added create date calculator for user and message.

message.go

@@ -1,6 +1,10 @@
 package revoltgo
 
-import "time"
+import (
+	"time"
+
+	"github.com/oklog/ulid/v2"
+)
 
 // Message struct
 type Message struct {
@@ -76,6 +80,18 @@ type MessageEmbeddedVideo struct {
 	Height int    `json:"height"`
 }
 
+// Calculate creation date and edit the struct.
+func (c *Message) CalculateCreationDate() error {
+	ulid, err := ulid.Parse(c.Id)
+
+	if err != nil {
+		return err
+	}
+
+	c.CreatedAt = time.UnixMilli(int64(ulid.Time()))
+	return nil
+}
+
 // Edit message content.
 func (m *Message) Edit(content string) error {
 	_, err := m.Client.Request("PATCH", "/channels/"+m.ChannelId+"/messages/"+m.Id, []byte("{\"content\": \""+content+"\"}"))

user.go

@@ -1,6 +1,10 @@
 package revoltgo
 
-import "time"
+import (
+	"time"
+
+	"github.com/oklog/ulid/v2"
+)
 
 // User struct.
 type User struct {
@@ -35,3 +39,15 @@ type UserStatus struct {
 type BotInformation struct {
 	Owner string `json:"owner"`
 }
+
+// Calculate creation date and edit the struct.
+func (c *User) CalculateCreationDate() error {
+	ulid, err := ulid.Parse(c.Id)
+
+	if err != nil {
+		return err
+	}
+
+	c.CreatedAt = time.UnixMilli(int64(ulid.Time()))
+	return nil
+}