// The Construct
//
// Copyright (C) The Construct Developers, Authors & Contributors
// Copyright (C) 2016-2020 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.

#include <boost/archive/iterators/binary_from_base64.hpp>
#include <boost/archive/iterators/transform_width.hpp>

#pragma GCC visibility push(internal)
namespace ircd::b64
{
	constexpr char pad
	{
		'='
	};

	[[gnu::aligned(64)]]
	extern const u8
	encode_permute_tab[64],
	encode_shift_ctrl[64];

	template<const u8 (&dict)[64]>
	static u8x64 encode_block(const u8x64 in) noexcept;
}
#pragma GCC visibility pop

decltype(ircd::b64::dict_rfc1421)
ircd::b64::dict_rfc1421
{
	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
	'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
	'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
	'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',
};

decltype(ircd::b64::dict_rfc3501)
ircd::b64::dict_rfc3501
{
	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
	'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
	'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
	'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', ',',
};

decltype(ircd::b64::dict_rfc4648)
ircd::b64::dict_rfc4648
{
	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
	'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
	'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
	'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_',
};

/// For vpermb
/// From arXiv:1910.05109v1 [Mula, Lemire] 2 Oct 2019
decltype(ircd::b64::encode_permute_tab)
ircd::b64::encode_permute_tab
{
	 0 + 1,    0 + 0,    0 + 2,    0 + 1,    3 + 1,    3 + 0,    3 + 2,    3 + 1,
	 6 + 1,    6 + 0,    6 + 2,    6 + 1,    9 + 1,    9 + 0,    9 + 2,    9 + 1,
	12 + 1,   12 + 0,   12 + 2,   12 + 1,   15 + 1,   15 + 0,   15 + 2,   15 + 1,
	18 + 1,   18 + 0,   18 + 2,   18 + 1,   21 + 1,   21 + 0,   21 + 2,   21 + 1,
	24 + 1,   24 + 0,   24 + 2,   24 + 1,   27 + 1,   27 + 0,   27 + 2,   27 + 1,
	30 + 1,   30 + 0,   30 + 2,   30 + 1,   33 + 1,   33 + 0,   33 + 2,   33 + 1,
	36 + 1,   36 + 0,   36 + 2,   36 + 1,   39 + 1,   39 + 0,   39 + 2,   39 + 1,
	42 + 1,   42 + 0,   42 + 2,   42 + 1,   45 + 1,   45 + 0,   45 + 2,   45 + 1,
};

/// For vpmultishiftqb
/// From arXiv:1910.05109v1 [Mula, Lemire] 2 Oct 2019
decltype(ircd::b64::encode_shift_ctrl)
ircd::b64::encode_shift_ctrl
{
	(10 +  0),  ( 4 +  0),  (22 +  0),  (16 +  0),  (10 + 32),  ( 4 + 32),  (22 + 32),  (16 + 32),
	(10 +  0),  ( 4 +  0),  (22 +  0),  (16 +  0),  (10 + 32),  ( 4 + 32),  (22 + 32),  (16 + 32),
	(10 +  0),  ( 4 +  0),  (22 +  0),  (16 +  0),  (10 + 32),  ( 4 + 32),  (22 + 32),  (16 + 32),
	(10 +  0),  ( 4 +  0),  (22 +  0),  (16 +  0),  (10 + 32),  ( 4 + 32),  (22 + 32),  (16 + 32),
	(10 +  0),  ( 4 +  0),  (22 +  0),  (16 +  0),  (10 + 32),  ( 4 + 32),  (22 + 32),  (16 + 32),
	(10 +  0),  ( 4 +  0),  (22 +  0),  (16 +  0),  (10 + 32),  ( 4 + 32),  (22 + 32),  (16 + 32),
	(10 +  0),  ( 4 +  0),  (22 +  0),  (16 +  0),  (10 + 32),  ( 4 + 32),  (22 + 32),  (16 + 32),
	(10 +  0),  ( 4 +  0),  (22 +  0),  (16 +  0),  (10 + 32),  ( 4 + 32),  (22 + 32),  (16 + 32),
};

/// Encoding in to base64 at out. Out must be 1.33+ larger than in
/// padding is not present in the returned view.
template<const ircd::u8 (&dict)[64]>
ircd::string_view
ircd::b64::encode(const mutable_buffer &out,
                  const const_buffer &in)
noexcept
{
	const auto pads
	{
		(3 - size(in) % 3) % 3
	};

	const auto encoded
	{
		encode_unpadded<dict>(out, in)
	};

	assert(size(encoded) + pads <= size(out));
	memset(data(out) + size(encoded), b64::pad, pads);

	const auto len
	{
		size(encoded) + pads
	};

	return string_view
	{
		data(out), len
	};
}
template ircd::string_view ircd::b64::encode<ircd::b64::standard>(const mutable_buffer &, const const_buffer &) noexcept;
template ircd::string_view ircd::b64::encode<ircd::b64::urlsafe>(const mutable_buffer &, const const_buffer &) noexcept;

