path: root/src/board/mod.rs

use crate::{bitboard::{Bitboard, serialize_bitboard, bitscan, pop_count}, moves::{Move, MoveKind}, attacks::Attacks, square::Square};
mod engine;

pub enum CastlingSide {
    King,
    Queen,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Board {
    pub pieces: [Bitboard; 12],

    pub occupancy: Bitboard,
    pub ply: u16,

    /// En passsant target square
    pub ep_target: Option<Square>,

    /// Castling rights indexed by Color and CastlingSide
    /// ```
    /// let can_castle = castling_rights[Color::White as usize][CastlingSide::Queen as usize];
    /// ```
    pub castling_rights: [[bool; 2]; 2],

    attacks: Attacks,
}


#[derive(Debug, Clone, Copy, PartialEq, Eq, num_enum::FromPrimitive)]
#[repr(usize)]
pub enum PieceType {
    #[default]
    Pawn,
    Knight,
    Bishop,
    Rook,
    Queen,
    King,
    PawnBlack,
    KnightBlack,
    BishopBlack,
    RookBlack,
    QueenBlack,
    KingBlack,
}

const PIECE_CHARS: [&str; 12] = [
    "♟︎", "♞", "♝", "♜", "♛", "♚",
    "♙", "♘", "♗", "♖", "♕", "♔",
];


#[allow(unused)]
impl Board {
    #[allow(non_snake_case)]
    pub fn from_FEN(fen: String) -> Self {
        let mut pieces = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];

        let mut rank = 7;
        let mut file = 0i32;

        for character in fen.chars() {
            let index = rank * 8 + file;
            let position = 1 << index.clamp(0, 63);

            if character.is_numeric() {
                let digit = match character.to_digit(10) {
                    None => todo!("What to do here?"),
                    Some(digit) => digit,
                };
                if digit > 0 && digit <= 8 {
                    file += digit as i32;
                }
            } else {
                match character {
                    'P' => pieces[PieceType::Pawn as usize] |= position,
                    'N' => pieces[PieceType::Knight as usize] |= position,
                    'B' => pieces[PieceType::Bishop as usize] |= position,
                    'R' => pieces[PieceType::Rook as usize] |= position,
                    'Q' => pieces[PieceType::Queen as usize] |= position,
                    'K' => pieces[PieceType::King as usize] |= position,
                    'p' => pieces[PieceType::PawnBlack as usize] |= position,
                    'n' => pieces[PieceType::KnightBlack as usize] |= position,
                    'b' => pieces[PieceType::BishopBlack as usize] |= position,
                    'r' => pieces[PieceType::RookBlack as usize] |= position,
                    'q' => pieces[PieceType::QueenBlack as usize] |= position,
                    'k' => pieces[PieceType::KingBlack as usize] |= position,
                    '/' => {
                        rank -= 1;
                        file = -1; // So it becomes 0
                    },
                    ' ' => { break }, // TODO: break for now, parse everything else later
                    '-' => {}, // TODO
                    'w' => {}, // TODO
                    _ => todo!("Unexpected character!"),
                }
                file += 1;
            }
        }

        let mut board = Self {
            pieces,
            occupancy: 0,
            ply: 0,
            attacks: Attacks::new(),
            castling_rights: [[true; 2]; 2], // TODO: actualy parse from FEN
            ep_target: None,
        };
        board.update_occupancy();
        board
    }

    pub fn new() -> Self {
        let default_fen = String::from("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
        Self::from_FEN(default_fen)
    }

