//
// Copyright 2016 Pixar
//
// Licensed under the Apache License, Version 2.0 (the "Apache License")
// with the following modification; you may not use this file except in
// compliance with the Apache License and the following modification to it:
// Section 6. Trademarks. is deleted and replaced with:
//
// 6. Trademarks. This License does not grant permission to use the trade
//    names, trademarks, service marks, or product names of the Licensor
//    and its affiliates, except as required to comply with Section 4(c) of
//    the License and to reproduce the content of the NOTICE file.
//
// You may obtain a copy of the Apache License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Apache License with the above modification is
// distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the Apache License for the specific
// language governing permissions and limitations under the Apache License.
//
#ifndef PXR_USD_PCP_LAYER_PREFETCH_REQUEST_H
#define PXR_USD_PCP_LAYER_PREFETCH_REQUEST_H

#include "pxr/pxr.h"
#include "pxr/usd/pcp/api.h"
#include "pxr/usd/sdf/layer.h"

#include <set>
#include <utility>

PXR_NAMESPACE_OPEN_SCOPE

class Pcp_MutedLayers;

/// \class PcpLayerPrefetchRequest
///
/// PcpLayerPrefetchRequest represents a request to pre-fetch and retain
/// a set of layers in memory. It performs the fetch as a parallel
/// operation using a thread pool. Fetched layers are retained by the
/// request to keep them alive until the client can decide what to do
/// with them.
///
class PcpLayerPrefetchRequest
{
public:
    /// Enqueue a request to pre-fetch of the sublayers of \a layer.
    /// This recursively includes any nested sublayers. Arguments in \a args
    /// will be passed to Sdf when finding or opening sublayers.
    PCP_API
    void RequestSublayerStack(
        const SdfLayerRefPtr &layer,
        const SdfLayer::FileFormatArguments &args);

    /// Run the queued requests, returning when complete.
    PCP_API
    void Run(const Pcp_MutedLayers& mutedLayers);

private:
    // The request object retains both the layer requests and
    // the pre-fetched sublayers.
    typedef std::pair<SdfLayerRefPtr, SdfLayer::FileFormatArguments> _Request;
    std::set<_Request> _sublayerRequests;

    std::set<SdfLayerRefPtr> _retainedLayers;
};

PXR_NAMESPACE_CLOSE_SCOPE

#endif // PXR_USD_PCP_LAYER_PREFETCH_REQUEST_H