// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#pragma once
#define HAVE_IRCD_BUFFER_H

// Forward declarations from boost::asio because it is not included here. IRCd
// buffers are not based directly on the boost ones but are easily converted
// when passing our buffer to an asio function.
namespace boost::asio
{
	struct const_buffer;
	struct mutable_buffer;
}

/// Lightweight buffer interface compatible with boost::asio IO buffers and vectors
///
/// A const_buffer is a pair of iterators like `const char *` meant for sending
/// data; a mutable_buffer is a pair of iterators meant for receiving.
///
/// These templates offer tools for individual buffers as well as tools for
/// iterations of buffers.  An iteration of buffers is an iovector that is
/// passed to our sockets etc. The ircd::iov template can host an iteration of
/// buffers. The `template template` functions are tools for a container of
/// buffers of any permutation.
///
namespace ircd::buffer
{
	template<class it> struct buffer;
	struct const_buffer;
	struct mutable_buffer;
	struct window_buffer;
	template<class buffer, size_t SIZE> struct fixed_buffer;
	template<class buffer, uint align = 16> struct unique_buffer;

	template<size_t SIZE> using fixed_const_buffer = fixed_buffer<const_buffer, SIZE>;
	template<size_t SIZE> using fixed_mutable_buffer = fixed_buffer<mutable_buffer, SIZE>;
	template<template<class> class I> using const_buffers = I<const_buffer>;
	template<template<class> class I> using mutable_buffers = I<mutable_buffer>;

	// Single buffer iteration of contents
	template<class it> const it &begin(const buffer<it> &buffer);
	template<class it> const it &end(const buffer<it> &buffer);
	template<class it> it &begin(buffer<it> &buffer);
	template<class it> it &end(buffer<it> &buffer);
	template<class it> std::reverse_iterator<it> rbegin(const buffer<it> &buffer);
	template<class it> std::reverse_iterator<it> rend(const buffer<it> &buffer);

	// Single buffer tools
	template<class it> bool null(const buffer<it> &buffer);
	template<class it> bool full(const buffer<it> &buffer);
	template<class it> bool empty(const buffer<it> &buffer);
	template<class it> bool operator!(const buffer<it> &buffer);
	template<class it> size_t size(const buffer<it> &buffer);
	template<class it> const it &data(const buffer<it> &buffer);
	template<class it> size_t consume(buffer<it> &buffer, const size_t &bytes);
	template<class it> buffer<it> operator+(const buffer<it> &buffer, const size_t &bytes);
	template<class it> it copy(it &dest, const it &stop, const const_buffer &);
	template<size_t SIZE> size_t copy(const mutable_buffer &dst, const char (&buf)[SIZE]);
	size_t copy(const mutable_buffer &dst, const const_buffer &src);
	size_t reverse(const mutable_buffer &dst, const const_buffer &src);
	void reverse(const mutable_buffer &buf);
	void zero(const mutable_buffer &buf);

	// Iterable of buffers tools
	template<template<class> class I, class T> size_t size(const I<T> &buffers);
	template<template<class> class I, class T> size_t copy(const mutable_buffer &, const I<T> &buffer);
	template<template<class> class I, class T> size_t consume(I<T> &buffers, const size_t &bytes);

	// Convenience copy to std stream
	template<class it> std::ostream &operator<<(std::ostream &s, const buffer<it> &buffer);
	template<template<class> class I, class T> std::ostream &operator<<(std::ostream &s, const I<T> &buffers);

	// Preconstructed null buffers
	extern const mutable_buffer null_buffer;
	extern const ilist<mutable_buffer> null_buffers;
}

// Export these important aliases down to main ircd namespace
namespace ircd
{
	using buffer::const_buffer;
	using buffer::mutable_buffer;
	using buffer::fixed_buffer;
	using buffer::unique_buffer;
	using buffer::null_buffer;
	using buffer::window_buffer;
	using buffer::fixed_const_buffer;
	using buffer::fixed_mutable_buffer;

	using buffer::const_buffers;
	using buffer::mutable_buffers;

	using buffer::size;
	using buffer::data;
	using buffer::copy;
	using buffer::consume;
}

