Gophercises SVGo example refactor

bars.go

package main

import (
	"os"

	"github.com/ajstarks/svgo"
)

func main() {
	canvas := svg.New(os.Stdout)
	data := []struct {
		Month string
		Usage int
	}{
		{"Jan", 171},
		{"Feb", 180},
		{"Mar", 100},
		{"Apr", 87},
		{"May", 65},
		{"Jun", 40},
		{"Jul", 32},
		{"Aug", 55},
		{"Sep", 0},
		{"Oct", 0},
		{"Nov", 0},
		{"Dec", 0},
	}

	// tweak these to control the width and separation of the bars
	barwidth := 50
	offset := 10

	width := len(data)*barwidth + offset
	height := 300
	threshold := 160
	barcolor := canvas.RGB(77, 200, 232)
	bottom := (height - 50)

	max := 0
	for _, item := range data {
		if item.Usage > max {
			max = item.Usage
		}
	}
	canvas.Start(width, height)
	canvas.Rect(0, 0, width, height, "fill:white")
	canvas.Gstyle("font-size:14pt;fill:rgb(150, 150, 150);text-anchor:middle")
	for i, val := range data {
		barx := i*barwidth + offset
		tx := barx + ((barwidth - offset) / 2)
		percent := val.Usage * bottom / max
		canvas.Rect(barx, bottom-percent, barwidth-offset, percent, barcolor)
		canvas.Text(tx, height-24, val.Month)
	}
	canvas.Gend()
	threshPercent := threshold * bottom / max
	canvas.Line(0, height-threshPercent, width, height-threshPercent, "stroke: rgb(255,100,100); opacity: 0.8; stroke-width: 2px")
	canvas.Rect(0, 0, width, height-threshPercent, "fill:rgb(255, 100, 100); opacity: 0.1")
	canvas.Line(0, bottom, width, bottom, "stroke: rgb(150, 150, 150); stroke-width:2")
	canvas.End()
}