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

#pragma once

#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iostream>
#include <string>
#include <string_view>
#include <variant>
#include <vector>

#include <jvalidate/compat/compare.h>
#include <jvalidate/forward.h>

namespace jvalidate::detail {
struct parent_t {};
constexpr parent_t parent;

class Pointer {
public:
  Pointer() = default;
  Pointer(std::vector<std::variant<std::string, size_t>> const & tokens) : tokens_(tokens) {}
  Pointer(std::string_view path) {
    if (path.empty()) {
      return;
    }

    auto append_with_parse = [this](std::string in) {
      if (not in.empty() && in.find_first_not_of("0123456789") == std::string::npos) {
        return tokens_.push_back(std::stoull(in));
      }

      for (size_t i = 0; i < in.size(); ++i) {
        if (in[i] == '%') {
          char const enc[3] = {in[i + 1], in[i + 2]};
          in.replace(i, 3, 1, char(std::stoi(enc, nullptr, 16)));
        } else if (in[i] != '~') {
          continue;
        }
        if (in[i + 1] == '0') {
          in.replace(i, 2, 1, '~');
        } else if (in[i + 1] == '1') {
          in.replace(i, 2, 1, '/');
        }
      }
      tokens_.push_back(std::move(in));
    };

    path.remove_prefix(1);
    // The rules of JSON-Pointer is that if a token were to contain a '/' as a
    // strict character: then that character would be escaped, using the above
    // rules. We take advantage of string_view's sliding view to make iteration
    // easy.
    for (size_t p = path.find('/'); p != std::string::npos;
         path.remove_prefix(p + 1), p = path.find('/')) {
      append_with_parse(std::string(path.substr(0, p)));
    }

    append_with_parse(std::string(path));
  }

  auto walk(Adapter auto document) const {
    for (auto const & token : tokens_) {
      document = std::visit([&document](auto const & next) { return document[next]; }, token);
    }
    return document;
  }

  std::string back() const {
    struct {
      std::string operator()(std::string const & in) const { return in; }
      std::string operator()(size_t in) const { return std::to_string(in); }
    } g_as_str;
    return tokens_.empty() ? "" : std::visit(g_as_str, tokens_.back());
  }

  bool empty() const { return tokens_.empty(); }

  bool starts_with(Pointer const & other) const {
    return other.tokens_.size() <= tokens_.size() &&
           std::equal(other.tokens_.begin(), other.tokens_.end(), tokens_.begin());
  }

  Pointer relative_to(Pointer const & other) const {
    assert(starts_with(other));
    return Pointer(std::vector(tokens_.begin() + other.tokens_.size(), tokens_.end()));
  }

  Pointer parent() const { return Pointer({tokens_.begin(), tokens_.end() - 1}); }

  Pointer & operator/=(Pointer const & relative) {
    tokens_.insert(tokens_.end(), relative.tokens_.begin(), relative.tokens_.end());
    return *this;
  }

  Pointer operator/(Pointer const & relative) const { return Pointer(*this) /= relative; }

  Pointer & operator/=(parent_t) {
    tokens_.pop_back();
    return *this;
  }

  Pointer operator/(parent_t) const { return parent(); }

  Pointer & operator/=(std::string_view key) {
    tokens_.emplace_back(std::string(key));
    return *this;
  }

  Pointer operator/(std::string_view key) const { return Pointer(*this) /= key; }

  Pointer & operator/=(size_t index) {
    tokens_.emplace_back(index);
    return *this;
  }

  Pointer operator/(size_t index) const { return Pointer(*this) /= index; }

  friend std::ostream & operator<<(std::ostream & os, Pointer const & self) {
    for (auto const & elem : self.tokens_) {
      std::visit([&os](auto const & v) { os << '/' << v; }, elem);
    }
    return os;
  }
  auto operator<=>(Pointer const &) const = default;

private:
  std::vector<std::variant<std::string, size_t>> tokens_{};
};
}