tui: add dashboard sparkline renderer

2 files changed, 117 insertions, 0 deletions

diff --git a/internal/tui/dashboard/sparkline.go b/internal/tui/dashboard/sparkline.go
new file mode 100644
index 0000000..1531ca6
--- /dev/null
+++ b/internal/tui/dashboard/sparkline.go
@@ -0,0 +1,74 @@
+package dashboard
+
+import "math"
+
+var sparkChars = []rune("▁▂▃▄▅▆▇█")
+
+func renderSparkline(data []float64, width int) string {
+	if len(data) == 0 || width <= 0 {
+		return ""
+	}
+
+	samples := sampleForWidth(data, width)
+	min, max := minMax(samples)
+	if min == max {
+		return repeatRune('▄', len(samples))
+	}
+
+	out := make([]rune, len(samples))
+	scale := float64(len(sparkChars) - 1)
+	denom := max - min
+	for i, value := range samples {
+		idx := int(math.Round((value - min) / denom * scale))
+		if idx < 0 {
+			idx = 0
+		}
+		if idx >= len(sparkChars) {
+			idx = len(sparkChars) - 1
+		}
+		out[i] = sparkChars[idx]
+	}
+	return string(out)
+}
+
+func sampleForWidth(data []float64, width int) []float64 {
+	if width >= len(data) {
+		return append([]float64(nil), data...)
+	}
+	if width == 1 {
+		return []float64{data[len(data)-1]}
+	}
+
+	last := len(data) - 1
+	samples := make([]float64, width)
+	for i := 0; i < width; i++ {
+		idx := int(math.Round(float64(i) * float64(last) / float64(width-1)))
+		samples[i] = data[idx]
+	}
+	return samples
+}
+
+func minMax(values []float64) (float64, float64) {
+	min := values[0]
+	max := values[0]
+	for _, v := range values[1:] {
+		if v < min {
+			min = v
+		}
+		if v > max {
+			max = v
+		}
+	}
+	return min, max
+}
+
+func repeatRune(r rune, count int) string {
+	if count <= 0 {
+		return ""
+	}
+	out := make([]rune, count)
+	for i := range out {
+		out[i] = r
+	}
+	return string(out)
+}
diff --git a/internal/tui/dashboard/sparkline_test.go b/internal/tui/dashboard/sparkline_test.go
new file mode 100644
index 0000000..d39d145
--- /dev/null
+++ b/internal/tui/dashboard/sparkline_test.go
@@ -0,0 +1,43 @@
+package dashboard
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestRenderSparklineEmptyOrInvalidWidth(t *testing.T) {
+	if got := renderSparkline(nil, 5); got != "" {
+		t.Fatalf("expected empty sparkline for nil data, got %q", got)
+	}
+	if got := renderSparkline([]float64{1, 2, 3}, 0); got != "" {
+		t.Fatalf("expected empty sparkline for width 0, got %q", got)
+	}
+}
+
+func TestRenderSparklineSingleValue(t *testing.T) {
+	got := renderSparkline([]float64{10}, 8)
+	if got != "▄" {
+		t.Fatalf("expected single mid-bar rune, got %q", got)
+	}
+}
+
+func TestRenderSparklineAllEqualValues(t *testing.T) {
+	got := renderSparkline([]float64{5, 5, 5, 5}, 4)
+	if got != "▄▄▄▄" {
+		t.Fatalf("expected flat sparkline, got %q", got)
+	}
+}
+
+func TestRenderSparklineRespectsWidthTruncation(t *testing.T) {
+	got := renderSparkline([]float64{1, 2, 3, 4, 5, 6, 7, 8}, 4)
+	if len([]rune(got)) != 4 {
+		t.Fatalf("expected 4 runes, got %q", got)
+	}
+}
+
+func TestRenderSparklineSpansLowToHigh(t *testing.T) {
+	got := renderSparkline([]float64{0, 10}, 2)
+	if !strings.Contains(got, "▁") || !strings.Contains(got, "█") {
+		t.Fatalf("expected low/high bars, got %q", got)
+	}
+}