feat(web): add calendar event detail view

internal/web/calendar.go

@@ -18,6 +18,7 @@ import (
 	"git.arnef.de/arnef/nidus/internal/birthdays"
 	"git.arnef.de/arnef/nidus/internal/db"
 	"git.arnef.de/arnef/nidus/internal/icalfix"
+	"git.arnef.de/arnef/nidus/internal/store"
 	"git.arnef.de/arnef/nidus/internal/web/templates"
 	ical "github.com/emersion/go-ical"
 )
@@ -636,6 +637,70 @@ func newEventFormDefaults(calRef, dateParam string) templates.EventFormData {
 	}
 }
 
+// handleEventView renders the read-only detail view for a single event. It
+// is the landing page when a user clicks an event in the month/week grid;
+// writable calendars link from here to the edit page.
+func (s *Server) handleEventView(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		w.Header().Set("Allow", "GET")
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	username := userFromContext(r.Context())
+	ref := r.PathValue("ref")
+	id := r.PathValue("id")
+
+	if !eventIDRe.MatchString(id) {
+		http.NotFound(w, r)
+		return
+	}
+	color, form, err := s.eventForDisplay(username, ref, id)
+	if errors.Is(err, store.ErrNotFound) {
+		http.NotFound(w, r)
+		return
+	}
+	if err != nil {
+		s.handleCalRefError(w, r, err)
+		return
+	}
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	_ = templates.EventDetail(username, templates.EventDetailData{Form: form, Color: color}).Render(context.Background(), w)
+}
+
+// eventForDisplay resolves a calendar reference for read access, loads and
+// decodes the event with the given id, populates the form's display fields
+// (CalRef, CalendarLabel, Writable), and returns the calendar's color for
+// the detail view's header dot.
+func (s *Server) eventForDisplay(username, ref, id string) (color string, form templates.EventFormData, err error) {
+	owner, name, err := s.resolveCalRef(username, ref, false)
+	if err != nil {
+		return "", form, err
+	}
+	data, err := s.store.GetObject(owner, "cal-"+name, id)
+	if err != nil {
+		return "", form, err
+	}
+	form, err = eventFormFromICS(id, data)
+	if err != nil {
+		s.logger.Error("decoding event", "error", err)
+		return "", form, err
+	}
+	form.CalRef = ref
+	label := name
+	if owner != username {
+		label = name + " (" + s.dbase.DisplayName(owner) + ")"
+	}
+	form.CalendarLabel = label
+	form.Writable = owner == username
+	if !form.Writable {
+		if share, err := s.dbase.CalendarShareFor(owner, name, username); err == nil {
+			form.Writable = share.Permission == db.PermWrite
+		}
+	}
+	color, _ = s.dbase.GetCalendarColor(owner, name)
+	return color, form, nil
+}
+
 func (s *Server) handleEventEdit(w http.ResponseWriter, r *http.Request) {
 	username := userFromContext(r.Context())
 	ref := r.PathValue("ref")