//
// Copyright (c) 2013-2017 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)
//

#ifndef BEAST_MULTI_BUFFER_HPP
#define BEAST_MULTI_BUFFER_HPP

#include <beast/config.hpp>
#include <beast/core/detail/empty_base_optimization.hpp>
#include <boost/asio/buffer.hpp>
#include <boost/intrusive/list.hpp>
#include <iterator>
#include <limits>
#include <memory>
#include <type_traits>

namespace beast {

/** A @b DynamicBuffer that uses multiple buffers internally.

    The implementation uses a sequence of one or more character arrays
    of varying sizes. Additional character array objects are appended to
    the sequence to accommodate changes in the size of the character
    sequence.

    @note Meets the requirements of @b DynamicBuffer.

    @tparam Allocator The allocator to use for managing memory.
*/
template<class Allocator>
class basic_multi_buffer
#if ! BEAST_DOXYGEN
    : private detail::empty_base_optimization<
        typename std::allocator_traits<Allocator>::
            template rebind_alloc<char>>
#endif
{
public:
#if BEAST_DOXYGEN
    /// The type of allocator used.
    using allocator_type = Allocator;
#else
    using allocator_type = typename
        std::allocator_traits<Allocator>::
            template rebind_alloc<char>;
#endif

private:
    // Storage for the list of buffers representing the input
    // and output sequences. The allocation for each element
    // contains `element` followed by raw storage bytes.
    class element;

    using alloc_traits = std::allocator_traits<allocator_type>;
    using list_type = typename boost::intrusive::make_list<element,
        boost::intrusive::constant_time_size<true>>::type;
    using iterator = typename list_type::iterator;
    using const_iterator = typename list_type::const_iterator;

    using size_type = typename std::allocator_traits<Allocator>::size_type;
    using const_buffer = boost::asio::const_buffer;
    using mutable_buffer = boost::asio::mutable_buffer;

    static_assert(std::is_base_of<std::bidirectional_iterator_tag,
        typename std::iterator_traits<iterator>::iterator_category>::value,
            "BidirectionalIterator requirements not met");

    static_assert(std::is_base_of<std::bidirectional_iterator_tag,
        typename std::iterator_traits<const_iterator>::iterator_category>::value,
            "BidirectionalIterator requirements not met");

    std::size_t max_ =
        (std::numeric_limits<std::size_t>::max)();
    list_type list_;        // list of allocated buffers
    iterator out_;          // element that contains out_pos_
    size_type in_size_ = 0; // size of the input sequence
    size_type in_pos_ = 0;  // input offset in list_.front()
    size_type out_pos_ = 0; // output offset in *out_
    size_type out_end_ = 0; // output end offset in list_.back()

public:
#if BEAST_DOXYGEN
    /// The type used to represent the input sequence as a list of buffers.
    using const_buffers_type = implementation_defined;

    /// The type used to represent the output sequence as a list of buffers.
    using mutable_buffers_type = implementation_defined;

#else
    class const_buffers_type;

    class mutable_buffers_type;

#endif

    /// Destructor.
    ~basic_multi_buffer();

    /// Default constructor.
    basic_multi_buffer();

    /** Move constructor.

        The new object will have the input sequence of
        the other stream buffer, and an empty output sequence.

        @note After the move, the moved-from object will have
        an empty input and output sequence, with no internal
        buffers allocated.
    */
    basic_multi_buffer(basic_multi_buffer&&);

    /** Move constructor.

        The new object will have the input sequence of
        the other stream buffer, and an empty output sequence.

        @note After the move, the moved-from object will have
        an empty input and output sequence, with no internal
        buffers allocated.

        @param alloc The allocator to associate with the
        stream buffer.
    */
    basic_multi_buffer(basic_multi_buffer&&,
        allocator_type const& alloc);

    /** Copy constructor.

        This object will have a copy of the other stream
        buffer's input sequence, and an empty output sequence.
    */
    basic_multi_buffer(basic_multi_buffer const&);

    /** Copy constructor.

