predicateExpression.h

//
// Copyright 2023 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_USD_SDF_PREDICATE_EXPRESSION_H
#define PXR_USD_SDF_PREDICATE_EXPRESSION_H
 
#include "pxr/pxr.h"
#include "pxr/usd/sdf/api.h"
#include "pxr/base/tf/hash.h"
#include "pxr/base/vt/value.h"
 
#include <iosfwd>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
 
PXR_NAMESPACE_OPEN_SCOPE
 
class SdfPredicateExpression
{
public:
 
    struct FnArg {
        static FnArg Positional(VtValue const &val) {
            return { std::string(), val };
        }
        static FnArg Keyword(std::string const &name, VtValue const &val) {
            return { name, val };
        }
        std::string argName;
        VtValue value;
 
        template <class HashState>
        friend void TfHashAppend(HashState &h, FnArg const &arg) {
            h.Append(arg.argName, arg.value);
        }
 
        friend bool operator==(FnArg const &l, FnArg const &r) {
            return std::tie(l.argName, l.value) == std::tie(r.argName, r.value);
        }
        friend bool operator!=(FnArg const &l, FnArg const &r) {
            return !(l == r);
        }
 
        friend void swap(FnArg &l, FnArg &r) {
            swap(l.argName, r.argName);
            swap(l.value, r.value);
        }
    };
 
    struct FnCall {
        enum Kind {
            BareCall,  
            ColonCall, 
            ParenCall  
        };
        
        Kind kind;
        std::string funcName;
        std::vector<FnArg> args;
 
        template <class HashState>
        friend void TfHashAppend(HashState &h, FnCall const &c) {
            h.Append(c.kind, c.funcName, c.args);
        }
 
        friend bool operator==(FnCall const &l, FnCall const &r) {
            return std::tie(l.kind, l.funcName, l.args) ==
                std::tie(r.kind, r.funcName, r.args);
        }
        friend bool operator!=(FnCall const &l, FnCall const &r) {
            return !(l == r);
        }
        friend void swap(FnCall &l, FnCall &r) {
            auto lt = std::tie(l.kind, l.funcName, l.args);
            auto rt = std::tie(r.kind, r.funcName, r.args);
            swap(lt, rt);
        }        
    };
 
    SdfPredicateExpression() = default;
 
    SdfPredicateExpression(SdfPredicateExpression const &) = default;
 
    SdfPredicateExpression(SdfPredicateExpression &&) = default;
 
    SDF_API
    explicit SdfPredicateExpression(std::string const &expr,
                                    std::string const &context = {});
 
    SdfPredicateExpression &
    operator=(SdfPredicateExpression const &) = default;
 
    SdfPredicateExpression &
    operator=(SdfPredicateExpression &&) = default;
 
    enum Op { Call, Not, ImpliedAnd, And, Or };
 
    SDF_API
    static SdfPredicateExpression
    MakeNot(SdfPredicateExpression &&right);
 
    SDF_API
    static SdfPredicateExpression
    MakeOp(Op op,
           SdfPredicateExpression &&left,
           SdfPredicateExpression &&right);
 
    SDF_API
    static SdfPredicateExpression
    MakeCall(FnCall &&call);
 
    SDF_API
    void Walk(TfFunctionRef<void (Op, int)> logic,
              TfFunctionRef<void (FnCall const &)> call) const;
 
    SDF_API
    void WalkWithOpStack(
        TfFunctionRef<void (std::vector<std::pair<Op, int>> const &)> logic,
        TfFunctionRef<void (FnCall const &)> call) const;
 
    SDF_API
    std::string GetText() const;
 
    bool IsEmpty() const {
        return _ops.empty();
    }
    
    explicit operator bool() const {
        return !IsEmpty();
    }
 
    std::string const &GetParseError() const & {
        return _parseError;
    }
 
    std::string GetParseError() && {
        return std::move(_parseError);
    }
 
private:
    template <class HashState>
    friend void TfHashAppend(HashState &h, SdfPredicateExpression const &expr) {
        h.Append(expr._ops, expr._calls, expr._parseError);
    }
 
    friend bool
    operator==(SdfPredicateExpression const &l,
               SdfPredicateExpression const &r) {
        return std::tie(l._ops, l._calls, l._parseError) ==
               std::tie(r._ops, r._calls, r._parseError);
    }
 
    friend bool
    operator!=(SdfPredicateExpression const &l,
               SdfPredicateExpression const &r) {
        return !(l == r);
    }
 
    SDF_API
    friend std::ostream &
    operator<<(std::ostream &, SdfPredicateExpression const &);
 
    // The expression is represented in function-call style, but *in reverse* to
    // facilitate efficient assembly.  For example, an expression like "a and b"
    // would be represented as { Call(b), Call(a), And } rather than { And,
    // Call(a), Call(b) }.  This way, joining two expressions like "a" 'and' "b"
    // can be done by appending to a vector, avoiding having to shift all the
    // elements down to insert the new operation at the head.  See the
    // implementation of Walk() for guidance.
    std::vector<Op> _ops;
 
    // On the contrary, the elements in _calls are in forward-order, so the last
    // Call in _ops corresponds to the first element of _calls.
    std::vector<FnCall> _calls;
 
    // This member holds a parsing error string if this expression was
    // constructed by the parser and errors were encountered during the parsing.
    std::string _parseError;
};
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_USD_SDF_PREDICATE_EXPRESSION_H