freecell 0.1.0

Game objects and rules for the solitaire card game FreeCell
Documentation 
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use crate::{Card, CardCollection, ACE};

//const CASCADE_MAX_SIZE: usize = 52;

/// A stack of arbitrary cards.
///
/// # Rules
///
/// Adding cards:
/// A card can be put on a cascade iff its rank is 1 lower than that of the top card of the cascade
/// and it has a different colour than the top card of the cascade.
///
/// Removing cards:
/// Only the top card of the cascade can be removed.
///
/// # Examples
///
/// TODO [high priority] Add examples
pub type Cascade = Vec<Card>;

fn fits_on_top_of(lower_card: Card, higher_card: Card) -> bool {
    lower_card.suit.colour() != higher_card.suit.colour() &&
    lower_card.rank + 1 == higher_card.rank
}

impl CardCollection for Cascade {
    fn add_card(&self, card: Card) -> Result<Cascade, ()> {
        // optimisation: aces cannot be put on cascades
        // this is technically a legal move, just not a very good one
        if card.rank == ACE {
            return Err(());
        }

        match self.last() {
            // the cascade contains at least one card
            Some(&top_card) => {
                if fits_on_top_of(card, top_card) {
                    // the new card can be put onto this cascade
                    let mut clone = (*self).clone();
                    clone.push(card);
                    Ok(clone)
                } else {
                    // the new card cannot be put onto this cascade
                    Err(())
                }
            }

            // the cascade is empty => the card can be put here, creating a cascade with one card
            None => Ok(vec![card]),
        }
    }

    fn pop_card(&self) -> Vec<(Cascade, Card)> {
        let mut clone = (*self).clone();
        match clone.pop() {
            Some(card) => vec![(clone, card)],
            None => Vec::new(),
        }
    }
}

pub type Cascades = [Cascade; 8];