phase2: markdown converter with goldmark, chroma, and ASCII-translit anchors

internal/converter/converter.go

@@ -0,0 +1,170 @@
+package converter
+
+import (
+	"bytes"
+	"fmt"
+	"html/template"
+	"io/fs"
+	"strings"
+	"sync"
+
+	chromahtml "github.com/alecthomas/chroma/v2/formatters/html"
+	"github.com/yuin/goldmark"
+	emoji "github.com/yuin/goldmark-emoji"
+	highlighting "github.com/yuin/goldmark-highlighting/v2"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/extension"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+)
+
+const documentLang = "ru"
+
+type Result struct {
+	HTML  []byte
+	Title string
+}
+
+type Converter struct {
+	md         goldmark.Markdown
+	tmpl       *template.Template
+	bufferPool sync.Pool
+}
+
+type templateData struct {
+	Lang      string
+	Title     string
+	Body      template.HTML
+	ShowTitle bool
+}
+
+func New(templateFS fs.FS) (*Converter, error) {
+	tmpl, err := template.ParseFS(templateFS, "document.html")
+	if err != nil {
+		return nil, err
+	}
+
+	return &Converter{
+		md: goldmark.New(
+			goldmark.WithExtensions(
+				extension.GFM,
+				extension.Footnote,
+				emoji.Emoji,
+				highlighting.NewHighlighting(
+					highlighting.WithStyle("github"),
+					highlighting.WithFormatOptions(chromahtml.WithClasses(false)),
+				),
+				&anchorExtension{},
+			),
+			goldmark.WithRendererOptions(
+				renderer.WithNodeRenderers(
+					util.Prioritized(&escapedRawHTMLRenderer{}, 999),
+				),
+			),
+		),
+		tmpl: tmpl,
+		bufferPool: sync.Pool{
+			New: func() any {
+				return new(bytes.Buffer)
+			},
+		},
+	}, nil
+}
+
+func (c *Converter) Convert(md []byte, fallbackTitle string) (Result, error) {
+	body, title, hasH1, err := c.render(md)
+	if err != nil {
+		return Result{}, err
+	}
+
+	if title == "" {
+		title = fallbackTitle
+	}
+
+	buf := c.getBuffer()
+	defer c.putBuffer(buf)
+
+	data := templateData{
+		Lang:      documentLang,
+		Title:     title,
+		Body:      template.HTML(body),
+		ShowTitle: !hasH1 && title != "",
+	}
+
+	if err := c.tmpl.Execute(buf, data); err != nil {
+		return Result{}, err
+	}
+
+	return Result{
+		HTML:  append([]byte(nil), buf.Bytes()...),
+		Title: title,
+	}, nil
+}
+
+func (c *Converter) RenderBody(md []byte) ([]byte, string, error) {
+	body, title, _, err := c.render(md)
+	if err != nil {
+		return nil, "", err
+	}
+	return body, title, nil
+}
+
+func (c *Converter) render(md []byte) ([]byte, string, bool, error) {
+	root := c.md.Parser().Parse(text.NewReader(md))
+	doc, ok := root.(*ast.Document)
+	if !ok {
+		return nil, "", false, fmt.Errorf("expected *ast.Document, got %T", root)
+	}
+	title, hasH1 := extractDocumentTitle(doc, md)
+
+	buf := c.getBuffer()
+	defer c.putBuffer(buf)
+
+	if err := c.md.Renderer().Render(buf, md, doc); err != nil {
+		return nil, "", false, err
+	}
+
+	return append([]byte(nil), buf.Bytes()...), title, hasH1, nil
+}
+
+func extractDocumentTitle(doc *ast.Document, src []byte) (string, bool) {
+	var (
+		title string
+		hasH1 bool
+	)
+
+	_ = ast.Walk(doc, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+
+		h, ok := n.(*ast.Heading)
+		if !ok {
+			return ast.WalkContinue, nil
+		}
+
+		if h.Level == 1 {
+			hasH1 = true
+		}
+
+		if title == "" {
+			title = strings.TrimSpace(extractHeadingText(h, src))
+		}
+
+		return ast.WalkContinue, nil
+	})
+
+	return title, hasH1
+}
+
+func (c *Converter) getBuffer() *bytes.Buffer {
+	buf := c.bufferPool.Get().(*bytes.Buffer)
+	buf.Reset()
+	return buf
+}
+
+func (c *Converter) putBuffer(buf *bytes.Buffer) {
+	buf.Reset()
+	c.bufferPool.Put(buf)
+}