add get-breadcrumb endpoint

app/service/menuService/menuService.go

@@ -1,6 +1,7 @@
 package menuService
 
 import (
+	"slices"
 	"sort"
 
 	"git.ma-al.com/goc_daniel/b2b/app/model"
@@ -112,6 +113,69 @@ func (a ByPosition) Len() int           { return len(a) }
 func (a ByPosition) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
 func (a ByPosition) Less(i, j int) bool { return a[i].Position < a[j].Position }
 
+func (s *MenuService) GetBreadcrumb(root_category_id uint, start_category_id uint, id_lang uint) ([]model.CategoryInBreadcrumb, error) {
+	all_categories, err := s.categoriesRepo.GetAllCategories(id_lang)
+	if err != nil {
+		return []model.CategoryInBreadcrumb{}, err
+	}
+
+	breadcrumb := []model.CategoryInBreadcrumb{}
+
+	start_index := 0
+	start_found := false
+	for i := 0; i < len(all_categories); i++ {
+		if all_categories[i].CategoryID == start_category_id {
+			start_index = i
+			start_found = true
+			break
+		}
+	}
+	if !start_found {
+		return []model.CategoryInBreadcrumb{}, responseErrors.ErrStartCategoryNotFound
+	}
+
+	// map category ids to indices
+	id_to_index := make(map[uint]int)
+	for i := 0; i < len(all_categories); i++ {
+		all_categories[i].Visited = false
+		id_to_index[all_categories[i].CategoryID] = i
+	}
+
+	// do a simple graph traversal, always jumping from node to its parent
+	index := start_index
+	success := true
+	for {
+		if all_categories[index].Visited {
+			success = false
+			break
+		}
+		all_categories[index].Visited = true
+
+		var next_category model.CategoryInBreadcrumb
+		next_category.CategoryID = all_categories[index].CategoryID
+		next_category.Name = all_categories[index].Name
+		breadcrumb = append(breadcrumb, next_category)
+
+		if all_categories[index].CategoryID == root_category_id {
+			break
+		}
+		next_index, ok := id_to_index[all_categories[index].ParentID]
+		if !ok {
+			success = false
+			break
+		}
+		index = next_index
+	}
+
+	slices.Reverse(breadcrumb)
+
+	if !success {
+		return breadcrumb, responseErrors.ErrRootNeverReached
+	}
+
+	return breadcrumb, nil
+}
+
 func (s *MenuService) GetTopMenu(id uint) ([]*model.B2BTopMenu, error) {
 	items, err := s.routesRepo.GetTopMenu(id)
 	if err != nil {