From 9c209a952e52661231f1212a208df79d3831602c Mon Sep 17 00:00:00 2001 From: Steve Cliff Date: Thu, 7 May 2026 18:50:23 +0100 Subject: [PATCH] web/sparkline: inline-SVG sparkline renderer (empty / single / multi) --- internal/web/sparkline/sparkline.go | 101 ++++++++++++++++++ internal/web/sparkline/sparkline_test.go | 41 +++++++ internal/web/sparkline/testdata/empty.svg | 1 + .../web/sparkline/testdata/single_point.svg | 1 + .../web/sparkline/testdata/three_points.svg | 1 + 5 files changed, 145 insertions(+) create mode 100644 internal/web/sparkline/sparkline.go create mode 100644 internal/web/sparkline/sparkline_test.go create mode 100644 internal/web/sparkline/testdata/empty.svg create mode 100644 internal/web/sparkline/testdata/single_point.svg create mode 100644 internal/web/sparkline/testdata/three_points.svg diff --git a/internal/web/sparkline/sparkline.go b/internal/web/sparkline/sparkline.go new file mode 100644 index 0000000..6d6f0f8 --- /dev/null +++ b/internal/web/sparkline/sparkline.go @@ -0,0 +1,101 @@ +// Package sparkline renders inline SVG sparklines and trend +// charts for the dashboard and host repo page. All output is +// pure server-rendered SVG with no JavaScript, no external +// stylesheet, and no client library. +package sparkline + +import ( + "fmt" + "html/template" + "math" + "strings" +) + +// RenderSparkline returns an inline SVG element of the +// given size containing a single polyline normalised across the +// full y-range of points. NaN entries break the polyline. With +// fewer than two real points the SVG still renders but contains +// only a faint baseline + an em-dash placeholder. +func RenderSparkline(points []float64, width, height int) template.HTML { + const pad = 2 + w := width + h := height + innerW := w - 2*pad + innerH := h - 2*pad + + var real []float64 + for _, p := range points { + if !math.IsNaN(p) { + real = append(real, p) + } + } + + var b strings.Builder + fmt.Fprintf(&b, + ``, + w, h) + + if len(real) < 2 { + fmt.Fprintf(&b, + ``, + pad, h/2, w-pad, h/2) + fmt.Fprintf(&b, + `—`, + w/2, h/2+4, h-6) + b.WriteString(``) + return template.HTML(b.String()) + } + + min, max := real[0], real[0] + for _, v := range real { + if v < min { + min = v + } + if v > max { + max = v + } + } + span := max - min + if span == 0 { + span = 1 + } + + stepX := 0.0 + if len(points) > 1 { + stepX = float64(innerW) / float64(len(points)-1) + } + + var seg strings.Builder + flush := func() { + if seg.Len() == 0 { + return + } + fmt.Fprintf(&b, + ``, + strings.TrimSpace(seg.String())) + seg.Reset() + } + for i, v := range points { + if math.IsNaN(v) { + flush() + continue + } + x := float64(pad) + stepX*float64(i) + y := float64(pad) + float64(innerH) - (v-min)/span*float64(innerH) + fmt.Fprintf(&seg, "%.2f,%.2f ", x, y) + } + flush() + + cur := real[len(real)-1] + first := real[0] + delta := cur - first + sign := "+" + if delta < 0 { + sign = "-" + delta = -delta + } + fmt.Fprintf(&b, `current %.0f, %s%.0f over window`, cur, sign, delta) + + b.WriteString(``) + return template.HTML(b.String()) +} diff --git a/internal/web/sparkline/sparkline_test.go b/internal/web/sparkline/sparkline_test.go new file mode 100644 index 0000000..f0af51b --- /dev/null +++ b/internal/web/sparkline/sparkline_test.go @@ -0,0 +1,41 @@ +package sparkline + +import ( + "os" + "path/filepath" + "strings" + "testing" +) + +func loadGolden(t *testing.T, name string) string { + t.Helper() + b, err := os.ReadFile(filepath.Join("testdata", name)) + if err != nil { + t.Fatalf("read golden %s: %v", name, err) + } + return strings.TrimRight(string(b), "\n") +} + +func TestSparkline_Empty(t *testing.T) { + got := strings.TrimRight(string(RenderSparkline(nil, 80, 20)), "\n") + want := loadGolden(t, "empty.svg") + if got != want { + t.Errorf("empty sparkline mismatch:\nwant:\n%s\ngot:\n%s", want, got) + } +} + +func TestSparkline_SinglePoint(t *testing.T) { + got := strings.TrimRight(string(RenderSparkline([]float64{100}, 80, 20)), "\n") + want := loadGolden(t, "single_point.svg") + if got != want { + t.Errorf("single_point sparkline mismatch:\nwant:\n%s\ngot:\n%s", want, got) + } +} + +func TestSparkline_ThreePoints(t *testing.T) { + got := strings.TrimRight(string(RenderSparkline([]float64{10, 30, 20}, 80, 20)), "\n") + want := loadGolden(t, "three_points.svg") + if got != want { + t.Errorf("three_points sparkline mismatch:\nwant:\n%s\ngot:\n%s", want, got) + } +} diff --git a/internal/web/sparkline/testdata/empty.svg b/internal/web/sparkline/testdata/empty.svg new file mode 100644 index 0000000..5f35061 --- /dev/null +++ b/internal/web/sparkline/testdata/empty.svg @@ -0,0 +1 @@ +— diff --git a/internal/web/sparkline/testdata/single_point.svg b/internal/web/sparkline/testdata/single_point.svg new file mode 100644 index 0000000..5f35061 --- /dev/null +++ b/internal/web/sparkline/testdata/single_point.svg @@ -0,0 +1 @@ +— diff --git a/internal/web/sparkline/testdata/three_points.svg b/internal/web/sparkline/testdata/three_points.svg new file mode 100644 index 0000000..1bbad3c --- /dev/null +++ b/internal/web/sparkline/testdata/three_points.svg @@ -0,0 +1 @@ +current 20, +10 over window