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/**
* Find all font files in the CSS response and determine which files should be preloaded.
* In Google Fonts responses, the @font-face's subset is above it in a comment.
* Walk through the CSS from top to bottom, keeping track of the current subset.
*/
export function findFontFilesInCss(css: string, subsetsToPreload?: string[]) {
// Find font files to download
const fontFiles: Array<{
googleFontFileUrl: string
preloadFontFile: boolean
}> = []
// Keep track of the current subset
let currentSubset = ''
for (const line of css.split('\n')) {
const newSubset = /\/\* (.+?) \*\//.exec(line)?.[1]
if (newSubset) {
// Found new subset in a comment above the next @font-face declaration
currentSubset = newSubset
} else {
const googleFontFileUrl = /src: url\((.+?)\)/.exec(line)?.[1]
if (
googleFontFileUrl &&
!fontFiles.some(
(foundFile) => foundFile.googleFontFileUrl === googleFontFileUrl
)
) {
// Found the font file in the @font-face declaration.
fontFiles.push({
googleFontFileUrl,
preloadFontFile: !!subsetsToPreload?.includes(currentSubset),
})
}
}
}
return fontFiles
}
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