

        let pawn_attacked_squares = opponent_pawns.serialize().iter().fold(0u64, |acc, square| {
            acc | self.attacks.pawn[color.flip() as usize][*square as usize]
        });

        // Exclude squares controlled by enemy pawns from mobility
        let empty = self.board.empty() & !pawn_attacked_squares;

        for (piece_type, piece) in player_pieces.iter().enumerate() {
            match Piece::from(piece_type) {
                Piece::Pawn => {
                    for source in piece.serialize() {
                        let ep_bitboard = match self.board.ep_target {
                            Some(square) => {
                                let rank = square.rank();
                                if (rank == 2 && color == Color::Black) || (rank == 5 && color == Color::White) {
                                    square.to_bitboard()
                                } else {
                                    0
                                }
                            }
                            None => 0,
                        };
                        mobility += (self.attacks.pawn[color as usize][source as usize] & (opponent_occupancy | ep_bitboard)).pop_count() as f32;
                        mobility += (self.attacks.pawn_pushes[color as usize][source as usize] & empty).pop_count() as f32;
                    }
                    let able_to_double_push_mask = match color {
                        Color::White => empty >> 8,
                        Color::Black => empty << 8,
                    };
                    for source in (*piece & able_to_double_push_mask).serialize() {
                        mobility += (self.attacks.pawn_double_pushes[color as usize][source as usize] & empty).pop_count() as f32;
                    }
                }
                Piece::King => {
                    for source in piece.serialize() {
                        mobility += (self.attacks.king[source as usize] & (empty | opponent_occupancy)).pop_count() as f32;

                        // Castling
                        let king_home_position = match color {
                            Color::White => Square::E1,
                            Color::Black => Square::E8,
                        };
                        if *piece == king_home_position.to_bitboard() {
                            for rook_square in player_pieces[Piece::Rook as usize]
                                .serialize()
                                .iter()
                                .filter(|rook_square| rook_square.rank() == king_home_position.rank())
                                {
                                    match rook_square.file() {
                                        0 => {
                                            let castle_line = [
                                                king_home_position.west_one(),
                                                king_home_position.west_one().west_one(),
                                            ];

                                            let all_empty = castle_line.iter().all(|square| empty & square.to_bitboard() > 0);
                                            let any_checks = castle_line.iter().any(|square| self.board.is_square_attacked(*square, color.flip()));

                                            if all_empty && !any_checks && self.board.castling_rights[color as usize][CastlingSide::Queen as usize] {
                                                mobility += 1.;
                                            }
                                        },
                                        7 => {
                                            let castle_line = [
                                                king_home_position.east_one(),
                                                king_home_position.east_one().east_one(),
                                            ];

                                            let all_empty = castle_line.iter().all(|square| empty & square.to_bitboard() > 0);
                                            let any_checks = castle_line.iter().any(|square| self.board.is_square_attacked(*square, color.flip()));

                                            if all_empty && !any_checks && self.board.castling_rights[color as usize][CastlingSide::King as usize] {
                                                mobility += 1.;
                                            }
                                        },
                                        _ => {},
                                    }
                                }
                        }
                    }
                }
                Piece::Knight => {
                    for source in piece.serialize() {
                        mobility += (self.attacks.knight[source as usize] & (empty | opponent_occupancy)).pop_count() as f32;
                    }
                }
                Piece::Bishop => {
                    for source in piece.serialize() {
                        mobility += (self.attacks.bishop(self.board.occupancy, source) & (empty | opponent_occupancy)).pop_count() as f32;
                    }
                }
                Piece::Rook => {
                    for source in piece.serialize() {
                        mobility += (self.attacks.rook(self.board.occupancy, source) & (empty | opponent_occupancy)).pop_count() as f32;
                    }
                }
                Piece::Queen => {
                    // Do not account queen in mobility
                }
                incorrect_type => panic!("Incorrect piece type: {:?}", incorrect_type),
            }
        }
        mobility
    }
}

#[cfg(test)]
mod tests {
    use crate::{board::{Board, io::IO}, moves::{Move, MoveKind}};

    use super::*;

    #[test]
    fn castle_bonus() {
        assert_eq!(KING_BONUS[Square::E1.mirror() as usize], 0.0);
        assert!(KING_BONUS[Square::G1.mirror() as usize] > 0.0);
        assert!(KING_BONUS[Square::C1.mirror() as usize] > 0.0);
        assert!(KING_BONUS[Square::D1.mirror() as usize] < 0.0);
        assert!(KING_BONUS[Square::E2.mirror() as usize] < 0.0);

        assert_eq!(KING_BONUS[Square::E8 as usize], 0.0);
        assert!(KING_BONUS[Square::G8 as usize] > 0.0);
        assert!(KING_BONUS[Square::C8 as usize] > 0.0);
        assert!(KING_BONUS[Square::D8 as usize] < 0.0);
        assert!(KING_BONUS[Square::E2 as usize] < 0.0);
    }

