Solution to Ray Wenderlich's Swift Ninja challenge

SwiftNinja2.swift

// Solution to ultimate Swift Nija challenge
// http://www.raywenderlich.com/77845/swift-ninja-part-2

enum Suit {
    case Clubs, Diamonds, Hearts, Spades
}

enum Rank {
    case Jack, Queen, King, Ace
    case Num(Int)
}

struct Card {
    let suit: Suit
    let rank: Rank
}

// ---- Implementation ----

extension Int {
    func isOdd() -> Bool {
        return (self % 2 == 1)
    }
}

struct CardCount {
    let previous:Card
    let sum:Int
}


func reduceFunc(upto:CardCount, card:Card) -> CardCount {
    let previousCard = upto.previous

    switch(card.rank, previousCard.suit, previousCard.rank) {

        case (Rank.Ace, Suit.Diamonds, Rank.Num(5)):
            return CardCount(previous:card, sum:upto.sum + 100)
        
        case (Rank.Num(let num), Suit.Hearts, _) where num.isOdd():
            return CardCount(previous: card, sum: upto.sum + num * 2)
        
        default:
            return CardCount(previous: card, sum: upto.sum)
    }
    
}



func countHand(cards:[Card]) -> Int {

    let tail = dropFirst(cards)
    
    return tail.reduce(CardCount(previous: cards.first!,sum: 0), combine: reduceFunc).sum
    
}


// ==== Test ====

countHand([
    Card(suit:Suit.Hearts, rank:Rank.Num(10)),
    Card(suit:Suit.Hearts, rank:Rank.Num(6)),
    Card(suit:Suit.Diamonds, rank:Rank.Num(5)),
    Card(suit:Suit.Clubs, rank:Rank.Ace),
    Card(suit:Suit.Diamonds, rank:Rank.Jack)
])