Integrating Chroma in Blackfriday

main.go

package main

import (
	"fmt"
	"io"

	"github.com/alecthomas/chroma"

	"github.com/alecthomas/chroma/formatters/html"
	"github.com/alecthomas/chroma/lexers"
	"github.com/alecthomas/chroma/styles"
	bf "gopkg.in/russross/blackfriday.v2"
)

var md = "This is some sample code.\n\n```go\n" +
	`func main() {
	fmt.Println("Hi")
}
` + "```"

func renderWithChroma(w io.Writer, text []byte, data bf.CodeBlockData) error {
	var lexer chroma.Lexer
	if len(data.Info) > 0 {
		lexer = lexers.Get(string(data.Info))
	} else {
		lexer = lexers.Analyse(string(text))
	}
	if lexer == nil {
		lexer = lexers.Fallback
	}
	style := styles.Get("monokai")
	if style == nil {
		style = styles.Fallback
	}
	formatter := html.New()
	iterator, err := lexer.Tokenise(nil, string(text))
	if err != nil {
		return err
	}
	return formatter.Format(w, style, iterator)
}

type chromaRenderer struct {
	defR *bf.HTMLRenderer
}

func (r *chromaRenderer) RenderNode(w io.Writer, node *bf.Node, entering bool) bf.WalkStatus {
	switch node.Type {
	case bf.CodeBlock:
		if err := renderWithChroma(w, node.Literal, node.CodeBlockData); err != nil {
			return r.defR.RenderNode(w, node, entering)
		}
		return bf.SkipChildren
	default:
		return r.defR.RenderNode(w, node, entering)
	}
}

func (r *chromaRenderer) RenderHeader(w io.Writer, ast *bf.Node) {
	r.defR.RenderHeader(w, ast)
}

func (r *chromaRenderer) RenderFooter(w io.Writer, ast *bf.Node) {
	r.defR.RenderFooter(w, ast)
}

func main() {
	r := chromaRenderer{
		defR: bf.NewHTMLRenderer(bf.HTMLRendererParameters{
			Flags: bf.CommonHTMLFlags,
		}),
	}
	html := bf.Run([]byte(md), bf.WithRenderer(&r))
	fmt.Println(string(html))
}