Simple VDF (Valve Data Format) parser

VDFParser.hpp

#pragma once

#include <fstream>
#include <istream>
#include <iomanip>
#include <memory>
#include <unordered_map>
#include <variant>

class VDFParser
{
public:
	class DataNode;

	using SubkeyType = std::unordered_map<std::string, const DataNode>;

	class DataNode : std::variant<std::string, SubkeyType>
	{
	public:
		const DataNode& operator[](const std::string key) const
		{
			return std::get<SubkeyType>(*this).at(key);
		}

		void SetString(std::string val)
		{
			*static_cast<std::variant<std::string, SubkeyType>*>(this) = std::move(val);
		}

		void SetSubkey(SubkeyType val)
		{
			*static_cast<std::variant<std::string, SubkeyType>*>(this) = std::move(val);
		}

		auto Value() const
		{
			std::string val;
			if (auto* ptr = std::get_if<std::string>(this); ptr != nullptr)
			{
				val = *ptr;
			}
			return val;
		}
	};

	static SubkeyType Load(const wchar_t* fileName)
	{
		SubkeyType result;

		std::ifstream file(fileName);
		if (file)
		{
			result = ReadSubkey(file);
		}

		return result;
	}

private:
	static SubkeyType ReadSubkey(std::istream& stream)
	{
		SubkeyType result;

		while (stream.good())
		{
			stream >> std::ws;
			int ch = stream.peek(); // TODO: EOF?
			if (ch == '"')
			{
				std::string key;
				stream >> std::quoted(key);
				result.emplace(std::move(key), ReadValue(stream));
			}
			else if (ch == '}')
			{
				stream.ignore(); // Advance past the closing bracket
				break;
			}
		}

		return result;
	}
	

	static DataNode ReadValue(std::istream& stream)
	{
		DataNode result;
		stream >> std::ws;
		int ch = stream.peek(); // TODO: EOF?
		if (ch == '"')
		{
			std::string value;
			stream >> std::quoted(value);
			result.SetString(std::move(value));
		}
		else if (ch == '{')
		{
			stream.ignore(); // Advance past the opening bracket
			result.SetSubkey(ReadSubkey(stream));
		}

		return result;
	}
};