[position] Implement FromFen for Position, Piece, and Color
I can now create Positions from FEN strings!
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5 changed files with 187 additions and 13 deletions
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@ -1,7 +1,7 @@
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// Eryn Wells <eryn@erynwells.me>
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use crate::{r#move::Castle, Position};
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use chessfriend_core::{Color, File, Piece, PlacedPiece, Rank, Square};
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use crate::{r#move::Castle, Position, PositionBuilder};
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use chessfriend_core::{piece, Color, File, Piece, PlacedPiece, Rank, Square};
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use std::fmt::Write;
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#[derive(Clone, Copy, Debug, Eq, PartialEq)]
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@ -9,11 +9,19 @@ pub enum ToFenError {
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FmtError(std::fmt::Error),
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}
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#[derive(Clone, Copy, Debug, Eq, PartialEq)]
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pub struct FromFenError;
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pub trait ToFen {
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type Error;
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fn to_fen(&self) -> Result<String, Self::Error>;
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}
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pub trait FromFen: Sized {
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type Error;
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fn from_fen_str(string: &str) -> Result<Self, Self::Error>;
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}
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impl ToFen for Position {
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type Error = ToFenError;
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@ -127,14 +135,131 @@ impl ToFen for PlacedPiece {
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}
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}
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impl FromFen for Position {
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type Error = FromFenError;
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fn from_fen_str(string: &str) -> Result<Self, Self::Error> {
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let mut builder = PositionBuilder::empty();
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let mut fields = string.split(" ");
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let placements = fields.next().ok_or(FromFenError)?;
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let ranks = placements.split("/");
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for (rank, pieces) in Rank::ALL.iter().rev().zip(ranks) {
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let mut files = File::ALL.iter();
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for ch in pieces.chars() {
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if let Some(skip) = ch.to_digit(10) {
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// TODO: Use advance_by() when it's available.
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for _ in 0..skip {
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files.next();
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}
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continue;
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}
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let file = files.next().ok_or(FromFenError)?;
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let piece = Piece::from_fen_str(&ch.to_string())?;
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builder.place_piece(PlacedPiece::new(
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piece,
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Square::from_file_rank(*file, *rank),
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));
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}
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debug_assert_eq!(files.next(), None);
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}
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let player_to_move = Color::from_fen_str(fields.next().ok_or(FromFenError)?)?;
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builder.to_move(player_to_move);
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let castling_rights = fields.next().ok_or(FromFenError)?;
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if castling_rights == "-" {
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builder.no_castling_rights();
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} else {
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for ch in castling_rights.chars() {
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match ch {
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'K' => builder.player_can_castle(Color::White, Castle::KingSide),
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'Q' => builder.player_can_castle(Color::White, Castle::QueenSide),
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'k' => builder.player_can_castle(Color::Black, Castle::KingSide),
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'q' => builder.player_can_castle(Color::Black, Castle::QueenSide),
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_ => return Err(FromFenError),
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};
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}
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}
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let en_passant_square = fields.next().ok_or(FromFenError)?;
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if en_passant_square != "-" {
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let square = Square::from_algebraic_str(en_passant_square).map_err(|_| FromFenError)?;
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builder.en_passant_square(Some(square));
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}
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let half_move_clock = fields.next().ok_or(FromFenError)?;
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let half_move_clock: u16 = half_move_clock.parse().map_err(|_| FromFenError)?;
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builder.ply_counter(half_move_clock);
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let full_move_counter = fields.next().ok_or(FromFenError)?;
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let full_move_counter: u16 = full_move_counter.parse().map_err(|_| FromFenError)?;
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builder.move_number(full_move_counter);
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debug_assert_eq!(fields.next(), None);
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Ok(builder.build())
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}
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}
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impl FromFen for Color {
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type Error = FromFenError;
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fn from_fen_str(string: &str) -> Result<Self, Self::Error> {
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if string.len() != 1 {
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return Err(FromFenError);
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}
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match string.chars().take(1).next().unwrap() {
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'w' => Ok(Color::White),
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'b' => Ok(Color::Black),
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_ => Err(FromFenError),
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}
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}
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}
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impl FromFen for Piece {
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type Error = FromFenError;
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fn from_fen_str(string: &str) -> Result<Self, Self::Error> {
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if string.len() != 1 {
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return Err(FromFenError);
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}
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match string.chars().take(1).next().unwrap() {
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'P' => Ok(piece!(White Pawn)),
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'N' => Ok(piece!(White Knight)),
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'B' => Ok(piece!(White Bishop)),
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'R' => Ok(piece!(White Rook)),
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'Q' => Ok(piece!(White Queen)),
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'K' => Ok(piece!(White King)),
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'p' => Ok(piece!(Black Pawn)),
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'n' => Ok(piece!(Black Knight)),
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'b' => Ok(piece!(Black Bishop)),
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'r' => Ok(piece!(Black Rook)),
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'q' => Ok(piece!(Black Queen)),
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'k' => Ok(piece!(Black King)),
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_ => Err(FromFenError),
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use crate::test_position;
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use super::*;
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#[test]
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fn starting_position() {
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let pos = Position::starting();
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println!("{pos:#?}");
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let pos = test_position!(starting);
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assert_eq!(
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pos.to_fen(),
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Ok(String::from(
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@ -142,4 +267,14 @@ mod tests {
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))
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);
