public override async Task <PageReadResult> MovePreviousAsync(CancellationToken cancellationToken)
{
int page;
lock (_pageLock)
{
page = CurrentPage - 1;
if (page < 1)
{
return(new PageReadResult(PagedFeed.GetUriForPage(page), new List <ScrapedSong>(), null, null, 0, new IndexOutOfRangeException($"Page {page} is below the minimum of 1."), PageErrorType.PageOutOfRange));
}
CurrentPage--;
}
if (cancellationToken.IsCancellationRequested)
{
return(PageReadResult.CancelledResult(PagedFeed.GetUriForPage(page)));
}
Task <PageReadResult> pageTask;
PageReadResult? result = null;
if (TryGetCachedPage(page, out Task <PageReadResult>?cachedTask) && cachedTask != null)
{
if (cachedTask.IsCompleted)
{
return(await cachedTask.ConfigureAwait(false));
}
else
{
using (CancellationTokenSource? tcs = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken))
{
bool completed = await Utilities.WaitUntil(() => cachedTask.IsCompleted, tcs.Token).ConfigureAwait(false);
if (completed)
{
result = await cachedTask.ConfigureAwait(false);
}
else
{
return(PageReadResult.CancelledResult(PagedFeed.GetUriForPage(page)));
}
}
}
}
else
{
if (cancellationToken.IsCancellationRequested)
{
return(PageReadResult.CancelledResult(PagedFeed.GetUriForPage(page)));
}
Uri uri = PagedFeed.GetUriForPage(page);
pageTask = PagedFeed.GetSongsAsync(uri, cancellationToken);
if (EnablePageCache && CachedPages != null)
{
CachedPages.TryAdd(page, pageTask);
}
result = await pageTask.ConfigureAwait(false);
}
return(result);
}
public override async Task <PageReadResult> MoveNextAsync(CancellationToken cancellationToken)
{
PageReadResult?result = null;
Uri? pageUri = null;
FeedDate feedDate = default;
bool criticalFailure = false;
try
{
await _semaphore.WaitAsync(cancellationToken);
feedDate = new FeedDate(CurrentEarliest, DateDirection.Before);
pageUri = DatedFeed.GetUriForDate(feedDate);
if (pageUri == LastFetchedUri)
{
criticalFailure = true;
throw new FeedReaderException($"URL '{pageUri}' was previously read, aborting to avoid possible infinite loop.");
}
result = await DatedFeed.GetSongsAsync(pageUri, cancellationToken).ConfigureAwait(false);
LastFetchedUri = pageUri;
}
catch (OperationCanceledException ex)
{
result = PageReadResult.CancelledResult(pageUri, ex);
}
catch (Exception ex)
{
if (criticalFailure)
{
throw;
}
result = new PageReadResult(pageUri, null, null, null, 0, ex, PageErrorType.Unknown);
}
finally
{
ProcessResult(result, feedDate.Direction);
_semaphore.Release();
}
return(result);
}
public override async Task <PageReadResult> MoveNextAsync(CancellationToken cancellationToken)
{
int page;
lock (_pageLock)
{
CurrentPage++;
page = CurrentPage;
}
if (cancellationToken.IsCancellationRequested)
{
return(PageReadResult.CancelledResult(PagedFeed.GetUriForPage(page)));
}
Task <PageReadResult> pageTask;
PageReadResult? result = null;
if (TryGetCachedPage(page, out Task <PageReadResult>?cachedTask) && cachedTask != null)
{
if (cachedTask.IsCompleted)
{
return(await cachedTask.ConfigureAwait(false));
}
else
{
using (CancellationTokenSource? tcs = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken))
{
bool completed = await Utilities.WaitUntil(() => cachedTask.IsCompleted, tcs.Token).ConfigureAwait(false);
if (completed)
{
result = await cachedTask.ConfigureAwait(false);
}
else
{
return(PageReadResult.CancelledResult(PagedFeed.GetUriForPage(page)));
}
}
}
}
else
{
if (cancellationToken.IsCancellationRequested)
{
return(PageReadResult.CancelledResult(PagedFeed.GetUriForPage(page)));
}
Uri uri = PagedFeed.GetUriForPage(page);
pageTask = PagedFeed.GetSongsAsync(uri, cancellationToken);
if (EnablePageCache && CachedPages != null)
{
CachedPages.TryAdd(page, pageTask);
}
result = await pageTask.ConfigureAwait(false);
}
if (result.IsLastPage)
{
CanMoveNext = false;
LastPage = Math.Min(LastPage, page);
}
return(result);
}