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markdown_viewer.go
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/
markdown_viewer.go
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package tmplrndr
import (
"bytes"
"fmt"
"github.com/alecthomas/chroma"
chromahtml "github.com/alecthomas/chroma/formatters/html"
"github.com/alecthomas/chroma/lexers"
"github.com/alecthomas/chroma/styles"
"github.com/gomarkdown/markdown"
"github.com/gomarkdown/markdown/ast"
"github.com/gomarkdown/markdown/html"
"io"
)
var (
htmlFormatter *chromahtml.Formatter
highlightStyle *chroma.Style
)
// the highlighter code was taken from this blog post https://blog.kowalczyk.info/article/cxn3/advanced-markdown-processing-in-go.html
func init() {
htmlFormatter = chromahtml.New(chromahtml.WithClasses(true), chromahtml.TabWidth(2))
if htmlFormatter == nil {
panic("couldn't create html formatter")
}
styleName := "base16-snazzy"
highlightStyle = styles.Get(styleName)
if highlightStyle == nil {
panic(fmt.Sprintf("didn't find style '%s'", styleName))
}
}
// based on https://github.com/alecthomas/chroma/blob/master/quick/quick.go
func htmlHighlight(w io.Writer, source, lang, defaultLang string) error {
if lang == "" {
lang = defaultLang
}
l := lexers.Get(lang)
if l == nil {
l = lexers.Analyse(source)
}
if l == nil {
l = lexers.Fallback
}
l = chroma.Coalesce(l)
it, err := l.Tokenise(nil, source)
if err != nil {
return err
}
return htmlFormatter.Format(w, highlightStyle, it)
}
func renderCode(w io.Writer, codeBlock *ast.CodeBlock, _ bool) {
defaultLang := ""
lang := string(codeBlock.Info)
htmlHighlight(w, string(codeBlock.Literal), lang, defaultLang)
}
func myRenderHook(w io.Writer, node ast.Node, entering bool) (ast.WalkStatus, bool) {
if code, ok := node.(*ast.CodeBlock); ok {
renderCode(w, code, entering)
return ast.GoToNext, true
}
return ast.GoToNext, false
}
type MarkdownViewerProps struct {
Markdown string
}
type markdownViewerTemplate struct{}
func NewMarkdownViewer() Template[MarkdownViewerProps] {
return &markdownViewerTemplate{}
}
func (m *markdownViewerTemplate) Render(props MarkdownViewerProps) io.Reader {
opts := html.RendererOptions{
Flags: html.CommonFlags | html.TOC | html.LazyLoadImages | html.UseXHTML,
RenderNodeHook: myRenderHook,
}
buf := bytes.NewBuffer([]byte{})
defer buf.Reset()
buf.WriteString("<style scoped>")
_ = htmlFormatter.WriteCSS(buf, highlightStyle)
buf.WriteString("</style>")
renderer := html.NewRenderer(opts)
buf.Write(markdown.ToHTML([]byte(props.Markdown), nil, renderer))
props.Markdown = buf.String()
out, _ := renderTemplate("markdown-viewer", props)
return out
}