/// <summary>
/// Downloads the attachment file, or gets it from the cache if it's already been downloaded.
/// </summary>
public async Task <string> DownloadOrCacheAsync(ITimelineService api)
{
string url = await GenerateGetPresignedUrlAsync(api);
// Download attachment if it doesn't exist in the cache.
var file = Path.Combine(api.CacheFolder, Name);
if (!api.FileExists(file))
{
await api.DownloadFileAsync(url, file);
}
Debug.WriteLine("URL: " + url);
Debug.WriteLine("Filename: " + file);
return(file);
}