feat: tag system

internal/storage/storage.go

@@ -14,6 +14,9 @@ type Storage interface {
 	Update(id string, n *note.Note)
 	Search(query string) []*note.Note
 	Count() int
+	AddTag(noteID, tag string) error
+	RemoveTag(noteID, tag string) error
+	GetTags(noteID string) []string
 }
 
 type NoteStorage struct {
@@ -70,3 +73,46 @@ func (ns *NoteStorage) Search(query string) []*note.Note {
 	}
 	return results
 }
+
+func (ns *NoteStorage) AddTag(noteID, tag string) error {
+	n, ok := ns.Index[noteID]
+	if !ok {
+		return fmt.Errorf("No note with id '%s'", noteID)
+	}
+
+	for _, existing := range n.Tags {
+		if existing == tag {
+			return nil
+		}
+	}
+
+	n.Tags = append(n.Tags, tag)
+	return nil
+}
+
+func (ns *NoteStorage) RemoveTag(noteID, tag string) error {
+	n, ok := ns.Index[noteID]
+	if !ok {
+		return fmt.Errorf("No note with id '%s'", noteID)
+	}
+
+	updated := n.Tags[:0]
+	for _, existing := range n.Tags {
+		if existing != tag {
+			updated = append(updated, existing)
+		}
+	}
+	n.Tags = updated
+	return nil
+}
+
+func (ns *NoteStorage) GetTags(noteID string) []string {
+	n, ok := ns.Index[noteID]
+	if !ok {
+		return []string{}
+	}
+
+	tags := make([]string, len(n.Tags))
+	copy(tags, n.Tags)
+	return tags
+}