json-validator/include/jvalidate/extension.h

#pragma once

#include <type_traits>

#include <jvalidate/constraint/extension_constraint.h>
#include <jvalidate/forward.h>
#include <jvalidate/status.h>

namespace jvalidate::extension {
struct VisitorBase {
  virtual ~VisitorBase() = default;
};

template <typename E>
concept Constraint = std::is_base_of_v<constraint::ExtensionConstraint::Impl, E>;

namespace detail {
template <Constraint E> struct TypedVisitor : VisitorBase {
  virtual Status visit(E const & cons) const = 0;
};

template <Constraint E, typename CRTP> struct TypedVisitorImpl : TypedVisitor<E> {
  Status visit(E const & cons) const final {
    return static_cast<CRTP const *>(this)->dispatch(cons);
  }
};
}

template <typename CRTP> struct ConstraintBase : constraint::ExtensionConstraint::Impl {
  Status visit(VisitorBase const & visitor) const final {
    return dynamic_cast<detail::TypedVisitor<CRTP> const &>(visitor).visit(
        static_cast<CRTP const &>(*this));
  }
};

template <typename CRTP, typename... Es> class Visitor {
private:
  template <Adapter A, typename V> class Impl : public detail::TypedVisitorImpl<Es, Impl<A, V>>... {
  public:
    Impl(Visitor const * self, A const & document, V const & visitor)
        : self_(self), document_(document), visitor_(visitor) {}

    using detail::TypedVisitorImpl<Es, Impl>::visit...;

    template <Constraint E> Status dispatch(E const & cons) const {
      // static_assert(Visitable<CRTP, E, A, V>, "Must implement all visitation functions");
      return static_cast<CRTP const *>(self_)->visit(cons, document_, visitor_);
    }

  private:
    Visitor const * self_;
    A const & document_;
    V const & visitor_;
  };

public:
  template <Adapter A, typename V>
  Status operator()(constraint::ExtensionConstraint const & cons, A const & document,
                    V const & visitor) const {
    return cons.pimpl->visit(Impl<A, V>{this, document, visitor});
  }
};
}