/*

    Copyright (C) 2017 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    A view controller that demostrates how to use `UIProgressView`. The `UIProgressView`s are updated via Key Value Observing of an `NSProgress` object's `frationCompleted` property. The `NSProgress` is updated via a repeating timer.

*/

import UIKit

/**

    The KVO context for `ProgressViewController` instances. This provides a stable

    address to use as the `context` parameter for KVO observation methods.

*/

private var progressViewKVOContext = 0

class ProgressViewController: UIViewController {

    // MARK: Properties

    @IBOutlet var progressViews: [UIProgressView]!

    /**

        An `NSProgress` object who's `fractionCompleted` is observed using

        KVO to update the `UIProgressView`s' `progress` properties.

    */

    private let progress = Progress(totalUnitCount: 10)

    /**

        A repeating timer that, when fired, updates the `NSProgress` object's

        `completedUnitCount` property.

    */

    private var updateTimer: Timer?

    // MARK: Initialization

    required init?(coder aDecoder: NSCoder) {

        super.init(coder: aDecoder)

        // Register as an observer of the `NSProgress`'s `fractionCompleted` property.

        progress.addObserver(self, forKeyPath: #keyPath(Progress.fractionCompleted), options: [.new], context: &progressViewKVOContext)

    }

    deinit {

        // Unregister as an observer of the `NSProgress`'s `fractionCompleted` property.

        progress.removeObserver(self, forKeyPath: #keyPath(Progress.fractionCompleted))

    }

    // MARK: UIViewController

    override func viewDidAppear(_ animated: Bool) {

        super.viewDidAppear(animated)

        // Reset the completed progress of the `UIProgressView`s.

        for progressView in progressViews {

            progressView.setProgress(0.0, animated: false)

        }

        /*

            Reset the `completedUnitCount` of the `NSProgress` object and create

            a repeating timer to increment it over time.

        */

        progress.completedUnitCount = 0

        updateTimer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ProgressViewController.timerDidFire), userInfo: nil, repeats: true)

    }

    override func viewDidDisappear(_ animated: Bool) {

        super.viewDidDisappear(animated)

        // Stop the timer from firing.

        updateTimer?.invalidate()

    }

    // MARK: Key Value Observing (KVO)

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey: Any]?, context: UnsafeMutableRawPointer?) {

        // Check if this is the KVO notification for our `NSProgress` object.

        if context == &progressViewKVOContext,

            keyPath == "fractionCompleted",

            let newProgress = object as? Progress,

            newProgress == progress {

            // Update the progress views.

            for progressView in progressViews {

                progressView.setProgress(Float(progress.fractionCompleted), animated: true)

            }

        }

        else {

            super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)

        }

    }

    // MARK: Convenience

    func timerDidFire() {

        /*

            Update the `completedUnitCount` of the `NSProgress` object if it's

            not completed. Otherwise, stop the timer.

        */

        if progress.completedUnitCount < progress.totalUnitCount {

            progress.completedUnitCount += 1

        }

        else {

            updateTimer?.invalidate()

        }

    }

}