MapViewController.swift

import UIKit
import MapKit
import CoreData


class MapViewController: UIViewController {

  @IBOutlet weak var mapView: MKMapView!

  var locations = [Location]()
  var managedObjectContext: NSManagedObjectContext! {
    didSet {
      NSNotificationCenter.defaultCenter().addObserverForName(
        NSManagedObjectContextObjectsDidChangeNotification,
        object: managedObjectContext,
        queue: NSOperationQueue.mainQueue()) { _ in
          if self.isViewLoaded() {
            self.updateLocations()
          }
        }
    }
  }


  @IBAction func showUser() {
    
    let region = MKCoordinateRegionMakeWithDistance(mapView.userLocation.coordinate, 1000, 1000)
    mapView.setRegion(mapView.regionThatFits(region), animated: true)

  }

  @IBAction func showLocations() {
    let region = regionForAnnotations(locations)
    mapView.setRegion(region, animated: true)
  }

  override func viewDidLoad() {
    super.viewDidLoad()
    updateLocations()

    if !locations.isEmpty {
      showLocations()
    }
  }

  func updateLocations() {
    mapView.removeAnnotations(locations)

    let entity = NSEntityDescription.entityForName("Location", inManagedObjectContext: managedObjectContext)

    let fetchRequest = NSFetchRequest()
    fetchRequest.entity = entity
    locations = try! managedObjectContext.executeFetchRequest(fetchRequest) as! [Location]

    mapView.addAnnotations(locations)
  }

  func regionForAnnotations(annotations: [MKAnnotation]) -> MKCoordinateRegion {
    var region: MKCoordinateRegion

    switch annotations.count {
    case 0:
      region = MKCoordinateRegionMakeWithDistance(mapView.userLocation.coordinate, 1000, 1000)
    case 1:
      let annotation = annotations[annotations.count - 1]
      region = MKCoordinateRegionMakeWithDistance(annotation.coordinate, 1000, 1000)
    default:
      var topLeftCoord = CLLocationCoordinate2D(latitude: -90, longitude: 180)
      var bottomRightCoord = CLLocationCoordinate2D(latitude: 90, longitude: 180)

      for annotation in annotations {
        topLeftCoord.latitude = max(topLeftCoord.latitude, annotation.coordinate.latitude)
        topLeftCoord.longitude = min(topLeftCoord.longitude, annotation.coordinate.longitude)
        bottomRightCoord.latitude = min(bottomRightCoord.latitude, annotation.coordinate.latitude)
        bottomRightCoord.longitude = max(bottomRightCoord.longitude, annotation.coordinate.longitude)
      }

      let centerLatitude = topLeftCoord.latitude - (topLeftCoord.latitude - bottomRightCoord.latitude) / 2
      let centerLongitude = topLeftCoord.longitude - (topLeftCoord.longitude - bottomRightCoord.longitude) / 2
      let center = CLLocationCoordinate2D(latitude: centerLatitude, longitude:  centerLongitude)

      let extraSpace = 1.1
      let span = MKCoordinateSpan(latitudeDelta: abs(topLeftCoord.latitude - bottomRightCoord.latitude) * extraSpace, longitudeDelta: abs(topLeftCoord.longitude - bottomRightCoord.longitude) * extraSpace)
      region = MKCoordinateRegion(center: center, span: span)
    }


    return mapView.regionThatFits(region)
  }

  override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "EditLocation" {
      let navigationController = segue.destinationViewController as! UINavigationController

      let controller = navigationController.topViewController as! LocationDetailsViewController

      controller.managedObjectContext = managedObjectContext

      let button = sender as! UIButton
      let location = locations[button.tag]

      controller.locationToEdit = location
    }
  }
}

extension MapViewController: MKMapViewDelegate {
  func mapView(mapView: MKMapView, viewForAnnotation annotation: MKAnnotation) -> MKAnnotationView? {
    guard annotation is Location else {
      return nil
    }
    let identifier = "Location"
    var annotationView = mapView.dequeueReusableAnnotationViewWithIdentifier(identifier) as! MKPinAnnotationView!
    if annotationView == nil {
      annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: identifier)
      annotationView.enabled = true
      annotationView.canShowCallout = true
      annotationView.animatesDrop = false
      annotationView.pinTintColor = UIColor(red: 0.32, green: 0.82, blue: 0.4, alpha: 1)
      annotationView.tintColor = UIColor(white: 0.0, alpha: 0.5)

      let rightButton = UIButton(type: .DetailDisclosure)
      rightButton.addTarget(self, action: #selector(MapViewController.showLocationDetails(_:)), forControlEvents: .TouchUpInside)
      annotationView.rightCalloutAccessoryView = rightButton
    } else {
      annotationView.annotation = annotation
    }


    let button = annotationView.rightCalloutAccessoryView as! UIButton
    if let index = locations.indexOf(annotation as! Location) {
      button.tag = index
    }

    return annotationView
  }

  func showLocationDetails(sender: UIButton) {
    performSegueWithIdentifier("EditLocation", sender: sender)
  }
}

extension MapViewController: UINavigationBarDelegate {
  func positionForBar(bar: UIBarPositioning) -> UIBarPosition {
    return .TopAttached
  }
}