feat: CategoriesView

yet to be tested fully

src/main/java/com/application/munera/views/MainLayout.java

@@ -1,5 +1,6 @@
 package com.application.munera.views;
 
+import com.application.munera.views.expenses.CategoriesView;
 import com.application.munera.views.expenses.ExpensesView;
 import com.vaadin.flow.component.applayout.AppLayout;
 import com.vaadin.flow.component.applayout.DrawerToggle;
@@ -51,6 +52,7 @@ public class MainLayout extends AppLayout {
         SideNav nav = new SideNav();
 
         nav.addItem(new SideNavItem("Expenses", ExpensesView.class, LineAwesomeIcon.COLUMNS_SOLID.create()));
+        nav.addItem(new SideNavItem("Categories", CategoriesView.class, LineAwesomeIcon.COLUMNS_SOLID.create()));
 
         return nav;
     }

src/main/java/com/application/munera/views/expenses/CategoriesView.java

@@ -0,0 +1,115 @@
+package com.application.munera.views.expenses;
+
+import com.application.munera.data.Category;
+import com.application.munera.services.CategoryService;
+import com.application.munera.views.MainLayout;
+import com.vaadin.flow.component.UI;
+import com.vaadin.flow.component.button.Button;
+import com.vaadin.flow.component.formlayout.FormLayout;
+import com.vaadin.flow.component.grid.Grid;
+import com.vaadin.flow.component.notification.Notification;
+import com.vaadin.flow.component.orderedlayout.VerticalLayout;
+import com.vaadin.flow.component.textfield.TextField;
+import com.vaadin.flow.data.binder.BeanValidationBinder;
+import com.vaadin.flow.router.BeforeEnterEvent;
+import com.vaadin.flow.router.BeforeEnterObserver;
+import com.vaadin.flow.router.PageTitle;
+import com.vaadin.flow.router.Route;
+import org.springframework.beans.factory.annotation.Autowired;
+
+import java.util.Optional;
+
+@PageTitle("Categories")
+@Route(value = "categories/:categoryID?/:action?(edit)", layout = MainLayout.class)
+public class CategoriesView extends VerticalLayout implements BeforeEnterObserver {
+
+    private final String CATEGORY_ID = "categoryID";
+    private final TextField categoryNameField = new TextField("Category Name");
+    private final Button addButton = new Button("Add Category");
+    private final Grid<Category> categoryGrid = new Grid<>(Category.class);
+    private final Button removeButton = new Button("Remove Category");
+
+    @Autowired
+    private final CategoryService categoryService;
+
+    private final BeanValidationBinder<Category> binder;
+    private Category category;
+
+    public CategoriesView(CategoryService categoryService) {
+        this.categoryService = categoryService;
+
+        FormLayout formLayout = new FormLayout();
+        formLayout.add(categoryNameField, addButton);
+
+        categoryGrid.setColumns("id", "name");
+        categoryGrid.setItems(categoryService.findAll());
+        categoryGrid.asSingleSelect().addValueChangeListener(event -> {
+            if (event.getValue() != null) {
+                UI.getCurrent().navigate(String.format("/manage-categories/%d/edit", event.getValue().getId()));
+            } else {
+                clearForm();
+                UI.getCurrent().navigate(CategoriesView.class);
+            }
+        });
+
+        removeButton.setEnabled(false);
+        removeButton.addClickListener(event -> removeCategory());
+
+        addButton.addClickListener(event -> addCategory());
+
+        binder = new BeanValidationBinder<>(Category.class);
+        binder.bindInstanceFields(this);
+
+        add(formLayout, categoryGrid, removeButton);
+    }
+
+    @Override
+    public void beforeEnter(BeforeEnterEvent event) {
+        Optional<Long> categoryId = event.getRouteParameters().get(CATEGORY_ID).map(Long::parseLong);
+        if (categoryId.isPresent()) {
+            Optional<Category> categoryFromBackend = categoryService.findById(categoryId.get());
+            if (categoryFromBackend.isPresent()) {
+                populateForm(categoryFromBackend.get());
+            } else {
+                Notification.show(
+                        String.format("The requested category was not found, ID = %s", categoryId.get()), 3000,
+                        Notification.Position.BOTTOM_START);
+                // when a row is selected but the data is no longer available,
+                // refresh grid
+                refreshGrid();
+                event.forwardTo(ExpensesView.class);
+            }
+        }
+    }
+
+    private void addCategory() {
+        Category newCategory = new Category();
+        binder.writeBeanIfValid(newCategory);
+        categoryService.update(newCategory);
+        refreshGrid();
+        Notification.show("Category added successfully");
+    }
+
+    private void removeCategory() {
+        if (category != null) {
+            categoryService.delete(category);
+            clearForm();
+            refreshGrid();
+            Notification.show("Category removed successfully");
+            UI.getCurrent().navigate(CategoriesView.class);
+        }
+    }
+
+    private void clearForm() {
+        populateForm(null);
+    }
+
+    private void populateForm(Category value) {
+        this.category = value;
+        binder.readBean(this.category);
+    }
+
+    private void refreshGrid() {
+        categoryGrid.setItems(categoryService.findAll());
+    }
+}