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}
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#[test]
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fn from_starting_fen() {
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let pos =
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Position::from_fen_str("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1")
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.unwrap();
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let expected = Position::starting();
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assert_eq!(pos, expected, "{pos:#?}\n{expected:#?}");
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}
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}
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@ -31,6 +31,7 @@ mod castle {
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check_squares: BitBoard,
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}
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#[derive(Debug)]
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pub(crate) struct Squares {
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pub king: Square,
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pub rook: Square,
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@ -13,7 +13,8 @@ pub struct Builder {
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player_to_move: Color,
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flags: Flags,
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pieces: BTreeMap<Square, Piece>,
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kings: [Square; 2],
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kings: [Option<Square>; 2],
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en_passant_square: Option<Square>,
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ply_counter: u16,
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move_number: u16,
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}
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@ -23,6 +24,18 @@ impl Builder {
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Self::default()
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}
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pub(crate) fn empty() -> Self {
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Self {
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player_to_move: Color::default(),
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flags: Flags::default(),
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pieces: BTreeMap::default(),
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kings: [None, None],
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en_passant_square: None,
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ply_counter: 0,
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move_number: 1,
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}
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}
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pub fn from_position(position: &Position) -> Self {
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let pieces = BTreeMap::from_iter(
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position
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@ -38,7 +51,8 @@ impl Builder {
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player_to_move: position.player_to_move(),
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flags: position.flags(),
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pieces,
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kings: [white_king, black_king],
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kings: [Some(white_king), Some(black_king)],
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en_passant_square: position.en_passant_square(),
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ply_counter: position.ply_counter(),
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move_number: position.move_number(),
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}
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@ -59,6 +73,11 @@ impl Builder {
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self
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}
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pub fn en_passant_square(&mut self, square: Option<Square>) -> &mut Self {
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self.en_passant_square = square;
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self
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}
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pub fn place_piece(&mut self, piece: PlacedPiece) -> &mut Self {
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let square = piece.square();
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let shape = piece.shape();
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@ -66,8 +85,11 @@ impl Builder {
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if shape == Shape::King {
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let color = piece.color();
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let color_index: usize = color as usize;
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self.pieces.remove(&self.kings[color_index]);
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self.kings[color_index] = square;
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if let Some(king_square) = self.kings[color_index] {
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self.pieces.remove(&king_square);
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}
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self.kings[color_index] = Some(square);
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}
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self.pieces.insert(square, *piece.piece());
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@ -75,6 +97,17 @@ impl Builder {
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self
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}
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pub fn player_can_castle(&mut self, color: Color, castle: Castle) -> &mut Self {
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self.flags
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.set_player_has_right_to_castle_flag(color, castle);
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self
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}
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pub fn no_castling_rights(&mut self) -> &mut Self {
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self.flags.clear_all_castling_rights();
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self
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}
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pub fn build(&self) -> Position {
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let pieces = PieceBitBoards::from_iter(
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self.pieces
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@ -93,7 +126,7 @@ impl Builder {
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.get(&starting_squares.rook)
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.is_some_and(|piece| piece.shape() == Shape::Rook);
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let king_is_on_starting_square =
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self.kings[color as usize] == starting_squares.king;
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self.kings[color as usize] == Some(starting_squares.king);
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if !king_is_on_starting_square || !has_rook_on_starting_square {
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flags.clear_player_has_right_to_castle_flag(color, castle);
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@ -105,7 +138,7 @@ impl Builder {
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self.player_to_move,
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flags,
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pieces,
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None,
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self.en_passant_square,
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self.ply_counter,
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self.move_number,
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)
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@ -139,7 +172,8 @@ impl Default for Builder {
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player_to_move: Color::White,
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flags: Flags::default(),
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pieces: pieces,
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kings: [white_king_square, black_king_square],
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kings: [Some(white_king_square), Some(black_king_square)],
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en_passant_square: None,
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ply_counter: 0,
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move_number: 1,
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}
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@ -24,6 +24,10 @@ impl Flags {
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pub(super) fn clear_player_has_right_to_castle_flag(&mut self, color: Color, castle: Castle) {
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self.0 &= !(1 << Self::player_has_right_to_castle_flag_offset(color, castle));
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}
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pub(super) fn clear_all_castling_rights(&mut self) {
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self.0 &= 0b11111100;
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}
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}
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impl fmt::Debug for Flags {
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@ -269,8 +269,8 @@ impl Position {
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pieces,
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sight: [OnceCell::new(), OnceCell::new()],
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moves: OnceCell::new(),
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half_move_counter: 0,
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full_move_number: 1,
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half_move_counter,
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full_move_number,
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}
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}
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