[Storefront] [Category] Create api to get the top n categories (#1220)

* Create api to get the top n category

* Configure variable name

product/src/it/java/com/yas/product/controller/CategoryControllerIT.java

@@ -90,6 +90,17 @@ void test_getAllCategoriesStorefront_shouldReturnListCategories() {
             .log().ifValidationFails();
     }
 
+    @Test
+    void test_getTopNthCategories_shouldReturnEmptyList() {
+        given(getRequestSpecification())
+            .when()
+            .get(CATEGORY_STOREFRONT_URL + "/suggestions")
+            .then()
+            .statusCode(HttpStatus.OK.value())
+            .body(".", hasSize(0))
+            .log().ifValidationFails();
+    }
+
     @Test
     void test_getCategoryById_shouldReturnCategory() {
         Long categoryId = categoryOne.getId();

product/src/main/java/com/yas/product/controller/CategoryController.java

@@ -1,6 +1,7 @@
 package com.yas.product.controller;
 
 import com.yas.commonlibrary.exception.BadRequestException;
+import com.yas.product.constants.PageableConstant;
 import com.yas.product.model.Category;
 import com.yas.product.repository.CategoryRepository;
 import com.yas.product.service.CategoryService;
@@ -43,6 +44,13 @@ public ResponseEntity<List<CategoryGetVm>> listCategories(
         return ResponseEntity.ok(categoryService.getCategories(categoryName));
     }
 
+    @GetMapping("/storefront/categories/suggestions")
+    public ResponseEntity<List<String>> listTopNthCategories(
+        @RequestParam(value = "limit", defaultValue = PageableConstant.DEFAULT_PAGE_SIZE, required = false)
+        final int limit) {
+        return ResponseEntity.ok(categoryService.getTopNthCategories(limit));
+    }
+
     @GetMapping("/backoffice/categories/{id}")
     @ApiResponses(value = {
         @ApiResponse(responseCode = "200", description = "Ok",

product/src/main/java/com/yas/product/repository/CategoryRepository.java

@@ -3,6 +3,7 @@
 import com.yas.product.model.Category;
 import java.util.List;
 import java.util.Optional;
+import org.springframework.data.domain.Pageable;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.stereotype.Repository;
@@ -15,4 +16,18 @@ public interface CategoryRepository extends JpaRepository<Category, Long> {
     Category findExistedName(String name, Long id);
 
     List<Category> findByNameContainingIgnoreCase(String name);
+
+    /**
+     * Retrieves a list of category names ordered by the number of associated products in descending order.
+     * Limits the results based on the given {@link Pageable} parameter.
+     *
+     * @param pageable specifies the number of results and pagination details.
+     * @return a list of category names sorted by product count in descending order.
+     */
+    @Query("SELECT c.name FROM Category c "
+        + "JOIN c.productCategories pc "
+        + "GROUP BY c.name "
+        + "ORDER BY COUNT(pc.product.id) DESC")
+    List<String> findCategoriesOrderedByProductCount(Pageable pageable);
+
 }

product/src/main/java/com/yas/product/service/CategoryService.java

@@ -170,4 +170,10 @@ private boolean checkParent(Long id, Category category) {
     public List<CategoryGetVm> getCategoryByIds(List<Long> ids) {
         return categoryRepository.findAllById(ids).stream().map(CategoryGetVm::fromModel).toList();
     }
+
+    public List<String> getTopNthCategories(int limit) {
+        // Use PageRequest.of(0, n) to limit the number of categories fetched to 'n'
+        Pageable pageable = PageRequest.of(0, limit);
+        return categoryRepository.findCategoriesOrderedByProductCount(pageable);
+    }
 }