added an api connection to Users in Andriod

NOTE Will have to change backend so staffs can access other staffs

android/app/src/main/java/com/example/petstoremobile/api/UserApi.java

@@ -0,0 +1,13 @@
+package com.example.petstoremobile.api;
+
+import com.example.petstoremobile.dtos.PageResponse;
+import com.example.petstoremobile.dtos.UserDTO;
+
+import retrofit2.Call;
+import retrofit2.http.GET;
+import retrofit2.http.Query;
+
+public interface UserApi {
+    @GET("api/v1/users")
+    Call<PageResponse<UserDTO>> getUsers(@Query("role") String role, @Query("page") int page, @Query("size") int size);
+}

android/app/src/main/java/com/example/petstoremobile/di/NetworkModule.java

@@ -173,4 +173,10 @@ public class NetworkModule {
     public static CategoryApi provideCategoryApi(Retrofit retrofit) {
         return retrofit.create(CategoryApi.class);
     }
+
+    @Provides
+    @Singleton
+    public static UserApi provideUserApi(Retrofit retrofit) {
+        return retrofit.create(UserApi.class);
+    }
 }

android/app/src/main/java/com/example/petstoremobile/fragments/listfragments/detailfragments/AppointmentDetailFragment.java

@@ -21,6 +21,7 @@ import com.example.petstoremobile.viewmodels.CustomerViewModel;
 import com.example.petstoremobile.viewmodels.PetViewModel;
 import com.example.petstoremobile.viewmodels.ServiceViewModel;
 import com.example.petstoremobile.viewmodels.StoreViewModel;
+import com.example.petstoremobile.viewmodels.UserViewModel;
 
 import java.util.*;
 
@@ -40,11 +41,13 @@ public class AppointmentDetailFragment extends Fragment {
     private long preselectedServiceId = -1;
     private long preselectedCustomerId = -1;
     private long preselectedStoreId = -1;
+    private long preselectedStaffId = -1;
 
     private List<PetDTO> petList = new ArrayList<>();
     private List<ServiceDTO> serviceList = new ArrayList<>();
     private List<CustomerDTO> customerList = new ArrayList<>();
     private List<StoreDTO> storeList = new ArrayList<>();
+    private List<UserDTO> staffList = new ArrayList<>();
 
     private final Integer[] HOURS = {9,10,11,12,13,14,15,16,17};
     private final Integer[] MINUTES = {0,15,30,45};
@@ -54,6 +57,7 @@ public class AppointmentDetailFragment extends Fragment {
     private ServiceViewModel serviceViewModel;
     private StoreViewModel storeViewModel;
     private CustomerViewModel customerViewModel;
+    private UserViewModel userViewModel;
 
     @Override
     public void onCreate(Bundle savedInstanceState) {
@@ -63,6 +67,7 @@ public class AppointmentDetailFragment extends Fragment {
         serviceViewModel = new ViewModelProvider(this).get(ServiceViewModel.class);
         storeViewModel = new ViewModelProvider(this).get(StoreViewModel.class);
         customerViewModel = new ViewModelProvider(this).get(CustomerViewModel.class);
+        userViewModel = new ViewModelProvider(this).get(UserViewModel.class);
     }
 
     @Override
@@ -128,6 +133,7 @@ public class AppointmentDetailFragment extends Fragment {
         loadServices();
         loadCustomers();
         loadStores();
+        loadStaff();
     }
 
     /**
@@ -215,6 +221,27 @@ public class AppointmentDetailFragment extends Fragment {
                 preselectedStoreId, StoreDTO::getStoreId);
     }
 
+    /**
+     * Loads the list of staff from the API.
+     */
+    private void loadStaff() {
+        userViewModel.getUsers("STAFF", 0, 100).observe(getViewLifecycleOwner(), resource -> {
+            if (resource.status == Resource.Status.SUCCESS && resource.data != null) {
+                staffList = resource.data.getContent();
+                refreshStaffSpinner();
+            }
+        });
+    }
+
+    /**
+     * Populates the staff selection spinner.
+     */
+    private void refreshStaffSpinner() {
+        SpinnerUtils.populateSpinner(requireContext(), binding.spinnerStaff, staffList,
+                UserDTO::getFullName, "-- Select Staff --",
+                preselectedStaffId, UserDTO::getId);
+    }
+
     /**
      * Handles arguments to determine if the fragment is in edit or add mode.
      */
@@ -247,6 +274,7 @@ public class AppointmentDetailFragment extends Fragment {
                 preselectedServiceId = (a.getServiceId() != null) ? a.getServiceId() : -1;
                 preselectedCustomerId = (a.getCustomerId() != null) ? a.getCustomerId() : -1;
                 preselectedStoreId = (a.getStoreId() != null) ? a.getStoreId() : -1;
+                preselectedStaffId = (a.getEmployeeId() != null) ? a.getEmployeeId() : -1;
 
                 binding.etAppointmentDate.setText(a.getAppointmentDate());
 
