Admin controller, Locations controller, requests to add available countries, request to get available countries

SchengenVisaApi/ApplicationLayer/DataAccessingServices/Locations/RequestHandlers/AdminRequests/EditLocationsRequestsHandler.cs

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+using ApplicationLayer.DataAccessingServices.Locations.NeededServices;
+using ApplicationLayer.DataAccessingServices.Locations.RequestHandlers.AdminRequests.Exceptions;
+using ApplicationLayer.DataAccessingServices.Locations.Requests;
+using ApplicationLayer.GeneralNeededServices;
+using Domains.LocationDomain;
+
+namespace ApplicationLayer.DataAccessingServices.Locations.RequestHandlers.AdminRequests
+{
+    /// <inheritdoc cref="IEditLocationsRequestsHandler"/>
+    public class EditLocationsRequestsHandler(ICountriesRepository countries, IUnitOfWork unitOfWork) : IEditLocationsRequestsHandler
+    {
+        async Task IEditLocationsRequestsHandler.AddCountryAsync(AddCountryRequest request, CancellationToken cancellationToken)
+        {
+            if (await countries.FindByName(request.CountryName, cancellationToken) is not null)
+            {
+                throw new CountryAlreadyExists(request.CountryName);
+            }
+
+            if (request.Cities.Distinct().Count() < request.Cities.Length)
+            {
+                throw new MultipleIdenticalCitiesInCountry();
+            }
+
+            var country = new Country
+            {
+                Name = request.CountryName,
+                IsSchengen = request.IsSchengen,
+                Cities = request.Cities.Select(cityName => new City { Name = cityName }).ToList()
+            };
+
+            await countries.AddAsync(country, cancellationToken);
+
+            await unitOfWork.SaveAsync(cancellationToken);
+        }
+    }
+}

SchengenVisaApi/ApplicationLayer/DataAccessingServices/Locations/RequestHandlers/AdminRequests/Exceptions/CountryAlreadyExists.cs

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+using ApplicationLayer.GeneralExceptions;
+
+namespace ApplicationLayer.DataAccessingServices.Locations.RequestHandlers.AdminRequests.Exceptions
+{
+    public class CountryAlreadyExists(string countryName) : AlreadyExistsException($"{countryName} already exists.");
+}

SchengenVisaApi/ApplicationLayer/DataAccessingServices/Locations/RequestHandlers/AdminRequests/Exceptions/MultipleIdenticalCitiesInCountry.cs

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+using ApplicationLayer.GeneralExceptions;
+
+namespace ApplicationLayer.DataAccessingServices.Locations.RequestHandlers.AdminRequests.Exceptions
+{
+    public class MultipleIdenticalCitiesInCountry() : ApiException("There are multiple cities with one name in the country.");
+}

SchengenVisaApi/ApplicationLayer/DataAccessingServices/Locations/RequestHandlers/AdminRequests/IEditLocationsRequestsHandler.cs

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+using ApplicationLayer.DataAccessingServices.Locations.Requests;
+
+namespace ApplicationLayer.DataAccessingServices.Locations.RequestHandlers.AdminRequests
+{
+    /// Handles edit requests of locations from admins
+    public interface IEditLocationsRequestsHandler
+    {
+        /// Handles add country requests
+        Task AddCountryAsync(AddCountryRequest request, CancellationToken cancellationToken);
+    }
+}