rust_fish_chess_engine 0.1.4

A chess engine and functionality built in Rust. Built for the intention of incorporating it into my Svelte chess project through WASM.
Documentation 
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use crate::{Piece, PieceType};
use super::{check::king_is_checked, move_piece::{move_piece, unmove_piece}, search_for_moves::search_for_moves, Move, SpecialRule};

#[derive(Debug, Clone)]
pub struct CastleState {
    pub white_king_moved: bool,
    pub white_left_rook_moved: bool,
    pub white_right_rook_moved: bool,
    pub black_king_moved: bool,
    pub black_left_rook_moved: bool,
    pub black_right_rook_moved: bool,
}

impl CastleState {
    pub fn new() -> CastleState {
        CastleState {
            white_king_moved: false,
            white_left_rook_moved: false,
            white_right_rook_moved: false,
            black_king_moved: false,
            black_left_rook_moved: false,
            black_right_rook_moved: false,
        }
    }
}

pub fn calculate_king_moves(
    board: &mut Vec<Vec<Option<Piece>>>,
    ir: usize,
    ic: usize,
    whites_turn: bool,
    previous_move: &Option<Move>,
    castle_state: &mut CastleState,
    only_including_captures: bool
) -> Result<Vec<Move>, String> {
    let possible_moves = search_for_moves(board, ir, ic, whites_turn, PieceType::King.directions(), 1)?;
    if only_including_captures {
        return Ok(possible_moves)
    }
    let possible_castling_moves = calculate_castling_moves(board, whites_turn, previous_move, castle_state)?;
    Ok(vec![possible_moves, possible_castling_moves].concat())
}

fn calculate_castling_moves(
    board: &mut Vec<Vec<Option<Piece>>>,
    whites_turn: bool,
    previous_move: &Option<Move>,
    castle_state: &mut CastleState,
) -> Result<Vec<Move>, String> {
    let mut possible_moves = Vec::new();
    if whites_turn {
        if !castle_state.white_king_moved {
            if !castle_state.white_right_rook_moved && board[7][5].is_none() && board[7][6].is_none() {
                match board[7][7] {
                    Some(Piece::White(PieceType::Rook)) => {
                        if all_tiles_free_from_check(vec![(7, 5), (7, 6)], (7, 4), board, whites_turn, previous_move, castle_state)? {
                            possible_moves.push(Move { current_pos: (7, 4), new_pos: (7, 6), special_rule: Some(SpecialRule::Castle) })
                        }
                    },
                    _ => {}
                };
            }
            if !castle_state.white_left_rook_moved && board[7][1].is_none() && board[7][2].is_none() && board[7][3].is_none() {
                // make sure rook is in fact there as it could have been taken
                match board[7][0] {
                    Some(Piece::White(PieceType::Rook)) => {
                        if all_tiles_free_from_check(vec![(7, 1), (7, 2), (7, 3)], (7, 4), board, whites_turn, previous_move, castle_state)? {
                            possible_moves.push(Move { current_pos: (7, 4), new_pos: (7, 2), special_rule: Some(SpecialRule::Castle) })
                        }
                    },
                    _ => {}
                };
            }
        }
    } else {
        if !castle_state.black_king_moved {
            if !castle_state.black_right_rook_moved && board[0][5].is_none() && board[0][6].is_none() {
                match board[0][7] {
                    Some(Piece::Black(PieceType::Rook)) => {
                        if all_tiles_free_from_check(vec![(0, 5), (0, 6)], (0, 4), board, whites_turn, previous_move, castle_state)? {
                            possible_moves.push(Move { current_pos: (0, 4), new_pos: (0, 6), special_rule: Some(SpecialRule::Castle) })
                        }
                    },
                    _ => {}
                };
            }
            if !castle_state.black_left_rook_moved && board[0][1].is_none() && board[0][2].is_none() && board[0][3].is_none() {
                match board[0][0] {
                    Some(Piece::Black(PieceType::Rook)) => {
                        if all_tiles_free_from_check(vec![(0, 1), (0, 2), (0, 3)], (0, 4), board, whites_turn, previous_move, castle_state)? {
                            possible_moves.push(Move { current_pos: (0, 4), new_pos: (0, 2), special_rule: Some(SpecialRule::Castle) })
                        }
                    },
                    _ => {}
                };
            }
        }
    }

    Ok(possible_moves)
}

fn all_tiles_free_from_check(
    tiles: Vec<(usize, usize)>,
    king_position: (usize, usize),
    board: &mut Vec<Vec<Option<Piece>>>,
    whites_turn: bool,
    previous_move: &Option<Move>,
    castle_state: &mut CastleState
) -> Result<bool, String> {
    if king_is_checked(board, whites_turn, previous_move, castle_state) == Ok(true) {
        return Ok(false)
    }

    for tile in tiles {
        let taken_piece = move_piece(
            &Move { current_pos: king_position, new_pos: tile, special_rule: None },
            board,
            castle_state
        );
        if king_is_checked(board, whites_turn, previous_move, &mut castle_state.clone())? {
            unmove_piece(&Move { current_pos: king_position, new_pos: tile, special_rule: None }, board, taken_piece)?;
            return Ok(false)
        }
        unmove_piece(&Move { current_pos: king_position, new_pos: tile, special_rule: None }, board, taken_piece)?;
    }

    Ok(true)
}