blackjack/src/hand.rs

use crate::card::Card;
use itertools::Itertools;
use std::fmt;

#[derive(Clone, Debug)]
pub struct Hand {
    cards: Vec<Card>,
}

impl Hand {
    pub fn new() -> Self {
        Self { cards: Vec::new() }
    }

    /// Returns the value of the hand. If there are any aces, this is the highest value without
    /// busting.
    pub fn value(&self) -> u8 {
        let mut num_aces = 0;
        let mut sum = 0;

        // count up the value of everything that's not an ace
        for card in &self.cards {
            if card.value == "A" {
                num_aces += 1;
            } else {
                sum += u8::from(card);
            }
        }

        if num_aces == 0 {
            return sum;
        }

        // Figure out the possible ace sums based on how many aces we have
        let mut values: Vec<u8> = [1, 11]
            .into_iter()
            .combinations_with_replacement(num_aces)
            .map(|a| a.iter().sum())
            .collect();

        // Find the highest value without busting, adding in the rest of the cards. If they all
        // bust, then take the lowest value.
        values.sort();
        values.reverse();
        let mut total = 0;
        for v in values.iter() {
            total = v + sum;
            if total <= 21 {
                break;
            }
        }

        total
    }

    /// Returns true if the hand is a blackjack, meaning we have an ace and a 10-valued card
    pub fn is_blackjack(&self) -> bool {
        self.cards.len() == 2 && self.value() == 21
    }

    /// Returns true if hand has an ace
    pub fn has_ace(&self) -> bool {
        for card in &self.cards {
            if card.value == "A" {
                return true;
            }
        }
        false
    }

    /// Returns true if the hand has a pair (can be split)
    pub fn is_pair(&self) -> bool {
        self.cards.len() == 2 && u8::from(&self.cards[0]) == u8::from(&self.cards[1])
    }

    /// Returns a read-only copy of the cards in the hand
    pub fn cards(&self) -> Vec<Card> {
        self.cards.clone()
    }

    /// Add a card to the hand
    pub fn push(&mut self, card: Card) {
        self.cards.push(card)
    }

    /// Split the hand into two
    pub fn split(&mut self) -> Hand {
        let other_cards: Vec<Card> = Vec::from(self.cards.pop().as_slice());

        Hand { cards: other_cards }
    }
}

impl Default for Hand {
    fn default() -> Self {
        Hand::new()
    }
}

impl From<Vec<Card>> for Hand {
    fn from(cards: Vec<Card>) -> Self {
        Self { cards }
    }
}

impl From<Vec<(&str, &str)>> for Hand {
    fn from(str_cards: Vec<(&str, &str)>) -> Self {
        Self {
            cards: str_cards.into_iter().map(|c| (c).into()).collect(),
        }
    }
}

impl fmt::Display for Hand {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        for (i, c) in self.cards.iter().enumerate() {
            if i != 0 {
                write!(f, " ")?;
            }
            write!(f, "{c}")?;
        }
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::card::{Card, Suit};

    #[test]
    fn no_aces() {
        let mut h = Hand::new();
        h.cards.push(Card::new(Suit::Club, "K"));
        h.cards.push(Card::new(Suit::Club, "7"));
        assert_eq!(h.value(), 17);
    }

    #[test]
    fn one_ace() {
        let mut h = Hand::new();
        h.cards.push(Card::new(Suit::Club, "K"));
        h.cards.push(Card::new(Suit::Club, "A"));
        assert_eq!(h.value(), 21);
    }

    #[test]
    fn three_aces() {
        let mut h = Hand::new();
        h.cards.push(Card::new(Suit::Club, "3"));
        h.cards.push(Card::new(Suit::Club, "A"));
        h.cards.push(Card::new(Suit::Club, "A"));
        h.cards.push(Card::new(Suit::Club, "A"));
        assert_eq!(h.value(), 16);
    }
}