/// <summary>
/// Maps data from a stream into a new form.
/// </summary>
public static IStream <TTo, TCursor> Map <TFrom, TTo, TCursor>(
this IStream <TFrom, TCursor> source,
Func <IEnumerable <TFrom>, IEnumerable <TTo> > map,
string id = null)
{
return(Create <TTo, TCursor>(
id: id ?? string.Format("{0}->Map(d:{1})", source.Id, typeof(TTo).ReadableName()),
query: async q =>
{
var query = source.CreateQuery(q.Cursor, q.BatchSize);
var sourceBatch = await source.Fetch(query);
var mappedItems = map(sourceBatch);
var mappedCursor = Cursor.New <TCursor>(sourceBatch.StartsAtCursorPosition);
var mappedBatch = StreamBatch.Create(mappedItems, mappedCursor);
return mappedBatch;
},
advanceCursor: (query, batch) =>
{
// don't advance the cursor in the map operation, since sourceStream.Fetch will already have done it
},
newCursor: source.NewCursor));
}
private static IStream <TData, TCursor> Create <TData, TCursor>(
Func <IStreamQuery <TCursor>, IEnumerable <TData> > query,
string id = null,
Action <IStreamQuery <TCursor>, IStreamBatch <TData> > advanceCursor = null,
Func <ICursor <TCursor> > newCursor = null, IEnumerable <TData> source = null)
{
return(new AnonymousStream <TData, TCursor>(
id,
async q => StreamBatch.Create(query(q), q.Cursor),
advanceCursor,
newCursor,
source));
}
/// <summary>
/// Creates a partitioned stream.
/// </summary>
/// <typeparam name="TData">The type of the data.</typeparam>
/// <typeparam name="TCursor">The type of the cursor.</typeparam>
/// <typeparam name="TPartition">The type of the partition.</typeparam>
/// <param name="query">The query.</param>
/// <param name="id">The base identifier for the partitioned stream.</param>
/// <param name="advanceCursor">A delegate that advances the cursor after a batch is pulled from the stream.</param>
/// <param name="newCursor">A delegate that returns a new cursor.</param>
public static IPartitionedStream <TData, TCursor, TPartition> PartitionedByValue <TData, TCursor, TPartition>(
Func <IStreamQuery <TCursor>, IStreamQueryValuePartition <TPartition>, Task <IEnumerable <TData> > > query,
string id = null,
Action <IStreamQuery <TCursor>, IStreamBatch <TData> > advanceCursor = null,
Func <ICursor <TCursor> > newCursor = null)
{
return(new AnonymousPartitionedStream <TData, TCursor, TPartition>(
id: id,
fetch: async(q, partition) =>
{
q.BatchSize = q.BatchSize ?? StreamBatch.MaxSize;
var batch = await query(q, (IStreamQueryValuePartition <TPartition>)partition);
return StreamBatch.Create(batch, q.Cursor);
},
advanceCursor: advanceCursor,
newCursor: newCursor));
}
/// <summary>
/// Creates a stream based on a queryable data source.
/// </summary>
/// <typeparam name="TData">The type of the stream's data.</typeparam>
/// <typeparam name="TCursor">The type of the cursor.</typeparam>
/// <param name="id">The stream identifier.</param>
/// <param name="query">The query.</param>
/// <param name="advanceCursor">A delegate that advances the cursor after a batch is pulled from the stream.</param>
/// <param name="newCursor">A delegate that returns a new cursor.</param>
/// <returns></returns>
public static IStream <TData, TCursor> Create <TData, TCursor>(
string id,
Func <IStreamQuery <TCursor>, Task <IEnumerable <TData> > > query,
Action <IStreamQuery <TCursor>, IStreamBatch <TData> > advanceCursor = null,
Func <ICursor <TCursor> > newCursor = null)
{
return(new AnonymousStream <TData, TCursor>(
id,
async q =>
{
var cursor = q.Cursor.Clone();
var data = await query(q);
return data as IStreamBatch <TData> ?? StreamBatch.Create(data, cursor);
},
advanceCursor,
newCursor));
}
