freecell 0.1.0

Game objects and rules for the solitaire card game FreeCell
Documentation 
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use super::super::GameState;
use crate::Card;
use crate::Suit::{Club, Diamond, Heart, Spade};

/// Checks whether each possible card exists exactly once
pub fn check_cards(game_state: &GameState) -> Result<(), String> {
    let card_count = count_cards(game_state);

    for (index, &count) in card_count.iter().enumerate() {
        if count != 1 {
            return Err(format!(
                "Card {} exists {} times, should exist once",
                card_from_index(index), count
            ));
        }
    }

    Ok(())
}

/// For each of the 52 possible cards, this function counts how many instances of this card exist.
fn count_cards(game_state: &GameState) -> [i32; 52] {
    let mut card_count = [0; 52];

    for cascade in game_state.cascades.iter() {
        for &card in cascade {
            card_count[card_index(card)] += 1;
        }
    }

    for foundation in game_state.foundations.0.iter() {
        for &card in foundation {
            card_count[card_index(card)] += 1;
        }
    }

    for &card in game_state.freecells.iter() {
        card_count[card_index(card)] += 1;
    }

    card_count
}

fn card_index(card: Card) -> usize {
    card.suit as usize * 13 + card.rank as usize - 1
}

fn card_from_index(index: usize) -> Card {
    Card {
        suit: match index / 13 {
            0 => Club,
            1 => Spade,
            2 => Heart,
            3 => Diamond,
            _ => unreachable!("invalid card index: {}", index),
        },
        rank: (index % 13) as u8 + 1,
    }
}