feat: filter and search by tag

internal/web/handler.go

@@ -54,6 +54,7 @@ type ViewState struct {
 	RenderedNote template.HTML
 	SortBy       string
 	SearchTerm   string
+	TagFilter    string
 	LastActive   string
 }
 
@@ -79,6 +80,7 @@ func (h *Handler) buildViewState(r *http.Request) (*ViewState, error) {
 	}
 
 	searchTerm := query.Get("search")
+	tagFilter := query.Get("tag")
 
 	// Get notes from service
 	var notes []*note.Note
@@ -111,10 +113,15 @@ func (h *Handler) buildViewState(r *http.Request) (*ViewState, error) {
 		}
 	}
 
+	if tagFilter != "" {
+		notes = filterNotesByTag(notes, tagFilter)
+	}
+
 	return &ViewState{
 		Notes:      notes,
 		SortBy:     sortBy,
 		SearchTerm: searchTerm,
+		TagFilter:  tagFilter,
 	}, nil
 }
 
@@ -166,6 +173,24 @@ func (h *Handler) handleNotes(w http.ResponseWriter, r *http.Request) {
 	h.templates.Render(w, "index", state)
 }
 
+func filterNotesByTag(notes []*note.Note, tag string) []*note.Note {
+	tag = strings.ToLower(strings.TrimSpace(tag))
+	if tag == "" {
+		return notes
+	}
+
+	filtered := make([]*note.Note, 0, len(notes))
+	for _, n := range notes {
+		for _, t := range n.Tags {
+			if strings.EqualFold(t, tag) {
+				filtered = append(filtered, n)
+				break
+			}
+		}
+	}
+	return filtered
+}
+
 func (h *Handler) handleTags(w http.ResponseWriter, r *http.Request) {
 	if r.Method != http.MethodPost {
 		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)