laura_core 0.4.0

/*
    Laura-Core: a fast and efficient move generator for chess engines.

    Copyright (C) 2024-2025 HansTibberio <hanstiberio@proton.me>

    Laura-Core is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    Laura-Core is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Laura-Core. If not, see <https://www.gnu.org/licenses/>.
*/

#[allow(unused_imports)]
use crate::{
    AllMoves, BitBoard, Board, CastleRights, Color, Move, MoveType, Piece, PieceType, SanBuffered,
    Square, Zobrist, gen_moves, get_rook_castling, to_san,
};

// This implementation is based on the approach used in Carp,
// which provides a clear and efficient way to apply moves and handling null moves to the board.
// Source: https://github.com/dede1751/carp/blob/main/chess/src/movegen/make_move.rs

impl Board {
    /// Executes a move on the chessboard, updating the board state, castling rights,
    /// en passant square, fifty-move rule counter, and [`Zobrist`] hash accordingly.
    ///
    /// This function clones the current board state, applies the given move,
    /// and returns the resulting board. The move can include special cases such as captures,
    /// pawn promotions, castling, and en passant captures.
    ///
    /// # Panics
    /// The function will panic if the source and destination squares of the move are the same.
    pub fn make_move(&self, mv: Move) -> Board {
        let mut board: Board = *self;

        // Ensure the source and destination squares are different.
        assert_ne!(mv.get_src(), mv.get_dest());

        let src: Square = mv.get_src();
        let dest: Square = mv.get_dest();
        let move_type: MoveType = mv.get_type();
        let is_capture: bool = mv.is_capture();

        let piece: Piece = self.piece_on(src).unwrap();
        let piece_type: PieceType = piece.piece_type();

        // Remove the piece from its source square
        board.remove_piece(src);

        // Update fifty-move rule counter
        board.fifty_move = if is_capture || piece_type == PieceType::Pawn {
            0
        } else {
            board.fifty_move + 1
        };

        if board.side == Color::Black {
            board.full_move = board.full_move.saturating_add(1);
        }

        // Handle special move types (En Passant, Castling, Captures)
        match move_type {
            MoveType::EnPassant => {
                board.remove_piece(dest.forward(!self.side));
            }
            MoveType::KingCastle | MoveType::QueenCastle => {
                let rook: Piece = Piece::new(PieceType::Rook, self.side);
                let (rook_src, rook_dest) = get_rook_castling(dest);
                board.remove_piece(rook_src);
                board.set_piece(rook, rook_dest);
            }
            _ if is_capture => {
                board.remove_piece(dest);
            }
            _ => {}
        }

        // Handle promotions or move the piece to its destination
        if mv.is_promotion() {
            board.set_piece(mv.get_prom(self.side), dest);
        } else {
            board.set_piece(piece, dest);
        }

        // Update en passant square and Zobrist hash
        if let Some(square) = self.enpassant_square {
            board.enpassant_square = None;
            board.zobrist.hash_enpassant(square);
        }

        if move_type == MoveType::DoublePawn {
            let enpassant_target: Square = src.forward(self.side);
            board.enpassant_square = Some(enpassant_target);
            board.zobrist.hash_enpassant(enpassant_target);
        }

        // Update castling rights and Zobrist hash
        let new_castling_rights: CastleRights = self.castling.update(src, dest);
        board.castling = new_castling_rights;
        board
            .zobrist
            .swap_castle_hash(self.castling, new_castling_rights);

        // Toggle side to move and update Zobrist hash
        board.side = !self.side;
        board.zobrist.hash_side();

        // Recalculate checkers for the new board state
        board.checkers = board.checkers();

        // Return the updated board
        board
    }

    /// Executes a null move, switching the turn to the opponent without making any actual moves.
    ///
    /// This function is useful for certain algorithms where you want to evaluate a position
    /// as if the current player passed their turn. It asserts that the current player is not in check
    /// before performing the null move. The function will reset the en passant square and clear any checkers
    /// on the board.
    ///
    /// # Panics
    /// This function will panic if the current player's checkers are not empty, indicating that the
    /// game state is invalid for performing a null move.
    pub fn null_move(&self) -> Board {
        // Ensure there are no checkers on the board.
        assert!(self.checkers.is_empty());

        // Create a copy of the current board, switch the side to move and update the Zobrist hash.
        let mut board: Board = *self;
        board.side = !self.side;
        board.zobrist.hash_side();

        // Reset the en passant square.
        board.enpassant_square = None;

        // If there was an en passant square, update the Zobrist hash for it.
        if let Some(square) = self.enpassant_square {
            board.zobrist.hash_enpassant(square);
        }

        // Clear the checkers state.
        board.checkers = BitBoard::EMPTY;

        // Return the new board state after the null move.
        board
    }

    /// Finds legal move in board from the uci-formatted move string
    #[inline]
    pub fn find_move(&self, move_str: &str) -> Option<Move> {
        gen_moves::<AllMoves>(self)
            .iter()
            .find(|&mv| *mv == move_str)
            .copied()
    }

    /// Attempts to make a move on the board using the UCI (Universal Chess Interface) notation.
    pub fn make_uci_move(&self, uci_move: &str) -> Result<Board, &str> {
        self.find_move(uci_move)
            .map(|mv| self.make_move(mv))
            .ok_or("Ilegal UCI move from the current board")
    }

    /// Converts the move to a San
    pub fn to_san(&self, mv: Move) -> SanBuffered {
        to_san(mv, self)
    }
}