Use HTMX fragements on the fitness dashboard

fitness.go

@@ -34,13 +34,42 @@ func (f *fitnessHandler) handle(root, fsPath, urlPath string, r *http.Request) *
 	if s == nil || s.Type != "fitness" {
 		return nil
 	}
-	q := r.URL.Query()
+	weightView, weeklyView := fitnessViews(r.URL.Query())
 	return &specialPage{
-		Content:     renderFitnessDashboard(fsPath, chartViewFrom(q, "weight", "3m"), chartViewFrom(q, "weekly", "1y")),
+		Content:     renderFitnessDashboard(fsPath, weightView, weeklyView),
 		SuppressTOC: true,
 	}
 }
 
+// serveFragment answers a chart's controls (htmx GET ?chart=<param> with
+// every chart's view state) with just that chart, and points the address bar
+// at the canonical dashboard URL so the view stays bookmarkable.
+func (f *fitnessHandler) serveFragment(w http.ResponseWriter, r *http.Request, root, fsPath, urlPath string) bool {
+	q := r.URL.Query()
+	param := q.Get("chart")
+	if param == "" {
+		return false
+	}
+	if s := readPageSettings(fsPath); s == nil || s.Type != "fitness" {
+		return false
+	}
+	weightView, weeklyView := fitnessViews(q)
+	dash := buildFitnessDash(fsPath, weightView, weeklyView, time.Now())
+	for _, c := range dash.Charts {
+		if c.Param != param {
+			continue
+		}
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.Header().Set("HX-Replace-Url", fitnessURL(urlPath, weightView, weeklyView))
+		if err := fitnessTmpl.ExecuteTemplate(w, "fitnessChart", c); err != nil {
+			log.Printf("fitness template: %v", err)
+		}
+		return true
+	}
+	http.Error(w, "Unknown chart: "+param, http.StatusNotFound)
+	return true
+}
+
 // === Time ranges ===
 
 type fitnessRange struct {
@@ -79,6 +108,36 @@ func chartViewFrom(q url.Values, param, fallback string) fitnessView {
 	}
 }
 
+// Default ranges of the two charts.
+const (
+	weightDefaultRange = "3m"
+	weeklyDefaultRange = "1y"
+)
+
+func fitnessViews(q url.Values) (weight, weekly fitnessView) {
+	return chartViewFrom(q, "weight", weightDefaultRange), chartViewFrom(q, "weekly", weeklyDefaultRange)
+}
+
+// fitnessURL is the dashboard URL for the given views; defaults are left out.
+func fitnessURL(urlPath string, weight, weekly fitnessView) string {
+	q := url.Values{}
+	add := func(param, fallback string, v fitnessView) {
+		if v.Range != fallback {
+			q.Set(param, v.Range)
+		}
+		if v.Absolute {
+			q.Set(param+"-absolute", "1")
+		}
+	}
+	add("weight", weightDefaultRange, weight)
+	add("weekly", weeklyDefaultRange, weekly)
+	target := pageURL(urlPath)
+	if len(q) > 0 {
+		target += "?" + q.Encode()
+	}
+	return target
+}
+
 func rangeMonths(v string) int {
 	for _, r := range fitnessRanges {
 		if r.Value == v {