package nvdmirror

//
// Sync NVD data files to destination directory based on given sync
// configuration and cache.
//
// Returns an array of file names which have been updated in the
// destination directory.
//
// This function does the following:
//
// 1. Fetch the contents of the source meta URLs for CVE feeds and
//    CPE matches.  All source URLs are fetched concurrently.
//
// 2. Check the size and hash from meta files against the existing
//    CVE feed and CPE match files in the destination directory.  All
//    file sizes and hashes are checked concurrently.
//
// 3. Fetch the contents of the changed CVE feeds, CPE match files, and
//    the CPE dictionary.
//
// All HTTP requests are sent with the following headers:
//
// * if-modified-since: The last-modified header from the previous
//   successful response, if it was set.
//
// * if-none-match: The etag header from the last successful response,
//   if it was set.
//
// * user-agent: User agent from config, or the default user agent if
//   the config value is unspecified.
//
func Sync(config SyncConfig, cache Cache, dstDir string) []string {
  // build sync context
  ctx := newSyncContext(config, cache, dstDir)

  // fetch meta files, check for updates, append cpe dictionary URL,
  // fetch updated files, and then return a list of changed files
  return ctx.syncUrls(append(
    ctx.checkMetas(ctx.fetchMetas()),
    config.GetCpeDictUrl(),
  ))
}