From d65687f45e9db42799065a3c864aa6a19e16597b Mon Sep 17 00:00:00 2001
From: ADAM David Alan Martin <adam@recursive.engineer>
Date: Tue, 17 Oct 2023 14:01:49 -0400
Subject: [PATCH] Start implementing a unified stackable streambuf framework.

---
 Utility/StackableStreambuf.h | 115 +++++++++++++++++++++++++++++++++++
 word_wrap.cpp                |   2 +
 2 files changed, 117 insertions(+)
 create mode 100644 Utility/StackableStreambuf.h

diff --git a/Utility/StackableStreambuf.h b/Utility/StackableStreambuf.h
new file mode 100644
index 0000000..81ad6ef
--- /dev/null
+++ b/Utility/StackableStreambuf.h
@@ -0,0 +1,115 @@
+static_assert( __cplusplus > 2020'00 );
+
+#pragma once
+
+#include <Alepha/Alepha.h>
+
+#include <ios>
+#include <exception>
+#include <stdexcept>
+
+namespace Alepha::Hydrogen::Utility  ::detail::  stackable_streambuf
+{
+	inline namespace exports
+	{
+		struct StackableStreambuf;
+
+		template< typename > struct PushStack;
+
+		template< typename > struct PopStack;
+	}
+
+	inline const auto index= std::ios::xalloc();
+
+	inline namespace impl
+	{
+		void releaseStack( std::ios_base &ios );
+		
+		void iosCallback( const std::ios_base::event event, std::ios_base &ios, const int idx );
+	}
+
+	struct exports::StackableStreambuf
+		: virtual public std::streambuf
+	{
+		public:
+			std::streambuf *underlying;
+
+			~StackableStreambuf() {}
+
+			explicit
+			StackableStreambuf( std::ostream &host )
+				: underlying( host.rdbuf( this ) )
+			{
+				// TODO: Atomicity for this:
+				if( not host.iword( index ) ) host.register_callback( iosCallback, index );
+				host.iword( index )= 1;
+			}
+
+			std::ostream out() const { return std::ostream{ underlying }; }
+
+			virtual void writeChar( const char ch )= 0;
+			virtual void drain()= 0;
+
+			int
+			overflow( const int ch ) override
+			{
+				if( ch == EOF ) throw std::logic_error( "EOF!" );
+				writeChar( ch );
+
+				return 1;
+			}
+
+			std::streamsize
+			xsputn( const char *const data, const std::streamsize amt ) override
+			{
+				for( std::streamsize i= 0; i< amt; ++i ) overflow( data[ i ] );
+				return amt;
+			}
+	};
+
+	void
+	impl::releaseStack( std::ios_base &ios )
+	{
+		auto &os= dynamic_cast< std::ostream & >( ios );
+		auto *streambuf= os.rdbuf();
+
+		while( auto *stacked= dynamic_cast< StackableStreambuf * >( streambuf ) )
+		{
+			streambuf= stacked->underlying;
+			stacked->drain();
+			os.rdbuf( stacked->underlying );
+			delete stacked;
+		}
+	}
+
+	inline void
+	impl::iosCallback( const std::ios_base::event event, std::ios_base &ios, const int idx )
+	{
+		if( index != idx ) throw std::logic_error{ "Wrong index." };
+
+		if( event == std::ios_base::erase_event ) releaseStack( ios );
+	}
+
+	template< typename T >
+	struct exports::PushStack : T {};
+
+	template< typename T >
+	struct exports::PopStack {};
+
+	template< typename T >
+	std::ostream &
+	operator << ( std::ostream &os, PushStack< T > &&params )
+	{
+		build_streambuf( os, params );
+		return os;
+	}
+
+	template< typename T >
+	std::ostream &
+	operator << ( std::ostream &os, PopStack< T > )
+	{
+		releaseStack( os );
+		return os;
+	}
+
+}
diff --git a/word_wrap.cpp b/word_wrap.cpp
index 79dc8d4..161c446 100644
--- a/word_wrap.cpp
+++ b/word_wrap.cpp
@@ -10,6 +10,8 @@ static_assert( __cplusplus > 2020 );
 #include <sstream>
 #include <memory>
 
+#include <Alepha/Utility/StackableStreambuf.h>
+
 #include "evaluation_helpers.h"
 
 namespace Alepha::Cavorite  ::detail::  word_wrap