BackgroundingSourceTracker.swift

import UIKit

enum BackgroundingSource: String {
    case lock = "lock", homeOrSwitch = "homeOrSwitch"
}

protocol BackgroundingSourceTrackerDelegate: class {
    func backgroundingSourceTracker(_ backgroundingSourceTracker: BackgroundingSourceTracker, didTrackBackgroundingWith source: BackgroundingSource)
}

final class BackgroundingSourceTracker {
    weak var delegate: BackgroundingSourceTrackerDelegate?
    
    private var source: BackgroundingSource? {
        didSet {
            guard let source = source else {
                return
            }
            delegate?.backgroundingSourceTracker(self, didTrackBackgroundingWith: source)
        }
    }
    
    private var brightness: CGFloat = 1
    
    private func didUserPressLockButton() -> Bool {
        UIScreen.main.brightness = brightness + (brightness <= 0.01 ? (0.01) : (-0.01))
        let testBrightness = UIScreen.main.brightness
        UIScreen.main.brightness = brightness
        return brightness != testBrightness
    }
    
    func didEnterBackground() {
        source = didUserPressLockButton() ? .lock : .homeOrSwitch
    }
    
    func didBecomeActive() {
        brightness = UIScreen.main.brightness
    }
}