make emitters async generators

quartz/util/theme.ts

@@ -90,6 +90,36 @@ export function googleFontHref(theme: Theme) {
   return `https://fonts.googleapis.com/css2?family=${bodyFont}&family=${headerFont}&family=${codeFont}&display=swap`
 }
 
+export interface GoogleFontFile {
+  url: string
+  filename: string
+  extension: string
+}
+
+export async function processGoogleFonts(
+  stylesheet: string,
+  baseUrl: string,
+): Promise<{
+  processedStylesheet: string
+  fontFiles: GoogleFontFile[]
+}> {
+  const fontSourceRegex = /url\((https:\/\/fonts.gstatic.com\/s\/[^)]+\.(woff2|ttf))\)/g
+  const fontFiles: GoogleFontFile[] = []
+  let processedStylesheet = stylesheet
+
+  let match
+  while ((match = fontSourceRegex.exec(stylesheet)) !== null) {
+    const url = match[1]
+    const [filename, extension] = url.split("/").pop()!.split(".")
+    const staticUrl = `https://${baseUrl}/static/fonts/${filename}.${extension}`
+
+    processedStylesheet = processedStylesheet.replace(url, staticUrl)
+    fontFiles.push({ url, filename, extension })
+  }
+
+  return { processedStylesheet, fontFiles }
+}
+
 export function joinStyles(theme: Theme, ...stylesheet: string[]) {
   return `
 ${stylesheet.join("\n\n")}