From 9324aeae5faf24e11c59a6c3db711248c009a266 Mon Sep 17 00:00:00 2001
From: Sergey Polygalin <sevil89@gmail.com>
Date: Sun, 17 Dec 2023 11:42:39 +0300
Subject: [PATCH] Add string key for changed fields

---
 changed_fields.go      | 15 +++++++++++++++
 changed_fields_test.go | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 changed_fields_test.go

diff --git a/changed_fields.go b/changed_fields.go
index 41e0fe6..4d1de4e 100644
--- a/changed_fields.go
+++ b/changed_fields.go
@@ -1,12 +1,18 @@
 package meta
 
+import "bytes"
+
 type ChangedFields struct {
 	fieldNames map[string]struct{}
+	fieldsKey  *bytes.Buffer
 }
 
 func NewChangedFields(fieldCount int) ChangedFields {
+	keyBuffer := bytes.NewBuffer(make([]byte, 0, fieldCount*2))
+
 	cf := ChangedFields{
 		fieldNames: make(map[string]struct{}, fieldCount),
+		fieldsKey:  keyBuffer,
 	}
 	return cf
 }
@@ -32,7 +38,12 @@ func (cf *ChangedFields) SetChanged(fields ...string) {
 	}
 
 	for _, field := range fields {
+		if _, exists := cf.fieldNames[field]; exists {
+			continue
+		}
+
 		cf.fieldNames[field] = struct{}{}
+		cf.fieldsKey.WriteString(field)
 	}
 }
 
@@ -43,3 +54,7 @@ func (cf ChangedFields) Empty() bool {
 func (cf ChangedFields) IsNil() bool {
 	return cf.fieldNames == nil
 }
+
+func (cf ChangedFields) GetFieldsKey() string {
+	return cf.fieldsKey.String()
+}
diff --git a/changed_fields_test.go b/changed_fields_test.go
new file mode 100644
index 0000000..263b93d
--- /dev/null
+++ b/changed_fields_test.go
@@ -0,0 +1,33 @@
+package meta
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestChangedFields(t *testing.T) {
+	t.Run("#SetChanged", func(t *testing.T) {
+		changedFields := NewChangedFields(3)
+
+		expectedFieldsMap := map[string]struct{}{
+			"a": {},
+			"b": {},
+			"c": {},
+		}
+
+		changedFields.SetChanged("a", "b", "c", "a")
+
+		assert.Equal(t, expectedFieldsMap, changedFields.fieldNames)
+	})
+
+	t.Run("#GetFieldsKey", func(t *testing.T) {
+		changedFields := NewChangedFields(3)
+		changedFields.SetChanged("b", "c", "a")
+		expectedKey := "bca"
+
+		actualKey := changedFields.GetFieldsKey()
+
+		assert.Equal(t, expectedKey, actualKey)
+	})
+}