    /// Color to move at this ply
    fn color(&self) -> Color {
        Color::from(self.ply as u8 % 2)
    }

    fn update_occupancy(&mut self) {
        self.occupancy = 0;
        // TODO: reduce
        for piece in self.pieces {
            self.occupancy |= piece;
        }
    }

    fn empty(&self) -> Bitboard {
        !self.occupancy
    }

    fn pieces_by_color(&self, color: Color) -> &[Bitboard] {
        match color {
            Color::White => &self.pieces[0..6],
            Color::Black => &self.pieces[6..12],
        }
    }

    fn color_occupancy(&self, color: Color) -> Bitboard {
        let mut occupancy = 0;
        for piece in self.pieces_by_color(color) {
            occupancy |= piece;
        }
        occupancy
    }

    pub fn color_to_move(&self) -> Color {
        Color::from((self.ply % 2) as u8)
    }

    pub fn print(&self) {
        println!();
        for rank in (0..8).rev() {
            print!("{}|", rank + 1);
            for file in 0..8 {
                let index = rank * 8 + file;
                let position: Bitboard = 1 << index;
                let mut found = false;
                for (piece_type, piece_bitboard) in self.pieces.iter().enumerate() {
                    if (piece_bitboard & position) > 0 {
                        found = true;
                        print!("{} ", PIECE_CHARS[piece_type]);
                    }
                }
                if !found {
                    print!(". ");
                }
            }
            println!();
        }
        println!("  a b c d e f g h");
    }

    pub fn generate_pseudolegal_moves(&self, color: Color) -> Vec<Move> {
        let mut moves = Vec::with_capacity(1024);
        let opponent_occupancy = self.color_occupancy(color.flip());
        let empty = self.empty();
        let available_targets = opponent_occupancy | empty;
        let player_pieces = self.pieces_by_color(color);

        for (piece_type, piece) in player_pieces.iter().enumerate() {
            match PieceType::from(piece_type) {
                PieceType::Pawn => {
                    for source in serialize_bitboard(*piece) {
                        let ep_bitboard = match self.ep_target {
                            Some(square) => square.to_bitboard(),
                            None => 0,
                        };
                        for target in serialize_bitboard(self.attacks.pawn[color as usize][source as usize] & opponent_occupancy) {
                            moves.push(Move { source, target, kind: MoveKind::Capture });
                        };
                        for target in serialize_bitboard(self.attacks.pawn[color as usize][source as usize] & ep_bitboard) {
                            moves.push(Move { source, target, kind: MoveKind::EnPassant });
                        }
                        for target in serialize_bitboard(self.attacks.pawn_pushes[color as usize][source as usize] & empty) {
                            moves.push(Move { source, target, kind: MoveKind::Quiet });
                        };
                    }

                    // Make sure no blocking piece is standing in front of the pawns
                    // that are potential double-push sources
                    let able_to_double_push_mask = match color {
                        Color::White => empty >> 8,
                        Color::Black => empty << 8,
                    };
                    for source in serialize_bitboard(*piece & able_to_double_push_mask) {
                        for target in serialize_bitboard(self.attacks.pawn_double_pushes[color as usize][source as usize] & empty) {
                            moves.push(Move { source, target, kind: MoveKind::DoublePush });
                        };
                    }
                }
                PieceType::King => {
                    for source in serialize_bitboard(*piece) {
                        for target in serialize_bitboard(self.attacks.king[source as usize] & empty) {
                            moves.push(Move { source, target, kind: MoveKind::Quiet });
                        };
                        for target in serialize_bitboard(self.attacks.king[source as usize] & opponent_occupancy) {
                            moves.push(Move { source, target, kind: MoveKind::Capture });
                        };

                        // 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 serialize_bitboard(player_pieces[PieceType::Rook as usize])
                                .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.is_square_attacked(*square, color.flip()));

                                            if all_empty && !any_checks && self.castling_rights[color as usize][CastlingSide::Queen as usize] {
                                                moves.push(Move {
                                                    source: king_home_position,
                                                    target: king_home_position.west_one().west_one(),
                                                    kind: MoveKind::Castle,
                                                })
                                            }
                                        },
                                        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.is_square_attacked(*square, color.flip()));

