#ifndef IRESEARCH_ATTRIBUTES_H
#define IRESEARCH_ATTRIBUTES_H

#include <map>

#include "map_utils.hpp"
#include "noncopyable.hpp"
#include "memory.hpp"
#include "string.hpp"
#include "timer_utils.hpp"
#include "bit_utils.hpp"
#include "type_id.hpp"
#include "noncopyable.hpp"
#include "string.hpp"

#include <set>

NS_ROOT

struct IRESEARCH_API attribute {

  class IRESEARCH_API type_id: public iresearch::type_id, util::noncopyable {
   public:
    type_id(const string_ref& name): name_(name) {}
    operator const type_id*() const { return this; }
    static bool exists(const string_ref& name);
    static const type_id* get(const string_ref& name);
    const string_ref& name() const { return name_; }

   private:
    string_ref name_;
  }; 
};

struct IRESEARCH_API stored_attribute : attribute {
  DECLARE_PTR(stored_attribute);
  virtual ~stored_attribute() = default;
};

#define DECLARE_ATTRIBUTE_TYPE() DECLARE_TYPE_ID(::iresearch::attribute::type_id)
#define DEFINE_ATTRIBUTE_TYPE_NAMED(class_type, class_name) DEFINE_TYPE_ID(class_type, ::iresearch::attribute::type_id) { \
  static ::iresearch::attribute::type_id type(class_name); \
  return type; \
}
#define DEFINE_ATTRIBUTE_TYPE(class_type) DEFINE_ATTRIBUTE_TYPE_NAMED(class_type, #class_type)

class IRESEARCH_API attribute_registrar {
 public:
  attribute_registrar(
    const attribute::type_id& type,
    const char* source = nullptr
  );
  operator bool() const NOEXCEPT;
 private:
  bool registered_;
};

#define REGISTER_ATTRIBUTE__(attribute_name, line, source) static ::iresearch::attribute_registrar attribute_registrar ## _ ## line(attribute_name::type(), source)
#define REGISTER_ATTRIBUTE_EXPANDER__(attribute_name, file, line) REGISTER_ATTRIBUTE__(attribute_name, line, file ":" TOSTRING(line))
#define REGISTER_ATTRIBUTE(attribute_name) REGISTER_ATTRIBUTE_EXPANDER__(attribute_name, __FILE__, __LINE__)

template<typename T>
struct IRESEARCH_API_TEMPLATE basic_attribute : attribute {
  typedef T value_t;

  explicit basic_attribute(const T& value = T())
    : value(value) {
  }

  bool operator==(const basic_attribute& rhs) const {
    return value == rhs.value;
  }

  bool operator==(const T& rhs) const {
    return value == rhs;
  }

  T value;
};

template<typename T>
struct IRESEARCH_API_TEMPLATE basic_stored_attribute : stored_attribute {
  typedef T value_t;

  explicit basic_stored_attribute(const T& value = T())
    : value(value) {
  }

  bool operator==(const basic_stored_attribute& rhs) const {
    return value == rhs.value;
  }

  bool operator==(const T& rhs) const {
    return value == rhs;
  }

  T value;
};

class IRESEARCH_API flags {
 public:  

  typedef std::set<const attribute::type_id*> type_map;

  static const flags& empty_instance();

  flags();
  flags(const flags&) = default;
  flags(flags&& rhs) NOEXCEPT;
  flags(std::initializer_list<const attribute::type_id*> flags);
  flags& operator=(std::initializer_list<const attribute::type_id*> flags);
  flags& operator=(flags&& rhs) NOEXCEPT;
  flags& operator=(const flags&) = default;

  type_map::const_iterator begin() const { return map_.begin(); }
  type_map::const_iterator end() const { return map_.end(); }

  template< typename T >
  flags& add() {
    typedef typename std::enable_if< 
      std::is_base_of< attribute, T >::value, T 
    >::type attribute_t;

    return add(attribute_t::type());
  }

  flags& add(const attribute::type_id& type) {
    map_.insert(&type);
    return *this;
  }

  template< typename T >
  flags& remove() {
    typedef typename std::enable_if< 
      std::is_base_of< attribute, T >::value, T 
    >::type attribute_t;

    return remove(attribute_t::type());
  }

  flags& remove(const attribute::type_id& type) {
    map_.erase(&type);
    return *this;
  }

  bool empty() const { return map_.empty(); }
  size_t size() const { return map_.size(); }
  void clear() NOEXCEPT { map_.clear(); }
  void reserve(size_t ) {

