added sparkline

the testing is very weak and I can get it to panic.

bps.go

@@ -131,6 +131,48 @@ func (b *BPS) HumanRate() string {
 	return human(uint64(b.Rate())) + "/s"
 }
 
+// Sparkline returns a human-friendly sprakline of history
+func (b *BPS) Sparkline(count int) string {
+	if count > len(b.buckets) {
+		return "bucket count inappropriate"
+	}
+	sparks := []string{"▁", "▂", "▃", "▄", "▅", "▆", "▇", "█"}
+	line := ""
+	bucketsPer := len(b.buckets) / count
+	b.Lock()
+	defer b.Unlock()
+
+	var max int64
+	var cur int64
+
+	// find max
+	for i := 0; i < len(b.buckets); i++ {
+		cur = b.buckets[i]
+		if cur > max {
+			max = cur
+		}
+	}
+
+	if max == 0 {
+		for i := 0; i < count; i++ {
+			line += sparks[0]
+		}
+		return line
+	}
+
+	cur = 0
+	for i := 0; i < len(b.buckets); i++ {
+		val := b.buckets[(b.timeI+i)%len(b.buckets)]
+		cur += val
+		if i%bucketsPer == 0 {
+			approx := int((float64(cur) / float64(max)) * float64(len(sparks)-1))
+			line += sparks[approx]
+			cur = 0
+		}
+	}
+	return line
+}
+
 // Close cleans up and shuts down a BPS.
 func (b *BPS) Close() {
 	close(b.quit)

bps_test.go

@@ -93,3 +93,33 @@ func TestHumanBytes(t *testing.T) {
 		t.Fatalf("did not get right human rate; got %v, want %v", got, want)
 	}
 }
+
+func TestSparkline(t *testing.T) {
+	bw := BPS{
+		buckets: make([]int64, 10),
+	}
+	t.Logf("%+v", bw.Sparkline(100))
+	bw.buckets[3] = 100
+	t.Logf("%+v", bw.Sparkline(10))
+	bw.buckets[7] = 300
+	for i := 1; i < 10; i++ {
+		t.Logf("%+v", bw.Sparkline(i))
+	}
+
+	for i := 0; i < 10; i++ {
+		bw.buckets[i] = int64(i * 10)
+		t.Logf("%+v", bw.Sparkline(10))
+	}
+	t.Logf("%+v", bw.Sparkline(10))
+	for i := 0; i < 10; i++ {
+		bw.buckets[i] = 0
+	}
+
+	for i := 0; i < 10; i++ {
+		bw.buckets[i] = int64((10 - i) * 10)
+		t.Logf("%+v", bw.Sparkline(10))
+	}
+	t.Logf("%+v", bw.Sparkline(10))
+	bw.buckets[5] = 200
+	t.Logf("%+v", bw.Sparkline(10))
+}