[AFP-91] ♻️ Refactor 'ManagerService' to accomodate route changes (@asegers)

src/main/java/com/afp/ordermanagement/service/ManagerService.java

 package com.afp.ordermanagement.service;
 
+import com.afp.ordermanagement.model.Manager;
+import com.afp.ordermanagement.repository.ManagerRepository;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import static com.afp.ordermanagement.config.BeanConfig.FieldCombiner;
+
+@Service
 public class ManagerService {
+    @Autowired
+    FieldCombiner fieldCombiner;
+
+    @Autowired
+    ManagerRepository managerRepository;
+
+    public Mono<Manager> getByEmail(String email) {
+        return managerRepository.findByEmail(email);
+    }
+
+    public Mono<Manager> create(Manager newManager) {
+        return managerRepository.save(newManager);
+    }
+
+    public Mono<Manager> updateByEmail(String email, Manager managerUpdates) {
+        return this.getByEmail(email)
+                .map(existingManager -> (Manager) fieldCombiner.combine(existingManager, managerUpdates, new String[] { "id", "email"}))
+                .flatMap(managerRepository::save);
+    }
+
+    public Mono<Void> delete(Manager manager) {
+        return managerRepository.delete(manager);
+    }
 }