Vatu/src/stats.rs

//! Board statistics used for heuristics.

use crate::board::*;
use crate::rules::{GameState, get_player_moves};

/// Storage for board pieces stats.
#[derive(Debug, Clone, PartialEq)]
pub struct BoardStats {
    pub num_pawns: i8,
    pub num_bishops: i8,
    pub num_knights: i8,
    pub num_rooks: i8,
    pub num_queens: i8,
    pub num_kings: i8,
    pub num_doubled_pawns: i8,   // Pawns that are on the same file as a friend.
    pub num_backward_pawns: i8,  // Pawns behind all other pawns on adjacent files.
    pub num_isolated_pawns: i8,  // Pawns that have no friend pawns on adjacent files.
    pub mobility: i32,
}

impl BoardStats {
    pub const fn new() -> BoardStats {
        BoardStats {
            num_pawns: 0, num_bishops: 0, num_knights: 0, num_rooks: 0, num_queens: 0,
            num_kings: 0, num_doubled_pawns: 0, num_backward_pawns: 0, num_isolated_pawns: 0,
            mobility: 0,
        }
    }

    /// Create two new BoardStats objects from the board, for both sides.
    ///
    /// The playing color will have its stats filled in the first
    /// BoardStats object, its opponent in the second.
    pub fn new_from(board: &Board, game_state: &GameState) -> (BoardStats, BoardStats) {
        let mut stats = (BoardStats::new(), BoardStats::new());
        let mut gs = game_state.clone();
        stats.0.compute(board, &gs);
        gs.color = opposite(gs.color);
        stats.1.compute(board, &gs);
        stats
    }

    /// Reset all stats to 0.
    pub fn reset(&mut self) {
        self.num_pawns = 0;
        self.num_bishops = 0;
        self.num_knights = 0;
        self.num_rooks = 0;
        self.num_queens = 0;
        self.num_kings = 0;
        self.num_doubled_pawns = 0;
        self.num_backward_pawns = 0;
        self.num_isolated_pawns = 0;
        self.mobility = 0;
    }

    /// Fill `stats` from given `board` and `game_state`.
    ///
    /// Only the current playing side stats are created,
    /// prepare the game_state accordingly.
    pub fn compute(&mut self, board: &Board, game_state: &GameState) {
        self.reset();
        let color = game_state.color;
        // Compute mobility for all pieces.
        self.mobility = get_player_moves(board, game_state, true).len() as i32;
        // Compute amount of each piece.
        for file in 0..8 {
            for rank in 0..8 {
                let square = sq(file, rank);
                if board.is_empty(square) || board.get_color(square) != color {
                    continue
                }
                match board.get_piece(square) {
                    ROOK => self.num_rooks += 1,
                    KNIGHT => self.num_knights += 1,
                    BISHOP => self.num_bishops += 1,
                    QUEEN => self.num_queens += 1,
                    KING => self.num_kings += 1,
                    PAWN => {
                        self.num_pawns += 1;
                        // FIXME redo pawn stats properly
                        // let mut doubled = false;
                        // let mut isolated = true;
                        // let mut backward = true;
                        // for r in 0..8 {
                        //     // Check for doubled pawns.
                        //     if !doubled {
                        //         let other_color = board.get_color(sq(file, r));
                        //         is_piece(get_square(board, &(pos_f, r)), color|SQ_P) && r != pos_r
                        //         doubled = true;
                        //     }
                        //     // Check for isolated pawns.
                        //     if
                        //         isolated &&
                        //         (
                        //             // Check on the left file if not on a-file...
                        //             (
                        //                 pos_f > POS_MIN &&
                        //                 is_piece(get_square(board, &(pos_f - 1, r)), color|SQ_P)
                        //             ) ||
                        //             // Check on the right file if not on h-file...
                        //             (
                        //                 pos_f < POS_MAX &&
                        //                 is_piece(get_square(board, &(pos_f + 1, r)), color|SQ_P)
                        //             )
                        //         )
                        //     {
                        //         isolated = false;
                        //     }
                        //     // Check for backward pawns.
                        //     if backward {
                        //         if color == SQ_WH && r <= pos_r {
                        //             if (
                        //                 pos_f > POS_MIN &&
                        //                 is_type(get_square(board, &(pos_f - 1, r)), SQ_P)
                        //             ) || (
                        //                 pos_f < POS_MAX &&
                        //                 is_type(get_square(board, &(pos_f + 1, r)), SQ_P)
                        //             ) {
                        //                 backward = false;
                        //             }
                        //         } else if color == SQ_BL && r >= pos_r {
                        //             if (
                        //                 pos_f > POS_MIN &&
                        //                 is_type(get_square(board, &(pos_f - 1, r)), SQ_P)
                        //             ) || (
                        //                 pos_f < POS_MAX &&
                        //                 is_type(get_square(board, &(pos_f + 1, r)), SQ_P)
                        //             ) {
                        //                 backward = false;
                        //             }
                        //         }
                        //     }
                        // }
                        // if doubled {
                        //     self.num_doubled_pawns += 1;
                        // }
                        // if isolated {
                        //     self.num_isolated_pawns += 1;
                        // }
                        // if backward {
                        //     self.num_backward_pawns += 1;
                        // }
                    },
                    _ => {}
                }
            }
        }
    }
}

