Miscellaneous fixes from dev branch

Includes:
Add FOREGROUND_SERVICE permission on Android, fixes #32
Fix check for data files when syncing
GPS skip no longer signaled as warning
Fix user log length
Tentative fix for accelerometer speed issue #35

src/Android/Properties/AndroidManifest.xml

@@ -9,6 +9,7 @@
 	<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
 	<uses-permission android:name="android.permission.WAKE_LOCK" />
 	<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
+	<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
 	<application android:icon="@drawable/ic_launcher" android:theme="@style/AppTheme" android:label="@string/Vernacular_P0_app_name">
 		<provider android:name="android.support.v4.content.FileProvider" android:authorities="it.uniurb.smartroadsense.fileprovider" android:exported="false" android:grantUriPermissions="true">
 			<meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/filepaths" />

src/Shared/Data/SensorPack.cs

@@ -16,7 +16,8 @@ public abstract class SensorPack {
 #endif
 
         public const int AccelerometerDesiredHz = 100;
-        public const int AccelerometerDesiredDelayMs = 1000 / AccelerometerDesiredHz;
+        public const int AccelerometerDesiredDelayMs = (int)(1000 / AccelerometerDesiredHz);
+        public const int AccelerometerToleratedDelayMs = (int)(AccelerometerDesiredDelayMs * 0.8);
 
         public const int LocationDesiredHz = 1;
         public const int LocationDesiredDelayMs = 1000 / LocationDesiredHz;
@@ -253,7 +254,7 @@ protected void ReportNewLocation(double latitude, double longitude, float speed,
                         IsMovingSlowly = false;
 
                         if (measuredSpeed >= GpsTooFastSpeed) {
-                            Log.Warning(new ArgumentOutOfRangeException(nameof(measuredSpeed)), "Unforeseen GPS skip of {0} m in {1} ms", measuredDistance, intervalTime.TotalMilliseconds);
+                            Log.Debug("Unforeseen GPS skip of {0} m in {1} ms", measuredDistance, intervalTime.TotalMilliseconds);
                             ResetGpsLocation();
                             return;
                         }
@@ -270,13 +271,30 @@ protected void ReportNewLocation(double latitude, double longitude, float speed,
             _gpsLastAccuracy = accuracy;
         }
 
+        private DateTime? _lastAcceleration = null;
+
         /// <summary>
         /// Reports new acceleration values from the sensor.
         /// </summary>
         /// <param name="accX">X-axis acceleration in m/s^2.</param>
         /// <param name="accY">Y-axis acceleration in m/s^2.</param>
         /// <param name="accZ">Z-axis acceleration in m/s^2.</param>
         protected void ReportNewAcceleration(double accX, double accY, double accZ) {
+            //NOTE: cannot use the sensor timestamp data, as this is HW dependent on Android
+            //      see https://code.google.com/p/android/issues/detail?id=56561
+            var timestamp = DateTime.UtcNow;
+
+            // Check accelerometer frequency
+            if(_lastAcceleration.HasValue) {
+                int accDelayMs = (int)((timestamp - _lastAcceleration.Value).TotalMilliseconds);
+                if(accDelayMs < AccelerometerToleratedDelayMs) {
+                    // Higher frequency than what was asked for, drop
+                    Log.Debug("Dropping accelerometer sample ({0}ms delay)", accDelayMs);
+                    return;
+                }
+            }
+            _lastAcceleration = timestamp;
+
             //Scale each axis individually
             accX *= _accelerometerScaleFactor;
             accY *= _accelerometerScaleFactor;
@@ -307,15 +325,6 @@ protected void ReportNewAcceleration(double accX, double accY, double accZ) {
                 return;
             }
 
-            //TODO: check for acceleration sampling frequency here
-
-            //TODO: computation is now sync-locked to the accelerometer instead of the intended
-            //      100 Hz frequency. This should be changed.
-
-            //NOTE: cannot use the sensor timestamp data, as this is HW dependent on Android
-            //      see https://code.google.com/p/android/issues/detail?id=56561
-            var timestamp = DateTime.UtcNow;
-
             //Check for unfixed GPS timeout
             if (timestamp - _gpsLastUpdate > GpsUnfixedTimeout) {
                 LocationSensorStatus = LocationSensorStatus.Fixing;
@@ -392,6 +401,7 @@ public void StartSensing() {
             _gpsLastUpdate = DateTime.UtcNow;
             _lastTimeFastEnough = DateTime.MinValue;
             _lastTimeMoved = DateTime.MinValue;
+            _lastAcceleration = null;
 
             _accelerometerScaleFactor = Settings.CalibrationScaleFactor;
             Log.Debug("Sensor pack using scale factor of {0:P2}", _accelerometerScaleFactor);
@@ -435,6 +445,8 @@ private void ResetGpsLocation() {
             _gpsLastBearing = 0f;
             _gpsLastAccuracy = 0;
 
+            _lastAcceleration = null;
+
             _engine.Reset();
         }
 

src/Shared/SyncManager.cs

@@ -170,7 +170,10 @@ private async Task<SyncResult> SynchronizeInner(CancellationToken token, SyncPol
 
             IList<DatabaseQueries.TrackAndCount> tracks = await Task.Run(() => {
                 using(var db = DatabaseUtility.OpenConnection()) {
-                    return db.GetAllPendingTracks();
+                    return (from t in db.GetAllPendingTracks()
+                            let trackFilepath = FileNaming.GetDataTrackFilepath(t.TrackId)
+                            where File.Exists(trackFilepath)
+                            select t).ToList();
                 }
             });
             if (tracks.Count == 0) {

src/Shared/UserLog.cs

@@ -119,11 +119,11 @@ await Task.Run(() => {
             Log.Debug("Log persisted");
         }
 
-        public const int MaximumLogSize = 100;
+        public const int MaximumLogSize = 200;
 
         private static readonly object _rootLock = new object();
 
-        private static Queue<LogEntry> _log = new Queue<LogEntry>(MaximumLogSize);
+        private static Queue<LogEntry> _log = new Queue<LogEntry>(MaximumLogSize + 1);
 
         /// <summary>
         /// Adds an iconless message to the log.
@@ -140,13 +140,17 @@ public static void Add(Icon icon, string format, params object[] args) {
 
             lock (_rootLock) {
                 _log.Enqueue(entry);
+
+                while(_log.Count > MaximumLogSize) {
+                    _log.Dequeue();
+                }
             }
 
             OnNewEntryAdded(entry);
         }
 
         /// <summary>
-        /// Gets the entries of the log.
+        /// Gets all entries of the log.
         /// </summary>
         public static IReadOnlyList<LogEntry> Entries {
             get {