/// Base for all buffer types
///
template<class it>
struct ircd::buffer::buffer
:std::tuple<it, it>
{
	using iterator = it;
	using value_type = typename std::remove_pointer<iterator>::type;

	operator string_view() const;
	explicit operator std::string_view() const;
	explicit operator std::string() const;

	auto &begin() const                { return std::get<0>(*this);            }
	auto &begin()                      { return std::get<0>(*this);            }
	auto &end() const                  { return std::get<1>(*this);            }
	auto &end()                        { return std::get<1>(*this);            }

	auto &operator[](const size_t &i) const
	{
		return *(begin() + i);
	}

	auto &operator[](const size_t &i)
	{
		return *(begin() + i);
	}

	buffer(const it &start, const it &stop)
	:std::tuple<it, it>{start, stop}
	{}

	buffer(const it &start, const size_t &size)
	:buffer{start, start + size}
	{}

	buffer()
	:buffer{nullptr, nullptr}
	{}
};

/// Base for mutable buffers, or buffers which can be written to because they
/// are not const.
///
struct ircd::buffer::mutable_buffer
:buffer<char *>
{
	// Conversion offered for the analogous asio buffer
	operator boost::asio::mutable_buffer() const;

	// Allows boost::spirit to append to the buffer; this means the size() of
	// this buffer becomes a consumption counter and the real size of the buffer
	// must be kept separately. This is the lowlevel basis for a stream buffer.
	void insert(char *const &it, const value_type &v)
	{
		assert(it >= this->begin() && it <= this->end());
		memmove(it + 1, it, std::distance(it, this->end()));
		*it = v;
		++std::get<1>(*this);
	}

	using buffer<char *>::buffer;

	mutable_buffer()
	:buffer<char *>{}
	{}

	mutable_buffer(const buffer<char *> &b)
	:buffer<char *>{b}
	{}

	template<size_t SIZE>
	mutable_buffer(char (&buf)[SIZE])
	:buffer<char *>{buf, SIZE}
	{}

	template<size_t SIZE>
	mutable_buffer(std::array<char, SIZE> &buf)
	:buffer<char *>{buf.data(), SIZE}
	{}

	// lvalue string reference offered to write through to a std::string as
	// the buffer. not explicit; should be hard to bind by accident...
	mutable_buffer(std::string &buf)
	:mutable_buffer{const_cast<char *>(buf.data()), buf.size()}
	{}

	mutable_buffer(const std::function<void (const mutable_buffer &)> &closure)
	{
		closure(*this);
	}
};

struct ircd::buffer::const_buffer
:buffer<const char *>
{
	operator boost::asio::const_buffer() const;

	using buffer<const char *>::buffer;

	const_buffer()
	:buffer<const char *>{}
	{}

	const_buffer(const buffer<const char *> &b)
	:buffer<const char *>{b}
	{}

	const_buffer(const buffer<char *> &b)
	:buffer<const char *>{data(b), size(b)}
	{}

	template<size_t SIZE>
	const_buffer(const char (&buf)[SIZE])
	:buffer<const char *>{buf, SIZE}
	{}

	template<size_t SIZE>
	const_buffer(const std::array<char, SIZE> &buf)
	:buffer<const char *>{reinterpret_cast<const char *>(buf.data()), SIZE}
	{}

	const_buffer(const mutable_buffer &b)
	:buffer<const char *>{data(b), size(b)}
	{}

	const_buffer(const string_view &s)
	:buffer<const char *>{data(s), size(s)}
	{}
};

