/// <summary>
        /// Get the coordination information of airport asynchronously
        /// Firstly, the method checks if airport informations exist in database.
        /// If exist, directly returns coordinates from database.
        /// If not exist, it calls external api and parse informations to get coordinations
        /// On the last step, it saves informations to database for get it on the next request and avoid api calls
        /// </summary>
        /// <param name="airportIataCode">Iata code of airport</param>
        /// <returns>coordination informations in Tuple: (Item1:latitude, Item2:longitude)</returns>
        private async Task <Tuple <double, double> > GetAirportCoordinations(string airportIataCode)
        {
            using (var con = new AppDbContext(new DbContextOptions <AppDbContext>()))
            {
                var    repository   = new AirportRepository(con);
                double latitude     = 0.0;
                double longitude    = 0.0;
                var    savedAirport = await repository.GetAirport(airportIataCode);

                // If airport exist in db, no need to call external api
                if (savedAirport != null)
                {
                    SetCoordinates(savedAirport, out latitude, out longitude);
                }
                else
                {
                    IRestResponse response = AirportHelper.CallApi(airportIataCode);
                    if (response.IsSuccessful == false)
                    {
                        throw new Exception(AirportHelper.ParseApiError(response));
                    }
                    var airport = AirportHelper.GetAirportFromResponse(response);
                    if (airport != null)
                    {
                        SetCoordinates(airport, out latitude, out longitude);
                        // Save airport to in-memory database using by repository
                        await repository.AddAirport(airport);
                    }
                }
                return(Tuple.Create(latitude, longitude));
            }
        }