2022-04-24 拓展extension

import Foundation

struct MemoryGame<CardContent> where CardContent: Equatable {
    private(set) var cards: Array<Card>
    
    private var indexOfTheOneAndOnlyMatchCard: Int? {
        get {cards.indices.filter({cards[$0].isFaceUp}).oneAndOnly}
        set {cards.indices.forEach{cards[$0].isFaceUp = ($0 == newValue)}}
    }
    mutating func choose(_ card: Card) {
        if let chosenIndex = cards.firstIndex(where: { $0.id == card.id }) {
            if let potentialMatchIndex = indexOfTheOneAndOnlyMatchCard {
                if cards[chosenIndex].content == cards[potentialMatchIndex].content {
                    cards[chosenIndex].isMatched = true
                    cards[potentialMatchIndex].isMatched = true
                }
                cards[chosenIndex].isFaceUp = true
            }
            else {
                
                indexOfTheOneAndOnlyMatchCard = chosenIndex
            }
        }
    }

    
    init(numberOfPairOfCards: Int, createCardContent: (Int) -> CardContent) {
        cards = []
        for pairIndex in 0..<numberOfPairOfCards {
            let content = createCardContent(pairIndex)
            cards.append(Card(content: content, id: pairIndex*2))
            cards.append(Card(content: content, id: pairIndex*2+1))
        }
    }
    
    struct Card: Identifiable {
        var isFaceUp = false
        var isMatched = false
        let content: CardContent
        let id: Int
    }
}

extension Array {
    var oneAndOnly: Element? {
        if count == 1 {
            return first
        } else {
            return nil
        }
    }
}