/// fixed_buffer wraps an std::array with construction and conversions apropos
/// the ircd::buffer suite. fixed_buffer should be punnable. Its only memory
/// footprint is the array itself and
///
template<class buffer,
         size_t SIZE>
struct ircd::buffer::fixed_buffer
:std::array<typename std::remove_const<typename buffer::value_type>::type, SIZE>
{
	using mutable_type = typename std::remove_const<typename buffer::value_type>::type;
	using const_type = typename std::add_const<mutable_type>::type;
	using array_type = std::array<mutable_type, SIZE>;

	operator buffer() const
	{
		return { std::begin(*this), std::end(*this) };
	}

	operator buffer()
	{
		return { std::begin(*this), std::end(*this) };
	}

	using array_type::array_type;
	fixed_buffer(const nullptr_t &)
	:array_type{{0}}
	{}

	fixed_buffer(const std::function<void (const mutable_buffer &)> &closure)
	{
		closure(mutable_buffer{reinterpret_cast<mutable_buffer::iterator>(this->data()), this->size()});
	}

	fixed_buffer(buffer b)
	:array_type{std::begin(b), std::end(b)}
	{}

	fixed_buffer() = default;
};

static_assert
(
	// Assertion over an arbitrary but common template configuration.
	std::is_standard_layout<ircd::buffer::fixed_buffer<ircd::buffer::const_buffer, 32>>::value,
	"ircd::buffer::fixed_buffer must be standard layout"
);

/// The window_buffer is just two mutable_buffers. One of the two buffers
/// just spans an underlying space and the other buffer is a window of the
/// remaining space which shrinks toward the end as the space is consumed.
/// The window_buffer object inherits from the latter, so it always has the
/// appearance of a mutable_buffer windowing on the the next place to write.
///
/// The recommended usage of this device is actually through the operator()
/// closure, which will automatically resize the window based on the return
/// value in the closure.
///
struct ircd::buffer::window_buffer
:mutable_buffer
{
	mutable_buffer base;

	/// Bytes remaining for writes to the stream buffer (same as size(*this))
	size_t remaining() const
	{
		assert(begin() <= base.end());
		const size_t ret(std::distance(begin(), base.end()));
		assert(ret == size(*this));
		return ret;
	}

	/// Bytes used by writes to the stream buffer
	size_t consumed() const
	{
		assert(begin() >= base.begin());
		assert(begin() <= base.end());
		return std::distance(base.begin(), begin());
	}

	/// View the completed portion of the stream
	const_buffer completed() const
	{
		assert(base.begin() <= begin());
		assert(base.begin() + consumed() <= base.end());
		return { base.begin(), base.begin() + consumed() };
	}

	/// View the completed portion of the stream
	mutable_buffer completed()
	{
		assert(base.begin() <= begin());
		assert(base.begin() + consumed() <= base.end());
		return { base.begin(), base.begin() + consumed() };
	}

	/// Convenience conversion to get the completed portion
	explicit operator const_buffer() const
	{
		return completed();
	}

	/// Convenience closure presenting the writable window and advancing the
	/// window with a consume() for the bytes written in the closure.
	using closure = std::function<size_t (const mutable_buffer &)>;
	void operator()(const closure &closure)
	{
		consume(*this, closure(*this));
	}

	window_buffer(const mutable_buffer &base)
	:mutable_buffer{base}
	,base{base}
	{}
};

/// Like unique_ptr, this template holds ownership of an allocated buffer
///
template<class buffer,
         uint alignment>
struct ircd::buffer::unique_buffer
:buffer
{
	unique_buffer(std::unique_ptr<uint8_t[]> &&, const size_t &size);
	unique_buffer(const size_t &size);
	unique_buffer();
	unique_buffer(unique_buffer &&) noexcept;
	unique_buffer(const unique_buffer &) = delete;
	unique_buffer &operator=(unique_buffer &&) noexcept;
	unique_buffer &operator=(const unique_buffer &) = delete;
	~unique_buffer() noexcept;
};

template<class buffer,
         uint alignment>
ircd::buffer::unique_buffer<buffer, alignment>::unique_buffer()
:buffer
{
	nullptr, nullptr
}
{}

template<class buffer,
         uint alignment>
ircd::buffer::unique_buffer<buffer, alignment>::unique_buffer(std::unique_ptr<uint8_t[]> &&b,
                                                              const size_t &size)
:buffer
{
	typename buffer::iterator(b.release()), size
}
{}

