// TODO: Should this be ListenAsync?
/// <summary>
/// Listen to this query for changes.
/// </summary>
/// <param name="callback">The callback to invoke each time the query results change. Must not be null.</param>
/// <param name="cancellationToken">Optional cancellation token which may be used to cancel the listening operation.</param>
/// <returns>A <see cref="SnapshotListener"/> which may be used to monitor the listening operation and stop it gracefully.</returns>
public SnapshotListener Listen(Func <QuerySnapshot, CancellationToken, Task> callback, CancellationToken cancellationToken = default)
{
GaxPreconditions.CheckNotNull(callback, nameof(callback));
var target = WatchStream.CreateTarget(this);
var stream = new WatchStream(new WatchState(this, callback), target, Database, cancellationToken);
return(SnapshotListener.Start(stream));
}
/// <summary>
/// Watch this document for changes.
/// </summary>
/// <param name="callback">The callback to invoke each time the document changes. Must not be null.</param>
/// <param name="cancellationToken">Optional cancellation token which may be used to cancel the listening operation.</param>
/// <returns>A <see cref="SnapshotListener"/> which may be used to monitor the listening operation and stop it gracefully.</returns>
public SnapshotListener Listen(Func <DocumentSnapshot, CancellationToken, Task> callback, CancellationToken cancellationToken = default)
{
GaxPreconditions.CheckNotNull(callback, nameof(callback));
var target = WatchStream.CreateTarget(this);
Func <QuerySnapshot, CancellationToken, Task> queryCallback = async(querySnapshot, localCancellationToken) =>
{
foreach (var doc in querySnapshot)
{
if (doc.Reference == this)
{
await callback(doc, localCancellationToken).ConfigureAwait(false);
return;
}
}
// TODO: This will mean parsing the path back to a DocumentReference. Maybe we should accept "this".
var missingDoc = DocumentSnapshot.ForMissingDocument(Database, Path, querySnapshot.ReadTime);
await callback(missingDoc, cancellationToken).ConfigureAwait(false);
};
var stream = new WatchStream(new WatchState(Parent, queryCallback), target, Database, cancellationToken);
return(SnapshotListener.Start(stream));
}