  }

  template< typename T >
  bool check() const NOEXCEPT {
    typedef typename std::enable_if< 
      std::is_base_of< attribute, T >::value, T 
    >::type attribute_t;

    return check(attribute_t::type());
  }

  bool check(const attribute::type_id& type) const NOEXCEPT {
    return map_.end() != map_.find( &type );
  }

  bool operator==(const flags& rhs) const {
    return map_ == rhs.map_;
  }

  bool operator!=(const flags& rhs) const {
    return !(*this == rhs);
  }

  flags& operator|=(const flags& rhs) {
    std::for_each(
      rhs.map_.begin(), rhs.map_.end() ,
      [this] ( const attribute::type_id* type ) {
        add( *type );
    } );
    return *this;
  }

  flags operator&(const flags& rhs) const {
    const type_map* lhs_map = &map_;
    const type_map* rhs_map = &rhs.map_;
    if (lhs_map->size() > rhs_map->size()) {
      std::swap(lhs_map, rhs_map);
    }

    flags out;
    out.reserve(lhs_map->size());

    for (auto lhs_it = lhs_map->begin(), lhs_end = lhs_map->end(); lhs_it != lhs_end; ++lhs_it) {
      auto rhs_it = rhs_map->find(*lhs_it);
      if (rhs_map->end() != rhs_it) {
        out.add(**rhs_it);
      }
    }

    return out;
  }

  flags operator|(const flags& rhs) const {
    flags out(*this);
    out.reserve(rhs.size());
    for (auto it = rhs.map_.begin(), end = rhs.map_.end(); it != end; ++it) {
      out.add(**it);
    }
    return out;
  }

  bool is_subset_of(const flags& rhs) const {
    auto& rhs_map = rhs.map_;
    for (auto entry : map_) {
      if (rhs_map.end() == rhs_map.find(entry)) {
        return false;
      }
    } 
    return true;
  } 

 private:
  IRESEARCH_API_PRIVATE_VARIABLES_BEGIN
  type_map map_;
  IRESEARCH_API_PRIVATE_VARIABLES_END
};

template<
  typename T,
  template <typename, typename...> class Ref,
  typename... Args
> class IRESEARCH_API_TEMPLATE attribute_map {
 public:
  template<typename U>
  struct ref {
    typedef Ref<U, Args...> type;

    IRESEARCH_HELPER_DLL_LOCAL static const type NIL;

    static_assert(
      sizeof(typename ref<T>::type) == sizeof(type),
      "sizeof(typename ref<T>::type) != sizeof(type)"
    );
  };

  attribute_map() = default;

  attribute_map(const attribute_map& other) = default;

  attribute_map(attribute_map&& other) NOEXCEPT {
    *this = std::move(other);
  }

  attribute_map& operator=(const attribute_map& other) = default;

  attribute_map& operator=(attribute_map&& other) NOEXCEPT {
    if (this != &other) {
      map_ = std::move(other.map_);
    }

    return *this;
  }

  void clear() {
    map_.clear();
  }

  bool contains(const attribute::type_id& type) const NOEXCEPT {
    return map_.find(type) != map_.end();
  }

  template<typename A>
  inline bool contains() const NOEXCEPT {
    typedef typename std::enable_if<
      std::is_base_of<attribute, A >::value, A
    >::type type;

    return contains(type::type());
  }

  flags features() const {
    flags features;

    features.reserve(size());

    for (auto& entry: map_) {
      features.add(*entry.first);
    }

    return features;
  }

  template<typename A>
  inline typename ref<A>::type* get() NOEXCEPT {
    typedef typename std::enable_if<
      std::is_base_of<attribute, A>::value, A
    >::type type;

    auto* value = get(type::type());

