Rudimentary configuration file system.

ConfigFile.h

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+#pragma once
+
+#include <map>
+#include <string>
+#include <istream>
+#include <ostream>
+#include <optional>
+
+namespace Config::inline Hydrogen {}
+
+namespace Config::Hydrogen  ::detail::  ConfigFile_m
+{
+	inline namespace exports
+	{
+		class ConfigFile;
+	}
+
+	class exports::ConfigFile
+	{
+		private:
+			std::map< std::string, std::string > config;
+
+			struct EoF {};
+
+			std::string
+			readLine( std::istream &input )
+			{
+				std::string rv;
+				std::getline( input, rv );
+				if( not input ) throw EoF{};
+
+				// SStrip trailing '#' comments...
+				const auto endComment= std::find( begin( rv ), end( rv ), '#' );
+				rv.erase( endComment, end( rv ) );
+				return rv;
+			}
+
+			std::string
+			trimWhitespace( std::string s )
+			{
+				// Trim from the front
+				std::reverse( begin( s ), end( s ) );
+				while( not s.empty() and s.back() == ' ' ) s.pop_back();
+
+				// Trim from the back
+				std::reverse( begin( s ), end( s ) );
+				while( not s.empty() and s.back() == ' ' ) s.pop_back();
+
+				return s;
+			}
+
+			auto
+			parseLine( const std::string &line )
+			{
+				const auto split= std::find( begin( line ), end( line ), '=' );
+				if( split == end( line ) ) throw std::runtime_error{ "Unable to parse configuration line: `" + line + "`" };
+				const auto key= trimWhitespace( { begin( line ), split } );
+				const auto value= trimWhitespace( { split + 1, end( line ) } );
+
+				return std::tuple{ key, value };
+			}
+
+		public:
+			explicit
+			ConfigFile( std::istream &&input, const std::map< std::string, std::string > &schema )
+			{
+				config= schema;
+				while( input )
+				try
+				{
+					const std::string line= trimWhitespace( readLine( input ) );
+					if( line.empty() ) continue; // Skip blank lines.
+					
+					const auto [ key, value ]= parseLine( line );
+
+					if( not schema.contains( key ) )
+					{
+						std::cerr << "Unrecognized key in config file: `" << key << "`" << std::endl;
+						continue;
+					}
+
+					config.at( key )= value;
+				}
+				catch( const EoF & ) { break; }
+
+				std::cerr << "Configuration parsed:" << std::endl;
+				for( const auto &[ key, value ]: config )
+				{
+					std::cerr << key << " = " << value << std::endl;
+				}
+			}
+
+			std::string get( const std::string &name ) const { return config.at( name ); }
+	};
+}
+
+namespace Config::Hydrogen::inline exports::inline ConfigFile_m
+{
+	using namespace detail::ConfigFile_m::exports;
+}