                                            if all_empty && !any_checks && self.castling_rights[color as usize][CastlingSide::King as usize] {
                                                moves.push(Move {
                                                    source: king_home_position,
                                                    target: king_home_position.east_one().east_one(),
                                                    kind: MoveKind::Castle,
                                                })
                                            }
                                        },
                                        _ => {},
                                    }
                                }
                        }
                    }
                }
                PieceType::Knight => {
                    for source in serialize_bitboard(*piece) {
                        for target in serialize_bitboard(self.attacks.knight[source as usize] & empty) {
                            moves.push(Move { source, target, kind: MoveKind::Quiet });
                        };
                        for target in serialize_bitboard(self.attacks.knight[source as usize] & opponent_occupancy) {
                            moves.push(Move { source, target, kind: MoveKind::Capture });
                        };
                    }
                }
                PieceType::Bishop => {
                    for source in serialize_bitboard(*piece) {
                        for target in serialize_bitboard(self.attacks.bishop(self.occupancy, source) & empty) {
                            moves.push(Move { source, target, kind: MoveKind::Quiet });
                        };
                        for target in serialize_bitboard(self.attacks.bishop(self.occupancy, source) & opponent_occupancy) {
                            moves.push(Move { source, target, kind: MoveKind::Capture });
                        };
                    }
                }
                PieceType::Rook => {
                    for source in serialize_bitboard(*piece) {
                        for target in serialize_bitboard(self.attacks.rook(self.occupancy, source) & empty) {
                            moves.push(Move { source, target, kind: MoveKind::Quiet });
                        };
                    }
                    for source in serialize_bitboard(*piece) {
                        for target in serialize_bitboard(self.attacks.rook(self.occupancy, source) & opponent_occupancy) {
                            moves.push(Move { source, target, kind: MoveKind::Capture });
                        };
                    }
                }
                PieceType::Queen => {
                    for source in serialize_bitboard(*piece) {
                        for target in serialize_bitboard(self.attacks.queen(self.occupancy, source) & empty) {
                            moves.push(Move { source, target, kind: MoveKind::Quiet });
                        };
                        for target in serialize_bitboard(self.attacks.queen(self.occupancy, source) & opponent_occupancy) {
                            moves.push(Move { source, target, kind: MoveKind::Capture });
                        };
                    }
                }
                _ => todo!("Incorrect piece type")
            }
        }
        moves
    }

    /// *Blindlessly* apply a move without any validation
    /// Move should be validated beforehand
    pub fn make_move(&mut self, mov: Move) -> Option<PieceType> {
        let move_source_bb = mov.source.to_bitboard();
        let move_target_bb = mov.target.to_bitboard();

        // Remove existing piece (if any) from target square
        let mut captured_piece = match self.pieces
            .iter()
            .enumerate()
            .find(|(piece_type, bitboard)| *bitboard & mov.target.to_bitboard() > 0)
            {
                Some((target_piece, _)) => {
                    self.pieces[target_piece] ^= move_target_bb;
                    Some(PieceType::from(target_piece))
                },
                None => None,
            };

        // En Passant captures diffirently
        if mov.kind == MoveKind::EnPassant {
            debug_assert!(captured_piece.is_none(), "No capture should be found at this point");
            let captured_bb = Square::from_coords(mov.source.rank(), mov.target.file()).to_bitboard();
            captured_piece = match self.pieces
                .iter()
                .enumerate()
                .find(|(piece_type, bitboard)| *bitboard & captured_bb > 0)
                {
                    Some((pawn_type, _)) => {
                        self.pieces[pawn_type] ^= captured_bb;
                        Some(PieceType::from(pawn_type))
                    }
                    None => panic!("Pawn captured by En Passant was not found"),
                }
        }

        // Move a piece from source square to target
        let source_piece = match self.pieces
            .iter()
            .enumerate()
            .find(|(piece_type, bitboard)| *bitboard & mov.source.to_bitboard() > 0)
            {
                Some((source_piece, _)) => {
                    self.pieces[source_piece] ^= move_source_bb;
                    self.occupancy            ^= move_source_bb;

                    self.pieces[source_piece] |= move_target_bb;
                    self.occupancy            |= move_target_bb;
                    PieceType::from(source_piece)
                },
                None => panic!("Move is malformed: source piece not found"),
            };