    return reinterpret_cast<typename ref<A>::type*>(value);
  }

  template<typename A>
  inline typename ref<A>::type& get(
      typename ref<A>::type& fallback
  ) NOEXCEPT {
    typedef typename std::enable_if<
      std::is_base_of<attribute, A>::value, A
    >::type type;

    auto& value = get(type::type(), reinterpret_cast<typename ref<T>::type&>(fallback));

    return reinterpret_cast<typename ref<A>::type&>(value);
  }

  template<typename A>
  inline const typename ref<A>::type& get(
      const typename ref<A>::type& fallback = ref<A>::NIL
  ) const NOEXCEPT {
    typedef typename std::enable_if<
      std::is_base_of<attribute, A>::value, A
    >::type type;

    auto& value = get(
      type::type(), reinterpret_cast<const typename ref<T>::type&>(fallback)
    );

    return reinterpret_cast<const typename ref<A>::type&>(value);
  }

  bool remove(const attribute::type_id& type) {
    return map_.erase(&type) > 0;
  }

  template<typename A>
  inline bool remove() {
    typedef typename std::enable_if<std::is_base_of<attribute, A>::value, A>::type type;

    return remove(type::type());
  }

  template<typename Visitor>
  bool visit(const Visitor& visitor) {
    return visit(*this, visitor);
  }

  template<typename Visitor>
  bool visit(const Visitor& visitor) const {
    return visit(*this, visitor);
  }

  size_t size() const NOEXCEPT { return map_.size(); }

 protected:
  typename ref<T>::type& emplace(bool& inserted, const attribute::type_id& type) {
    auto res = map_utils::try_emplace(map_, &type);

    inserted = res.second;

    return res.first->second;
  }

  typename ref<T>::type* get(const attribute::type_id& type) NOEXCEPT {
    auto itr = map_.find(&type);

    return map_.end() == itr ? nullptr : &(itr->second);
  }

  typename ref<T>::type& get(
      const attribute::type_id& type,
      typename ref<T>::type& fallback
  ) NOEXCEPT {
    auto itr = map_.find(&type);

    return map_.end() == itr ? fallback : itr->second;
  }

  const typename ref<T>::type& get(
      const attribute::type_id& type,
      const typename ref<T>::type& fallback = ref<T>::NIL
  ) const NOEXCEPT {
    return const_cast<attribute_map*>(this)->get(type, const_cast<typename ref<T>::type&>(fallback));
  }

 private:

  typedef std::map<const attribute::type_id*, typename ref<T>::type> map_t;

  IRESEARCH_API_PRIVATE_VARIABLES_BEGIN
  map_t map_;
  IRESEARCH_API_PRIVATE_VARIABLES_END

  template<typename Attributes, typename Visitor>
  static bool visit(Attributes& attrs, const Visitor& visitor) {
    for (auto& entry : attrs.map_) {
      if (!visitor(*entry.first, entry.second)) {
        return false;
      }
    }
    return true;
  }
}; 

template<typename T, template <typename, typename...> class Ref, typename... Args>
template<typename U>
typename attribute_map<T, Ref, Args...>::template ref<U>::type
const attribute_map<T, Ref, Args...>::ref<U>::NIL;

MSVC_ONLY(template class IRESEARCH_API irs::attribute_map<stored_attribute, std::shared_ptr>);

class IRESEARCH_API attribute_store
    : public attribute_map<stored_attribute, std::shared_ptr> {
 public:
  typedef attribute_map<stored_attribute, std::shared_ptr> base_t;

  static const attribute_store& empty_instance();

  explicit attribute_store(size_t reserve = 0);

  attribute_store(const attribute_store&) = default;

  attribute_store(attribute_store&& rhs) NOEXCEPT
    : base_t(std::move(rhs)) {
  }

