fix: decouple images from app config service (#965)

Co-authored-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>

backend/internal/service/app_images_service.go

@@ -0,0 +1,82 @@
+package service
+
+import (
+	"fmt"
+	"mime/multipart"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"github.com/pocket-id/pocket-id/backend/internal/common"
+	"github.com/pocket-id/pocket-id/backend/internal/utils"
+)
+
+type AppImagesService struct {
+	mu         sync.RWMutex
+	extensions map[string]string
+}
+
+func NewAppImagesService(extensions map[string]string) *AppImagesService {
+	return &AppImagesService{extensions: extensions}
+}
+
+func (s *AppImagesService) GetImage(name string) (string, string, error) {
+	ext, err := s.getExtension(name)
+	if err != nil {
+		return "", "", err
+	}
+
+	mimeType := utils.GetImageMimeType(ext)
+	if mimeType == "" {
+		return "", "", fmt.Errorf("unsupported image type '%s'", ext)
+	}
+
+	imagePath := filepath.Join(common.EnvConfig.UploadPath, "application-images", fmt.Sprintf("%s.%s", name, ext))
+	return imagePath, mimeType, nil
+}
+
+func (s *AppImagesService) UpdateImage(file *multipart.FileHeader, imageName string) error {
+	fileType := strings.ToLower(utils.GetFileExtension(file.Filename))
+	mimeType := utils.GetImageMimeType(fileType)
+	if mimeType == "" {
+		return &common.FileTypeNotSupportedError{}
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	currentExt, ok := s.extensions[imageName]
+	if !ok {
+		return fmt.Errorf("unknown application image '%s'", imageName)
+	}
+
+	imagePath := filepath.Join(common.EnvConfig.UploadPath, "application-images", fmt.Sprintf("%s.%s", imageName, fileType))
+
+	if err := utils.SaveFile(file, imagePath); err != nil {
+		return err
+	}
+
+	if currentExt != "" && currentExt != fileType {
+		oldImagePath := filepath.Join(common.EnvConfig.UploadPath, "application-images", fmt.Sprintf("%s.%s", imageName, currentExt))
+		if err := os.Remove(oldImagePath); err != nil && !os.IsNotExist(err) {
+			return err
+		}
+	}
+
+	s.extensions[imageName] = fileType
+
+	return nil
+}
+
+func (s *AppImagesService) getExtension(name string) (string, error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	ext, ok := s.extensions[name]
+	if !ok || ext == "" {
+		return "", fmt.Errorf("unknown application image '%s'", name)
+	}
+
+	return strings.ToLower(ext), nil
+}