#ifndef THIRD_PARTY_CEL_CPP_EVAL_EVAL_ATTRIBUTE_TRAIL_H_

#define THIRD_PARTY_CEL_CPP_EVAL_EVAL_ATTRIBUTE_TRAIL_H_

#include <string>

#include <utility>

#include "absl/types/optional.h"

#include "absl/utility/utility.h"

#include "base/attribute.h"

namespace google::api::expr::runtime {

// AttributeTrail reflects current attribute path.

// It is functionally similar to cel::Attribute, yet intended to have better

// complexity on attribute path increment operations.

// TODO(issues/41) Current AttributeTrail implementation is equivalent to

// cel::Attribute - improve it.

// Intended to be used in conjunction with cel::Value, describing the attribute

// value originated from.

// Empty AttributeTrail denotes object with attribute path not defined

// or supported.

class AttributeTrail {

 public:

  AttributeTrail() : attribute_(absl::nullopt) {}

  explicit AttributeTrail(std::string variable_name)

      : attribute_(absl::in_place, std::move(variable_name)) {}

  explicit AttributeTrail(cel::Attribute attribute)

      : attribute_(std::move(attribute)) {}

  // NOLINTNEXTLINE(google-explicit-constructor)

  AttributeTrail(absl::nullopt_t) : AttributeTrail() {}

  AttributeTrail(const AttributeTrail&) = default;

  AttributeTrail& operator=(const AttributeTrail&) = default;

  AttributeTrail(AttributeTrail&&) = default;

  AttributeTrail& operator=(AttributeTrail&&) = default;

  AttributeTrail& operator=(absl::nullopt_t) {

    attribute_.reset();

    return *this;

  }

  // Creates AttributeTrail with attribute path incremented by "qualifier".

  AttributeTrail Step(cel::AttributeQualifier qualifier) const;

  // Creates AttributeTrail with attribute path incremented by "qualifier".

  AttributeTrail Step(const std::string* qualifier) const {

    if (empty()) return AttributeTrail();

    return Step(cel::AttributeQualifier::OfString(*qualifier));

  }

  // Returns CelAttribute that corresponds to content of AttributeTrail.

  const cel::Attribute& attribute() const { return attribute_.value(); }

  bool empty() const { return !attribute_.has_value(); }

 private:

  absl::optional<cel::Attribute> attribute_;

};

}  // namespace google::api::expr::runtime

#endif  // THIRD_PARTY_CEL_CPP_EVAL_EVAL_ATTRIBUTE_TRAIL_H_