    #[test]
    fn mobility() {
        let board = Board::new();
        let gm = Grossmeister::new(board);
        let white = gm.mobility(Color::White);
        let black = gm.mobility(Color::Black);

        assert_eq!(white, 20.);
        assert_eq!(black, 20.);
    }

    #[test]
    fn material() {
        let board = Board::new();
        let gm = Grossmeister::new(board);
        assert_eq!(gm.material(Color::Black), gm.material(Color::White));

    }

    #[test]
    fn initial_eval() {
        let board = Board::new();
        let gm = Grossmeister::new(board);
        assert_eq!(gm.evaluate(), 0.0);
    }

    #[test]
    fn king_tropism() {
        let board = Board::new();
        let mut gm = Grossmeister::new(board);
        gm.board.make_move(Move { source: Square::D1, target: Square::F5, kind: MoveKind::Quiet });
        let score = gm.evaluate();
        gm.board.print();
        println!("Score {}", score);

        assert!(score < 0.0);
        assert!(score > -1.0);
    }

    #[test]
    fn white_winning() {
        let fen = String::from("8/5pk1/6p1/R4b1p/3P4/1P2N3/P1r2PPP/R5K1 b - - 1 27");
        let board = Board::from_FEN(fen);
        let gm = Grossmeister::new(board);
        let score = gm.evaluate();
        gm.board.print();
        println!("Score {}", score);

        assert!(score > 7.0);
    }

    #[test]
    fn black_winning() {
        let fen = String::from("8/p7/1k4K1/8/4P3/8/PP5r/8 b - - 1 38");
        let board = Board::from_FEN(fen);
        let gm = Grossmeister::new(board);
        let score = gm.evaluate();
        gm.board.print();
        println!("Score {}", score);

        assert!(score < -3.0);
    }

    #[test]
    fn encourage_center_pawns() {
        let score1 = {
            let fen = String::from("rnbqkbnr/pppp1ppp/8/4p3/4P3/8/PPPP1PPP/RNBQKBNR w KQkq - 0 2");
            let board = Board::from_FEN(fen);
            let gm = Grossmeister::new(board);
            let score = gm.evaluate();
            gm.board.print();
            println!("Score {}", score);
            score
        };

        let score2 = {
            let fen = String::from("rnbqkbnr/pppp1ppp/8/4p3/2P5/8/PP1PPPPP/RNBQKBNR w KQkq - 0 2");
            let board = Board::from_FEN(fen);
            let gm = Grossmeister::new(board);
            let score = gm.evaluate();
            gm.board.print();
            println!("Score {}", score);
            score
        };

        assert!(score1 > score2);
    }

    #[test]
    fn discourage_edge_knights() {
        let score1 = {
            let fen = String::from("r1bqkbnr/pppp1ppp/2n5/4p3/4P3/5N2/PPPP1PPP/RNBQKB1R w KQkq - 2 3");
            let board = Board::from_FEN(fen);
            let gm = Grossmeister::new(board);
            let score = gm.evaluate();
            gm.board.print();
            println!("Score {}", score);
            score
        };

        let score2 = {
            let fen = String::from("r1bqkbnr/pppp1ppp/2n5/4p3/4P3/7N/PPPP1PPP/RNBQKB1R w KQkq - 2 3");
            let board = Board::from_FEN(fen);
            let gm = Grossmeister::new(board);
            let score = gm.evaluate();
            gm.board.print();
            println!("Score {}", score);
            score
        };

        assert!(score1 > score2);
    }

    #[test]
    fn mirrored_evaluation() {
        let score1 = {
            let fen = String::from("r3k2r/Pppp1ppp/1b3nbN/nP6/BBP1P3/q4N2/Pp1P2PP/R2Q1RK1 w kq - 0 1");
            let board = Board::from_FEN(fen);
            let gm = Grossmeister::new(board);
            let score = gm.evaluate();
            gm.board.print();
            println!("Score {}", score);
            score
        };

        let score2 = {
            let fen = String::from("r2q1rk1/pP1p2pp/Q4n2/bbp1p3/Np6/1B3NBn/pPPP1PPP/R3K2R b KQ - 0 1 ");
            let board = Board::from_FEN(fen);
            let mut gm = Grossmeister::new(board);
            gm.board.ply += 1; // TODO: remove me when FEN parsing includes side to move
            let score = gm.evaluate();
            gm.board.print();
            println!("Score {}", score);
            score
        };

        assert_eq!(score1.abs(), score2.abs());
    }

}