json-validator/include/jvalidate/adapter.h

#pragma once

#include <cstdint>
#include <cstdlib>
#include <filesystem>
#include <fstream>
#include <memory>
#include <optional>
#include <ostream>
#include <string>
#include <string_view>
#include <utility>
#include <vector>

#include <jvalidate/compat/expected.h>
#include <jvalidate/detail/number.h>
#include <jvalidate/enum.h>
#include <jvalidate/forward.h>
#include <jvalidate/status.h>

namespace jvalidate::adapter {
/**
 * @brief An interface for a type-erased reference-wrapper around a JSON node.
 *
 * Unlike languages like python, there are dozens of different C++ Libraries
 * for JSON parsing/construction. Each of these libraries has its own set of
 * getter functions, rules for handling missing values, and degree to which it
 * can engage in fuzziness of types.
 *
 * Adapter has two main groups of methods:
 * - as_*() and *_size() virtual functions
 * - maybe_*() concrete functions
 *
 * Most interaction with Adapter will be done via the maybe_*() functions,
 * with or without strictness enabled depending on what constraint is being
 * checked.
 */
class Adapter {
public:
  virtual ~Adapter() = default;

  /**
   * @brief Get the jvalidate::adapter::Type that this adapter represents.
   * This represents the types recognized by json-schema:
   *    null, bool, integer, number, string, array, object
   * This function is meant to be used internally - and not by any of the
   * Constraint objects.
   */
  virtual Type type() const = 0;

  /**
   * @brief Obtain an immutable copy of the current node.
   * Because an Adapter stores a reference to the underlying JSON, it cannot
   * be stored by e.g. a Const/Enum Constraint without risking a Segfault.
   */
  virtual std::unique_ptr<Const const> freeze() const = 0;

  /**
   * @brief Extract a boolean value from this JSON node.
   * @pre type() == Type::Boolean
   *
   * @throws If the pre-condition is not valid, then this function may throw
   * or produce other undefined behavior, depending on the implementation
   * details of the underlying type.
   */
  virtual bool as_boolean() const = 0;
  /**
   * @brief Extract an integer value from this JSON node.
   * @pre type() == Type::Integer
   *
   * @throws If the pre-condition is not valid, then this function may throw
   * or produce other undefined behavior, depending on the implementation
   * details of the underlying type.
   */
  virtual int64_t as_integer() const = 0;
  /**
   * @brief Extract a decimal value from this JSON node.
   * @pre type() == Type::Number
   *
   * @throws If the pre-condition is not valid, then this function may throw
   * or produce other undefined behavior, depending on the implementation
   * details of the underlying type.
   */
  virtual double as_number() const = 0;
  /**
   * @brief Extract a string value from this JSON node.
   * @pre type() == Type::String
   *
   * @throws If the pre-condition is not valid, then this function may throw
   * or produce other undefined behavior, depending on the implementation
   * details of the underlying type.
   */
  virtual std::string as_string() const = 0;

  /**
   * @brief Get the size of the JSON array in this node.
   * @pre type() == Type::Array
   *
   * @throws If the pre-condition is not valid, then this function may throw
   * or produce other undefined behavior, depending on the implementation
   * details of the underlying type.
   */
  virtual size_t array_size() const = 0;
  /**
   * @brief Get the size of the JSON object in this node.
   * @pre type() == Type::Object
   *
   * @throws If the pre-condition is not valid, then this function may throw
   * or produce other undefined behavior, depending on the implementation
   * details of the underlying type.
   */
  virtual size_t object_size() const = 0;

  /**
   * @brief Loop through every element of the JSON array in this node, applying
   * the given callback function to them.
   *
   * @param callback A callback of the form Adapter => Status
   *
   * @return Status::Accept iff there are no errors
   */
  virtual Status apply_array(AdapterCallback const & callback) const = 0;
  /**
   * @brief Loop through every element of the JSON object in this node, applying
   * the given callback function to them.
   *
   * @param callback A callback of the form (string, Adapter) => Status
   *
   * @return Status::Accept iff there are no errors
   */
  virtual Status apply_object(ObjectAdapterCallback const & callback) const = 0;

  virtual bool equals(Adapter const & lhs, bool strict) const = 0;

