variableExpression.h

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//
// Copyright 2023 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_USD_SDF_VARIABLE_EXPRESSION
#define PXR_USD_SDF_VARIABLE_EXPRESSION
 
 
#include "pxr/pxr.h"
#include "pxr/usd/sdf/api.h"
 
#include "pxr/base/vt/array.h"
#include "pxr/base/vt/dictionary.h"
#include "pxr/base/vt/value.h"
 
#include <memory>
#include <string>
#include <unordered_set>
#include <vector>
 
PXR_NAMESPACE_OPEN_SCOPE
 
namespace Sdf_VariableExpressionImpl {
    class Node;
}
 
class SdfVariableExpression
{
public:
    SDF_API
    explicit SdfVariableExpression(const std::string& expr);
 
    SDF_API
    explicit SdfVariableExpression(std::string&& expr);
 
    SDF_API
    SdfVariableExpression();
 
    SDF_API
    ~SdfVariableExpression();
 
    SDF_API
    static bool IsExpression(const std::string& s);
 
    SDF_API
    static bool IsValidVariableType(const VtValue& value);
 
    SDF_API
    explicit operator bool() const;
 
    SDF_API
    const std::string& GetString() const;
 
    SDF_API
    const std::vector<std::string>& GetErrors() const;
 
 
    class EmptyList { };
 
    class Result
    {
    public:
        VtValue value;
 
        std::vector<std::string> errors;
 
        std::unordered_set<std::string> usedVariables;
    };
 
    SDF_API
    Result Evaluate(const VtDictionary& variables) const;
 
    template <class ResultType>
    Result EvaluateTyped(const VtDictionary& variables) const
    {
        Result r = Evaluate(variables);
 
        if (VtIsArray<ResultType>::value && r.value.IsHolding<EmptyList>()) {
            r.value = VtValue(ResultType());
        }
        else if (!r.value.IsEmpty() && !r.value.IsHolding<ResultType>()) {
            r.errors.push_back(
                _FormatUnexpectedTypeError(r.value, VtValue(ResultType())));
            r.value = VtValue();
        }
        return r;
    }
 
 
 
    class Builder
    {
    public:
        SDF_API operator SdfVariableExpression() const;
 
    private:
        friend class SdfVariableExpression;
        Builder(std::string&& expr) : _expr(std::move(expr)) { }
        std::string _expr;
    };
 
    class FunctionBuilder
    {
    public:
        template <class Argument>
        FunctionBuilder& AddArgument(Argument&& arg);
 
        SDF_API operator SdfVariableExpression() const;
        SDF_API operator Builder() const &;
        SDF_API operator Builder() &&;
 
    private:
        friend class SdfVariableExpression;
        FunctionBuilder(const std::string& name) : _expr(name + '(') { }
        std::string _expr;
    };
 
    class ListBuilder
    {
    public:
        template <class Element>
        ListBuilder& AddElement(Element&& elem);
 
        template <class T>
        ListBuilder& AddLiteralValues(const std::vector<T>& values);
 
        SDF_API operator SdfVariableExpression() const;
        SDF_API operator Builder() const &;
        SDF_API operator Builder() &&;
 
    private:
        friend class SdfVariableExpression;
        ListBuilder() : _expr("[") { }
 
        std::string _expr;
    };
 
    template <class... Arguments>
    static FunctionBuilder
    MakeFunction(const std::string& fnName, Arguments&&... fnArgs)
    {
        FunctionBuilder b(fnName);
        (b.AddArgument(std::forward<Arguments>(fnArgs)), ...);
        return b;
    }
 
    template <class... Elements>
    static ListBuilder
    MakeList(Elements&&... elems)
    {
        ListBuilder b;
        (b.AddElement(std::forward<Elements>(elems)), ...);
        return b;
    }
 
    template <class T>
    static ListBuilder
    MakeListOfLiterals(const std::vector<T>& values)
    {
        return ListBuilder().AddLiteralValues(values);
    }
 
    SDF_API static Builder MakeLiteral(int64_t value);
    SDF_API static Builder MakeLiteral(bool value);
    SDF_API static Builder MakeLiteral(const std::string& value);
    SDF_API static Builder MakeLiteral(const char* value);
 
    SDF_API static Builder MakeNone();
 
    SDF_API static Builder MakeVariable(const std::string& name);
 
    SDF_API static Builder MakeVariable(const std::string& name,
                                        const Builder& fallbackValue);
 
    SDF_API static Builder MakeVariable(const std::string& name,
                                        const SdfVariableExpression& fallbackValue);
 
private:
    SDF_API
    static std::string
    _FormatUnexpectedTypeError(const VtValue& got, const VtValue& expected);
 
    SDF_API
    static void
    _AppendExpression(
        std::string* expr, const SdfVariableExpression& arg, bool first);
    
    SDF_API
    static void
    _AppendBuilder(std::string* expr, const Builder& b, bool first);
 
    template <class Argument>
    static void
    _Append(std::string* expr, Argument&& arg, bool first)
    {
        // Avoid implicitly converting arg to an SdfVariableExpression
        // since that would incur unnecessary parsing costs.
        if constexpr (std::is_same_v<
            std::decay_t<Argument>, SdfVariableExpression>) {
            _AppendExpression(expr, std::forward<Argument>(arg), first);
        }
        else {
            _AppendBuilder(expr, std::forward<Argument>(arg), first);
        }
    }
 
    std::vector<std::string> _errors;
    std::shared_ptr<Sdf_VariableExpressionImpl::Node> _expression;
    std::string _expressionStr;
};
 
inline bool
operator==(
    const SdfVariableExpression::EmptyList&,
    const SdfVariableExpression::EmptyList&)
{
    return true;
}
 
inline bool
operator!=(
    const SdfVariableExpression::EmptyList&,
    const SdfVariableExpression::EmptyList&)
{
    return false;
}
 
template <class Argument>
inline SdfVariableExpression::FunctionBuilder&
SdfVariableExpression::FunctionBuilder::AddArgument(Argument&& arg)
{
    SdfVariableExpression::_Append(
        &_expr, std::forward<Argument>(arg), 
        /* first = */ *_expr.rbegin() == '(');
    return *this;
}
 
template <class Element>
inline SdfVariableExpression::ListBuilder&
SdfVariableExpression::ListBuilder::AddElement(Element&& arg)
{
    SdfVariableExpression::_Append(
        &_expr, std::forward<Element>(arg), 
        /* first = */ *_expr.rbegin() == '[');
    return *this;
}
 
template <class T>
inline SdfVariableExpression::ListBuilder&
SdfVariableExpression::ListBuilder::AddLiteralValues(
    const std::vector<T>& values)
{            
    for (const T& v : values) {
        AddElement(SdfVariableExpression::MakeLiteral(v));
    }
    return *this;
}
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif