markdown to pdf converter

md_to_pdf.go

package main

import (
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"os"

	"github.com/jung-kurt/gofpdf"
	blackfriday "gopkg.in/russross/blackfriday.v2"
)

const FONT = "Times"

func renderHeading(pdf *gofpdf.Fpdf, node *blackfriday.Node) {
	text := node.FirstChild
	if text != nil {
		switch node.HeadingData.Level {
		case 1:
			pdf.SetFont(FONT, "B", 32)
		case 2:
			pdf.SetFont(FONT, "B", 24)
		case 3:
			pdf.SetFont(FONT, "B", 18.72)
		case 4:
			pdf.SetFont(FONT, "B", 18.4)
		case 5:
			pdf.SetFont(FONT, "B", 13.28)
		case 6:
			fallthrough
		default:
			pdf.SetFont(FONT, "B", 10.72)
		}
		_, ht := pdf.GetFontSize()
		pdf.Cell(0, ht, string(text.Literal))
		pdf.Ln(16)
	}
}

func renderParagraph(pdf *gofpdf.Fpdf, node *blackfriday.Node, margin float64) {
	cn := node.FirstChild
	for cn != nil {
		switch cn.Type {
		case blackfriday.Text:
			pdf.SetFont(FONT, "", 12)
			_, ht := pdf.GetFontSize()
			pdf.Write(ht, pdf.UnicodeTranslatorFromDescriptor("")(string(cn.Literal)))
		case blackfriday.Link:
			pdf.SetFont(FONT, "", 12)
			_, ht := pdf.GetFontSize()
			tit := cn.LinkData.Destination
			if cn.FirstChild != nil {
				tit = cn.FirstChild.Literal
			}
			trans := pdf.UnicodeTranslatorFromDescriptor("")
			pdf.WriteLinkString(ht, trans(string(tit)), string(cn.LinkData.Destination))
		default:
			fmt.Println("renderParagraph new type:", cn.Type)
		}
		cn = cn.Next
	}
	pdf.Ln(margin)
}

func renderList(pdf *gofpdf.Fpdf, node *blackfriday.Node, margin float64) {
	left, _, _, _ := pdf.GetMargins()
	pdf.SetLeftMargin(left * 2)
	item := node.FirstChild
	for item != nil {
		c := item.FirstChild
		for c != nil {
			switch c.Type {
			case blackfriday.Paragraph:
				pdf.SetFont(FONT, "", 12)
				_, ht := pdf.GetFontSize()
				pdf.Write(ht, "- ")
				renderParagraph(pdf, c, 5)
			case blackfriday.List:
				renderList(pdf, c, 0)
			default:
				fmt.Println("renderParagraph new type:", c.Type)
			}
			c = c.Next
		}
		item = item.Next
	}
	pdf.SetLeftMargin(left)
	pdf.Ln(margin)
}

func main() {
	var opts struct {
		In  string
		Out string
	}
	flag.StringVar(&opts.In, "i", "", "input markdown file, if not supplied use stdin")
	flag.StringVar(&opts.Out, "o", "", "output pdf file, if not supplied use stdout")
	flag.Parse()

	var in io.Reader
	if opts.In == "" {
		in = os.Stdin
	} else {
		fd, err := os.Open(opts.In)
		if err != nil {
			panic(err)
		}
		defer fd.Close()
		in = fd
	}

	var out io.Writer
	if opts.Out == "" {
		out = os.Stdout
	} else {
		fd, err := os.OpenFile(opts.Out, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0750)
		if err != nil {
			panic(err)
		}
		defer fd.Close()
		out = fd
	}

	raw, err := ioutil.ReadAll(in)
	if err != nil {
		panic(err)
	}
	root := blackfriday.New().Parse(raw)
	node := root.FirstChild
	pdf := gofpdf.New("P", "mm", "A4", "")
	pdf.AddPage()
	for node != nil {
		switch node.Type {
		case blackfriday.Heading:
			renderHeading(pdf, node)
		case blackfriday.Paragraph:
			renderParagraph(pdf, node, 10)
		case blackfriday.List:
			renderList(pdf, node, 5)
		case blackfriday.HorizontalRule:
			_, y := pdf.GetXY()
			left, _, right, _ := pdf.GetMargins()
			w, _ := pdf.GetPageSize()
			pdf.Line(left, y, w-right, y)
			pdf.DrawPath("")
			pdf.Ln(5)
		}
		node = node.Next
	}
	if err := pdf.Output(out); err != nil {
		panic(err)
	}
}