private static CursorPagingRange SliceRange(
CursorPagingArguments arguments,
int maxElementCount)
{
// [SPEC] if after is set then remove all elements of edges before and including
// afterEdge.
//
// The cursor is increased by one so that the index points to the element after
var startIndex = arguments.After is { } a
? IndexEdge <TEntity> .DeserializeCursor(a) + 1
: 0;
// [SPEC] if before is set then remove all elements of edges before and including
// beforeEdge.
var before = arguments.Before is { } b
? IndexEdge <TEntity> .DeserializeCursor(b)
: maxElementCount;
// if after is negative we have know how much of the offset was in the negative range.
// The amount of positions that are in the negative range, have to be subtracted from
// the take or we will fetch too many items.
var startOffsetCorrection = 0;
if (startIndex < 0)
{
startOffsetCorrection = Math.Abs(startIndex);
startIndex = 0;
}
CursorPagingRange range = new(startIndex, before);
//[SPEC] If first is less than 0 throw an error
ValidateFirst(arguments, out var first);
if (first is not null)
{
first -= startOffsetCorrection;
if (first < 0)
{
first = 0;
}
}
//[SPEC] Slice edges to be of length first by removing edges from the end of edges.
range.Take(first);
//[SPEC] if last is less than 0 throw an error
ValidateLast(arguments, out var last);
//[SPEC] Slice edges to be of length last by removing edges from the start of edges.
range.TakeLast(last);
return(range);
}
private async ValueTask <Connection> ResolveAsync(
IQueryable <TEntity> source,
CursorPagingArguments arguments = default,
CancellationToken cancellationToken = default)
{
var count = await Task.Run(source.Count, cancellationToken)
.ConfigureAwait(false);
int?after = arguments.After is { } a
? (int?)IndexEdge <TEntity> .DeserializeCursor(a)
: null;
int?before = arguments.Before is { } b
? (int?)IndexEdge <TEntity> .DeserializeCursor(b)
: null;
IReadOnlyList <IndexEdge <TEntity> > selectedEdges =
await GetSelectedEdgesAsync(
source, arguments.First, arguments.Last, after, before, cancellationToken)
.ConfigureAwait(false);
IndexEdge <TEntity>?firstEdge = selectedEdges.Count == 0
? null
: selectedEdges[0];
IndexEdge <TEntity>?lastEdge = selectedEdges.Count == 0
? null
: selectedEdges[selectedEdges.Count - 1];
var pageInfo = new ConnectionPageInfo(
lastEdge?.Index < count - 1,
firstEdge?.Index > 0,
firstEdge?.Cursor,
lastEdge?.Cursor,
count);
return(new Connection <TEntity>(
selectedEdges,
pageInfo,
ct => new ValueTask <int>(pageInfo.TotalCount ?? 0)));
}
protected virtual async ValueTask <IReadOnlyList <IndexEdge <TEntity> > > ExecuteQueryableAsync(
IQueryable <TEntity> queryable,
int offset,
CancellationToken cancellationToken)
{
var list = new List <IndexEdge <TEntity> >();
if (queryable is IAsyncEnumerable <TEntity> enumerable)
{
var index = offset;
await foreach (TEntity item in enumerable.WithCancellation(cancellationToken)
.ConfigureAwait(false))
{
list.Add(IndexEdge <TEntity> .Create(item, index++));
}
}
else
{
await Task.Run(() =>
{
var index = offset;
foreach (TEntity item in queryable)
{
if (cancellationToken.IsCancellationRequested)
{
break;
}
list.Add(IndexEdge <TEntity> .Create(item, index++));
}
},
cancellationToken)
.ConfigureAwait(false);
}
return(list);
}