  /**
   * @brief Test if this object is null-like
   *
   * @param strict Does this function allow for fuzzy comparisons with strings?
   */
  bool maybe_null(bool strict) const {
    switch (type()) {
    case Type::Null:
      return true;
    case Type::String:
      return not strict and as_string().empty();
    default:
      return false;
    }
  }

  /**
   * @brief Attempts to extract a boolean value from this JSON node
   *
   * @param strict Does this function allow for fuzzy comparisons with strings?
   *
   * @return The boolean value contained if it is possible to deduce
   * (or type() == Type::Boolean), else nullopt.
   */
  std::optional<bool> maybe_boolean(bool strict) const {
    switch (type()) {
    case Type::Boolean:
      return as_boolean();
    case Type::String:
      if (not strict) {
        auto str = as_string();
        if (str == "true") {
          return true;
        }
        if (str == "false") {
          return false;
        }
      }
      return std::nullopt;
    default:
      return std::nullopt;
    }
  }

  /**
   * @brief Attempts to extract a integer value from this JSON node
   *
   * @param strict Does this function allow for fuzzy comparisons with strings
   * and/or booleans?
   *
   * @return The integer value contained if it is possible to deduce from an
   * integer, number, boolean, or string. Else nullopt
   */
  std::optional<int64_t> maybe_integer(bool strict) const {
    switch (type()) {
    case Type::Number:
      if (double value = as_number(); jvalidate::detail::fits_in_integer(value)) {
        return static_cast<int64_t>(value);
      }
      return std::nullopt;
    case Type::Integer:
      return as_integer();
    case Type::Boolean:
      if (not strict) {
        return as_boolean() ? 1 : 0;
      }
      return std::nullopt;
    case Type::String:
      if (not strict) {
        auto str = as_string();
        size_t end = 0;
        int64_t rval = std::stoll(str, &end);
        if (end == str.size()) {
          return rval;
        }
      }
      return std::nullopt;
    default:
      return std::nullopt;
    }
  }

  /**
   * @brief Attempts to extract a number value from this JSON node
   *
   * @param strict Does this function allow for fuzzy comparisons with strings?
   *
   * @return The number value contained if it is possible to deduce
   * (or type() == Type::Integer || type() == Type::Number), else nullopt.
   */
  std::optional<double> maybe_number(bool strict) const {
    switch (type()) {
    case Type::Number:
      return as_number();
    case Type::Integer:
      return as_integer();
    case Type::String:
      if (not strict) {
        auto str = as_string();
        size_t end = 0;
        double rval = std::stod(str, &end);
        if (end == str.size()) {
          return rval;
        }
      }
      return std::nullopt;
    default:
      return std::nullopt;
    }
  }

  /**
   * @brief Attempts to extract a string value from this JSON node
   *
   * @param strict Does this function allow for fuzzy comparisons with other
   * types?
   *
   * @return The string value contained if it is possible to deduce from a
   * scalar type, else nullopt.
   */
  std::optional<std::string> maybe_string(bool strict) const {
    switch (type()) {
    case Type::Null:
      return strict ? std::nullopt : std::make_optional("");
    case Type::String:
      return as_string();
    case Type::Number:
      if (not strict) {
        return std::to_string(as_number());
      }
      return std::nullopt;
    case Type::Integer:
      if (not strict) {
        return std::to_string(as_integer());
      }
      return std::nullopt;
    case Type::Boolean:
      if (not strict) {
        return as_boolean() ? "true" : "false";
      }
      return std::nullopt;
    default:
      return std::nullopt;
    }
  }

