Bonus Time code for Stanford CS193p Spring 2020 Memorize animation lecture

bonusSnippet.swift

// place this code block inside the Card struct

// MARK: - Bonus Time

// this could give matching bonus points
// if the user matches the card
// before a certain amount of time passes during which the card is face up

// can be zero which means "no bonus available" for this card
var bonusTimeLimit: TimeInterval = 6

// how long this card has ever been face up
private var faceUpTime: TimeInterval {
	if let lastFaceUpDate = self.lastFaceUpDate {
		return pastFaceUpTime + Date().timeIntervalSince(lastFaceUpDate)
	} else {
		return pastFaceUpTime
	}
}
// the last time this card was turned face up (and is still face up)
var lastFaceUpDate: Date?
// the accumulated time this card has been face up in the past
// (i.e. not including the current time it's been face up if it is currently so)
var pastFaceUpTime: TimeInterval = 0

// how much time left before the bonus opportunity runs out
var bonusTimeRemaining: TimeInterval {
	max(0, bonusTimeLimit - faceUpTime)
}
// percentage of the bonus time remaining
var bonusRemaining: Double {
	(bonusTimeLimit > 0 && bonusTimeRemaining > 0) ? bonusTimeRemaining/bonusTimeLimit : 0
}
// whether the card was matched during the bonus time period
var hasEarnedBonus: Bool {
	isMatched && bonusTimeRemaining > 0
}
// whether we are currently face up, unmatched and have not yet used up the bonus window
var isConsumingBonusTime: Bool {
	isFaceUp && !isMatched && bonusTimeRemaining > 0
}
// called when the card transitions to face up state
private mutating func startUsingBonusTime() {
	if isConsumingBonusTime, lastFaceUpDate == nil {
		lastFaceUpDate = Date()
	}
}
// called when the card goes back face down (or gets matched)
private mutating func stopUsingBonusTime() {
	pastFaceUpTime = faceUpTime
	self.lastFaceUpDate = nil
}