add api endpoint to fetch file usage

api/v1/api.go

@@ -98,6 +98,10 @@ func InstallHandler(r *mux.Router, st *store.Store, im *importer.Importer, infoL
 	fileHandler["DELETE"] = api.DeleteFileOfGroup()
 	r.Handle("/groups/{group-id}/files/{file-id}", fileHandler)
 
+	usageHandler := make(handlers.MethodHandler)
+	usageHandler["GET"] = api.ReadUsageOfFile()
+	r.Handle("/groups/{group-id}/files/{file-id}/usage", usageHandler)
+
 	importHandler := make(handlers.MethodHandler)
 	importHandler["GET"] = api.ReadImportOfFile()
 	importHandler["PUT"] = api.UploadFile()

api/v1/api_files.go

@@ -121,3 +121,20 @@ func (api *API) DeleteFileOfGroup() http.Handler {
 		sendWebResponse(w, http.StatusNoContent, nil)
 	})
 }
+
+func (api *API) ReadUsageOfFile() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		vars := mux.Vars(r)
+		id, err := idFromString(vars["file-id"])
+		if err != nil {
+			sendWebResponse(w, http.StatusBadRequest, ErrorResponse{Error: "invalid file-id: " + err.Error()})
+			return
+		}
+		result := FileUsageListing{}
+		if result.Usage.Playlists, err = api.store.GetFileUsage(vars["group-id"], id); err != nil {
+			sendStoreError(w, err)
+			return
+		}
+		sendWebResponse(w, http.StatusOK, result)
+	})
+}

api/v1/types.go

@@ -55,6 +55,12 @@ type FilesListing struct {
 	Files store.Files `json:"results"`
 }
 
+type FileUsageListing struct {
+	Usage struct {
+		Playlists store.Playlists `json:"playlists"`
+	} `json:"results"`
+}
+
 type PlaylistsListing struct {
 	Playlists store.Playlists `json:"results"`
 }

store/files.go

@@ -74,9 +74,9 @@ func (st *Store) UpdateFile(group string, id uint64, file File) (*File, error) {
 	return &file, err
 }
 
-func (st *Store) getFileUsage(id uint64) (playlists Playlists, err error) {
+func (st *Store) getFileUsage(id uint64, playlists *Playlists) (err error) {
 	sub := st.db.Model(PlaylistEntry{}).Select("playlist_id").Where("file_id = ?", id).Group("playlist_id").SubQuery()
-	err = st.db.Where("id in ?", sub).Find(&playlists).Error
+	err = st.db.Where("id in ?", sub).Find(playlists).Error
 	return
 }
 
@@ -90,7 +90,7 @@ func (st *Store) GetFileUsage(group string, id uint64) (playlists Playlists, err
 	if cnt == 0 {
 		return nil, ErrNotFound
 	}
-	playlists, err = st.getFileUsage(id)
+	err = st.getFileUsage(id, &playlists)
 	return
 }
 
@@ -100,11 +100,11 @@ func (st *Store) DeleteFile(group string, id uint64) (err error) {
 	result := st.db.Where("group_name = ?", group).Delete(&File{ID: id})
 	if err = result.Error; err != nil {
 		// we assume this is due to a FK constraint -> file in use by playlist_entry
-		playlists, err := st.getFileUsage(id)
-		if err != nil {
-			return err
+		usageErr := &ErrFileInUse{}
+		if err = st.getFileUsage(id, &(usageErr.Playlists)); err != nil {
+			return
 		}
-		return &ErrFileInUse{Playlists: playlists}
+		return usageErr
 	}
 	if result.RowsAffected == 0 {
 		return ErrNotFound

store/types.go

@@ -56,7 +56,7 @@ type ErrFileInUse struct {
 }
 
 func (e *ErrFileInUse) Error() string {
-	return fmt.Sprintf("the file is in use by %d playlist", len(e.Playlists))
+	return fmt.Sprintf("the file is still in use by %d playlist(s)", len(e.Playlists))
 }
 
 //******* Groups