feat(structs): add FilterStructToMap utility function

structs/structs.go

@@ -40,19 +40,13 @@ func Walk(s interface{}, callback CallbackFunc) {
 	}
 }
 
-// FilterStruct filters the struct based on include and exclude fields and returns a new struct.
-// - input: the original struct.
-// - includeFields: list of fields to include (if empty, includes all).
-// - excludeFields: list of fields to exclude (processed after include).
-func FilterStruct[T any](input T, includeFields, excludeFields []string) (T, error) {
-	var zeroValue T
+func walkFilteredFields[T any](input T, includeFields, excludeFields []string, walker func(field reflect.StructField, value reflect.Value)) error {
 	val := reflect.ValueOf(input)
 	if val.Kind() == reflect.Ptr {
 		val = val.Elem()
 	}
-
 	if val.Kind() != reflect.Struct {
-		return zeroValue, errors.New("input must be a struct")
+		return errors.New("input must be a struct")
 	}
 
 	includeMap := make(map[string]bool)
@@ -66,7 +60,6 @@ func FilterStruct[T any](input T, includeFields, excludeFields []string) (T, err
 	}
 
 	typeOfStruct := val.Type()
-	filteredStruct := reflect.New(typeOfStruct).Elem()
 
 	for i := 0; i < val.NumField(); i++ {
 		field := typeOfStruct.Field(i)
@@ -77,13 +70,62 @@ func FilterStruct[T any](input T, includeFields, excludeFields []string) (T, err
 		fieldValue := val.Field(i)
 
 		if (len(includeMap) == 0 || includeMap[fieldName]) && !excludeMap[fieldName] {
-			filteredStruct.Field(i).Set(fieldValue)
+			walker(field, fieldValue)
 		}
 	}
+	return nil
+}
+
+// FilterStruct filters the struct based on include and exclude fields and returns a new struct.
+// - input: the original struct.
+// - includeFields: list of fields to include (if empty, includes all).
+// - excludeFields: list of fields to exclude (processed after include).
+func FilterStruct[T any](input T, includeFields, excludeFields []string) (T, error) {
+	var zeroValue T
+	val := reflect.ValueOf(input)
+	if val.Kind() == reflect.Ptr {
+		val = val.Elem()
+	}
+
+	filteredStruct := reflect.New(val.Type()).Elem()
+
+	walker := func(field reflect.StructField, value reflect.Value) {
+		filteredStruct.FieldByName(field.Name).Set(value)
+	}
+
+	if err := walkFilteredFields(input, includeFields, excludeFields, walker); err != nil {
+		return zeroValue, err
+	}
 
 	return filteredStruct.Interface().(T), nil
 }
 
+func FilterStructToMap[T any](input T, includeFields, excludeFields []string) (map[string]any, error) {
+	resultMap := make(map[string]any)
+
+	walker := func(field reflect.StructField, value reflect.Value) {
+		jsonTag := field.Tag.Get("json")
+		jsonKey := strings.Split(jsonTag, ",")[0]
+
+		if jsonKey == "" || jsonKey == "-" {
+			return
+		}
+
+		fieldValue := value.Interface()
+		if strings.Contains(jsonTag, "omitempty") && value.IsZero() {
+			return
+		}
+
+		resultMap[jsonKey] = fieldValue
+	}
+
+	if err := walkFilteredFields(input, includeFields, excludeFields, walker); err != nil {
+		return nil, err
+	}
+
+	return resultMap, nil
+}
+
 // GetStructFields returns all the top-level field names from the given struct.
 // - input: the original struct.
 // Returns a slice of field names or an error if the input is not a struct.

structs/structs_test.go

@@ -16,6 +16,15 @@ type NestedStruct struct {
 	PtrField *TestStruct
 }
 
+type MapTestStruct struct {
+	Name     string `json:"name"`
+	Age      int    `json:"age,omitempty"`
+	Password string `json:"-"`
+	IsActive bool   `json:"is_active"`
+	Address  string `json:"address"`
+	Country  string `json:"country,omitempty"`
+}
+
 func TestFilterStruct(t *testing.T) {
 	s := TestStruct{
 		Name:    "John",
@@ -25,7 +34,7 @@ func TestFilterStruct(t *testing.T) {
 
 	tests := []struct {
 		name          string
-		input         interface{}
+		input         any
 		includeFields []string
 		excludeFields []string
 		want          TestStruct
@@ -79,6 +88,94 @@ func TestFilterStruct(t *testing.T) {
 	}
 }
 
+func TestFilterStructToMap(t *testing.T) {
+	s := MapTestStruct{
+		Name:     "John",
+		Age:      30,                // To test omitempty on a non zero value
+		Password: "secret-password", // To test an ignored tag (json:"-")
+		IsActive: true,
+		Address:  "New York",
+		Country:  "", // To test omitempty on a zero value
+	}
+
+	tests := []struct {
+		name          string
+		input         any
+		includeFields []string
+		excludeFields []string
+		want          map[string]any
+		wantErr       bool
+	}{
+		{
+			name:          "no filtering",
+			input:         s,
+			includeFields: nil,
+			excludeFields: nil,
+			want: map[string]any{
+				"name":      "John",
+				"age":       30,
+				"is_active": true,
+				"address":   "New York",
+			},
+			wantErr: false,
+		},
+		{
+			name:          "include specific fields",
+			input:         s,
+			includeFields: []string{"Name", "Address"},
+			excludeFields: []string{},
+			want: map[string]any{
+				"name":    "John",
+				"address": "New York",
+			},
+			wantErr: false,
+		},
+		{
+			name:          "exclude specific fields",
+			input:         s,
+			includeFields: []string{},
+			excludeFields: []string{"Address", "IsActive"},
+			want: map[string]any{
+				"name": "John",
+				"age":  30,
+			},
+			wantErr: false,
+		},
+		{
+			name:          "include and exclude",
+			input:         s,
+			includeFields: []string{"Name", "Age", "Address"},
+			excludeFields: []string{"Age"},
+			want: map[string]any{
+				"name":    "John",
+				"address": "New York",
+			},
+			wantErr: false,
+		},
+		{
+			name:          "non-struct input",
+			input:         "not a struct",
+			includeFields: []string{},
+			excludeFields: []string{},
+			want:          nil,
+			wantErr:       true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := FilterStructToMap(tt.input, tt.includeFields, tt.excludeFields)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("FilterStructToMap() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("FilterStructToMap() got = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestGetStructFields(t *testing.T) {
 	s := TestStruct{
 		Name:    "John",
@@ -88,7 +185,7 @@ func TestGetStructFields(t *testing.T) {
 
 	tests := []struct {
 		name    string
-		input   interface{}
+		input   any
 		want    []string
 		wantErr bool
 	}{