/// Encoding in to base64 at out. Out must be 1.33+ larger than in.
template<const ircd::u8 (&dict)[64]>
ircd::string_view
ircd::b64::encode_unpadded(const mutable_buffer &out,
                           const const_buffer &in)
noexcept
{
	const size_t res_len
	{
		size_t(ceil(size(in) * (4.0 / 3.0)))
	};

	const size_t out_len
	{
		std::min(res_len, size(out))
	};

	size_t i(0), j(0);
	for(; i + 1 < (size(in) / 48) && i < (out_len / 64); ++i)
	{
		// Destination is indexed at 64 byte stride
		const auto di
		{
			reinterpret_cast<u512x1_u *__restrict__>(data(out) + (i * 64))
		};

		// Source is indexed at 48 byte stride
		const auto si
		{
			reinterpret_cast<const u512x1_u *__restrict__>(data(in) + (i * 48))
		};

		*di = encode_block<dict>(*si);
	}

	for(; i * 48 < size(in); ++i)
	{
		u8x64 block{0};
		for(j = 0; i * 48 + j < size(in); ++j)
			block[j] = in[i * 48 + j];

		block = encode_block<dict>(block);
		for(j = 0; i * 64 + j < out_len; ++j)
			out[i * 64 + j] = block[j];
	}

	return string_view
	{
		data(out), out_len
	};
}
template ircd::string_view ircd::b64::encode_unpadded<ircd::b64::standard>(const mutable_buffer &, const const_buffer &) noexcept;
template ircd::string_view ircd::b64::encode_unpadded<ircd::b64::urlsafe>(const mutable_buffer &, const const_buffer &) noexcept;

/// Returns 64 base64-encoded characters from 48 input characters. For any
/// inputs less than 48 characters trail with null characters; caller computes
/// result size. The following operations are performed on each triple of input
/// characters resulting in four output characters:
/// 0.  in[0] / 4;
/// 1.  (in[1] / 16) + ((in[0] * 16) % 64);
/// 2.  ((in[1] * 4) % 64) + (in[2] / 64);
/// 3.  in[2] % 64;
/// Based on https://arxiv.org/pdf/1910.05109 (and earlier work). No specific
/// intrinsics are used here; instead we recite a kotodama divination known
/// as "vector extensions" which by chance is visible to humans as C syntax.
template<const ircd::u8 (&dict)[64]>
ircd::u8x64
ircd::b64::encode_block(const u8x64 in)
noexcept
{
	size_t i, j, k;

	// vpermb
	u8x64 _perm;
	for(k = 0; k < 64; ++k)
		_perm[k] = in[encode_permute_tab[k]];

	// TODO: currently does not achieve vpmultshiftqb on avx512vbmi
	u64x8 sh[8], perm(_perm);
	for(i = 0; i < 8; ++i)
		for(j = 0; j < 8; ++j)
			sh[i][j] = perm[i] >> encode_shift_ctrl[i * 8 + j];

	// TODO: not needed if vpmultishiftqb is emitted.
	for(i = 0; i < 8; ++i)
		for(j = 0; j < 8; ++j)
			sh[i][j] &= 0x3f;

	u8x64 ret;
	for(i = 0, k = 0; i < 8; ++i)
		for(j = 0; j < 8; ++j)
			ret[k++] = dict[sh[i][j]];

	return ret;
}

//
// Base64 decode
//

/// Decode base64 from in to the buffer at out; out can be 75% of the size
/// of in.
ircd::const_buffer
ircd::b64::decode(const mutable_buffer &out,
                  const string_view &in)
{
	namespace iterators = boost::archive::iterators;
	using b64bf = iterators::binary_from_base64<const char *>;
	using transform = iterators::transform_width<b64bf, 8, 6>;

	const auto pads
	{
		endswith_count(in, b64::pad)
	};

	const auto e
	{
		std::copy(transform(begin(in)), transform(begin(in) + size(in) - pads), begin(out))
	};

	const auto len
	{
		std::distance(begin(out), e)
	};

	assert(size_t(len) <= size(out));
	return const_buffer
	{
		data(out), size_t(len)
	};
}