Advanced-NSOperations/Earthquakes/EarthquakeTableViewController.swift

/*
Copyright (C) 2015 Apple Inc. All Rights Reserved.
See LICENSE.txt for this sample’s licensing information

Abstract:
A static UITableViewController to display details of an earthquake
*/

import UIKit
import MapKit

class EarthquakeTableViewController: UITableViewController {
    // MARK: Properties

    var queue: EarthquakeOperationQueue?
    var earthquake: Earthquake?
    var locationRequest: LocationOperation?

    @IBOutlet var map: MKMapView!
    @IBOutlet var nameLabel: UILabel!
    @IBOutlet var magnitudeLabel: UILabel!
    @IBOutlet var depthLabel: UILabel!
    @IBOutlet var timeLabel: UILabel!
    @IBOutlet var distanceLabel: UILabel!

    // MARKL View Controller

    override func viewDidLoad() {
        super.viewDidLoad()

        // Default all labels if there's no earthquake.
        guard let earthquake = earthquake else {
            nameLabel.text = ""
            magnitudeLabel.text = ""
            depthLabel.text = ""
            timeLabel.text = ""
            distanceLabel.text = ""

            return
        }

        let span = MKCoordinateSpan(latitudeDelta: 15, longitudeDelta: 15)
        map.region = MKCoordinateRegion(center: earthquake.coordinate, span: span)

        let annotation = MKPointAnnotation()
        annotation.coordinate = earthquake.coordinate
        map.addAnnotation(annotation)

        nameLabel.text = earthquake.name
        magnitudeLabel.text = Earthquake.magnitudeFormatter.string(from: NSNumber(value: earthquake.magnitude))
        depthLabel.text = Earthquake.depthFormatter.string(fromMeters: earthquake.depth)
        timeLabel.text = Earthquake.timestampFormatter.string(from: earthquake.timestamp as Date)

        /*
            We can use a `LocationOperation` to retrieve the user's current location.
            Once we have the location, we can compute how far they currently are
            from the epicenter of the earthquake.

            If this operation fails (ie, we are denied access to their location),
            then the text in the `UILabel` will remain as what it is defined to
            be in the storyboard.
        */
        let locationOperation = LocationOperation(accuracy: kCLLocationAccuracyKilometer) { location in
            if let earthquakeLocation = self.earthquake?.location {
                let distance = location.distance(from: earthquakeLocation)
                self.distanceLabel.text = Earthquake.distanceFormatter.string(fromMeters: distance)
            }

            self.locationRequest = nil
        }

        queue?.addOperation(locationOperation)
        locationRequest = locationOperation
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        // If the LocationOperation is still going on, then cancel it.
        locationRequest?.cancel()
    }

    @IBAction func shareEarthquake(sender: UIBarButtonItem) {
        guard let earthquake = earthquake else { return }
        guard let url = URL(string: earthquake.webLink) else { return }

        let location = earthquake.location

        let items = [url, location] as [Any]

        /*
            We could present the share sheet manually, but by putting it inside
            an `EarthquakeOperation`, we can make it mutually exclusive with other operations
            that modify the view controller hierarchy.
        */
        let shareOperation = EarthquakeBlockOperation { (continuation: @escaping () -> Void) in
            DispatchQueue.main.async {
                let shareSheet = UIActivityViewController(activityItems: items, applicationActivities: nil)

                shareSheet.popoverPresentationController?.barButtonItem = sender

                shareSheet.completionWithItemsHandler = { _, _, _, _ in
                    // End the operation when the share sheet completes.
                    continuation()
                }

                self.present(shareSheet, animated: true, completion: nil)
            }
        }

        /*
            Indicate that this operation modifies the View Controller hierarchy
            and is thus mutually exclusive.
        */
        shareOperation.addCondition(condition: MutuallyExclusive<UIViewController>())

        queue?.addOperation(shareOperation)
    }

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        if indexPath.section == 1 && indexPath.row == 0 {
            // The user has tapped the "More Information" button.
            if let link = earthquake?.webLink, let url = URL(string: link) {
                // If we have a link, present the "More Information" dialog.
                let moreInformation = MoreInformationOperation(URL: url)

                queue?.addOperation(moreInformation)
            }
            else {
                // No link; present an alert.
                let alert = AlertOperation()
                alert.title = "No Information"
                alert.message = "No other information is available for this earthquake"
                queue?.addOperation(alert)
            }
        }

        tableView.deselectRow(at: indexPath as IndexPath, animated: true)
    }
}

extension EarthquakeTableViewController: MKMapViewDelegate {
    func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        guard let earthquake = earthquake else { return nil }

        var view = mapView.dequeueReusableAnnotationView(withIdentifier: "pin") as? MKPinAnnotationView

        view = view ?? MKPinAnnotationView(annotation: annotation, reuseIdentifier: "pin")

        guard let pin = view else { return nil }

        switch earthquake.magnitude {
        case 0..<3: pin.pinTintColor = UIColor.gray
        case 3..<4: pin.pinTintColor = UIColor.blue
        case 4..<5: pin.pinTintColor = UIColor.orange
        default:    pin.pinTintColor = UIColor.red
        }

        pin.isEnabled = false

        return pin
    }
}