json-validator/include/jvalidate/constraint/extension_constraint.h

#pragma once

#include <memory>

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

namespace jvalidate::constraint {
/**
 * @brief A plugin class that allows the for Domain-Specific Grammers to be
 * implemented for a json-schema.
 *
 * These custom Constraints are implemented by creating two extension classes:
 * - A constraint inheriting from {@see jvalidate::ConstraintBase}, which in
 *   turn inherits from ExtensionConstraint::Impl. This acts as a simple data
 *   wrapper for describing the Constraint.
 * - A visitor inheriting from {@see jvalidate::extension::Visitor}.
 *
 * https://json-schema.org/draft/2020-12/json-schema-core#section-6.5
 */
struct ExtensionConstraint {
public:
  struct Impl {
    virtual ~Impl() = default;
    virtual Status visit(extension::VisitorBase const &) const = 0;
  };

public:
  /**
   * @brief Convenience function for constructing this ExtensionConstraint from
   * the concrete underlying extension in the format that is required for use
   * with {@see jvalidate::ConstraintFactory}.
   *
   * @tparam T A concrete type subtyping ExtensionConstraint::Impl
   * @tparam Args The argument types for initializing the object
   *
   * @params args... The constructor arguments for T
   *
   * @return A unique_ptr to a new ExtensionConstraint of underlying type T,
   * wrapped in the Constraint variant type.
   */
  template <typename T, typename... Args> static std::unique_ptr<Constraint> make(Args &&... args) {
    return std::make_unique<Constraint>(
        ExtensionConstraint{std::make_unique<T>(std::forward<Args>(args)...)});
  }

public:
  std::unique_ptr<Impl> pimpl;
};
}