template<class buffer,
         uint alignment>
ircd::buffer::unique_buffer<buffer, alignment>::unique_buffer(const size_t &size)
:unique_buffer<buffer, alignment>
{
	std::unique_ptr<uint8_t[]>
	{
		//TODO: Can't use a template parameter to the attribute even though
		// it's known at compile time. Hardcoding this until fixed with better
		// aligned dynamic memory.
		//new __attribute__((aligned(alignment))) uint8_t[size]
		new __attribute__((aligned(16))) uint8_t[size]
	},
	size
}
{
	// Alignment can only be 16 bytes for now
	assert(alignment == 16);
}

template<class buffer,
         uint alignment>
ircd::buffer::unique_buffer<buffer, alignment>::unique_buffer(unique_buffer &&other)
noexcept
:buffer
{
	std::move(static_cast<buffer &>(other))
}
{
	get<0>(other) = nullptr;
}

template<class buffer,
         uint alignment>
ircd::buffer::unique_buffer<buffer, alignment> &
ircd::buffer::unique_buffer<buffer, alignment>::operator=(unique_buffer &&other)
noexcept
{
	this->~unique_buffer();

	static_cast<buffer &>(*this) = std::move(static_cast<buffer &>(other));
	get<0>(other) = nullptr;

	return *this;
}

template<class buffer,
         uint alignment>
ircd::buffer::unique_buffer<buffer, alignment>::~unique_buffer()
noexcept
{
	delete[] data(*this);
}

template<template<class>
         class buffers,
         class T>
std::ostream &
ircd::buffer::operator<<(std::ostream &s, const buffers<T> &b)
{
	using it = typename T::iterator;

	std::for_each(std::begin(b), std::end(b), [&s]
	(const buffer<it> &b)
	{
		s << b;
	});

	return s;
}

template<template<class>
         class buffers,
         class T>
size_t
ircd::buffer::consume(buffers<T> &b,
                      const size_t &bytes)
{
	ssize_t remain(bytes);
	for(auto it(std::begin(b)); it != std::end(b) && remain > 0; ++it)
	{
		using buffer = typename buffers<T>::value_type;
		using iterator = typename buffer::iterator;

		buffer &b(const_cast<buffer &>(*it));
		const ssize_t bsz(size(b));
		const ssize_t csz{std::min(remain, bsz)};
		remain -= consume(b, csz);
		assert(remain >= 0);
	}

	assert(ssize_t(bytes) >= remain);
	return bytes - remain;
}

template<template<class>
         class buffers,
         class T>
size_t
ircd::buffer::copy(const mutable_buffer &dest,
                   const buffers<T> &b)
{
	using it = typename T::iterator;

	size_t ret(0);
	for(const buffer<it> &b : b)
		ret += copy(data(dest) + ret, size(dest) - ret, b);

	return ret;
}

template<template<class>
         class buffers,
         class T>
size_t
ircd::buffer::size(const buffers<T> &b)
{
	using it = typename T::iterator;

	return std::accumulate(std::begin(b), std::end(b), size_t(0), []
	(auto ret, const buffer<it> &b)
	{
		return ret += size(b);
	});
}

template<class it>
std::ostream &
ircd::buffer::operator<<(std::ostream &s, const buffer<it> &buffer)
{
	assert(!null(buffer) || get<1>(buffer) == nullptr);
	s.write(data(buffer), size(buffer));
	return s;
}

inline void
ircd::buffer::reverse(const mutable_buffer &buf)
{
	std::reverse(data(buf), data(buf) + size(buf));
}

inline size_t
ircd::buffer::reverse(const mutable_buffer &dst,
                      const const_buffer &src)
{
	const size_t ret{std::min(size(dst), size(src))};
	std::reverse_copy(data(src), data(src) + ret, data(dst));
	return ret;
}

template<size_t SIZE>
__attribute__((error
(
	"Copy source is an array. Is this a string literal? Do you want to copy the \\0?"
	" Disambiguate this by typing the source string_view or const_buffer."
)))
inline size_t
ircd::buffer::copy(const mutable_buffer &dst,
                   const char (&buf)[SIZE])
{
	return copy(dst, const_buffer{buf});
}

