new endpoint to return product list

app/utils/query/find/find.go

@@ -0,0 +1,159 @@
+package find
+
+import (
+	"errors"
+	"reflect"
+	"strings"
+
+	"git.ma-al.com/goc_daniel/b2b/app/utils/i18n"
+	"gorm.io/gorm"
+)
+
+type Paging struct {
+	Page     uint `json:"page_number" example:"5"`
+	Elements uint `json:"elements_per_page" example:"30"`
+}
+
+func (p Paging) Offset() int {
+	return int(p.Elements) * int(p.Page-1)
+}
+
+func (p Paging) Limit() int {
+	return int(p.Elements)
+}
+
+type Found[T any] struct {
+	Items []T                    `json:"items,omitempty"`
+	Count uint                   `json:"items_count" example:"56"`
+	Spec  map[string]interface{} `json:"spec,omitempty"`
+}
+
+// Wraps given query adding limit, offset clauses and SQL_CALC_FOUND_ROWS to it
+// and running SELECT FOUND_ROWS() afterwards to fetch the total number
+// (ignoring LIMIT) of results. The final results are wrapped into the
+// [find.Found] type.
+func Paginate[T any](langID uint, paging Paging, stmt *gorm.DB) (Found[T], error) {
+	var items []T
+	var count uint64
+
+	// stmt.Debug()
+
+	err := stmt.
+		Clauses(SqlCalcFound()).
+		Offset(paging.Offset()).
+		Limit(paging.Limit()).
+		Find(&items).
+		Error
+	if err != nil {
+		return Found[T]{}, err
+	}
+
+	countInterface, ok := stmt.Get(FOUND_ROWS_CTX_KEY)
+	if !ok {
+		return Found[T]{}, errors.New(FOUND_ROWS_CTX_KEY + " value was not found in the gorm db context")
+	}
+	if count, ok = countInterface.(uint64); !ok {
+		return Found[T]{}, errors.New("failed to cast value under " + FOUND_ROWS_CTX_KEY + " to uint64")
+	}
+
+	columnsSpec := GetColumnsSpec[T](langID)
+
+	return Found[T]{
+		Items: items,
+		Count: uint(count),
+		Spec: map[string]interface{}{
+			"columns": columnsSpec,
+		},
+	}, err
+}
+
+// GetColumnsSpec[T any] generates a column specification map for a given struct type T.
+// Each key is the JSON property name, and the value is a map containing:
+//   - "filter_type": suggested filter type based on field type or `filt` tag
+//   - To disable filtering for a field, set `filt:"none"` in the struct tag
+//   - "sortable": currently hardcoded to true
+//   - "order": order of fields as they appear
+//
+// Returns nil if T is not a struct.
+func GetColumnsSpec[T any](langID uint) map[string]map[string]interface{} {
+	result := make(map[string]map[string]interface{})
+	typ := reflect.TypeOf((*T)(nil)).Elem()
+	if typ.Kind() != reflect.Struct {
+		return nil
+	}
+	order := 1
+	processStructFields(langID, typ, result, &order)
+	return result
+}
+
+type FilterType string
+
+const (
+	FilterTypeRange     FilterType = "range"
+	FilterTypeTimerange FilterType = "timerange"
+	FilterTypeLike      FilterType = "like"
+	FilterTypeSwitch    FilterType = "switch"
+	FilterTypeNone      FilterType = "none"
+)
+
+func isValidFilterType(ft string) bool {
+	switch FilterType(ft) {
+	case FilterTypeRange, FilterTypeTimerange, FilterTypeLike, FilterTypeSwitch:
+		return true
+	default:
+		return false
+	}
+}
+
+// processStructFields recursively processes struct fields to populate the result map.
+// It handles inline structs, reads `json` and `filt` tags, and determines filter types
+// based on the field type when `filt` tag is absent.
+// `order` is incremented for each field to track field ordering.
+func processStructFields(langID uint, typ reflect.Type, result map[string]map[string]interface{}, order *int) {
+	for i := 0; i < typ.NumField(); i++ {
+		field := typ.Field(i)
+		jsonTag := field.Tag.Get("json")
+		if jsonTag == "" || jsonTag == "-" {
+			continue
+		}
+		propName := strings.Split(jsonTag, ",")[0]
+		if propName == "" {
+			propName = field.Name
+		}
+		if strings.Contains(jsonTag, ",inline") && field.Type.Kind() == reflect.Struct {
+			processStructFields(langID, field.Type, result, order)
+			continue
+		}
+
+		filterType := field.Tag.Get("filt")
+		if filterType != "" {
+			if !isValidFilterType(filterType) {
+				filterType = string(FilterTypeNone)
+			}
+		} else {
+			fieldType := field.Type.String()
+			switch {
+			case strings.HasPrefix(fieldType, "int"), strings.HasPrefix(fieldType, "uint"), strings.HasPrefix(fieldType, "float"), strings.HasPrefix(fieldType, "decimal.Decimal"):
+				filterType = string(FilterTypeRange)
+			case strings.Contains(fieldType, "Time"):
+				filterType = string(FilterTypeTimerange)
+			case fieldType == "string":
+				filterType = string(FilterTypeLike)
+			case fieldType == "bool":
+				filterType = string(FilterTypeSwitch)
+			default:
+				filterType = string(FilterTypeNone)
+			}
+		}
+
+		result[propName] = map[string]interface{}{
+			"filter_type": filterType,
+			"sortable":    func() bool { val, ok := field.Tag.Lookup("sortable"); return !ok || val == "true" }(),
+			"order":       *order,
+			"title":       i18n.T___(langID, field.Tag.Get("title")),
+			"display":     func() bool { val, ok := field.Tag.Lookup("display"); return !ok || val == "true" }(),
+			"hidden":      field.Tag.Get("hidden") == "true",
+		}
+		*order++
+	}
+}