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

  attribute_store& operator=(attribute_store&& rhs) NOEXCEPT {
    base_t::operator=(std::move(rhs));
    return *this;
  }

  template<typename T, typename... Args>
  typename ref<T>::type& emplace(Args&&... args) {
    REGISTER_TIMER_DETAILED();

    typedef typename std::enable_if<
      std::is_base_of<stored_attribute, T>::value, T
    >::type type;

    bool inserted;
    auto& attr = attribute_map::emplace(inserted, type::type());

    if (inserted) {
      attr = type::make(std::forward<Args>(args)...);
    }

    return reinterpret_cast<typename ref<T>::type&>(attr);
  }
}; 

template<typename T>
class pointer_wrapper {
 public:
  FORCE_INLINE pointer_wrapper(T* p = nullptr) NOEXCEPT : p_(p) { }
  FORCE_INLINE T* get() const NOEXCEPT { return p_; }
  FORCE_INLINE T* operator->() const NOEXCEPT { return get(); }
  FORCE_INLINE T& operator*() const NOEXCEPT { return *get(); }
  FORCE_INLINE pointer_wrapper& operator=(T* p) NOEXCEPT {
    p_ = p;
    return *this;
  }
  FORCE_INLINE operator bool() const NOEXCEPT {
    return p_ != nullptr;
  }

 private:
  T* p_;
}; 

MSVC_ONLY(template class IRESEARCH_API irs::attribute_map<attribute, pointer_wrapper>);

class IRESEARCH_API attribute_view
    : public attribute_map<attribute, pointer_wrapper> {
 public:
  typedef attribute_map<attribute, pointer_wrapper> base_t;

  static const attribute_view& empty_instance();

  explicit attribute_view(size_t reserve = 0);

  attribute_view(attribute_view&& rhs) NOEXCEPT
    : base_t(std::move(rhs)) {
  }

  attribute_view& operator=(attribute_view&& rhs) NOEXCEPT {
    base_t::operator=(std::move(rhs));
    return *this;
  }

  template<typename T>
  inline typename ref<T>::type& emplace() {
    return emplace_internal<T>();
  }

  template<typename T>
  inline typename ref<T>::type& emplace(T& value) {
    return emplace_internal(&value);
  }

 private:
  template<typename T>
  typename ref<T>::type& emplace_internal(T* value = nullptr) {
    REGISTER_TIMER_DETAILED();

    typedef typename std::enable_if<
      std::is_base_of<attribute, T>::value, T
    >::type type;

    bool inserted;
    auto& attr = attribute_map::emplace(inserted, type::type());

    if (inserted) {

      attr = reinterpret_cast<attribute*>(value);
    }

    return reinterpret_cast<typename ref<T>::type&>(attr);
  }
}; 

NS_END

#endif
////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2016 by EMC Corporation, All Rights Reserved
///
/// 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.
///
/// Copyright holder is EMC Corporation
///
/// @author Andrey Abramov
/// @author Vasiliy Nabatchikov
////////////////////////////////////////////////////////////////////////////////

#ifndef IRESEARCH_ATTRIBUTES_H
#define IRESEARCH_ATTRIBUTES_H

#include <map>

#include "map_utils.hpp"
#include "noncopyable.hpp"
#include "memory.hpp"
#include "string.hpp"
#include "timer_utils.hpp"
#include "bit_utils.hpp"
#include "type_id.hpp"
#include "noncopyable.hpp"
#include "string.hpp"

#include <set>

NS_ROOT

//////////////////////////////////////////////////////////////////////////////
/// @class attribute 
/// @brief base class for all attributes that can be used with attribute_map
///        an empty struct tag type with no virtual methods
///        all derived classes must implement the following function:
///        static const attribute::type_id& type() NOEXCEPT
///          via DECLARE_ATTRIBUTE_TYPE()/DEFINE_ATTRIBUTE_TYPE(...)
//////////////////////////////////////////////////////////////////////////////
struct IRESEARCH_API attribute {
  //////////////////////////////////////////////////////////////////////////////
  /// @class type_id 
  //////////////////////////////////////////////////////////////////////////////
  class IRESEARCH_API type_id: public iresearch::type_id, util::noncopyable {
   public:
    type_id(const string_ref& name): name_(name) {}
    operator const type_id*() const { return this; }
    static bool exists(const string_ref& name);
    static const type_id* get(const string_ref& name);
    const string_ref& name() const { return name_; }

   private:
    string_ref name_;
  }; // type_id
};

