GoJDB/include/database.hpp

#pragma once
#include "fsized_map.h"
#include <chrono>

struct metadata_t{
	bitops::regulated<uint64_t> record_cnt;
	bitops::regulated<uint64_t> page_cnt;
	bitops::regulated<uint64_t> delete_cnt;
	bitops::regulated<uint64_t> last_page;
	bitops::regulated<uint64_t> last_delete;
};

class database {

	database(){}

public:
	mmap_array<std::pair<bitops::regulated<uint64_t>, record>> records;

	mmap_array<db_page> pages;

	mmap_array<metadata_t> metadata;

	mmap_array<size_t> delete_table;

	database(
		const std::string& records, 
		const std::string& pages, 
		const std::string& deletions,
		const std::string& meta,
		const size_t& record_cnt = 4096,
		const size_t& page_cnt   = 4096,
		const size_t& delete_cnt = 512
	)
	: records{record_cnt, records}
	, pages{page_cnt, pages}
	, metadata{(size_t)1, meta}
	, delete_table{delete_cnt, deletions}
	{}

	static database&& create(const std::string dir, size_t page_nb) {
		database ret{
			dir+"records",
			dir+"pages",
			dir+"deleted",
			dir+"meta",
			page_nb+page_nb/2,
			page_nb,
			page_nb/8
		};

		for(auto& n : ret.records)
		{
			n.second.timestamp = 0;
			n.second.offset = 0;
		}

		for(auto& n : ret.delete_table)
		{
			n = std::numeric_limits<size_t>::max();
		}

		(*ret.metadata).last_page = 0;
		(*ret.metadata).last_delete = 0;
		(*ret.metadata).record_cnt = page_nb+page_nb/2;
		(*ret.metadata).page_cnt = page_nb;
		(*ret.metadata).delete_cnt = page_nb/8;

		#pragma GCC diagnostic push
		#pragma GCC diagnostic ignored "-Wreturn-local-addr"
		return std::move(ret);
		#pragma GCC diagnostic pop
	}

	static database&& open(const std::string dir) {
		mmap_array<metadata_t> tmp{(size_t)1, dir+"meta"};
		
		database ret{
			dir+"records",
			dir+"pages",
			dir+"deleted",
			dir+"meta",
			(*tmp).record_cnt,
			(*tmp).page_cnt,
			(*tmp).delete_cnt
		};
		
		tmp.clear();

		#pragma GCC diagnostic push
		#pragma GCC diagnostic ignored "-Wreturn-local-addr"
		return std::move(ret);
		#pragma GCC diagnostic pop
	}

	void write(const record_identifier& target, const db_page& value){
		uint64_t page = std::numeric_limits<uint64_t>::max();;
		size_t off = std::numeric_limits<size_t>::max();
		if(metadata[0].last_delete>0)
		{
			off = (*metadata).last_delete;
			page = delete_table[off-1];
		} else {
			page = (*metadata).last_page;
			if(page>=pages.size()) {
				throw std::runtime_error("PAGE STARVATION! MUST EXIT NOW");
			}
		}

		if(page == std::numeric_limits<uint64_t>::max())
		{
			throw std::runtime_error("PAGE ERROR! MUST EXIT NOW");
		}

		pages[page] = value;

		uint64_t hashed = std::hash<record_identifier>{}(target);
		uint64_t hashed_roll = hashed;
		bool succeed = false;


		uint64_t ts = std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::system_clock::now().time_since_epoch()).count();
		std::pair<bitops::regulated<uint64_t>,record> tmp{0, record{}};
		tmp.first = hashed;
		tmp.second.record_head.split = target;
		tmp.second.timestamp = ts;
		tmp.second.offset = page;
		do{
			uint64_t pos = hashed_roll % records.size();

			switch (static_cast<uint64_t>(records[pos].second.timestamp)) {
				case 0: 
					[[fallthrough]];
				case std::numeric_limits<uint64_t>::max():
					records[pos] = tmp;
					succeed = true;
					break;
				default:
					break;
			}

			hashed_roll++;
		}while(!succeed);

		if(off != std::numeric_limits<size_t>::max())
		{
			(*metadata).last_delete += -1;
			delete_table[off] = std::numeric_limits<size_t>::max();
		} else {
			(*metadata).last_page += (size_t)1;
		}
	}

	std::pair<uint64_t, db_page> read(const record_identifier& target) {
		std::pair<uint64_t, db_page> ret;
		ret.first = 0;
		ret.second.fill(0);

		uint64_t hashed = std::hash<record_identifier>{}(target);
		uint64_t hashed_roll = hashed;

		do{
			uint64_t pos = hashed_roll % records.size();

			auto& value = records[pos].second;
			switch (static_cast<uint64_t>(value.timestamp)) {
				case 0: 
					return ret;
				case std::numeric_limits<uint64_t>::max():
					break;
				default:
					if(records[pos].first == hashed)
					if(std::hash<record_identifier>{}(value.record_head.split) == hashed)
					{
						if(ret.first<value.timestamp)
						{
							ret.first = value.timestamp;
							ret.second = pages[value.offset];
						}
						break;
				}
			}

			hashed_roll++;
		}while(true);
		return ret;
	}

	void remove(const record_identifier& target) {
		uint64_t hashed = std::hash<record_identifier>{}(target);
		uint64_t hashed_roll = hashed;

		do{
			uint64_t pos = hashed_roll % records.size();

			auto& value = records[pos].second;
			switch (static_cast<uint64_t>(value.timestamp)) {
				case 0: 
					return;
				case std::numeric_limits<uint64_t>::max():
					break;
				default:
					if(records[pos].first == hashed)
					if(std::hash<record_identifier>{}(value.record_head.split) == hashed)
					{
						value.timestamp = std::numeric_limits<uint64_t>::max();
						(*metadata).last_delete+=1;
						delete_table[(*metadata).last_delete-1] = value.offset;
						value.offset = 0;
						break;
				}
			}

			hashed_roll++;
		}while(true); // return only happens on hitting a case 0
	}

	void rollback(const record_identifier&) {

	}
};