//
// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/boostorg/beast
//

#ifndef MYX_BACKPORTS_CPP_SPAN_HPP_
#define MYX_BACKPORTS_CPP_SPAN_HPP_

#pragma once

#if ( __cplusplus >= 201103L ) && ( __cplusplus < 201703L )

#include <myx/backports/cpp/helpers.hpp>

#include <algorithm>
#include <iterator>
#include <string>
#include <type_traits>

namespace std {

template< class T, class E, class = void >
struct is_contiguous_container : std::false_type {}; // NOLINT

template< class T, class E >
struct is_contiguous_container< T, E, void_t<
					decltype(
						std::declval< std::size_t& >() = std::declval< T const& >().size(),
						std::declval< E*& >() = std::declval< T& >().data() ),
					typename std::enable_if<
						std::is_same<
							typename std::remove_cv< E >::type,
							typename std::remove_cv<
								typename std::remove_pointer<
									decltype( std::declval< T& >().data() )
									>::type
								>::type
							>::value
						>::type > > : std::true_type
{};


/** A range of bytes expressed as a ContiguousContainer

    This class implements a non-owning reference to a storage
    area of a certain size and having an underlying integral
    type with size of 1.

    @tparam T The type pointed to by span iterators
*/
template< class T >
class span                                           // NOLINT
{
	T*          m_data = nullptr;
	std::size_t m_size = 0;

public:
	/// The type of value, including cv qualifiers
	using ElementType = T;

	/// The type of value of each span element
	using ValueType = typename std::remove_const< T >::type;

	/// The type of integer used to index the span
	using IndexType = std::ptrdiff_t;

	/// A pointer to a span element
	using Pointer = T*;

	/// A reference to a span element
	using Reference = T&;

	/// The iterator used by the container
	using Iterator = Pointer;

	/// The const pointer used by the container
	using ConstPointer = T const*;

	/// The const reference used by the container
	using ConstReference = T const&;

	/// The const iterator used by the container
	using ConstIterator = ConstPointer;

	/// Constructor
	span() = default;

	/// Constructor
	span( span const& ) = default;

	/// Assignment
	span& operator=( span const& ) = default;

	/** Constructor
	 *  @param data A pointer to the beginning of the range of elements
	 *  @param size The number of elements pointed to by `data`
	 */
	span( T* data, std::size_t size ) :
		m_data( data ),
		m_size( size )
	{
	}

	/** Constructor
	 *  @param container The container to construct from
	 */
	template< class ContiguousContainer,
	          class = typename std::enable_if<
			  is_contiguous_container<
				  ContiguousContainer, T >::value >::type
	          >
	explicit
	span( ContiguousContainer&& container ) :
		m_data( container.data() ),
		m_size( container.size() )
	{
	}

	template< class CharT, class Traits, class Allocator >
	explicit
	span( std::basic_string< CharT, Traits, Allocator >& s ) :
		m_data( &s[0] ),
		m_size( s.size() )
	{
	}

	template< class CharT, class Traits, class Allocator >
	explicit
	span( std::basic_string< CharT, Traits, Allocator > const& s ) :
		m_data( s.data() ),
		m_size( s.size() )
	{
	}

	/** Assignment
	 *  @param container The container to assign from
	 */
	template< class ContiguousContainer >
	typename std::enable_if< is_contiguous_container< //NOLINT
					 ContiguousContainer, T >::value,
	                         span& >::type
	operator=( ContiguousContainer&& container )
	{
		m_data = container.data();
		m_size = container.size();
		return( *this );
	}

	template< class CharT, class Traits, class Allocator >
	span&
	operator=( std::basic_string<
			   CharT, Traits, Allocator >& s )
	{
		m_data = &s[0];
		m_size = s.size();
		return( *this );
	}

	template< class CharT, class Traits, class Allocator >
	span&
	operator=( std::basic_string<
			   CharT, Traits, Allocator > const& s )
	{
		m_data = s.data();
		m_size = s.size();
		return( *this );
	}

	/// Returns `true` if the span is empty
	bool
	empty() const
	{
		return( m_size == 0 );
	}

	/// Returns a pointer to the beginning of the span
	T*
	data() const
	{
		return( m_data );
	}

	/// Returns the number of elements in the span
	std::size_t
	size() const
	{
		return( m_size );
	}

	/// Returns an iterator to the beginning of the span
	Iterator
	begin() const
	{
		return( m_data );
	}

	/// Returns an iterator to the beginning of the span
	ConstIterator
	cbegin() const
	{
		return( m_data );
	}

	/// Returns an iterator to one past the end of the span
	Iterator
	end() const
	{
		return( m_data + m_size );
	}

	/// Returns an iterator to one past the end of the span
	ConstIterator
	cend() const
	{
		return( m_data + m_size );
	}
}; // class span

} // namespace std

#endif // if ( __cplusplus >= 201103L ) && ( __cplusplus < 201703L )

#endif // ifndef MYX_BACKPORTS_CPP_SPAN_HPP_