cosmos change feed processor library

cosmos change feed processor library.cs

public class ChangeFeedProcessorSDK
    {

        private readonly DocumentCollectionInfo _monitoredCollection;
        private readonly DocumentCollectionInfo _leaseCollection;
        public ChangeFeedProcessorSDK(DocumentCollectionInfo monitorCollection, DocumentCollectionInfo leaseCollection)
        {
            _monitoredCollection = monitorCollection;
            _leaseCollection = leaseCollection;
        }

        public async Task<int> GetChangesAsync()
        {
            var hostName = $"Host - {Guid.NewGuid().ToString()}";
            var builder = new ChangeFeedProcessorBuilder();

            builder
                .WithHostName(hostName)
                .WithFeedCollection(_monitoredCollection)
                .WithLeaseCollection(_leaseCollection)
                .WithObserverFactory(new CustomObserverFactory());

            var processor = await builder.BuildAsync();
            await processor.StartAsync();

            Console.WriteLine($"Started host - {hostName}");
            Console.WriteLine("Press any key to stop");
            Console.ReadKey();

            await processor.StopAsync();

            return 0;
        }
    }


    public class CustomObserverFactory : Microsoft.Azure.Documents.ChangeFeedProcessor.FeedProcessing.IChangeFeedObserverFactory
    {
        public Microsoft.Azure.Documents.ChangeFeedProcessor.FeedProcessing.IChangeFeedObserver CreateObserver()
        {
            return new CustomObserver();
        }
    }

    public class CustomObserver : Microsoft.Azure.Documents.ChangeFeedProcessor.FeedProcessing.IChangeFeedObserver
    {
        public Task CloseAsync(IChangeFeedObserverContext context, Microsoft.Azure.Documents.ChangeFeedProcessor.FeedProcessing.ChangeFeedObserverCloseReason reason)
        {
            Console.WriteLine($"Closing the listener to the partition key range {context.PartitionKeyRangeId} because {reason}");
            return Task.CompletedTask;
        }

        public Task OpenAsync(IChangeFeedObserverContext context)
        {
            Console.WriteLine($"Openning the listener to the partition key range {context.PartitionKeyRangeId}");
            return Task.CompletedTask;
        }

        public Task ProcessChangesAsync(IChangeFeedObserverContext context, IReadOnlyList<Document> docs, CancellationToken cancellationToken)
        {
            foreach(var document in docs)
            {
                // TODO :: processing logic
                Console.WriteLine($"Changed document Id - {document.Id}");
            }
            return Task.CompletedTask;
        }
    }