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package export
import (
"encoding/base64"
"fmt"
"os"
"path/filepath"
"strings"
"golang.org/x/image/font/sfnt"
)
// A fontFace is one resolved face of a configured family, ready to embed.
type fontFace struct {
family string
weight int
italic bool
ext string // ".otf" / ".ttf"
data []byte
}
// embedFontFaces returns base64 @font-face rules for every configured family
// whose font files are found on disk. WebKit (Safari/Orion) refuses to render
// locally-installed user fonts referenced only by name, so the export inlines
// the files. Best-effort: families with no file found are simply skipped (the
// name reference + fallbacks in fontOverride still apply).
func embedFontFaces(opts Options) string {
seen := map[string]bool{}
var b strings.Builder
for _, stack := range []string{opts.FontDisplay, opts.FontBody, opts.FontMono} {
fam := primaryFamily(stack)
if fam == "" || seen[strings.ToLower(fam)] {
continue
}
seen[strings.ToLower(fam)] = true
for _, f := range discoverFaces(fam) {
b.WriteString(f.faceCSS())
}
}
return b.String()
}
// faceCSS renders one @font-face rule with the file inlined as a data URL.
func (f fontFace) faceCSS() string {
style := "normal"
if f.italic {
style = "italic"
}
mime, format := "font/ttf", "truetype"
if f.ext == ".otf" {
mime, format = "font/otf", "opentype"
}
enc := base64.StdEncoding.EncodeToString(f.data)
return fmt.Sprintf(
`@font-face{font-family:"%s";font-style:%s;font-weight:%d;font-display:swap;src:url("data:%s;base64,%s") format("%s");}`,
f.family, style, f.weight, mime, enc, format,
)
}
// primaryFamily is the first real (non-generic) family name in a CSS stack,
// unquoted — the family to look up and embed. Returns "" if the stack holds
// only generic keywords or is empty.
func primaryFamily(stack string) string {
for _, seg := range strings.Split(stack, ",") {
seg = strings.TrimSpace(seg)
seg = strings.Trim(seg, `"'`)
seg = strings.TrimSpace(seg)
if seg == "" || isGenericFamily(seg) {
continue
}
return seg
}
return ""
}
func isGenericFamily(name string) bool {
switch strings.ToLower(name) {
case "serif", "sans-serif", "monospace", "cursive", "fantasy",
"system-ui", "ui-serif", "ui-sans-serif", "ui-monospace", "ui-rounded",
"-apple-system", "blinkmacsystemfont", "math", "emoji", "fangsong":
return true
}
return false
}
// userFontDirs are the macOS locations user/admin-installed fonts live. System
// fonts are skipped: they're already on WebKit's allowed list, so they render
// without embedding.
func userFontDirs() []string {
var dirs []string
if home, err := os.UserHomeDir(); err == nil {
dirs = append(dirs, filepath.Join(home, "Library", "Fonts"))
}
dirs = append(dirs, "/Library/Fonts")
return dirs
}
// discoverFaces scans the user font directories for every face of family,
// parsing each font's name table to match. Unreadable/unparsable files and
// non-font files are skipped.
func discoverFaces(family string) []fontFace {
want := strings.ToLower(strings.TrimSpace(family))
var faces []fontFace
dedup := map[string]bool{}
for _, dir := range userFontDirs() {
entries, err := os.ReadDir(dir)
if err != nil {
continue
}
for _, e := range entries {
if e.IsDir() {
continue
}
ext := strings.ToLower(filepath.Ext(e.Name()))
if ext != ".otf" && ext != ".ttf" {
continue
}
path := filepath.Join(dir, e.Name())
data, err := os.ReadFile(path)
if err != nil {
continue
}
f, err := sfnt.Parse(data)
if err != nil {
continue
}
fam := familyName(f)
if strings.ToLower(strings.TrimSpace(fam)) != want {
continue
}
sub := subfamilyName(f)
face := fontFace{family: family, weight: weightOf(sub), italic: italicOf(sub), ext: ext, data: data}
// Markdown only needs regular + bold (roman + italic). Skip the
// other weights so a many-weight family doesn't bloat the export.
if face.weight != 400 && face.weight != 700 {
continue
}
key := fmt.Sprintf("%d/%v", face.weight, face.italic)
if dedup[key] {
continue
}
dedup[key] = true
faces = append(faces, face)
}
}
return faces
}
func familyName(f *sfnt.Font) string {
if n, err := f.Name(nil, sfnt.NameIDTypographicFamily); err == nil && n != "" {
return n
}
n, _ := f.Name(nil, sfnt.NameIDFamily)
return n
}
func subfamilyName(f *sfnt.Font) string {
if n, err := f.Name(nil, sfnt.NameIDTypographicSubfamily); err == nil && n != "" {
return n
}
n, _ := f.Name(nil, sfnt.NameIDSubfamily)
return n
}
// weightOf maps a subfamily/style string to a CSS numeric weight.
func weightOf(sub string) int {
s := strings.ToLower(sub)
switch {
case strings.Contains(s, "thin"), strings.Contains(s, "hairline"):
return 100
case strings.Contains(s, "extralight"), strings.Contains(s, "ultralight"):
return 200
case strings.Contains(s, "semibold"), strings.Contains(s, "demibold"):
return 600
case strings.Contains(s, "extrabold"), strings.Contains(s, "ultrabold"):
return 800
case strings.Contains(s, "black"), strings.Contains(s, "heavy"):
return 900
case strings.Contains(s, "bold"):
return 700
case strings.Contains(s, "medium"):
return 500
case strings.Contains(s, "light"):
return 300
default:
return 400
}
}
func italicOf(sub string) bool {
s := strings.ToLower(sub)
return strings.Contains(s, "italic") || strings.Contains(s, "oblique")
}
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