Prefetch audio instructions

MapboxNavigation/PollyVoiceController.swift

@@ -31,11 +31,21 @@ public class PollyVoiceController: RouteVoiceController {
      */
     public var timeoutIntervalForRequest:TimeInterval = 2
 
+    /**
+     Number of steps ahead of the current step to cache spoken instructions.
+     */
+    public var stepsAheadToCache: Int = 3
+
     var pollyTask: URLSessionDataTask?
 
     let sessionConfiguration = URLSessionConfiguration.default
     var urlSession: URLSession
 
+    var cacheURLSession: URLSession
+    var cachePollyTask: URLSessionDataTask?
+
+    var spokenInstructionsForRoute: [String: Data] = [:]
+
     public init(identityPoolId: String) {
         self.identityPoolId = identityPoolId
 
@@ -45,6 +55,7 @@ public class PollyVoiceController: RouteVoiceController {
 
         sessionConfiguration.timeoutIntervalForRequest = timeoutIntervalForRequest;
         urlSession = URLSession(configuration: sessionConfiguration)
+        cacheURLSession = URLSession(configuration: URLSessionConfiguration.default)
 
         super.init()
     }
@@ -57,14 +68,31 @@ public class PollyVoiceController: RouteVoiceController {
 
         pollyTask?.cancel()
         audioPlayer?.stop()
+        startAnnouncementTimer()
+
+        for (stepIndex, step) in routeProgresss.currentLegProgress.leg.steps.suffix(from: routeProgresss.currentLegProgress.stepIndex).enumerated() {
+            let adjustedStepIndex = stepIndex + routeProgresss.currentLegProgress.stepIndex
+
+            guard adjustedStepIndex < routeProgresss.currentLegProgress.stepIndex + stepsAheadToCache else { continue }
+            guard let instructions = step.instructionsSpokenAlongStep else { continue }
+
+            for instruction in instructions {
+                guard spokenInstructionsForRoute[instruction.ssmlText] == nil else { continue }
+
+                cacheSpokenInstruction(instruction: instruction.ssmlText)
+            }
+        }
+
+
+        guard spokenInstructionsForRoute[instruction] == nil else {
+            play(spokenInstructionsForRoute[instruction]!)
+            return
+        }
 
         speak(instruction, error: nil)
-        startAnnouncementTimer()
     }
 
-    override func speak(_ text: String, error: String?) {
-        assert(!text.isEmpty)
-
+    func pollyURL(for instruction: String) ->  AWSPollySynthesizeSpeechURLBuilderRequest {
         let input = AWSPollySynthesizeSpeechURLBuilderRequest()
         input.textType = .ssml
         input.outputFormat = .mp3
@@ -108,15 +136,22 @@ public class PollyVoiceController: RouteVoiceController {
         case ("tr", _):
             input.voiceId = .filiz
         default:
-            callSuperSpeak(fallbackText, error: "Voice \(langCode)-\(countryCode) not found")
-            return
+            input.voiceId = .joanna
         }
 
         if let voiceId = globalVoiceId {
             input.voiceId = voiceId
         }
 
-        input.text = text
+        input.text = instruction
+
+        return input
+    }
+
+    override func speak(_ text: String, error: String?) {
+        assert(!text.isEmpty)
+
+        let input = pollyURL(for: text)
 
         let builder = AWSPollySynthesizeSpeechURLBuilder.default().getPreSignedURL(input)
         builder.continueWith { [weak self] (awsTask: AWSTask<NSURL>) -> Any? in
@@ -172,29 +207,63 @@ public class PollyVoiceController: RouteVoiceController {
                 return
             }
 
+            strongSelf.play(data)
+        }
+
+        pollyTask?.resume()
+    }
+
+    func cacheSpokenInstruction(instruction: String) {
+
+        let pollyRequestURL = pollyURL(for: instruction)
+
+        let builder = AWSPollySynthesizeSpeechURLBuilder.default().getPreSignedURL(pollyRequestURL)
+        builder.continueWith { [weak self] (awsTask: AWSTask<NSURL>) -> Any? in
+            guard let strongSelf = self else {
+                return nil
+            }
+
+            guard let url = awsTask.result else { return nil }
+
+            strongSelf.cachePollyTask = strongSelf.cacheURLSession.dataTask(with: url as URL) { (data, response, error) in
+
+                if let error = error {
+                    print(error.localizedDescription)
+                }
+
+                if let data = data {
+                    strongSelf.spokenInstructionsForRoute[instruction] = data
+                }
+            }
+
+            strongSelf.cachePollyTask?.resume()
+
+            return nil
+        }
+    }
+
+    func play(_ data: Data) {
+        DispatchQueue.global(qos: .userInitiated).async {
             do {
-                strongSelf.audioPlayer = try AVAudioPlayer(data: data)
-                let prepared = strongSelf.audioPlayer?.prepareToPlay() ?? false
+                self.audioPlayer = try AVAudioPlayer(data: data)
+                let prepared = self.audioPlayer?.prepareToPlay() ?? false
 
                 guard prepared else {
-                    strongSelf.callSuperSpeak(strongSelf.fallbackText, error: "Audio player failed to prepare")
+                    self.callSuperSpeak(self.fallbackText, error: "Audio player failed to prepare")
                     return
                 }
 
-                DispatchQueue.main.async {
-                    strongSelf.audioPlayer?.delegate = self
-                    let played = strongSelf.audioPlayer?.play() ?? false
-
-                    guard played else {
-                        strongSelf.callSuperSpeak(strongSelf.fallbackText, error: "Audio player failed to play")
-                        return
-                    }
+                self.audioPlayer?.delegate = self
+                let played = self.audioPlayer?.play() ?? false
+
+                guard played else {
+                    self.callSuperSpeak(self.fallbackText, error: "Audio player failed to play")
+                    return
                 }
+
             } catch  let error as NSError {
-                strongSelf.callSuperSpeak(strongSelf.fallbackText, error: error.localizedDescription)
+                self.callSuperSpeak(self.fallbackText, error: error.localizedDescription)
             }
         }
-
-        pollyTask?.resume()
     }
 }