Add line-comment filter for streambuf.

IOStreams/LineComments.h

@@ -0,0 +1,170 @@
+static_assert( __cplusplus > 2023'00 );
+
+#pragma once
+
+#include <Alepha/Alepha.h>
+
+#include <cstdint>
+#include <cassert>
+
+#include <vector>
+#include <iostream>
+#include <string_view>
+#include <algorithm>
+
+#include <Alepha/error.h>
+
+#include "StackableStreambuf.h"
+#include "StreamState.h"
+
+namespace Alepha::Hydrogen::IOStreams  ::detail::  LineComments_m
+{
+	namespace C
+	{
+		const bool debug= false;
+		const bool debugUnderflow= false or C::debug;
+	}
+
+	inline namespace exports {}
+
+	struct LineComments_params {};
+
+	namespace exports
+	{
+		struct LineCommentsStreambuf;
+
+		using DropComments= IOStreams::PushStack< LineComments_params >;
+	}
+
+	struct exports::LineCommentsStreambuf
+		: public virtual StackableStreambuf, public virtual std::streambuf
+	{
+		private:
+			enum { Active, Commented } state= Active;
+
+		public:
+			explicit
+			LineCommentsStreambuf( std::ios &is )
+				: StackableStreambuf( is )
+			{}
+
+			void writeChar( char ch ) override { throw "Unimpl"; }
+			void drain() override { throw "Unimpl"; }
+
+			int
+			underflow() override
+			{
+				std::string_view view{ gptr(), egptr() };
+				while( view.empty() )
+				{
+					if( gptr() == nullptr or gptr() >= underlying_egptr() )
+					{
+						if( C::debugUnderflow )
+						{
+							Alepha::error() << "Current view of buffer is empty." << std::endl;
+						}
+						const auto rv= forwardUnderflow();
+						if( C::debugUnderflow )
+						{
+							Alepha::error() << "Underlying underflow returned `" << rv << "`" << std::endl;
+						}
+						if( rv == EOF )
+						{
+							Alepha::error() << "Returning EOF from initial-kind read." << std::endl;
+							setg( nullptr, nullptr, nullptr );
+							return rv;
+						}
+						view= { underlying_gptr(), underlying_egptr() };
+					}
+
+					while( state == Commented )
+					{
+						if( C::debugUnderflow )
+						{
+							Alepha::error() << "Current state is `Commented`, underlying view peek is `" << view << "`" << std::endl;
+						}
+						while( not view.empty() )
+						{
+							if( C::debugUnderflow )
+							{
+								Alepha::error() << "Examining: `" << view.front() << "`" << std::endl;
+							}
+							if( view.front() == '\n' )
+							{
+								if( C::debugUnderflow )
+								{
+									Alepha::error() << "Found end of line." << std::endl;
+								}
+								state= Active;
+								break;
+							}
+							underlying_sbumpc();
+							view.remove_prefix( 1 );
+						}
+						if( state == Active ) break;
+						if( C::debugUnderflow )
+						{
+							Alepha::error() << "Underlying view exhausted, getting more..." << std::endl;
+						}
+						const auto rv= forwardUnderflow();
+						if( C::debugUnderflow )
+						{
+							Alepha::error() << "Underlying view underflow returned `" << rv << "`" << std::endl;
+						}
+						if( rv == EOF )
+						{
+							Alepha::error() << "Returning EOF from mid-comment read." << std::endl;
+							setg( nullptr, nullptr, nullptr );
+							return rv;
+						}
+						view= { underlying_gptr(), underlying_egptr() };
+					}
+					assert( state == Active );
+					assert( not view.empty() );
+
+					if( C::debugUnderflow )
+					{
+						Alepha::error() << "Current state is `Active`, underlying view peek is `" << view << "`" << std::endl;
+					}
+
+					for( std::size_t i= 0; i < view.size(); ++i )
+					{
+						if( C::debugUnderflow )
+						{
+							Alepha::error() << "Looking at `" << view.at( i ) << "`'" << std::endl;
+						}
+						underlying_sbumpc();
+						if( view.at( i ) == '#' )
+						{
+							view= view.substr( 0, i );
+							state= Commented;
+							break;
+						}
+					}
+
+					if( C::debugUnderflow )
+					{
+						Alepha::error() << "Current state is `Active`, setting underlying view to `" << view << "`" << std::endl;
+					}
+					setg( (char *) view.data(), (char *) view.data(), (char *) view.data() + view.size() );
+				}
+
+				if( C::debugUnderflow )
+				{
+					Alepha::error() << "Normal return with first char being `" << view.front() << "`" << std::endl;
+				}
+				return view.front();
+			}
+	};
+
+	inline void
+	build_streambuf( std::istream &is, DropComments && )
+	{
+		new LineCommentsStreambuf{ is };
+	}
+}
+
+namespace Alepha::Hydrogen::IOStreams::inline exports::inline LineComments_m
+{
+	using namespace detail::LineComments_m::exports;
+}