//////////////////////////////////////////////////////////////////////////////
/// @brief base class for all attributes that can be deallocated via a ptr of
///        this struct type using a virtual destructor
///        an empty struct tag type with a virtual destructor
///        all derived classes must implement the following functions:
///        static const attribute::type_id& type() NOEXCEPT
///          via DECLARE_ATTRIBUTE_TYPE()/DEFINE_ATTRIBUTE_TYPE(...)
///        static ptr make(Args&&... args)
///          via DECLARE_FACTORY()/DECLARE_FACTORY_DEFAULT()
//////////////////////////////////////////////////////////////////////////////
struct IRESEARCH_API stored_attribute : attribute {
  DECLARE_PTR(stored_attribute);
  virtual ~stored_attribute() = default;
};

// -----------------------------------------------------------------------------
// --SECTION--                                              Attribute definition
// -----------------------------------------------------------------------------

#define DECLARE_ATTRIBUTE_TYPE() DECLARE_TYPE_ID(::iresearch::attribute::type_id)
#define DEFINE_ATTRIBUTE_TYPE_NAMED(class_type, class_name) DEFINE_TYPE_ID(class_type, ::iresearch::attribute::type_id) { \
  static ::iresearch::attribute::type_id type(class_name); \
  return type; \
}
#define DEFINE_ATTRIBUTE_TYPE(class_type) DEFINE_ATTRIBUTE_TYPE_NAMED(class_type, #class_type)

// -----------------------------------------------------------------------------
// --SECTION--                                            Attribute registration
// -----------------------------------------------------------------------------

class IRESEARCH_API attribute_registrar {
 public:
  attribute_registrar(
    const attribute::type_id& type,
    const char* source = nullptr
  );
  operator bool() const NOEXCEPT;
 private:
  bool registered_;
};

#define REGISTER_ATTRIBUTE__(attribute_name, line, source) static ::iresearch::attribute_registrar attribute_registrar ## _ ## line(attribute_name::type(), source)
#define REGISTER_ATTRIBUTE_EXPANDER__(attribute_name, file, line) REGISTER_ATTRIBUTE__(attribute_name, line, file ":" TOSTRING(line))
#define REGISTER_ATTRIBUTE(attribute_name) REGISTER_ATTRIBUTE_EXPANDER__(attribute_name, __FILE__, __LINE__)

//////////////////////////////////////////////////////////////////////////////
/// @class basic_attribute
/// @brief represents simple attribute holds a single value 
//////////////////////////////////////////////////////////////////////////////
template<typename T>
struct IRESEARCH_API_TEMPLATE basic_attribute : attribute {
  typedef T value_t;

  explicit basic_attribute(const T& value = T())
    : value(value) {
  }

  bool operator==(const basic_attribute& rhs) const {
    return value == rhs.value;
  }

  bool operator==(const T& rhs) const {
    return value == rhs;
  }

  T value;
};

//////////////////////////////////////////////////////////////////////////////
/// @class basic_stored_attribute
/// @brief represents simple attribute holds a single value
//////////////////////////////////////////////////////////////////////////////
template<typename T>
struct IRESEARCH_API_TEMPLATE basic_stored_attribute : stored_attribute {
  typedef T value_t;

  explicit basic_stored_attribute(const T& value = T())
    : value(value) {
  }

  bool operator==(const basic_stored_attribute& rhs) const {
    return value == rhs.value;
  }

  bool operator==(const T& rhs) const {
    return value == rhs;
  }

  T value;
};

//////////////////////////////////////////////////////////////////////////////
/// @class flags
/// @brief represents a set of features enabled for the particular field 
//////////////////////////////////////////////////////////////////////////////
class IRESEARCH_API flags {
 public:  
  // std::set<...> is 25% faster than std::unordered_set<...> as per profile_bulk_index test
  typedef std::set<const attribute::type_id*> type_map;

  static const flags& empty_instance();

  flags();
  flags(const flags&) = default;
  flags(flags&& rhs) NOEXCEPT;
  flags(std::initializer_list<const attribute::type_id*> flags);
  flags& operator=(std::initializer_list<const attribute::type_id*> flags);
  flags& operator=(flags&& rhs) NOEXCEPT;
  flags& operator=(const flags&) = default;