        // When castling, also move a rook
        if mov.kind == MoveKind::Castle {
            debug_assert!(mov.source.file() == 4, "Castle can only be done from E file");
            let (rook_source_file, rook_target_file) = match mov.target.file() {
                2 => (0, 3),
                6 => (7, 5),
                _ => panic!("Malformed castle, target square invalid: {:?}", mov),
            };
            let rook_source_bb = Square::from_coords(mov.target.rank(), rook_source_file).to_bitboard();
            let rook_target_bb = Square::from_coords(mov.target.rank(), rook_target_file).to_bitboard();

            match self.pieces
                .iter()
                .enumerate()
                .find(|(rook_type, bitboard)| *bitboard & rook_source_bb > 0)
                {
                    Some((rook_type, _)) => {
                        self.pieces[rook_type] ^= rook_source_bb;
                        self.occupancy         ^= rook_source_bb;

                        self.pieces[rook_type] |= rook_target_bb;
                        self.occupancy         |= rook_target_bb;
                    },
                    None => panic!("Rook was not found when castling"),
                }
        }

        // Double push should set En Passant target square
        self.ep_target = if mov.kind == MoveKind::DoublePush {
            match mov.source.rank() {
                1 => Some(mov.source.nort_one()),
                6 => Some(mov.source.sout_one()),
                rank => panic!("Double-push was used from invalid rank({}) when trying to make {:?}", rank, mov),
            }
        } else { None };

        // Withdraw castling rights when moving rooks or king
        match source_piece {
            PieceType::King => {
                self.castling_rights[Color::from_piece(source_piece) as usize][CastlingSide::King as usize] = false;
                self.castling_rights[Color::from_piece(source_piece) as usize][CastlingSide::Queen as usize] = false;
            },
            PieceType::Rook => {
                match mov.source.file() {
                    0 => self.castling_rights[Color::from_piece(source_piece) as usize][CastlingSide::Queen as usize] = false,
                    7 => self.castling_rights[Color::from_piece(source_piece) as usize][CastlingSide::King as usize] = false,
                    _ => {},
                }
            },
            _ => {},
        }

        self.ply += 1;

        captured_piece
    }

    /// Completely reverse make_move as if it never happened
    pub fn unmake_move(&mut self, mov: Move, captured_piece: Option<PieceType>, previous_ep_target: Option<Square>, previous_castling_rights: [[bool; 2]; 2]) {
        let move_source_bb = mov.source.to_bitboard();
        let move_target_bb = mov.target.to_bitboard();

        // Move a piece from target square back to source square
        match self.pieces
            .iter()
            .enumerate()
            .find(|(piece_type, bitboard)| *bitboard & mov.target.to_bitboard() > 0)
            {
                Some((source_piece, _)) => {
                    self.pieces[source_piece] ^= move_target_bb;
                    self.occupancy            ^= move_target_bb;

                    self.pieces[source_piece] |= move_source_bb;
                    self.occupancy            |= move_source_bb;
                },
                None => panic!("Trying to unmake move which was not made: no piece was found on target square"),
            };

        // If unmaking castle, also return rook to its place
        if mov.kind == MoveKind::Castle {
            let (rook_source_file, rook_target_file) = match mov.target.file() {
                2 => (0, 3),
                6 => (7, 5),
                _ => panic!("Malformed castle, target square invalid: {:?}", mov),
            };
            let rook_source_bb = Square::from_coords(mov.target.rank(), rook_source_file).to_bitboard();
            let rook_target_bb = Square::from_coords(mov.target.rank(), rook_target_file).to_bitboard();

            match self.pieces
                .iter()
                .enumerate()
                .find(|(rook_type, bitboard)| *bitboard & rook_target_bb > 0)
                {
                    Some((rook_type, _)) => {
                        self.pieces[rook_type] |= rook_source_bb;
                        self.occupancy         |= rook_source_bb;

                        self.pieces[rook_type] ^= rook_target_bb;
                        self.occupancy         ^= rook_target_bb;
                    },
                    None => panic!("Rook was not found when castling"),
                }
        }

