refactor file2 and add span with ownership

solanaceae/file/file2_stack.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include "./file2.hpp"
+
+#include <stack>
+#include <memory>
+
+// wrapper/container for a file "stack"
+// has no file functionallity by itself
+
+struct File2Stack : public File2I {
+	std::stack<std::unique_ptr<File2I>> _stack;
+
+	// TODO: change interface again and make r/w non const data members!
+	File2Stack(void) : File2I(false, false), _stack() {}
+	File2Stack(std::stack<std::unique_ptr<File2I>>&& stack) : File2I(false, false), _stack(std::move(stack)) {}
+	File2Stack(std::unique_ptr<File2I>&& file) : File2I(false, false), _stack({std::move(file)}) {}
+	virtual ~File2Stack(void) {}
+
+	bool isGood(void) override {
+		return _stack.top()->isGood();
+	}
+
+	bool write(const ByteSpan data, int64_t pos = -1) override {
+		return _stack.top()->write(data, pos);
+	}
+
+	ByteSpanWithOwnership read(uint64_t size, int64_t pos = -1) override {
+		return _stack.top()->read(size, pos);
+	}
+};
+