  type_map::const_iterator begin() const { return map_.begin(); }
  type_map::const_iterator end() const { return map_.end(); }

  template< typename T >
  flags& add() {
    typedef typename std::enable_if< 
      std::is_base_of< attribute, T >::value, T 
    >::type attribute_t;

    return add(attribute_t::type());
  }

  flags& add(const attribute::type_id& type) {
    map_.insert(&type);
    return *this;
  }
  
  template< typename T >
  flags& remove() {
    typedef typename std::enable_if< 
      std::is_base_of< attribute, T >::value, T 
    >::type attribute_t;

    return remove(attribute_t::type());
  }

  flags& remove(const attribute::type_id& type) {
    map_.erase(&type);
    return *this;
  }
  
  bool empty() const { return map_.empty(); }
  size_t size() const { return map_.size(); }
  void clear() NOEXCEPT { map_.clear(); }
  void reserve(size_t /*capacity*/) {
    // NOOP for std::set
  }

  template< typename T >
  bool check() const NOEXCEPT {
    typedef typename std::enable_if< 
      std::is_base_of< attribute, T >::value, T 
    >::type attribute_t;

    return check(attribute_t::type());
  }

  bool check(const attribute::type_id& type) const NOEXCEPT {
    return map_.end() != map_.find( &type );
  }

  bool operator==(const flags& rhs) const {
    return map_ == rhs.map_;
  }

  bool operator!=(const flags& rhs) const {
    return !(*this == rhs);
  }

  flags& operator|=(const flags& rhs) {
    std::for_each(
      rhs.map_.begin(), rhs.map_.end() ,
      [this] ( const attribute::type_id* type ) {
        add( *type );
    } );
    return *this;
  }

  flags operator&(const flags& rhs) const {
    const type_map* lhs_map = &map_;
    const type_map* rhs_map = &rhs.map_;
    if (lhs_map->size() > rhs_map->size()) {
      std::swap(lhs_map, rhs_map);
    }
    
    flags out;
    out.reserve(lhs_map->size());

    for (auto lhs_it = lhs_map->begin(), lhs_end = lhs_map->end(); lhs_it != lhs_end; ++lhs_it) {
      auto rhs_it = rhs_map->find(*lhs_it);
      if (rhs_map->end() != rhs_it) {
        out.add(**rhs_it);
      }
    }

    return out;
  }

  flags operator|(const flags& rhs) const {
    flags out(*this);
    out.reserve(rhs.size());
    for (auto it = rhs.map_.begin(), end = rhs.map_.end(); it != end; ++it) {
      out.add(**it);
    }
    return out;
  }

  bool is_subset_of(const flags& rhs) const {
    auto& rhs_map = rhs.map_;
    for (auto entry : map_) {
      if (rhs_map.end() == rhs_map.find(entry)) {
        return false;
      }
    } 
    return true;
  } 

 private:
  IRESEARCH_API_PRIVATE_VARIABLES_BEGIN
  type_map map_;
  IRESEARCH_API_PRIVATE_VARIABLES_END
};

//////////////////////////////////////////////////////////////////////////////
/// @brief common interface for attribute storage implementations
//////////////////////////////////////////////////////////////////////////////
template<
  typename T,
  template <typename, typename...> class Ref,
  typename... Args
> class IRESEARCH_API_TEMPLATE attribute_map {
 public:
  template<typename U>
  struct ref {
    typedef Ref<U, Args...> type;

    IRESEARCH_HELPER_DLL_LOCAL static const type NIL;

    static_assert(
      sizeof(typename ref<T>::type) == sizeof(type),
      "sizeof(typename ref<T>::type) != sizeof(type)"
    );
  };

  attribute_map() = default;

  attribute_map(const attribute_map& other) = default;

  attribute_map(attribute_map&& other) NOEXCEPT {
    *this = std::move(other);
  }

  attribute_map& operator=(const attribute_map& other) = default;

  attribute_map& operator=(attribute_map&& other) NOEXCEPT {
    if (this != &other) {
      map_ = std::move(other.map_);
    }

