stuff

main.go

@@ -157,7 +157,7 @@ func (s *server) handleIndex(w http.ResponseWriter, r *http.Request) {
 		updatedLabel = updatedAt.Format("02.01.2006 15:04:05")
 	}
 	if err := page.Execute(w, map[string]any{
-		"Watts":        watts,
+		"Watts":        formatGermanNumber(watts),
 		"UpdatedAt":    updatedLabel,
 		"HistoryChart": buildHistoryChart(history, s.chartMax),
 	}); err != nil {
@@ -165,6 +165,34 @@ func (s *server) handleIndex(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func formatGermanNumber(n int) string {
+	s := strconv.Itoa(n)
+	if len(s) <= 3 {
+		return s
+	}
+
+	neg := false
+	if s[0] == '-' {
+		neg = true
+		s = s[1:]
+	}
+
+	var b strings.Builder
+	if neg {
+		b.WriteByte('-')
+	}
+	rem := len(s) % 3
+	if rem == 0 {
+		rem = 3
+	}
+	b.WriteString(s[:rem])
+	for i := rem; i < len(s); i += 3 {
+		b.WriteByte('.')
+		b.WriteString(s[i : i+3])
+	}
+	return b.String()
+}
+
 func buildHistoryChart(history []sample, maxWatts int) template.HTML {
 	const (
 		width  = 640
@@ -242,8 +270,8 @@ func buildHistoryChart(history []sample, maxWatts int) template.HTML {
 	fmt.Fprintf(&b, `<path d="M %.1f %.1f V %.1f"/>`, x1, yTop, yBottom)
 	b.WriteString(`</g>`)
 	b.WriteString(`<g fill="#64748b" font-size="12" font-family="system-ui, sans-serif">`)
-	fmt.Fprintf(&b, `<text x="%.1f" y="%d" text-anchor="end">%d W</text>`, x0-10, int(yTop)+14, maxV)
-	fmt.Fprintf(&b, `<text x="%.1f" y="%d" text-anchor="end">%d W</text>`, x0-10, int(yMid)+14, midV)
+	fmt.Fprintf(&b, `<text x="%.1f" y="%d" text-anchor="end">%s W</text>`, x0-10, int(yTop)+14, formatGermanNumber(maxV))
+	fmt.Fprintf(&b, `<text x="%.1f" y="%d" text-anchor="end">%s W</text>`, x0-10, int(yMid)+14, formatGermanNumber(midV))
 	fmt.Fprintf(&b, `<text x="%.1f" y="%d" text-anchor="end">0 W</text>`, x0-10, int(yBottom)+14)
 	fmt.Fprintf(&b, `<text x="%.1f" y="%d" text-anchor="middle">%s</text>`, x0, int(height)-10, start.Format("15:04"))
 	fmt.Fprintf(&b, `<text x="%.1f" y="%d" text-anchor="middle">%s</text>`, x0+(plotW/2), int(height)-10, midT.Format("15:04"))

main_test.go

@@ -31,6 +31,23 @@ func TestHandleIndexRendersWatts(t *testing.T) {
 	}
 }
 
+func TestFormatGermanNumber(t *testing.T) {
+	tests := map[int]string{
+		0:       "0",
+		12:      "12",
+		999:     "999",
+		1000:    "1.000",
+		10000:   "10.000",
+		1234567: "1.234.567",
+		-1000:   "-1.000",
+	}
+	for input, want := range tests {
+		if got := formatGermanNumber(input); got != want {
+			t.Fatalf("formatGermanNumber(%d) = %q, want %q", input, got, want)
+		}
+	}
+}
+
 func TestHandleWriteRequiresSecret(t *testing.T) {
 	srv := &server{secret: "secret", store: &store{}}
 	req := httptest.NewRequest(http.MethodPost, "/write", bytes.NewBufferString(`{"watts":456}`))
@@ -116,7 +133,7 @@ func TestBuildHistoryChartRendersPolyline(t *testing.T) {
 func TestBuildHistoryChartUsesConfiguredMax(t *testing.T) {
 	history := []sample{{at: time.Date(2026, 4, 20, 12, 0, 0, 0, time.UTC), value: 250}}
 	chart := buildHistoryChart(history, 1000)
-	if !strings.Contains(string(chart), "1000 W") {
+	if !strings.Contains(string(chart), "1.000 W") {
 		t.Fatalf("chart did not include configured max: %s", string(chart))
 	}
 	if strings.Contains(string(chart), "250 W") {

static/index.html

@@ -18,8 +18,7 @@
 </head>
 <body>
     <main>
-      <div class="value">{{.Watts}}</div>
-      <div class="unit">watts</div>
+      <div class="value">{{.Watts}} W</div>
       <div class="updated-at">Last updated: {{.UpdatedAt}}</div>
       <div class="chart">{{.HistoryChart}}</div>
     </main>