From 71c5280bc6393669777147b5036dc510e74d93c4 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sat, 17 Apr 2021 21:41:26 +0100
Subject: Second swing persistance

Mostly functional JSON deserialising for most types.
---
 lib/persistance.h | 201 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 201 insertions(+)
 create mode 100644 lib/persistance.h

(limited to 'lib/persistance.h')

diff --git a/lib/persistance.h b/lib/persistance.h
new file mode 100644
index 0000000..75222e0
--- /dev/null
+++ b/lib/persistance.h
@@ -0,0 +1,201 @@
+#ifndef PERSISTANCE_H
+#define PERSISTANCE_H
+
+#include <functional>
+#include <glm/glm.hpp>
+#include <iosfwd>
+#include <memory>
+#include <special_members.hpp>
+#include <stack>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+namespace glm {
+	template<glm::length_t L, typename T, glm::qualifier Q> struct vec;
+}
+
+namespace Persistanace {
+	struct Selection;
+	using SelectionPtr = std::unique_ptr<Selection>;
+	using Stack = std::stack<SelectionPtr>;
+
+	struct Selection {
+		Selection() = default;
+		virtual ~Selection() = default;
+		DEFAULT_MOVE_COPY(Selection);
+
+		virtual void operator()(float &);
+		virtual void operator()(bool &);
+		virtual void operator()(const std::nullptr_t &);
+		virtual void operator()(std::string &);
+		virtual void BeginArray(Stack &);
+		virtual SelectionPtr BeginObject();
+		virtual void beforeValue(Stack &);
+		virtual SelectionPtr select(const std::string &);
+	};
+
+	template<typename T> struct SelectionT : public Selection {
+		explicit SelectionT(T & value) : v {value} { }
+
+		void
+		beforeValue(Stack &) override
+		{
+		}
+
+		void
+		operator()(T & evalue) override
+		{
+			std::swap(v, evalue);
+		}
+
+		static constexpr bool ArrayLike {false};
+		T & v;
+	};
+
+	struct PersistanceStore {
+		// virtual bool persistType(const std::type_info &) = 0;
+		template<typename T>
+		bool
+		persistValue(const std::string_view & key, T & value)
+		{
+			if (key == name) {
+				sel = std::make_unique<SelectionT<T>>(std::ref(value));
+				return false;
+			}
+			return true;
+		}
+		const std::string & name;
+		SelectionPtr sel {};
+	};
+
+	template<glm::length_t L, typename T, glm::qualifier Q> struct SelectionT<glm::vec<L, T, Q>> : public Selection {
+		explicit SelectionT(glm::vec<L, float, Q> & value) : v {value} { }
+
+		void
+		BeginArray(Stack &) override
+		{
+		}
+
+		void
+		beforeValue(Stack & stk) override
+		{
+			stk.push(std::make_unique<SelectionT<T>>(std::ref(v[idx++])));
+		}
+
+		static constexpr bool ArrayLike {true};
+		glm::vec<L, T, Q> & v;
+		glm::length_t idx {0};
+	};
+
+	template<typename T> struct SelectionT<std::vector<T>> : public Selection {
+		explicit SelectionT(std::vector<T> & value) : v {value} { }
+
+		void
+		BeginArray(Stack &) override
+		{
+		}
+
+		void
+		beforeValue(Stack & stk) override
+		{
+			stk.push(std::make_unique<SelectionT<T>>(std::ref(v.emplace_back())));
+		}
+
+		static constexpr bool ArrayLike {true};
+		std::vector<T> & v;
+	};
+
+	template<typename T>
+	concept ArrayLike = SelectionT<T>::ArrayLike;
+
+	template<ArrayLike T> struct SelectionT<std::vector<T>> : public Selection {
+		explicit SelectionT(std::vector<T> & value) : v {value} { }
+
+		void
+		BeginArray(Stack & stk) override
+		{
+			stk.push(std::make_unique<SelectionT<T>>(std::ref(v.emplace_back())));
+		}
+
+		static constexpr bool ArrayLike {true};
+		std::vector<T> & v;
+	};
+
+	struct Persistable {
+		Persistable() = default;
+		virtual ~Persistable() = default;
+		DEFAULT_MOVE_COPY(Persistable);
+
+		virtual void persist(PersistanceStore & store) = 0;
+
+		static void addFactory(const std::string_view, std::function<std::unique_ptr<Persistable>()>);
+		static std::unique_ptr<Persistable> callFactory(const std::string_view);
+	};
+
+	template<typename T> struct SelectionT<std::unique_ptr<T>> : public Selection {
+		using Ptr = std::unique_ptr<T>;
+		struct SelectionObj : public Selection {
+			struct MakeObjectByTypeName : public Selection {
+				explicit MakeObjectByTypeName(Ptr & o) : o {o} { }
+
+				void
+				beforeValue(Stack &) override
+				{
+				}
+
+				void
+				operator()(std::string & type) override
+				{
+					auto no = Persistable::callFactory(type);
+					if (dynamic_cast<T *>(no.get())) {
+						o.reset(static_cast<T *>(no.release()));
+					}
+				}
+
+				Ptr & o;
+			};
+
+			explicit SelectionObj(Ptr & o) : v {o} { }
+
+			SelectionPtr
+			select(const std::string & mbr) override
+			{
+				using namespace std::literals;
+				if (mbr == "@typeid"sv) {
+					if (v) {
+						throw std::runtime_error("cannot set object type after creation");
+					}
+					return std::make_unique<MakeObjectByTypeName>(std::ref(v));
+				}
+				else {
+					if (!v) {
+						if constexpr (!std::is_abstract_v<T>) {
+							v = std::make_unique<T>();
+						}
+						throw std::runtime_error("cannot select member of null object");
+					}
+					PersistanceStore ps {mbr};
+					v->persist(ps);
+					return std::move(ps.sel);
+				}
+			}
+
+			Ptr & v;
+		};
+
+		explicit SelectionT(std::unique_ptr<T> & o) : v {o} { }
+
+		SelectionPtr
+		BeginObject() override
+		{
+			return std::make_unique<SelectionObj>(v);
+		}
+
+		std::unique_ptr<T> & v;
+	};
+}
+
+#endif
-- 
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