/*
 * Copyright 2015 - 2024 gary@drinkingtea.net
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

#pragma once

#include <ox/std/array.hpp>
#include <ox/std/bit.hpp>
#include <ox/std/error.hpp>
#include <ox/std/types.hpp>
#include <ox/std/reader.hpp>

#include "err.hpp"

namespace ox {

template<Reader_c Reader>
class FieldBitmapReader {
	protected:
		mutable std::size_t m_mapBlockIdx = ~std::size_t{0};
		mutable uint64_t m_mapBlock = 0;
		std::size_t m_mapStart = 0;
		Reader &m_reader;

	public:
		explicit constexpr FieldBitmapReader(Reader &reader) noexcept;

		constexpr Result<bool> get(std::size_t i) const noexcept;

	private:
		constexpr ox::Error loadMapBlock(std::size_t id) const noexcept;

};

template<Reader_c Reader>
constexpr FieldBitmapReader<Reader>::FieldBitmapReader(Reader &reader) noexcept:
	m_mapStart(reader.tellg()),
	m_reader(reader) {
}

template<Reader_c Reader>
constexpr Result<bool> FieldBitmapReader<Reader>::get(std::size_t idx) const noexcept {
	constexpr auto blockBits = sizeof(m_mapBlock);
	auto const blockIdx = idx / blockBits;
	if (m_mapBlockIdx != blockIdx) [[unlikely]] {
		OX_RETURN_ERROR(loadMapBlock(blockIdx));
	}
	idx %= blockBits;
	return (m_mapBlock >> idx) & 1;
}

template<Reader_c Reader>
constexpr ox::Error FieldBitmapReader<Reader>::loadMapBlock(std::size_t idx) const noexcept {
	OX_REQUIRE(g, m_reader.tellg());
	OX_RETURN_ERROR(m_reader.seekg(static_cast<int>(m_mapStart + idx), ox::ios_base::beg));
	ox::Array<char, sizeof(m_mapBlock)> mapBlock{};
	OX_RETURN_ERROR(m_reader.read(mapBlock.data(), sizeof(m_mapBlock)));
	// Warning: narrow-conv
	OX_RETURN_ERROR(m_reader.seekg(static_cast<int>(g), ox::ios_base::beg));
	m_mapBlock = 0;
	for (auto i = 0ull; auto b : mapBlock) {
		m_mapBlock |= static_cast<uint64_t>(std::bit_cast<uint8_t>(b)) << i;
		i += 8;
	}
	m_mapBlockIdx = idx;
	return {};
}


template<typename T>
class FieldBitmapWriterBase {
	protected:
		T m_map = nullptr;
		std::size_t m_mapLen = 0;

	public:
		constexpr FieldBitmapWriterBase(T map, std::size_t maxLen) noexcept;

		constexpr auto setBuffer(T map, std::size_t maxLen) noexcept;

		constexpr Result<bool> get(std::size_t i) const noexcept;

		constexpr void setFields(int) noexcept;

		constexpr void setMaxLen(int) noexcept;

		[[nodiscard]]
		constexpr int64_t getMaxLen() const noexcept;

};

template<typename T>
constexpr FieldBitmapWriterBase<T>::FieldBitmapWriterBase(T map, std::size_t maxLen) noexcept {
	m_map = map;
	m_mapLen = maxLen;
}

template<typename T>
constexpr auto FieldBitmapWriterBase<T>::setBuffer(T map, std::size_t maxLen) noexcept {
	m_map = map;
	m_mapLen = maxLen;
}

template<typename T>
constexpr Result<bool> FieldBitmapWriterBase<T>::get(std::size_t i) const noexcept {
	if (i / 8 < m_mapLen) {
		return (m_map[i / 8] >> (i % 8)) & 1;
	} else {
		return ox::Error(McPresenceMapOverflow);
	}
}

template<typename T>
constexpr void FieldBitmapWriterBase<T>::setFields(int fields) noexcept {
	m_mapLen = static_cast<std::size_t>((fields / 8 + 1) - (fields % 8 == 0));
}

template<typename T>
constexpr void FieldBitmapWriterBase<T>::setMaxLen(int maxLen) noexcept {
	m_mapLen = static_cast<std::size_t>(maxLen);
}

template<typename T>
constexpr int64_t FieldBitmapWriterBase<T>::getMaxLen() const noexcept {
	return static_cast<int64_t>(m_mapLen);
}

extern template class FieldBitmapWriterBase<uint8_t*>;
extern template class FieldBitmapWriterBase<const uint8_t*>;

class FieldBitmap: public FieldBitmapWriterBase<uint8_t*> {

	public:
		constexpr FieldBitmap(uint8_t *map, std::size_t maxLen) noexcept;

		constexpr Error set(std::size_t i, bool on) noexcept;

};

constexpr FieldBitmap::FieldBitmap(uint8_t *map, std::size_t maxLen) noexcept:
	FieldBitmapWriterBase<uint8_t*>(map, maxLen) {
}

constexpr Error FieldBitmap::set(std::size_t i, bool on) noexcept {
	if (i / 8 < m_mapLen) {
OX_ALLOW_UNSAFE_BUFFERS_BEGIN
		if (on) {
			m_map[i / 8] |= 1 << (i % 8);
		} else {
			m_map[i / 8] &= ~static_cast<uint8_t>(1 << (i % 8));
		}
OX_ALLOW_UNSAFE_BUFFERS_END
		return {};
	} else {
		return ox::Error(McPresenceMapOverflow);
	}
}

}