        // Return captured piece to target square
        match captured_piece {
            Some(target_piece) => {
                match mov.kind {
                    // Return pawn captured by En Passant pawn if needed
                    MoveKind::EnPassant => {
                        let original_dead_pawn_bb = Square::from_coords(mov.source.rank(), mov.target.file()).to_bitboard();
                        self.pieces[target_piece as usize] |= original_dead_pawn_bb;
                        self.occupancy                     |= original_dead_pawn_bb;
                    },
                    _ => {
                        self.pieces[target_piece as usize] |= move_target_bb;
                        self.occupancy                     |= move_target_bb;
                    },
                }
            },
            None => {}
        }


        self.ep_target = previous_ep_target;
        self.castling_rights = previous_castling_rights;
        self.ply -= 1;
    }

    fn is_square_attacked(&self, square: Square, attacker_color: Color) -> bool {
        let square_bb = square.to_bitboard();
        for (piece_type, piece) in self.pieces_by_color(attacker_color).iter().enumerate() {
            match PieceType::from(piece_type) {
                PieceType::Pawn => {
                    if (self.attacks.pawn[attacker_color.flip() as usize][square as usize] & piece > 0) {
                        return true
                    }
                }
                PieceType::Knight => {
                    if (self.attacks.knight[square as usize] & piece > 0) {
                        return true
                    }
                }
                PieceType::Bishop => {
                    if (self.attacks.bishop(self.occupancy, square) & piece > 0) {
                        return true
                    }
                }
                PieceType::Rook => {
                    if (self.attacks.rook(self.occupancy, square) & piece > 0) {
                        return true
                    }
                }
                PieceType::Queen => {
                    if (self.attacks.queen(self.occupancy, square) & piece > 0) {
                        return true
                    }
                }
                PieceType::King => {}
                _ => panic!("Unexpected piece type! Pieces by color should be considered white")
            }
        }
        false
    }

    fn is_king_in_check(&self, color: Color) -> bool {
        let king_bb = match color {
            Color::White => self.pieces[PieceType::King as usize],
            Color::Black => self.pieces[PieceType::KingBlack as usize],
        };
        let square = bitscan(king_bb);
        self.is_square_attacked(square, color.flip())
    }
}


#[derive(Debug, Clone, Copy, PartialEq, num_enum::FromPrimitive)]
#[repr(u8)]
pub enum Color {
    #[default]
    White,
    Black,
}
impl Color {
    pub fn flip(&self) -> Self {
        match self {
            Self::White => Self::Black,
            Self::Black => Self::White,
        }
    }
    pub fn from_piece(piece: PieceType) -> Self {
        if (piece as u8) < 6 {
            Self::White
        } else {
            Self::Black
        }
    }
}

#[cfg(test)]
mod tests {
    use std::f32::INFINITY;

    use super::*;
    use crate::{bitboard::{pop_count, bitscan, print}, square::Square};

    #[test]
    fn square_enum() {
        assert_eq!(Square::A1 as u8, 0);
        assert_eq!(Square::F1 as u8, 5);
        assert_eq!(Square::H8 as u8, 63);
    }

    #[test]
    fn new_from_default_fen() {
        let board = Board::new();

        board.print();
        print(board.empty(), "Empty squares");

        assert_eq!(pop_count(board.pieces[PieceType::Pawn as usize]), 8);
        assert_eq!(pop_count(board.pieces[PieceType::Knight as usize]), 2);
        assert_eq!(pop_count(board.pieces[PieceType::Bishop as usize]), 2);
        assert_eq!(pop_count(board.pieces[PieceType::Rook as usize]), 2);
        assert_eq!(pop_count(board.pieces[PieceType::Queen as usize]), 1);
        assert_eq!(pop_count(board.pieces[PieceType::King as usize]), 1);