@@ -276,6 +304,7 @@ public class AppointmentDetailFragment extends Fragment {
                 refreshServiceSpinner();
                 refreshCustomerSpinner();
                 refreshStoreSpinner();
+                refreshStaffSpinner();
             } else if (resource.status == Resource.Status.ERROR) {
                 Toast.makeText(getContext(), "Failed to load appointment: " + resource.message, Toast.LENGTH_SHORT).show();
             }
@@ -308,6 +337,11 @@ public class AppointmentDetailFragment extends Fragment {
         PetDTO pet           = petList.get(binding.spinnerPet.getSelectedItemPosition() - 1);
         ServiceDTO service   = serviceList.get(binding.spinnerService.getSelectedItemPosition() - 1);
         
+        Long employeeId = null;
+        if (binding.spinnerStaff.getSelectedItemPosition() > 0) {
+            employeeId = staffList.get(binding.spinnerStaff.getSelectedItemPosition() - 1).getId();
+        }
+
         String time = String.format("%02d:%02d",
                 HOURS[binding.spinnerHour.getSelectedItemPosition()],
                 MINUTES[binding.spinnerMinute.getSelectedItemPosition()]);
@@ -346,6 +380,7 @@ public class AppointmentDetailFragment extends Fragment {
                 customer.getCustomerId(),
                 store.getStoreId(),
                 service.getServiceId(),
+                employeeId,
                 date,
                 time,
                 status,

android/app/src/main/java/com/example/petstoremobile/repositories/UserRepository.java

@@ -0,0 +1,26 @@
+package com.example.petstoremobile.repositories;
+
+import androidx.lifecycle.LiveData;
+
+import com.example.petstoremobile.api.UserApi;
+import com.example.petstoremobile.dtos.PageResponse;
+import com.example.petstoremobile.dtos.UserDTO;
+import com.example.petstoremobile.utils.Resource;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+@Singleton
+public class UserRepository extends BaseRepository {
+    private final UserApi userApi;
+
+    @Inject
+    public UserRepository(UserApi userApi) {
+        super("UserRepository");
+        this.userApi = userApi;
+    }
+
+    public LiveData<Resource<PageResponse<UserDTO>>> getUsers(String role, int page, int size) {
+        return executeCall(userApi.getUsers(role, page, size));
+    }
+}

android/app/src/main/java/com/example/petstoremobile/viewmodels/UserViewModel.java

@@ -0,0 +1,27 @@
+package com.example.petstoremobile.viewmodels;
+
+import androidx.lifecycle.LiveData;
+import androidx.lifecycle.ViewModel;
+
+import com.example.petstoremobile.dtos.PageResponse;
+import com.example.petstoremobile.dtos.UserDTO;
+import com.example.petstoremobile.repositories.UserRepository;
+import com.example.petstoremobile.utils.Resource;
+
+import javax.inject.Inject;
+
+import dagger.hilt.android.lifecycle.HiltViewModel;
+
+@HiltViewModel
+public class UserViewModel extends ViewModel {
+    private final UserRepository userRepository;
+
+    @Inject
+    public UserViewModel(UserRepository userRepository) {
+        this.userRepository = userRepository;
+    }
+
+    public LiveData<Resource<PageResponse<UserDTO>>> getUsers(String role, int page, int size) {
+        return userRepository.getUsers(role, page, size);
+    }
+}

android/app/src/main/res/layout/fragment_appointment_detail.xml

@@ -124,15 +124,27 @@
                     android:textSize="12sp"
                     android:layout_marginBottom="4dp"/>
 
-
-
-
                 <Spinner
                     android:id="@+id/spinnerService"
                     android:layout_width="match_parent"
                     android:layout_height="wrap_content"
                     android:layout_marginBottom="16dp"/>
 
+                <!-- Staff -->
+                <TextView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="Staff"
+                    android:textColor="@color/text_dark"
+                    android:textSize="12sp"
+                    android:layout_marginBottom="4dp"/>
+
+                <Spinner
+                    android:id="@+id/spinnerStaff"
+                    android:layout_width="match_parent"
+                    android:layout_height="wrap_content"
+                    android:layout_marginBottom="16dp"/>
+
                 <!-- Appointment Date -->
 
                 <TextView