//
// Copyright 2019 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_DYNAMIC_FILE_FORMAT_INTERFACE_H
#define PXR_USD_PCP_DYNAMIC_FILE_FORMAT_INTERFACE_H

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

PXR_NAMESPACE_OPEN_SCOPE

class PcpDynamicFileFormatContext;
class VtValue;

/// \class PcpDynamicFileFormatInterface
///
/// Interface mixin that can be included by SdfFileFormat subclasses to enable
/// dynamic file format argument generation for a file format plugin.
/// When prim index composition encounters a payload to an asset of a file 
/// format that implements this interface, it will call 
/// ComposeFieldsForFileFormatArguments to generate arguments from the current
/// composition context at which the payload is being added. The derived file
/// format is on the hook for using the provided context to compute any prim
/// field values it needs and generate the relevant file format arguments for
/// its content.
class PcpDynamicFileFormatInterface
{
public:
    /// Empty virtual destructor to prevent build errors with some compilers.
    PCP_API
    virtual ~PcpDynamicFileFormatInterface();

    /// Derived classes must implement this function to compose prim fields 
    /// using the given \p context and use them to generate file format 
    /// arguments for the layer at \p assetPath. The context provides methods 
    /// to compose field values at the current point in prim index composition
    /// which can be used to generate the relevant file format arguments. These
    /// arguments need to be added to the set of file format arguments provided 
    /// by \p args. 
    /// 
    /// Additionally, implementations can output \p dependencyContextData of
    /// any value type that will then be passed back in to calls to 
    /// CanFieldChangeAffectFileFormatArguments during change processing.
    /// This can be used to provide more that context that is specific to the
    /// file format when determining whether a field change really does affect 
    /// the arguments generated by a particular call to this function.
    PCP_API
    virtual void ComposeFieldsForFileFormatArguments(
        const std::string& assetPath, 
        const PcpDynamicFileFormatContext &context,
        SdfFileFormat::FileFormatArguments* args,
        VtValue *dependencyContextData) const = 0;

    /// Derived classes must implement this function to return true if the 
    /// change to scene description of the field named \p field can affect the 
    /// dynamic file format arguments generated by 
    /// ComposeFieldsForFileFormatArguments. This function will be called during 
    /// change processing to determine whether a change to a field affects 
    /// the dynamic file format arguments of a payload that a prim index depends
    /// on.
    ///
    /// \p oldValue and \p newValue contain the old and new values of the field.
    /// \p dependencyContextData is the arbitrary typed data that was generated
    /// by the call to ComposeFieldsForFileFormatArguments when the payload arc
    /// was computed.
    PCP_API
    virtual bool CanFieldChangeAffectFileFormatArguments(
        const TfToken& field,
        const VtValue& oldValue,
        const VtValue& newValue,
        const VtValue &dependencyContextData) const = 0;
};

PXR_NAMESPACE_CLOSE_SCOPE

#endif // PXR_USD_PCP_DYNAMIC_FILE_FORMAT_INTERFACE_H
