json-validator/include/jvalidate/vocabulary.h

#pragma once

#include <functional>
#include <memory>
#include <string_view>

#include <jvalidate/forward.h>

namespace jvalidate::detail {
template <Adapter A> struct ParserContext;
}

namespace jvalidate::vocabulary {

/**
 * @brief Metadata tag for marking a keyword as no longer supported. This is
 * needed because we store the constraints by version using
 * std::map::lower_bound, instead of needing to pound them out for every version
 * of the JSON Schema specification.
 *
 * While it is permitted to reuse keywords that have been removed, it should be
 * avoided to minimize confusion.
 */
constexpr struct {
} Removed;

constexpr struct {
} Literal;

/**
 * @brief Metadata tag for marking a keyword as containing either a single
 * subschema, or an array of subschema (e.g. "not", "oneOf", etc.). When parsing
 * a schema, we need to be able to identify these to search for "$id" and
 * "$anchor" tags, as they can allow us to jump into otherwise unreachable
 * sections of the schema.
 */
constexpr struct {
} Keyword;

/**
 * @brief Metadata tag for marking a keyword as containing a map of names onto
 * subschemas (e.g. "properties"). Because the keys in this node of the schema
 * are arbitrary strings, we need to jump past them whe searching for the "$id"
 * and "$anchor" tags.
 * We cannot simply do a blind recursive-walk of the schema JSON, because you
 * could put an "$id" tag in an "example" block, where it should not be scanned.
 */
constexpr struct {
} KeywordMap;

/**
 * @brief Metadata tag for marking a keyword as needing to wait until after all
 * other (non-PostConstraint) keywords are validated.
 * This tag is used specifically to mark "unevaluatedItems" and
 * "unevaluatedProperties", since the rules they use to decide where to run
 * cannot be compiled the way that "additionalItems" and "additionalProperties"
 * can.
 */
constexpr struct {
} PostConstraint;

/**
 * @brief A Metadata tag for marking a keyword as participating as dependent on
 * another keyword in order to generate annotations or validate instances.
 * However - we still must evaluate the keyword for "$id" and "$anchor" tags,
 * since jumping past the keyword is permissible.
 * Currently the only example of this is the handling of "if"/"then"/"else",
 * where the "then" and "else" clauses should not be directly used if the "if"
 * clause is not present in the schema.
 */
struct DependentKeyword : std::string_view {};

enum class KeywordType : char { None, Keyword, KeywordMap };

/**
 * @brief This type represents a union of several different "parsing handler"
 * states, aligned to a specific starting version:
 * A) Annotation keywords
 * A.1) Removed              - This keyword is no longer supported.
 * A.2) Literal              - This is a pure annotation. e.g. "$comment".
 * A.3) KeywordMap           - This keyword does not produce any constraints,
 *      but must be evaluated for annotations and anchors. e.g. "$defs".
 * A.4) DependentKeyword(id) - A keyword whose annotations are only evaluated
 *      if the depended on keyword is also present in the current schema. It
 *      may be connected to a constraint, but that constraint will be parsed
 *      in the depended keyword.
 *
 * B) Constraint keywords
 * B.1) Make                 - A parser that does not contain any subschemas.
 * B.2) Make, Keyword        - A parser that contains either a single
 *      subschema or an array of subschemas. e.g. "not", "oneOf".
 * B.3) Make, KeywordMap     - A parser that contains a key-value mapping onto
 *      subschemas. e.g. "properties".
 * B.4) Make, PostConstraint - A parser whose constraint applies in
 *      Unevaluated Locations (11). Assumed to be a single subschema.
 */
template <Adapter A> struct Metadata {
  using pConstraint = std::unique_ptr<constraint::Constraint>;

  Metadata(decltype(Removed)) : valid(false) {}
  Metadata(decltype(Literal)) {}
  Metadata(decltype(KeywordMap)) : type(KeywordType::KeywordMap) {}
  Metadata(DependentKeyword dep) : type(KeywordType::Keyword) {}

  template <typename F> Metadata(F make) : make(make) {}
  template <typename F>
  Metadata(F make, decltype(Keyword)) : make(make), type(KeywordType::Keyword) {}
  template <typename F>
  Metadata(F make, decltype(KeywordMap)) : make(make), type(KeywordType::KeywordMap) {}
  template <typename F>
  Metadata(F make, decltype(PostConstraint))
      : make(make), type(KeywordType::Keyword), is_post_constraint(true) {}

  explicit operator bool() const { return valid; }
  operator std::function<pConstraint(detail::ParserContext<A> const &)>() const { return make; }

  std::function<pConstraint(detail::ParserContext<A> const &)> make = nullptr;
  bool valid = true;
  KeywordType type = KeywordType::None;
  bool is_post_constraint = false;
};
}