WdtWeatherSource: add checks to avoid updating one location multiple times simultaneously.

1Weather/Network/Weather/WdtWeatherSource.swift

@@ -10,10 +10,12 @@ import CoreLocation
 import XMLCoder
 
 public enum WdtWeatherSourceError: Error {
+    case insufficientLocationInfo
     case badUrl
     case networkError(Error?)
     case badServerResponse(Error?)
     case dataMergeError(String)
+    case alreadyBeingUpdated
 }
 
 public class WdtWeatherSource: WeatherSource {
@@ -21,10 +23,39 @@ public class WdtWeatherSource: WeatherSource {
     private static let updateUrlMega = "https://1weather.onelouder.com/feeds/onelouder/mega.php"
     private static let updateUrlMicro = "https://1weather.onelouder.com/feeds/onelouder2/fm.php"
     
+    /// This queue is needed to synchronize access to locationsBeingUpdated. Also, to make logging more clear.
+    private let internalQueue: OperationQueue = {
+        let queue = OperationQueue()
+        queue.name = "WdtWeatherSource Queue"
+        queue.maxConcurrentOperationCount = 1
+        return queue
+    }()
+    
+    /// This is used
+    private var locationsBeingUpdated = Set<Location>()
+    
     public let weatherUpdateInterval = TimeInterval(15 * 60) // 15 minutes
     
     public func updateWeather(for location: Location, completion: @escaping WeatherSourceCompletion) {
-        log.debug("Start update.")
+        internalQueue.addOperation { [weak self] in
+            let extendedCompletion: WeatherSourceCompletion = { [weak self] (updatedLocation, error) in
+                self?.internalQueue.addOperation {
+                    completion(updatedLocation, error)
+                    self?.locationsBeingUpdated.remove(location)
+                }
+            }
+            self?.updateWeatherInternal(for: location, completion: extendedCompletion)
+        }
+    }
+    
+    /// This method should only be run from the internalQueue.
+    private func updateWeatherInternal(for location: Location, completion: @escaping WeatherSourceCompletion) {
+        guard !locationsBeingUpdated.contains(location) else {
+            completion(nil, WdtWeatherSourceError.alreadyBeingUpdated)
+            return
+        }
+
+        log.debug("Start update for \(location)")
         guard var urlComponents = URLComponents(string: WdtWeatherSource.updateUrlMega) else {
             assertionFailure("Should never happen. The URL should be correct.")
             return
@@ -42,6 +73,11 @@ public class WdtWeatherSource: WeatherSource {
             queryParameters["STATE"] = location.region
             queryParameters["COUNTRY"] = location.countryName
         }
+        guard !queryParameters.isEmpty else {
+            completion(nil, WdtWeatherSourceError.insufficientLocationInfo)
+            log.error("Not enough information about location.")
+            return
+        }
         queryParameters["UNITS"] = "all"
         urlComponents.queryItems = queryParameters.map { URLQueryItem(name: $0, value: $1) }
         
@@ -49,6 +85,7 @@ public class WdtWeatherSource: WeatherSource {
             completion(nil, WdtWeatherSourceError.badUrl)
             return
         }
+        log.debug("query params: \(queryParameters)")
         
         let urlSession = URLSession.shared
         let dataTask = urlSession.dataTask(with: url) { [weak self] (data, reponse, error) in
@@ -60,7 +97,7 @@ public class WdtWeatherSource: WeatherSource {
             let decoder = XMLDecoder()
             do {
                 let locationResponse = try decoder.decode(WdtLocationResponse.self, from: data)
-                guard let newLocation = try self.update(location: location, from: locationResponse) else {
+                guard let newLocation = try self.applyChangesTo(location: location, from: locationResponse) else {
                     completion(nil, WdtWeatherSourceError.badServerResponse(error))
                     return
                 }
@@ -74,7 +111,7 @@ public class WdtWeatherSource: WeatherSource {
         dataTask.resume()
     }
     
-    func update(location: Location, from locationResponse: WdtLocationResponse) throws -> Location? {
+    private func applyChangesTo(location: Location, from locationResponse: WdtLocationResponse) throws -> Location? {
         guard let wdtLocation = locationResponse.locations.first else {
             return nil
         }