json-validator/include/jvalidate/detail/anchor.h

#pragma once

#include <algorithm>
#include <cctype>
#include <compare>
#include <string>
#include <string_view>

#include <jvalidate/compat/compare.h>
#include <jvalidate/detail/expect.h>

namespace jvalidate::detail {
/**
 * @brief An Anchor is a simple name that refers to a named location (shorhand)
 * in a JSON-schema. As compared to a URI - which can refer to either internal
 * starting-points in the active schema or external documents on disk or at an
 * external URL-location.
 *
 * Anchors are useful in cases where there is a complicated or long path to a
 * commonly used definition. Consider for example:
 * { "$ref": "#/properties/Column/definitions/Row" }
 * vs.
 * { "$ref": "#ColRow" }
 *
 * This can be much easier to read, or find an object when doing a quick lookup,
 * since editors generally don't have a "lookup this JSON-Pointer" option.
 *
 * An anchor may only be a plain-name fragment (first character is alpha or '_',
 * all other characters are alphanumeric, '_', '.', or '-').
 * When defining an anchor using the "$anchor" or "$dynamicAnchor" tags, only
 * this fragment is used. When defining an anchor as part of an "$id" tag, the
 * form is `<URI>#<ANCHOR>`, the same as when accessing the anchor through a
 * "$ref". In the same document - you can reference the anchor by `#<ANCHOR>`,
 * just like how you can eschew the URI in a JSON-Pointer within the same doc.
 *
 * @see https://json-schema.org/draft/2020-12/draft-bhutton-json-schema-01#section-8.2.2
 */
class Anchor {
private:
  std::string content_;

public:
  Anchor() = default;

  explicit Anchor(std::string_view content) : content_(content) {
    EXPECT_M(content.empty() || content[0] == '_' || std::isalpha(content[0]),
             "First character of an Anchor must be alphabetic or '_'");
    EXPECT_M(
        std::all_of(content.begin(), content.end(),
                    [](char c) { return std::isalnum(c) || c == '_' || c == '.' || c == '-'; }),
        "Illegal character(s) in anchor");
  }

  explicit operator std::string const &() const { return content_; }
  bool empty() const { return content_.empty(); }

  friend std::ostream & operator<<(std::ostream & os, Anchor const & self) {
    return os << self.content_;
  }

  auto operator<=>(Anchor const & lhs) const = default;
};
}