1 files changed, 107 insertions, 0 deletions
diff --git a/pkg/plot/linechart.go b/pkg/plot/linechart.go
new file mode 100644
index 0000000..f3c47f1
--- /dev/null
+++ b/pkg/plot/linechart.go
@@ -0,0 +1,107 @@
+package plot
+
+import (
+	"bytes"
+	"math"
+
+	"github.com/sgreben/jp/pkg/draw"
+)
+
+// LineChart is a line chart
+type LineChart struct{ draw.Canvas }
+
+// NewLineChart returns a new line chart
+func NewLineChart(canvas draw.Canvas) *LineChart { return &LineChart{canvas} }
+
+func (c *LineChart) drawAxes(paddingX, paddingY int, minX, maxX, minY, maxY float64) {
+	buffer := c.GetBuffer()
+	// X axis
+	buffer.SetRow(1, paddingX, buffer.Width, draw.HorizontalLine)
+	// Y axis
+	buffer.SetColumn(1, buffer.Height, paddingX, draw.VerticalLine)
+	// Corner
+	buffer.Set(1, paddingX, draw.CornerBottomLeft)
+	// Labels
+	buffer.WriteRight(1, 1, Ff(minY))
+	buffer.WriteLeft(buffer.Height-1, paddingX, Ff(maxY))
+	buffer.WriteRight(0, paddingX, Ff(minX))
+	buffer.WriteLeft(0, buffer.Width, Ff(maxX))
+}
+
+// Draw implements Chart
+func (c *LineChart) Draw(data *DataTable) string {
+	var scaleY, scaleX float64
+	var prevX, prevY int
+
+	minX, maxX, minY, maxY := minMax(data)
+	minLabelWidth := len(Ff(minY))
+	maxLabelWidth := len(Ff(maxY))
+
+	paddingX := minLabelWidth + 1
+	paddingY := 2
+	if minLabelWidth < maxLabelWidth {
+		paddingX = maxLabelWidth + 1
+	}
+	chartWidth := c.Size().Width - (paddingX+1)*c.RuneSize().Width
+	chartHeight := c.Size().Height - paddingY*c.RuneSize().Height
+	scaleX = float64(chartWidth) / (maxX - minX)
+	scaleY = float64(chartHeight) / (maxY - minY)
+
+	first := true
+	for _, point := range data.Rows {
+		if len(point) < 2 {
+			continue
+		}
+		x := int((point[0]-minX)*scaleX + float64((paddingX+1)*c.RuneSize().Width))
+		y := int((point[1]-minY)*scaleY + float64(paddingY*c.RuneSize().Height))
+
+		if first {
+			first = false
+			prevX = x
+			prevY = y
+		}
+
+		if prevX <= x {
+			c.DrawLine(prevY, prevX, y, x)
+		}
+
+		prevX = x
+		prevY = y
+	}
+	c.drawAxes(paddingX, paddingY, minX, maxX, minY, maxY)
+
+	b := bytes.NewBuffer(nil)
+	c.GetBuffer().Render(b)
+	return b.String()
+}
+
+func roundDownToPercentOfRange(x, d float64) float64 {
+	return math.Floor((x*(100-math.Copysign(5, x)))/d) * d / 100
+}
+
+func roundUpToPercentOfRange(x, d float64) float64 {
+	return math.Ceil((x*105)/d) * d / 100
+}
+
+func minMax(data *DataTable) (minX, maxX, minY, maxY float64) {
+	minX, minY = math.Inf(1), math.Inf(1)
+	maxX, maxY = math.Inf(-1), math.Inf(-1)
+
+	for _, r := range data.Rows {
+		if len(r) < 2 {
+			continue
+		}
+		maxX = math.Max(maxX, r[0])
+		minX = math.Min(minX, r[0])
+		maxY = math.Max(maxY, r[1])
+		minY = math.Min(minY, r[1])
+	}
+
+	xRange := maxX - minX
+	yRange := maxY - minY
+	minX = roundDownToPercentOfRange(minX, xRange)
+	minY = roundDownToPercentOfRange(minY, yRange)
+	maxX = roundUpToPercentOfRange(maxX, xRange)
+	maxY = roundUpToPercentOfRange(maxY, yRange)
+	return
+}