    return *this;
  }

  void clear() {
    map_.clear();
  }

  bool contains(const attribute::type_id& type) const NOEXCEPT {
    return map_.find(type) != map_.end();
  }

  template<typename A>
  inline bool contains() const NOEXCEPT {
    typedef typename std::enable_if<
      std::is_base_of<attribute, A >::value, A
    >::type type;

    return contains(type::type());
  }

  flags features() const {
    flags features;

    features.reserve(size());

    for (auto& entry: map_) {
      features.add(*entry.first);
    }

    return features;
  }

  template<typename A>
  inline typename ref<A>::type* get() NOEXCEPT {
    typedef typename std::enable_if<
      std::is_base_of<attribute, A>::value, A
    >::type type;

    auto* value = get(type::type());

    // safe to reinterpret because layout/size is identical
    return reinterpret_cast<typename ref<A>::type*>(value);
  }

  template<typename A>
  inline typename ref<A>::type& get(
      typename ref<A>::type& fallback
  ) NOEXCEPT {
    typedef typename std::enable_if<
      std::is_base_of<attribute, A>::value, A
    >::type type;

    auto& value = get(type::type(), reinterpret_cast<typename ref<T>::type&>(fallback));

    // safe to reinterpret because layout/size is identical
    return reinterpret_cast<typename ref<A>::type&>(value);
  }

  template<typename A>
  inline const typename ref<A>::type& get(
      const typename ref<A>::type& fallback = ref<A>::NIL
  ) const NOEXCEPT {
    typedef typename std::enable_if<
      std::is_base_of<attribute, A>::value, A
    >::type type;

    auto& value = get(
      type::type(), reinterpret_cast<const typename ref<T>::type&>(fallback)
    );

    // safe to reinterpret because layout/size is identical
    return reinterpret_cast<const typename ref<A>::type&>(value);
  }

  bool remove(const attribute::type_id& type) {
    return map_.erase(&type) > 0;
  }

  template<typename A>
  inline bool remove() {
    typedef typename std::enable_if<std::is_base_of<attribute, A>::value, A>::type type;

    return remove(type::type());
  }

  template<typename Visitor>
  bool visit(const Visitor& visitor) {
    return visit(*this, visitor);
  }

  template<typename Visitor>
  bool visit(const Visitor& visitor) const {
    return visit(*this, visitor);
  }

  size_t size() const NOEXCEPT { return map_.size(); }

 protected:
  typename ref<T>::type& emplace(bool& inserted, const attribute::type_id& type) {
    auto res = map_utils::try_emplace(map_, &type);

    inserted = res.second;

    return res.first->second;
  }

  typename ref<T>::type* get(const attribute::type_id& type) NOEXCEPT {
    auto itr = map_.find(&type);

    return map_.end() == itr ? nullptr : &(itr->second);
  }

  typename ref<T>::type& get(
      const attribute::type_id& type,
      typename ref<T>::type& fallback
  ) NOEXCEPT {
    auto itr = map_.find(&type);

    return map_.end() == itr ? fallback : itr->second;
  }

  const typename ref<T>::type& get(
      const attribute::type_id& type,
      const typename ref<T>::type& fallback = ref<T>::NIL
  ) const NOEXCEPT {
    return const_cast<attribute_map*>(this)->get(type, const_cast<typename ref<T>::type&>(fallback));
  }

 private:
  // std::map<...> is 25% faster than std::unordered_map<...> as per profile_bulk_index test
  typedef std::map<const attribute::type_id*, typename ref<T>::type> map_t;

  IRESEARCH_API_PRIVATE_VARIABLES_BEGIN
  map_t map_;
  IRESEARCH_API_PRIVATE_VARIABLES_END

  template<typename Attributes, typename Visitor>
  static bool visit(Attributes& attrs, const Visitor& visitor) {
    for (auto& entry : attrs.map_) {
      if (!visitor(*entry.first, entry.second)) {
        return false;
      }
    }
    return true;
  }
}; // attribute_map

template<typename T, template <typename, typename...> class Ref, typename... Args>
template<typename U>
typename attribute_map<T, Ref, Args...>::template ref<U>::type
const attribute_map<T, Ref, Args...>::ref<U>::NIL;

