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

#pragma once

#include <cstddef>
#include <iterator>
#include <string>
#include <utility>

#include <jvalidate/detail/deref_proxy.h>

namespace jvalidate::adapter::detail {
/**
 * @brief An iterator for binding JSON values of type Object - which are
 * congruent to a map<string, JSON>.
 *
 * Conventionally - many JSON libraries use the same iterator object to
 * represent both Array iteration and Object iteration, either by returning
 * the Array index as a string-key, or by providing a special method e.g.
 * `key()` which accesses the Object key, while dereferencing the iterator
 * always returns the pointed-to JSON, regardless of Array/Object-ness.
 *
 * @tparam It The underlying iterator type being operated on
 * @tparam Adapter The owning adapter type, must fulfill the following
 * contracts:
 *    - is constructible from the value_type of It
 *    - has a static method key() which extracts the Object key from an It
 * Additionally, Adapter is expected to conform to the jvalidate::Adapter
 * concept.
 */
template <typename It, typename Adapter> class JsonObjectIterator : public It {
public:
  using value_type = std::pair<std::string, Adapter>;
  // Cannot return key by reference - because we don't know for certain
  // that the key-extraction function on It will return a string by reference
  // (such as if they do not store a default empty key).
  using reference = std::pair<std::string, Adapter>;
  using pointer = ::jvalidate::detail::DerefProxy<reference>;
  using difference_type = ptrdiff_t;
  using iterator_category = std::forward_iterator_tag;

  JsonObjectIterator() = default; // Sentinel for handling null objects
  explicit(false) JsonObjectIterator(It const & it) : It(it) {}

  reference operator*() const { return {Adapter::key(*this), Adapter(It::operator->())}; }

  pointer operator->() const { return {operator*()}; }

  JsonObjectIterator operator++(int) {
    auto tmp = *this;
    ++*this;
    return tmp;
  }

  JsonObjectIterator & operator++() {
    It::operator++();
    return *this;
  }
};
}