gistfile1.swift

protocol Landmarkable {
    var coordinate: CLLocation? { get } //classes must provide at least a Read-Only location called "coordinate"
    func distanceFrom(location: CLLocation) -> CLLocationDistance //classes must provide a distance from another location
}

protocol Outlineable: Landmarkable {
    var outline: [CLLocation]? { get } //must provide an outline represented by an array of locations
    var center: CLLocation? { get } //must provide a center location
}

extension Landmarkable {
    //this is a default implementation for all Landmarkable objects
    //calculates the distance from an arbitrary location to the landmark
    //if it can't be done, returns the maximum distance
    final func distanceFrom(location: CLLocation) -> CLLocationDistance {
        if let co = self.coordinate {
            return co.distanceFromLocation(location)
        }
        return CLLocationDistanceMax
    }
}

extension Outlineable {
    //provides an unweighted average of the location array
    //returns nil if unable to get location array or if that array has no locations in it
    var center: CLLocation? {
        if let locations = self.outline where locations.count > 0 {
            let total = locations.reduce((x: 0.0, y: 0.0, z: 0.0), combine: { (totals, nextLocation) -> (Double, Double, Double) in
                return (totals.x + nextLocation.coordinate.latitude,
                    totals.y + nextLocation.coordinate.longitude,
                    totals.z + nextLocation.altitude)
            })
            let count = Double(locations.count)
            let coordinate = CLLocationCoordinate2D(latitude: total.x / count, longitude: total.y / count)
            let altitude = total.z / count
            
            let computedCenter = CLLocation(coordinate: coordinate, altitude: altitude, horizontalAccuracy: kCLLocationAccuracyBest, verticalAccuracy: kCLLocationAccuracyBest, timestamp: NSDate())
            return computedCenter
        }
        return nil
    }
}