inkwell/src/eval.rs

use chess::{Board, BoardStatus, ChessMove, Color, MoveGen, Piece};

pub fn eval_board(
    board: Board,
    playing_as: Color,
    curr_depth: u8,
    move_history: Vec<(ChessMove, Board)>,
) -> i128 {
    let mut current_eval: i128 = 0;

    let moves_iter = MoveGen::new_legal(&board).into_iter();

    moves_iter.for_each(|mov| {
        let tmp_board = board.make_move_new(mov);

        // force it to not draw (and cockblock someone trying *to* draw)
        if move_history.len() > 6 {
            if move_history[move_history.len() - 2].0 == mov
                && move_history[move_history.len() - 6].0 == mov
            {
                current_eval -= 6666666666666666666666666666;
                return;
            }
        }

        // basic material counting
        tmp_board.color_combined(playing_as).for_each(|square| {
            match tmp_board.piece_on(square) {
                Some(Piece::Pawn) => current_eval += 1,
                Some(Piece::Knight) => current_eval += 3,
                Some(Piece::Bishop) => current_eval += 5,
                Some(Piece::Rook) => current_eval += 5,
                Some(Piece::Queen) => current_eval += 8,
                _ => { /* do nothing */ }
            }
        });

        tmp_board.color_combined(!playing_as).for_each(|square| {
            match tmp_board.piece_on(square) {
                Some(Piece::Pawn) => current_eval -= 1,
                Some(Piece::Knight) => current_eval -= 3,
                Some(Piece::Bishop) => current_eval -= 5,
                Some(Piece::Rook) => current_eval -= 5,
                Some(Piece::Queen) => current_eval -= 8,
                _ => { /* do nothing */ }
            }
        });

        // checking heuristic
        let mut are_we_in_check = false;
        let mut is_opponent_in_check = false;
        tmp_board
            .checkers()
            .filter(|sq| tmp_board.color_on(*sq).unwrap() == playing_as)
            .for_each(|_| {
                if !are_we_in_check {
                    current_eval -= 666;
                    are_we_in_check = true;
                } else {
                    current_eval -= 15;
                }
            });
        tmp_board
            .checkers()
            .filter(|sq| tmp_board.color_on(*sq).unwrap() == !playing_as)
            .for_each(|_| {
                if !is_opponent_in_check {
                    current_eval += 15;
                    is_opponent_in_check = true;
                } else {
                    current_eval += 5;
                }
            });

        // die
        if tmp_board.status() == BoardStatus::Checkmate && tmp_board.side_to_move() == playing_as {
            current_eval -= 666_666;
        }

        // go for checkmate
        if tmp_board.status() == BoardStatus::Checkmate && tmp_board.side_to_move() == !playing_as {
            current_eval += 666_666;
        }

        // deprioritize king movement
        if board.piece_on(mov.get_source()).unwrap() == Piece::King && !are_we_in_check {
            current_eval -= 10;
        }

        if curr_depth != 0 {
            let mut new_move_history = move_history.clone();
            new_move_history.push((mov, tmp_board));
            current_eval += eval_board(tmp_board, playing_as, curr_depth - 1, new_move_history);
        }
    });

    return current_eval;
}