para_variables.cpp

/*
 * Copyright (c) 2021, Adam Boardman
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <iostream>
#include <numeric>
#include "para_variables.h"

static const std::string signature("ENV_v1");

ParaVariables::ParaVariables() = default;

ParaVarErrors ParaVariables::ReadFromStream(std::ifstream &stream) {
	stream.seekg(ParaEnvBlockRWStart);
	std::string para_env_block(ParaEnvBlockSize, ParaEnvNullChar);
	if (!stream.read(&para_env_block[0], ParaEnvBlockSize)) {
		return ParaVarErrorReadBlock;
	}

	if (para_env_block.compare(ParaEnvBlockSig1Pos, signature.length(), signature) != 0) {
		return ParaVarErrorBadSig;
	}

	size_t start;
	size_t end = signature.length();
	while ((start = para_env_block.find_first_not_of(ParaEnvNullChar, end)) != std::string::npos) {
		end = para_env_block.find(ParaEnvNullChar, start);
		std::string variable_block(para_env_block.data() + start, end - start);
		size_t mid = variable_block.find('=');
		if (mid != std::string::npos) {
			std::string variable_name(variable_block.substr(0, mid));
			std::string variable_value(variable_block.substr(mid + 1));
			variables.insert(std::pair<std::string, std::string>(variable_name, variable_value));
		}
	}

	if (para_env_block.compare(ParaEnvBlockSig2Pos, signature.length(), signature) != 0) {
		return ParaVarErrorBadSig;
	}

	uint32_t sum = std::accumulate(&para_env_block[signature.length()], &para_env_block[ParaEnvBlockSig2Pos], 0);
	std::string checksum(reinterpret_cast<char *>(&sum), sizeof sum);
	if (para_env_block.compare(ParaEnvBlockSize - sizeof sum, sizeof sum, checksum) != 0) {
		return ParaVarErrorBadCheckSum;
	}

	return ParaVarErrorNone;
}

std::string &ParaVariables::operator[](const std::string &key) {
	return variables[key];
}

void ParaVariables::Clear() {
	variables.clear();
}

void ParaVariables::WriteToStream(std::ofstream &stream) {
	stream.seekp(ParaEnvBlockRWStart);
	stream << signature;

	stream.seekp(ParaEnvBlockRWStart + ParaEnvBlockSigSize);
	for (auto const &x : variables) {
		stream << x.first << "=" << x.second;
		stream.write(reinterpret_cast<char *>(&ParaEnvNullChar), sizeof(char));
	}
	while (stream.tellp() < ParaEnvBlockRWStart + ParaEnvBlockSigSize) {
		stream.write(reinterpret_cast<char *>(&ParaEnvNullChar), sizeof(char));
	}

	stream.seekp(ParaEnvBlockRWStart + ParaEnvBlockSig2Pos);
	stream << signature;

	uint32_t sum = 0;
	for (const auto &x : variables) {
		sum += std::accumulate(&x.first[0], &x.first[x.first.length()], 0);
		sum += '=';
		sum += std::accumulate(&x.second[0], &x.second[x.second.length()], 0);
	}
	stream.seekp(ParaEnvBlockRWStart + ParaEnvBlockSize - sizeof sum);
	stream.write(reinterpret_cast<char *>(&sum), sizeof sum);
}