  /**
   * @brief Attempts to extract the array length from this JSON node
   *
   * @param strict Does this function allow for fuzzy comparisons with other
   * types?
   *
   * @return array_size() if this is an array, else 0 or nullopt, depending
   * on some factors.
   */
  std::optional<size_t> maybe_array_size(bool strict) const {
    switch (type()) {
    case Type::Array:
      return array_size();
    case Type::Null:
      return strict ? std::nullopt : std::make_optional(0UL);
    case Type::Object:
      return (strict || object_size() != 0) ? std::nullopt : std::make_optional(0UL);
    default:
      return std::nullopt;
    }
  }

  /**
   * @brief Attempts to extract the object length from this JSON node
   *
   * @param strict Does this function allow for fuzzy comparisons with other
   * types?
   *
   * @return object_size() if this is an object, else 0 or nullopt, depending
   * on some factors.
   */
  std::optional<size_t> maybe_object_size(bool strict) const {
    switch (type()) {
    case Type::Object:
      return object_size();
    case Type::Null:
      return strict ? std::nullopt : std::make_optional(0UL);
    case Type::Array:
      return (strict || array_size() != 0) ? std::nullopt : std::make_optional(0UL);
    default:
      return std::nullopt;
    }
  }

  virtual void write(std::ostream & os) const {
    std::string_view div;
    switch (type()) {
    case Type::Null:
      os << "null";
      break;
    case Type::Boolean:
      os << (as_boolean() ? "true" : "false");
      break;
    case Type::Integer:
      os << as_integer();
      break;
    case Type::Number:
      os << as_number();
      break;
    case Type::String:
      os << '"' << as_string() << '"';
      break;
    case Type::Array:
      os << '[';
      apply_array([&os, &div](Adapter const & elem) {
        os << std::exchange(div, ", ") << elem;
        return Status::Accept;
      });
      os << ']';
      break;
    case Type::Object:
      os << '{';
      apply_object([&os, &div](std::string const & key, Adapter const & elem) {
        os << std::exchange(div, ", ") << '"' << key << '"' << ':' << elem;
        return Status::Accept;
      });
      os << '}';
      break;
    }
  }

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

/**
 * @brief An interface for an immutable, owning handle to a type-erased JSON
 * node. {@see Adapter::freeze} for more explaination why this is necessary.
 */
class Const {
public:
  virtual ~Const() = default;
  /**
   * @brief Perform an action on this object, such as copying or testing
   * equality.
   *
   * @param callback A callback function of the form Adapter => Status
   *
   * @return the result of callback on the contained JSON
   */
  virtual Status apply(AdapterCallback const & callback) const = 0;
  friend std::ostream & operator<<(std::ostream & os, Const const & self) {
    self.apply([&os](Adapter const & adapter) {
      adapter.write(os);
      return Status::Accept;
    });
    return os;
  }
};

template <typename JSON>
auto load_file(std::filesystem::path const & path, JSON & out) noexcept
    -> detail::expected<void, std::string> {
  std::ifstream in(path);
  if (in.bad()) {
    return detail::unexpected("file error");
  }
  return load_stream(in, out);
}
}

namespace jvalidate::adapter::detail {
/**
 * @brief The simplest implementation of Const.
 * Depends on the AdapterTraits struct.
 *
 * @tparam JSON The type being adapted
 */
template <typename JSON> class GenericConst final : public Const {
public:
  explicit GenericConst(JSON value) : value_(std::move(value)) {}

  Status apply(AdapterCallback const & callback) const final {
    return callback(typename AdapterTraits<JSON>::ConstAdapter(value_));
  }

  JSON const & value() const { return value_; }

private:
  JSON value_;
};
}

namespace std {
inline ostream & operator<<(ostream & os, unique_ptr<jvalidate::adapter::Const const> const & ptr) {
  return os << *ptr;
}

inline ostream & operator<<(ostream & os,
                            vector<unique_ptr<jvalidate::adapter::Const const>> const & items) {
  std::string_view div;
  os << '[';
  for (auto const & ptr : items) {
    os << std::exchange(div, ", ") << *ptr;
  }
  return os << ']';
}
}