impl std::fmt::Display for BoardStats {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(
            f,
            "{}P {}B {}N {}R {}Q {}K {}dp {}bp {}ip {}m",
            self.num_pawns, self.num_bishops, self.num_knights, self.num_rooks,
            self.num_queens, self.num_kings,
            self.num_doubled_pawns, self.num_backward_pawns, self.num_isolated_pawns,
            self.mobility
        )
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_compute_stats() {
        // Check that initial stats are correct.
        let b = Board::new();
        let gs = GameState::new();
        let initial_stats = BoardStats {
            num_pawns: 8,
            num_bishops: 2,
            num_knights: 2,
            num_rooks: 2,
            num_queens: 1,
            num_kings: 1,
            num_doubled_pawns: 0,
            num_backward_pawns: 0,
            num_isolated_pawns: 0,
            mobility: 20,
        };
        let mut stats = BoardStats::new_from(&b, &gs);
        eprintln!("{}", stats.0);
        eprintln!("{}", stats.1);
        assert!(stats.0 == stats.1);
        assert!(stats.0 == initial_stats);

        // Check that doubled pawns are correctly counted.
        let mut b = Board::new_empty();
        b.set_square(D4, WHITE, PAWN);
        b.set_square(D6, WHITE, PAWN);
        stats.0.compute(&b, &gs);
        assert_eq!(stats.0.num_doubled_pawns, 2);
        // Add a pawn on another file, no changes expected.
        b.set_square(E6, WHITE, PAWN);
        stats.0.compute(&b, &gs);
        assert_eq!(stats.0.num_doubled_pawns, 2);
        // Add a pawn backward in the d-file: there are now 3 doubled pawns.
        b.set_square(D2, WHITE, PAWN);
        stats.0.compute(&b, &gs);
        assert_eq!(stats.0.num_doubled_pawns, 3);

        // Check that isolated and backward pawns are correctly counted.
        assert_eq!(stats.0.num_isolated_pawns, 0);
        assert_eq!(stats.0.num_backward_pawns, 2);  // A bit weird?
        // Protect d4 pawn with a friend in e3: it is not isolated nor backward anymore.
        b.set_square(E3, WHITE, PAWN);
        stats.0.compute(&b, &gs);
        assert_eq!(stats.0.num_doubled_pawns, 5);
        assert_eq!(stats.0.num_isolated_pawns, 0);
        assert_eq!(stats.0.num_backward_pawns, 1);
        // Add an adjacent friend to d2 pawn: no pawns are left isolated or backward.
        b.set_square(C2, WHITE, PAWN);
        stats.0.compute(&b, &gs);
        assert_eq!(stats.0.num_doubled_pawns, 5);
        assert_eq!(stats.0.num_isolated_pawns, 0);
        assert_eq!(stats.0.num_backward_pawns, 0);
        // Add an isolated/backward white pawn in a far file.
        b.set_square(A2, WHITE, PAWN);
        stats.0.compute(&b, &gs);
        assert_eq!(stats.0.num_doubled_pawns, 5);
        assert_eq!(stats.0.num_isolated_pawns, 1);
        assert_eq!(stats.0.num_backward_pawns, 1);

        // Check for pawns that are backward but not isolated.
        let mut b = Board::new_empty();
        // Here, d4 pawn protects both e5 and e3, but it is backward.
        b.set_square(D4, WHITE, PAWN);
        b.set_square(E5, WHITE, PAWN);
        b.set_square(E3, WHITE, PAWN);
        stats.0.compute(&b, &gs);
        assert_eq!(stats.0.num_doubled_pawns, 2);
        assert_eq!(stats.0.num_isolated_pawns, 0);
        assert_eq!(stats.0.num_backward_pawns, 1);
    }
}