inline size_t
ircd::buffer::copy(const mutable_buffer &dst,
                   const const_buffer &src)
{
	auto e{begin(dst)};
	copy(e, end(dst), src);
	assert(std::distance(begin(dst), e) >= 0);
	return std::distance(begin(dst), e);
}

template<class it>
it
ircd::buffer::copy(it &dest,
                   const it &stop,
                   const const_buffer &src)
{
	const it ret{dest};
	const ssize_t srcsz(size(src));
	assert(ret <= stop);
	const ssize_t remain{std::distance(ret, stop)};
	const ssize_t cpsz{std::min(srcsz, remain)};
	assert(cpsz <= srcsz);
	assert(cpsz <= remain);
	assert(remain >= 0);
	memcpy(ret, data(src), cpsz);
	dest += cpsz;
	assert(dest <= stop);
	return ret;
}

template<class it>
ircd::buffer::buffer<it>
ircd::buffer::operator+(const buffer<it> &buffer,
                        const size_t &bytes)
{
	const size_t advance
	{
		std::min(bytes, size(buffer))
	};

	return
	{
		begin(buffer) + advance, size(buffer) - advance
	};
}

template<class it>
size_t
ircd::buffer::consume(buffer<it> &buffer,
                      const size_t &bytes)
{
	assert(!null(buffer));
	assert(bytes <= size(buffer));
	get<0>(buffer) += bytes;
	assert(get<0>(buffer) <= get<1>(buffer));
	return size(buffer);
}

template<class it>
const it &
ircd::buffer::data(const buffer<it> &buffer)
{
	return get<0>(buffer);
}

template<class it>
size_t
ircd::buffer::size(const buffer<it> &buffer)
{
	assert(get<0>(buffer) <= get<1>(buffer));
	assert(!null(buffer) || get<1>(buffer) == nullptr);
	return std::distance(get<0>(buffer), get<1>(buffer));
}

template<class it>
bool
ircd::buffer::operator!(const buffer<it> &buffer)
{
	return empty(buffer);
}

template<class it>
bool
ircd::buffer::empty(const buffer<it> &buffer)
{
	return null(buffer) || std::distance(get<0>(buffer), get<1>(buffer)) == 0;
}

template<class it>
bool
ircd::buffer::full(const buffer<it> &buffer)
{
	return std::distance(get<0>(buffer), get<1>(buffer)) == 0;
}

template<class it>
bool
ircd::buffer::null(const buffer<it> &buffer)
{
	return get<0>(buffer) == nullptr;
}

template<class it>
std::reverse_iterator<it>
ircd::buffer::rend(const buffer<it> &buffer)
{
	return std::reverse_iterator<it>(get<0>(buffer));
}

template<class it>
std::reverse_iterator<it>
ircd::buffer::rbegin(const buffer<it> &buffer)
{
	return std::reverse_iterator<it>(get<0>(buffer) + size(buffer));
}

template<class it>
it &
ircd::buffer::end(buffer<it> &buffer)
{
	return get<1>(buffer);
}

template<class it>
it &
ircd::buffer::begin(buffer<it> &buffer)
{
	return get<0>(buffer);
}

template<class it>
const it &
ircd::buffer::end(const buffer<it> &buffer)
{
	return get<1>(buffer);
}

template<class it>
const it &
ircd::buffer::begin(const buffer<it> &buffer)
{
	return get<0>(buffer);
}

template<class it>
ircd::buffer::buffer<it>::operator std::string()
const
{
	return { reinterpret_cast<const char *>(data(*this)), size(*this) };
}

template<class it>
ircd::buffer::buffer<it>::operator std::string_view()
const
{
	return { reinterpret_cast<const char *>(data(*this)), size(*this) };
}

template<class it>
ircd::buffer::buffer<it>::operator string_view()
const
{
	return { reinterpret_cast<const char *>(data(*this)), size(*this) };
}