//////////////////////////////////////////////////////////////////////////////
/// @brief storage of shared_ptr to attributes
//////////////////////////////////////////////////////////////////////////////

MSVC_ONLY(template class IRESEARCH_API irs::attribute_map<stored_attribute, std::shared_ptr>);

class IRESEARCH_API attribute_store
    : public attribute_map<stored_attribute, std::shared_ptr> {
 public:
  typedef attribute_map<stored_attribute, std::shared_ptr> base_t;

  static const attribute_store& empty_instance();

  explicit attribute_store(size_t reserve = 0);

  attribute_store(const attribute_store&) = default;

  attribute_store(attribute_store&& rhs) NOEXCEPT
    : base_t(std::move(rhs)) {
  }

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

  attribute_store& operator=(attribute_store&& rhs) NOEXCEPT {
    base_t::operator=(std::move(rhs));
    return *this;
  }

  template<typename T, typename... Args>
  typename ref<T>::type& emplace(Args&&... args) {
    REGISTER_TIMER_DETAILED();

    typedef typename std::enable_if<
      std::is_base_of<stored_attribute, T>::value, T
    >::type type;

    bool inserted;
    auto& attr = attribute_map::emplace(inserted, type::type());

    if (inserted) {
      attr = type::make(std::forward<Args>(args)...);
    }

    return reinterpret_cast<typename ref<T>::type&>(attr);
  }
}; // attribute_store

//////////////////////////////////////////////////////////////////////////////
/// @brief Contains a pointer to an object of type `T`.
/// An adaptor for `attribute_map` container.
///
/// Can't use `std::unique_ptr<T, memory::noop_deleter>` becuase of
/// the bugs in MSVC2013-2015 related to move semantic in std::map
//////////////////////////////////////////////////////////////////////////////
template<typename T>
class pointer_wrapper {
 public:
  FORCE_INLINE pointer_wrapper(T* p = nullptr) NOEXCEPT : p_(p) { }
  FORCE_INLINE T* get() const NOEXCEPT { return p_; }
  FORCE_INLINE T* operator->() const NOEXCEPT { return get(); }
  FORCE_INLINE T& operator*() const NOEXCEPT { return *get(); }
  FORCE_INLINE pointer_wrapper& operator=(T* p) NOEXCEPT {
    p_ = p;
    return *this;
  }
  FORCE_INLINE operator bool() const NOEXCEPT {
    return p_ != nullptr;
  }

 private:
  T* p_;
}; // pointer_wrapper

//////////////////////////////////////////////////////////////////////////////
/// @brief storage of data pointers to attributes
//////////////////////////////////////////////////////////////////////////////

MSVC_ONLY(template class IRESEARCH_API irs::attribute_map<attribute, pointer_wrapper>);

class IRESEARCH_API attribute_view
    : public attribute_map<attribute, pointer_wrapper> {
 public:
  typedef attribute_map<attribute, pointer_wrapper> base_t;

  static const attribute_view& empty_instance();

  explicit attribute_view(size_t reserve = 0);

  attribute_view(attribute_view&& rhs) NOEXCEPT
    : base_t(std::move(rhs)) {
  }

  attribute_view& operator=(attribute_view&& rhs) NOEXCEPT {
    base_t::operator=(std::move(rhs));
    return *this;
  }

  template<typename T>
  inline typename ref<T>::type& emplace() {
    return emplace_internal<T>();
  }

  template<typename T>
  inline typename ref<T>::type& emplace(T& value) {
    return emplace_internal(&value);
  }

 private:
  template<typename T>
  typename ref<T>::type& emplace_internal(T* value = nullptr) {
    REGISTER_TIMER_DETAILED();

    typedef typename std::enable_if<
      std::is_base_of<attribute, T>::value, T
    >::type type;

    bool inserted;
    auto& attr = attribute_map::emplace(inserted, type::type());

    if (inserted) {
      // reinterpret_cast to avoid layout related problems
      attr = reinterpret_cast<attribute*>(value);
    }

    return reinterpret_cast<typename ref<T>::type&>(attr);
  }
}; // attribute_view

NS_END

#endif