        This object will have a copy of the other stream
        buffer's input sequence, and an empty output sequence.

        @param alloc The allocator to associate with the
        stream buffer.
    */
    basic_multi_buffer(basic_multi_buffer const&,
        allocator_type const& alloc);

    /** Copy constructor.

        This object will have a copy of the other stream
        buffer's input sequence, and an empty output sequence.
    */
    template<class OtherAlloc>
    basic_multi_buffer(basic_multi_buffer<OtherAlloc> const&);

    /** Copy constructor.

        This object will have a copy of the other stream
        buffer's input sequence, and an empty output sequence.

        @param alloc The allocator to associate with the
        stream buffer.
    */
    template<class OtherAlloc>
    basic_multi_buffer(basic_multi_buffer<OtherAlloc> const&,
        allocator_type const& alloc);

    /** Constructor.

        @param limit The maximum allowed sum of the input and
        output sequence sizes.
    */
    explicit
    basic_multi_buffer(std::size_t limit);

    /** Constructor.

        @param limit The maximum allowed sum of the input and
        output sequence sizes.

        @param alloc The allocator to use.
    */
    basic_multi_buffer(
        std::size_t limit, Allocator const& alloc);

    /** Move assignment.

        This object will have the input sequence of
        the other stream buffer, and an empty output sequence.

        @note After the move, the moved-from object will have
        an empty input and output sequence, with no internal
        buffers allocated.
    */
    basic_multi_buffer&
    operator=(basic_multi_buffer&&);

    /** Copy assignment.

        This object will have a copy of the other stream
        buffer's input sequence, and an empty output sequence.
    */
    basic_multi_buffer& operator=(basic_multi_buffer const&);

    /** Copy assignment.

        This object will have a copy of the other stream
        buffer's input sequence, and an empty output sequence.
    */
    template<class OtherAlloc>
    basic_multi_buffer& operator=(basic_multi_buffer<OtherAlloc> const&);

    /// Returns a copy of the associated allocator.
    allocator_type
    get_allocator() const
    {
        return this->member();
    }

    /// Returns the size of the input sequence.
    size_type
    size() const
    {
        return in_size_;
    }

    /// Returns the permitted maximum sum of the sizes of the input and output sequence.
    size_type
    max_size() const
    {
        return max_;
    }

    /// Returns the maximum sum of the sizes of the input sequence and output sequence the buffer can hold without requiring reallocation.
    std::size_t
    capacity() const;

    /** Get a list of buffers that represents the input sequence.

        @note These buffers remain valid across subsequent calls to `prepare`.
    */
    const_buffers_type
    data() const;

    /** Get a list of buffers that represents the output sequence, with the given size.

        @note Buffers representing the input sequence acquired prior to
        this call remain valid.
    */
    mutable_buffers_type
    prepare(size_type n);

    /** Move bytes from the output sequence to the input sequence.

        @note Buffers representing the input sequence acquired prior to
        this call remain valid.
    */
    void
    commit(size_type n);

    /// Remove bytes from the input sequence.
    void
    consume(size_type n);

private:
    void
    clear();

    void
    move_assign(basic_multi_buffer& other, std::false_type);

    void
    move_assign(basic_multi_buffer& other, std::true_type);

    void
    copy_assign(basic_multi_buffer const& other, std::false_type);

    void
    copy_assign(basic_multi_buffer const& other, std::true_type);

    void
    delete_list();

    void
    debug_check() const;
};

#if 0
/// Helper for boost::asio::read_until
template<class Allocator>
std::size_t
read_size_helper(
    basic_multi_buffer<Allocator> const& buffer,
        std::size_t max_size);
#endif

/// A typical multi buffer
using multi_buffer = basic_multi_buffer<std::allocator<char>>;

} // beast

#include <beast/core/impl/multi_buffer.ipp>

#endif