Add helper functions for checking/setting invite expiration (#3698)

* Add helper functions for checking/setting invite expiration

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

* Update internal/invite/invite.go

Co-authored-by: Eleftheria Stein-Kousathana <eleftheria@stacklok.com>

---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>
Co-authored-by: Eleftheria Stein-Kousathana <eleftheria@stacklok.com>

internal/invite/invite.go

@@ -19,19 +19,34 @@ package invite
 import (
 	"crypto/rand"
 	"encoding/base64"
+	"time"
+
+	"google.golang.org/protobuf/types/known/timestamppb"
 )
 
 const (
-	// CodeByteLength = 48 is the length of the invite code in bytes
-	CodeByteLength = 48
+	// codeByteLength = 48 is the length of the invite code in bytes
+	codeByteLength = 48
+	// expireIn7Days is the duration for which an invitation is valid - 7 days
+	expireIn7Days = 7 * 24 * time.Hour
 )
 
 // GenerateCode generates a random invite code
 func GenerateCode() string {
-	bytes := make([]byte, CodeByteLength)
+	bytes := make([]byte, codeByteLength)
 	// Generate random bytes
 	if _, err := rand.Read(bytes); err != nil {
 		return ""
 	}
 	return base64.URLEncoding.EncodeToString(bytes)
 }
+
+// GetExpireIn7Days returns the expiration date of the invitation 7 days from t.Now()
+func GetExpireIn7Days(t time.Time) *timestamppb.Timestamp {
+	return timestamppb.New(t.Add(expireIn7Days))
+}
+
+// IsExpired checks if the invitation has expired
+func IsExpired(t time.Time) bool {
+	return time.Now().After(t.Add(expireIn7Days))
+}