key: String,
    index: Int,
  ) = cacheDir / "$key.$index.tmp"

  private fun readFile(file: Path): String {
    return filesystem.read(file) {
      readUtf8()
    }
  }

  private fun readFileOrNull(file: Path): String? {
    return try {
      filesystem.read(file) {
        readUtf8()
      }
    } catch (_: FileNotFoundException) {
      null
    }
  }