private async Task TelemetryReceived(DeviceTelemetry telemetry)
{
//query device with serial number
var device = _deviceRepository.AsQueryable().FirstOrDefault(q => q.SerialNumber == telemetry.SerialNumber);
//check if device is known
if (device == null)
{
Console.WriteLine($"WARN: Received telemetry for unknown device: {telemetry.SerialNumber}");
return;
}
//check if this telemetry is first entry for the device
if (!device.LastKnownLatitue.HasValue || !device.LastKnownLongitude.HasValue)
{
device.LastKnownLongitude = telemetry.Longitude;
device.LastKnownLatitue = telemetry.Latitude;
device.LastContact = telemetry.DeviceDate;
//this is first telemetry so we can not calculate speed for the device
await _deviceRepository.UpdateAsync(device);
return;
}
//calculate distance in meters
var distance = Math.Round(new Coordinates(device.LastKnownLatitue.Value, device.LastKnownLongitude.Value)
.DistanceTo(
new Coordinates(telemetry.Latitude, telemetry.Longitude),
UnitOfLength.Meter
), 2);
//calculate speed meters per hour
double speed = 0;
if (distance > 0)
{
speed = Math.Round(
GeolocationDistanceCalculator.SpeedAsMeterPerHour(distance, telemetry.DeviceDate,
device.LastContact.Value), 2);
}
//set last known speed for the device
device.LastKnownSpeed = speed;
//check device behaviour
device.State = distance <= DeviceConstants.MoveAlertInMeters
? DeviceState.OperatingAbnormally
: DeviceState.OperatingNormally;
device.LastContact = telemetry.DeviceDate;
//update device
await _deviceRepository.UpdateAsync(device);
}
public void SpeedAsMeterPerHour()
{
//Scenario
//assume subject moves 1 meter per second
// calculates speed meters per hour
var distance = 1; //1 meter
var shouldBe = distance * 60 * 60; // object should move 3600 meter per hour, distance * second * minute
var date1 = DateTime.UtcNow;
var date2 = date1.AddSeconds(1);
var speed = GeolocationDistanceCalculator.SpeedAsMeterPerHour(distance, date2, date1);
Assert.AreEqual(speed, shouldBe);
}