// Copyright 2021 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef SRC_UTILS_ENUM_SET_H_
#define SRC_UTILS_ENUM_SET_H_

#include <cstdint>
#include <functional>
#include <type_traits>

namespace tint {
namespace utils {

/// EnumSet is a set of enum values.
/// @note As the EnumSet is backed by a single uint64_t value, it can only hold
/// enum values in the range [0 .. 63].
template <typename ENUM>
struct EnumSet {
 public:
  /// Enum is the enum type this EnumSet wraps
  using Enum = ENUM;

  /// Constructor. Initializes the EnumSet with zero.
  constexpr EnumSet() = default;

  /// Constructor. Initializes the EnumSet with the given values.
  /// @param values the enumerator values to construct the set with
  template <typename... VALUES>
  explicit constexpr EnumSet(VALUES... values) : set(Union(values...)) {}

  /// Adds e to this set
  /// @param e the enum value
  /// @return this set so calls can be chained
  inline EnumSet& Add(Enum e) {
    set |= Bit(e);
    return *this;
  }

  /// Removes e from this set
  /// @param e the enum value
  /// @return this set so calls can be chained
  inline EnumSet& Remove(Enum e) {
    set &= ~Bit(e);
    return *this;
  }

  /// @param e the enum value
  /// @return true if the set contains `e`
  inline bool Contains(Enum e) { return (set & Bit(e)) != 0; }

  /// Equality operator
  /// @param rhs the other EnumSet to compare this to
  /// @return true if this EnumSet is equal to rhs
  inline bool operator==(const EnumSet& rhs) const { return set == rhs.set; }

  /// Inequality operator
  /// @param rhs the other EnumSet to compare this to
  /// @return true if this EnumSet is not equal to rhs
  inline bool operator!=(const EnumSet& rhs) const { return set != rhs.set; }

  /// @return the underlying value for the EnumSet
  inline uint64_t Value() const { return set; }

 private:
  static constexpr uint64_t Bit(Enum value) {
    return static_cast<uint64_t>(1) << static_cast<uint64_t>(value);
  }

  static constexpr uint64_t Union() { return 0; }

  template <typename FIRST, typename... VALUES>
  static constexpr uint64_t Union(FIRST first, VALUES... values) {
    return Bit(first) | Union(values...);
  }

  uint64_t set = 0;
};

}  // namespace utils
}  // namespace tint

namespace std {

/// Custom std::hash specialization for tint::utils::EnumSet<T>
template <typename T>
class hash<tint::utils::EnumSet<T>> {
 public:
  /// @param e the EnumSet to create a hash for
  /// @return the hash value
  inline std::size_t operator()(const tint::utils::EnumSet<T>& e) const {
    return std::hash<uint64_t>()(e.Value());
  }
};

}  // namespace std

#endif  // SRC_UTILS_ENUM_SET_H_