handle zero values

bar_chart.go

@@ -2,6 +2,7 @@ package chart
 
 import (
 	"errors"
+	"fmt"
 	"io"
 	"math"
 
@@ -85,7 +86,7 @@ func (bc BarChart) GetBarWidth() int {
 // Render renders the chart with the given renderer to the given io.Writer.
 func (bc BarChart) Render(rp RendererProvider, w io.Writer) error {
 	if len(bc.Bars) == 0 {
-		return errors.New("Please provide at least one bar.")
+		return errors.New("please provide at least one bar")
 	}
 
 	r, err := rp(bc.GetWidth(), bc.GetHeight())
@@ -111,6 +112,9 @@ func (bc BarChart) Render(rp RendererProvider, w io.Writer) error {
 
 	canvasBox = bc.getDefaultCanvasBox()
 	yr = bc.getRanges()
+	if yr.GetMax()-yr.GetMin() == 0 {
+		return fmt.Errorf("invalid data range; cannot be zero")
+	}
 	yr = bc.setRangeDomains(canvasBox, yr)
 	yf = bc.getValueFormatters()
 

bar_chart_test.go

@@ -34,6 +34,28 @@ func TestBarChartRender(t *testing.T) {
 	assert.NotZero(buf.Len())
 }
 
+func TestBarChartRenderZero(t *testing.T) {
+	assert := assert.New(t)
+
+	bc := BarChart{
+		Width:      1024,
+		Title:      "Test Title",
+		TitleStyle: StyleShow(),
+		XAxis:      StyleShow(),
+		YAxis: YAxis{
+			Style: StyleShow(),
+		},
+		Bars: []Value{
+			{Value: 0.0, Label: "One"},
+			{Value: 0.0, Label: "Two"},
+		},
+	}
+
+	buf := bytes.NewBuffer([]byte{})
+	err := bc.Render(PNG, buf)
+	assert.NotNil(err)
+}
+
 func TestBarChartProps(t *testing.T) {
 	assert := assert.New(t)