        assert_eq!(pop_count(board.pieces[PieceType::PawnBlack as usize]), 8);
        assert_eq!(pop_count(board.pieces[PieceType::KnightBlack as usize]), 2);
        assert_eq!(pop_count(board.pieces[PieceType::BishopBlack as usize]), 2);
        assert_eq!(pop_count(board.pieces[PieceType::RookBlack as usize]), 2);
        assert_eq!(pop_count(board.pieces[PieceType::QueenBlack as usize]), 1);
        assert_eq!(pop_count(board.pieces[PieceType::KingBlack as usize]), 1);

        assert_eq!(bitscan(board.pieces[PieceType::King as usize]), Square::E1);
        assert_eq!(bitscan(board.pieces[PieceType::QueenBlack as usize]), Square::D8);

        assert_eq!(pop_count(board.occupancy), 32);
        assert_eq!(pop_count(board.empty()), 32);
        assert_eq!(pop_count(board.color_occupancy(Color::White)), 16);
        assert_eq!(pop_count(board.color_occupancy(Color::Black)), 16);
    }

    #[test]
    fn generate_pseudolegal_moves_starting_position() {
        let board = Board::new();
        let moves = board.generate_pseudolegal_moves(Color::White);
        let black_moves = board.generate_pseudolegal_moves(Color::Black);

        assert_eq!(moves.len(), 20);
        assert_eq!(black_moves.len(), 20);

        for mov in moves {
            mov.print();
        }
    }

    #[test]
    fn make_move() {
        let fen = String::from("q1b2k2/5p1p/4p1pb/pPPp4/3N4/3nPB2/P2QKnR1/1R6 w - - 0 25");
        let mut board = Board::from_FEN(fen);
        let initial_board = board.clone();
        board.print();

        let black_move = Move { source: Square::F7, target: Square::F5, kind: MoveKind::Quiet };
        println!("\n{:?}", black_move);

        match board.make_move(black_move) {
            Some(..) => panic!("No piece should be captured"),
            None => {},
        };

        board.print();

        assert!(board.pieces[PieceType::PawnBlack as usize] & Square::F7.to_bitboard() == 0);
        assert!(board.pieces[PieceType::PawnBlack as usize] & Square::F5.to_bitboard() > 0);
        assert!(board.ply == 1);

        let white_move = Move { source: Square::D2, target: Square::A5, kind: MoveKind::Capture };
        println!("\n{:?}", white_move);

        match board.make_move(white_move) {
            Some(captured) => assert!(captured == PieceType::PawnBlack),
            None => panic!("A piece should be captured"),
        };

        board.print();

        assert!(board.pieces[PieceType::PawnBlack as usize] & Square::A5.to_bitboard() == 0, "Target piece should be captured");
        assert!(board.pieces[PieceType::Queen as usize] & Square::D2.to_bitboard() == 0);
        assert!(board.pieces[PieceType::Queen as usize] & Square::A5.to_bitboard() > 0);
        assert_ne!(board.occupancy, initial_board.occupancy, "Occupancy should change after make_move");
        assert!(board.ply == 2);
    }

    #[test]
    fn unmake_move() {
        let fen = String::from("q1b2k2/5p1p/4p1pb/pPPp4/3N4/3nPB2/P2QKnR1/1R6 w - - 0 25");
        let mut board = Board::from_FEN(fen);
        let initial_board = board.clone();

        let mov = Move { source: Square::D2, target: Square::A5, kind: MoveKind::Capture };

        board.print();

        let captured_piece = board.make_move(mov);
        board.print();

        board.unmake_move(mov, captured_piece, None, board.castling_rights);
        board.print();

        assert_eq!(board, initial_board, "Board state after unmake_move should be the same as before make_move");
    }

    #[test]
    fn is_square_attacked() {
        let board = Board::new();

        assert_eq!(board.is_square_attacked(Square::E2, Color::White), true);
        assert_eq!(board.is_square_attacked(Square::E2, Color::Black), false);
        assert_eq!(board.is_square_attacked(Square::E4, Color::White), false);
        assert_eq!(board.is_square_attacked(Square::B6, Color::Black), true);
    }

}