Workbox warm caching spine files and their associated image files

WorkboxSpineWarmHandle.ts

/**
 * A spine export produces 3 file types- one JSON file and one atlas.txt that maps
 * any number of PNGs. We know the JSON and atlas paths ahead of time, but not the PNGs.
 * This method will return a promise that completes when the files are loaded. If the
 * path is an atlas.txt file, it will wait for the response and read the file contents
 * in order to start loading the associated PNGs as well.
 */
async function loadSpineFiles(event: ExtendableEvent, strategy: Strategy, path: string) {
  const pending = Array.of<Promise<void>>()

  const [asyncResponse, finished] = strategy.handleAll({ event, request: new Request(path) })
  pending.push(finished)

  if (path.toLowerCase().endsWith("atlas.txt")) {
    const pathFolder = path.split("/").slice(0, -1).join("/")
    const response = await asyncResponse
    const content = await response.text()
    const associatedImagePaths = content.split("\n").filter(line => line.toLowerCase().endsWith(".webp"))
      .map(imageFilename => `${pathFolder}/${imageFilename}`)

    pending.push(...associatedImagePaths.map(imagePath => strategy.handleAll({ event, request: new Request(imagePath) })[1]))
  }

  return Promise.all(pending)
}