fix: create reusable default profile pictures (#406)

Co-authored-by: Elias Schneider <login@eliasschneider.com>

backend/internal/service/user_service.go

@@ -1,6 +1,7 @@
 package service
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
@@ -59,28 +60,58 @@ func (s *UserService) GetProfilePicture(userID string) (io.Reader, int64, error)
 		return nil, 0, &common.InvalidUUIDError{}
 	}
 
+	// First check for a custom uploaded profile picture (userID.png)
 	profilePicturePath := common.EnvConfig.UploadPath + "/profile-pictures/" + userID + ".png"
 	file, err := os.Open(profilePicturePath)
 	if err == nil {
 		// Get the file size
 		fileInfo, err := file.Stat()
 		if err != nil {
+			file.Close()
 			return nil, 0, err
 		}
 		return file, fileInfo.Size(), nil
 	}
 
-	// If the file does not exist, return the default profile picture
+	// If no custom picture exists, get the user's data for creating initials
 	user, err := s.GetUser(userID)
 	if err != nil {
 		return nil, 0, err
 	}
 
-	defaultPicture, err := profilepicture.CreateDefaultProfilePicture(user.FirstName, user.LastName)
+	// Check if we have a cached default picture for these initials
+	defaultProfilePicturesDir := common.EnvConfig.UploadPath + "/profile-pictures/defaults/"
+	defaultPicturePath := defaultProfilePicturesDir + user.Initials() + ".png"
+	file, err = os.Open(defaultPicturePath)
+	if err == nil {
+		fileInfo, err := file.Stat()
+		if err != nil {
+			file.Close()
+			return nil, 0, err
+		}
+		return file, fileInfo.Size(), nil
+	}
+
+	// If no cached default picture exists, create one and save it for future use
+	defaultPicture, err := profilepicture.CreateDefaultProfilePicture(user.Initials())
 	if err != nil {
 		return nil, 0, err
 	}
 
+	// Save the default picture for future use (in a goroutine to avoid blocking)
+	defaultPictureCopy := bytes.NewBuffer(defaultPicture.Bytes())
+	go func() {
+		// Ensure the directory exists
+		err = os.MkdirAll(defaultProfilePicturesDir, os.ModePerm)
+		if err != nil {
+			log.Printf("Failed to create directory for default profile picture: %v", err)
+			return
+		}
+		if err := utils.SaveFileStream(defaultPictureCopy, defaultPicturePath); err != nil {
+			log.Printf("Failed to cache default profile picture for initials %s: %v", user.Initials(), err)
+		}
+	}()
+
 	return defaultPicture, int64(defaultPicture.Len()), nil
 }