src/movegen.rs

use crate::types::*;
use crate::bitboard::{Bitboard, EMPTY, pop_lsb};
use crate::position::Position;

pub fn knight_mask(sq: Square) -> Bitboard {
    let b: Bitboard = 1 << (sq as u8);
    let mut mask = EMPTY;
    mask |= (b << 17) & !crate::bitboard::FILE_A;
    mask |= (b << 10) & !(crate::bitboard::FILE_A | 0x0202020202020202);
    mask |= (b >> 6) & !(crate::bitboard::FILE_A | 0x0202020202020202);
    mask |= (b >> 15) & !crate::bitboard::FILE_A;
    mask |= (b << 15) & !crate::bitboard::FILE_H;
    mask |= (b << 6) & !(crate::bitboard::FILE_H | 0x4040404040404040);
    mask |= (b >> 10) & !(crate::bitboard::FILE_H | 0x4040404040404040);
    mask |= (b >> 17) & !crate::bitboard::FILE_H;
    mask
}

pub fn king_mask(sq: Square) -> Bitboard {
    let b: Bitboard = 1 << (sq as u8);
    let mut mask = EMPTY;
    mask |= (b << 8) | (b >> 8);
    mask |= (b << 1) & !crate::bitboard::FILE_A;
    mask |= (b >> 7) & !crate::bitboard::FILE_A;
    mask |= (b << 9) & !crate::bitboard::FILE_A;
    mask |= (b >> 1) & !crate::bitboard::FILE_H;
    mask |= (b >> 9) & !crate::bitboard::FILE_H;
    mask |= (b << 7) & !crate::bitboard::FILE_H;
    mask
}

pub fn pawn_attack_mask(sq: Square, side: Color) -> Bitboard {
    let b: Bitboard = 1 << (sq as u8);
    let mut mask = EMPTY;
    if side == Color::White {
        mask |= (b << 7) & !crate::bitboard::FILE_H;
        mask |= (b << 9) & !crate::bitboard::FILE_A;
    } else {
        mask |= (b >> 9) & !crate::bitboard::FILE_H;
        mask |= (b >> 7) & !crate::bitboard::FILE_A;
    }
    mask
}

pub fn sliding_attacks(sq: Square, occ: Bitboard, diagonal: bool) -> Bitboard {
    let mut attacks = EMPTY;
    let r = (sq as u8) / 8;
    let f = (sq as u8) % 8;

    let dirs: &[(i8, i8)] = if diagonal {
        &[(1, 1), (1, -1), (-1, 1), (-1, -1)]
    } else {
        &[(1, 0), (-1, 0), (0, 1), (0, -1)]
    };

    for &(dr, df) in dirs {
        let mut nr = r as i8 + dr;
        let mut nf = f as i8 + df;
        while nr >= 0 && nr < 8 && nf >= 0 && nf < 8 {
            let n_sq = nr * 8 + nf;
            attacks |= 1 << n_sq;
            if (occ & (1 << n_sq)) != 0 {
                break;
            }
            nr += dr;
            nf += df;
        }
    }
    attacks
}

pub fn generate_moves(pos: &Position, list: &mut Vec<Move>) {
    let us = pos.side_to_move;
    let occ = pos.colors[0] | pos.colors[1];
    let target = !pos.colors[us as usize];

    let mut knights = pos.pieces[PieceType::Knight as usize] & pos.colors[us as usize];
    while knights != EMPTY {
        let from_sq = pop_lsb(&mut knights);
        let mut attacks = knight_mask(Square::from_u8(from_sq)) & target;
        while attacks != EMPTY {
            let to_sq = pop_lsb(&mut attacks);
            list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(to_sq), PieceType::None));
        }
    }

    let mut king = pos.pieces[PieceType::King as usize] & pos.colors[us as usize];
    if king != EMPTY {
        let from_sq = pop_lsb(&mut king);
        let mut attacks = king_mask(Square::from_u8(from_sq)) & target;
        while attacks != EMPTY {
            let to_sq = pop_lsb(&mut attacks);
            list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(to_sq), PieceType::None));
        }
    }

    let mut sliders = (pos.pieces[PieceType::Bishop as usize] | pos.pieces[PieceType::Queen as usize]) & pos.colors[us as usize];
    while sliders != EMPTY {
        let from_sq = pop_lsb(&mut sliders);
        let mut attacks = sliding_attacks(Square::from_u8(from_sq), occ, true) & target;
        while attacks != EMPTY {
            let to_sq = pop_lsb(&mut attacks);
            list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(to_sq), PieceType::None));
        }
    }

    let mut straights = (pos.pieces[PieceType::Rook as usize] | pos.pieces[PieceType::Queen as usize]) & pos.colors[us as usize];
    while straights != EMPTY {
        let from_sq = pop_lsb(&mut straights);
        let mut attacks = sliding_attacks(Square::from_u8(from_sq), occ, false) & target;
        while attacks != EMPTY {
            let to_sq = pop_lsb(&mut attacks);
            list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(to_sq), PieceType::None));
        }
    }

    let mut pawns = pos.pieces[PieceType::Pawn as usize] & pos.colors[us as usize];
    while pawns != EMPTY {
        let from_sq = pop_lsb(&mut pawns);
        let f_rank = from_sq / 8;
        
        if us == Color::White {
            let single_push = from_sq + 8;
            if (occ & (1 << single_push)) == 0 {
                if f_rank == 6 {
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::Queen));
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::Rook));
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::Bishop));
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::Knight));
                } else {
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::None));
                    let double_push = from_sq + 16;
                    if f_rank == 1 && (occ & (1 << double_push)) == 0 {
                        list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(double_push), PieceType::None));
                    }
                }
            }
            
            let mut attacks = pawn_attack_mask(Square::from_u8(from_sq), Color::White) & pos.colors[Color::Black as usize];
            if pos.ep_square != Square::None && (pawn_attack_mask(Square::from_u8(from_sq), Color::White) & (1 << (pos.ep_square as u8))) != 0 {
                attacks |= 1 << (pos.ep_square as u8);
            }
            while attacks != EMPTY {
                let to_sq = pop_lsb(&mut attacks);
                if f_rank == 6 {
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(to_sq), PieceType::Queen));
                } else {
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(to_sq), PieceType::None));
                }
            }
        } else {
            let single_push = from_sq - 8;
            if (occ & (1 << single_push)) == 0 {
                if f_rank == 1 {
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::Queen));
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::Rook));
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::Bishop));
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::Knight));
                } else {
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(single_push), PieceType::None));
                    let double_push = from_sq - 16;
                    if f_rank == 6 && (occ & (1 << double_push)) == 0 {
                        list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(double_push), PieceType::None));
                    }
                }
            }

            let mut attacks = pawn_attack_mask(Square::from_u8(from_sq), Color::Black) & pos.colors[Color::White as usize];
            if pos.ep_square != Square::None && (pawn_attack_mask(Square::from_u8(from_sq), Color::Black) & (1 << (pos.ep_square as u8))) != 0 {
                attacks |= 1 << (pos.ep_square as u8);
            }
            while attacks != EMPTY {
                let to_sq = pop_lsb(&mut attacks);
                if f_rank == 1 {
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(to_sq), PieceType::Queen));
                } else {
                    list.push(Move::new(Square::from_u8(from_sq), Square::from_u8(to_sq), PieceType::None));
                }
            }
        }
    }
}